SMPS inverter voltage feedback methods

[Terry Given]

MooseFET wrote:

On Jan 27, 4:43 am, Jamie Morken <[email protected]> wrote:

MooseFET wrote:

[...]

How about this parts intensive idea?
Do it FM radio style
Vin>VCO(1Ghz)>xformer>FM demod>Vout isolated

If you go down to much lower frequencies, the idea works quite well.
At 1MHz or so, the VCO doesn't take very many parts.
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1010,C1096,P2186

The suggested circuit plus one resistor makes not too bad of a VCO
The receiver side can be a PLL that uses a tri-state phase detector
built into your PCLD or FPGA or whatever and a second VCO like the
first.

This is the way I'd like to do the voltage feedback, with a VCO feeding
a transformer, and then the PLL circuit, but I think that part is too
slow to react, the maximum VCO modulation bandwidth of the LTC6900 is
25kHz, I'm running the PWM at 200kHz.

The servo feedback needs a bandwith much higher than 60Hz but not
higher than the 200KHz. For the AC feedback, you can just use a
transformer drivien with the output signal. The DC feedback is just
to ensure that you don't have a DC component in the output.

The PWM dutycycle needs to be set each cycle, using the voltage
and current feedback, I'm using small inductors so it can change quite
rapidly. Would you be able to help me design this modulator/demodulator
ready to feed into the 200kHz ADC if I put it in the public domain and
pay you or at least send you some chocolates?

I already am going to use a bipolar ADC floating with the 120VAC and SPI
optocoupled, but its good to have a backup, as I'm not sure if I can get
12bits resolution from that ADC.

cheers,
Jamie

think Nyquist. no matter how hard you try, you cant organise closed-loop
voltage or current control beyond 100kHz.

That isn't quite true. Depending on the sort of PWM modulator you
use, you get two samples per cycle because both edges of the on time
can be moved by the input.

true. most dont work like this though.

This still ends up about the right limit. When you move both edges in
a PWM, you usually end up with a giant noise spike right at Nyquist.




The is true for moderately large values of "slowly". Since the OP is
trying to construct a 60Hz sine wave, he has a lower limit on the
voltage feedback frequency responce of perhaps 1KHz or so.

I should have mentioned that, of course.....

If he has a microcontroller in the system, he can also use the
information from this point in the previous cycle to improve his
waveform for a constant load.

He should look up one of the papers D.G. Holmes has written on resonant
controllers. take a synchronous-reference-frame controller, and run it
backwards thru the rotating-to-stationary transformation, and voila out
pops a resonant controller. very cute, and lower computational overhead.

Cheers
Terry

 

[Joerg]

Joerg wrote: [....]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr, send some AC there if you can't feed the HV side
circuitry locally (toroid xfmr or something), sample, then send sample
across another toroid xfmr back to LV side. I use little #43 ferrites
for those jobs, sometimes #77. Mostly #43 because there always seems to
come a time when someone asks for even more bandwidth later.

Is this the same as what Moosefet is talking about with the VCO on the
transformer primary? Can the sampling be tied into the PWM signals sent
to the SMPS fets? So that the modulation and demodulation is done by
these signals, not sure if this would work with variable dutycycle PWM?

From my reading of it, it isn't but it is worthy of consideration. A
balanced modulator and balanced demodulator will bring DC across with
no trouble. If you pick the right sort of running frequency, it will
be quite insensitive to all the switching noise.

With a bit of trichery, you could get any imbalance between the two
sides to come across on the same transformer. The second channel
could be phase or an even harmonic.

Addendum, mostly for Jamie: "Balanced" or "synchronous" demodulator is
in this sense just a glorified old-fashioned clamp circuit. Just like
the one in a TV set where a correct DC black level must be gleaned from
a source that cannot reliably transmit DC levels directly. Except that
you don't have to fish the clamp pulse out of a noisy morass but it's
already there.

IOW you clamp both sides to their respective grounds while the pulse is
not present. When the pulse cometh then the source side is switched to
the signal. Now you sample the value on the receiving end while the
pulse is there and hold it until the next pulse. Or have a fast enough
ADC log it during the pulse and stash the result. That's pretty much it.

 

[Terry Given]

Joerg wrote:
[....]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr, send some AC there if you can't feed the HV side
circuitry locally (toroid xfmr or something), sample, then send sample
across another toroid xfmr back to LV side. I use little #43 ferrites
for those jobs, sometimes #77. Mostly #43 because there always seems to
come a time when someone asks for even more bandwidth later.

Is this the same as what Moosefet is talking about with the VCO on the
transformer primary? Can the sampling be tied into the PWM signals sent
to the SMPS fets? So that the modulation and demodulation is done by
these signals, not sure if this would work with variable dutycycle PWM?

From my reading of it, it isn't but it is worthy of consideration. A
balanced modulator and balanced demodulator will bring DC across with
no trouble. If you pick the right sort of running frequency, it will
be quite insensitive to all the switching noise.

With a bit of trichery, you could get any imbalance between the two
sides to come across on the same transformer. The second channel
could be phase or an even harmonic.

Addendum, mostly for Jamie: "Balanced" or "synchronous" demodulator is
in this sense just a glorified old-fashioned clamp circuit. Just like
the one in a TV set where a correct DC black level must be gleaned from
a source that cannot reliably transmit DC levels directly. Except that
you don't have to fish the clamp pulse out of a noisy morass but it's
already there.

IOW you clamp both sides to their respective grounds while the pulse is
not present. When the pulse cometh then the source side is switched to
the signal. Now you sample the value on the receiving end while the
pulse is there and hold it until the next pulse. Or have a fast enough
ADC log it during the pulse and stash the result. That's pretty much it.

Hi Joerg,

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Cheers
Terry

 

[Joerg]

Joerg wrote:

[....]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr, send some AC there if you can't feed the HV side
circuitry locally (toroid xfmr or something), sample, then send sample
across another toroid xfmr back to LV side. I use little #43 ferrites
for those jobs, sometimes #77. Mostly #43 because there always
seems to
come a time when someone asks for even more bandwidth later.

Is this the same as what Moosefet is talking about with the VCO on the
transformer primary? Can the sampling be tied into the PWM signals
sent
to the SMPS fets? So that the modulation and demodulation is done by
these signals, not sure if this would work with variable dutycycle PWM?



From my reading of it, it isn't but it is worthy of consideration. A
balanced modulator and balanced demodulator will bring DC across with
no trouble. If you pick the right sort of running frequency, it will
be quite insensitive to all the switching noise.

With a bit of trichery, you could get any imbalance between the two
sides to come across on the same transformer. The second channel
could be phase or an even harmonic.

Addendum, mostly for Jamie: "Balanced" or "synchronous" demodulator is
in this sense just a glorified old-fashioned clamp circuit. Just like
the one in a TV set where a correct DC black level must be gleaned
from a source that cannot reliably transmit DC levels directly. Except
that you don't have to fish the clamp pulse out of a noisy morass but
it's already there.

IOW you clamp both sides to their respective grounds while the pulse
is not present. When the pulse cometh then the source side is switched
to the signal. Now you sample the value on the receiving end while the
pulse is there and hold it until the next pulse. Or have a fast enough
ADC log it during the pulse and stash the result. That's pretty much it.

Hi Joerg,

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

The Unitrode UC1901 does something similar but not to the precision that
my designs usually need:

http://focus.ti.com/lit/ds/symlink/uc1901.pdf

Possibly this chip is heading for lalaland. Found it only at Arrow and
IMHO outrageously expensive. Maybe because guys like me always roll
their own ;-)

Can't draw in ASCII but in a nutshell it works like this:

The goal is to obtain an AM signal. A square wave, but a bit bandlimited
so the Federales won't come after you. Its amplitude has to become
proportional to the voltage to be measured on the isolated side.

One way to do that is to generate a clock, let's call it SENSECLK and
transfer that over to the isolated side via XFMR1. On the iso side you
use SENSECLK to switch a MUX such as a 74HC4051. SENSECLK low -> switch
to ISOGND. SENSECLK high -> Switch to the voltage node to be measured.
Might have to buffer first it it's a hi-Z node. Send the MUX output to a
buffer amp and then to another iso transformer called XFMR2.

At the other end (the system side) you can restore the measured value
with its DC component in many ways. The good news is that you have
SENSECLK right there because it is generated on the system side. One
method: Couple to XFMR2 with a small capacitor and connect the other end
to a high input impedance amp. Pull that side to SYSGND whenever
SENSECLK is low. Let go when SENSECLK is high. The output of that buffer
gets a track-and-hold and will now track the signal that was measured on
the isolated side. Including DC even though it has to be transported
over via an iso transformer.

Hope this helps. At the end of the day those circuits look quite busy on
a schematic but it's all mundane jelly-bean stuff, meaning it costs a
lot less in production than all those fancy single-source chips. And you
don't have to worry about parts obsolescence. I still remember that poor
Burr-Brown sales rep 20 years ago. He wanted to sell me on a
dielectrically isolated "super-duper iso amp". Nice product idea. I
asked him what it costs. "Oh, these are a bargain, less than $75". When
I told him that my discrete version was about five bucks including the
transformers he walked away with a sad face.

 

[Terry Given]

Hi Joerg,

MooseFET wrote:


Joerg wrote:


[....]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr, send some AC there if you can't feed the HV side
circuitry locally (toroid xfmr or something), sample, then send
sample
across another toroid xfmr back to LV side. I use little #43 ferrites
for those jobs, sometimes #77. Mostly #43 because there always
seems to
come a time when someone asks for even more bandwidth later.


Is this the same as what Moosefet is talking about with the VCO on the
transformer primary? Can the sampling be tied into the PWM signals
sent
to the SMPS fets? So that the modulation and demodulation is done by
these signals, not sure if this would work with variable dutycycle
PWM?




From my reading of it, it isn't but it is worthy of consideration. A
balanced modulator and balanced demodulator will bring DC across with
no trouble. If you pick the right sort of running frequency, it will
be quite insensitive to all the switching noise.

With a bit of trichery, you could get any imbalance between the two
sides to come across on the same transformer. The second channel
could be phase or an even harmonic.


Addendum, mostly for Jamie: "Balanced" or "synchronous" demodulator
is in this sense just a glorified old-fashioned clamp circuit. Just
like the one in a TV set where a correct DC black level must be
gleaned from a source that cannot reliably transmit DC levels
directly. Except that you don't have to fish the clamp pulse out of a
noisy morass but it's already there.

IOW you clamp both sides to their respective grounds while the pulse
is not present. When the pulse cometh then the source side is
switched to the signal. Now you sample the value on the receiving end
while the pulse is there and hold it until the next pulse. Or have a
fast enough ADC log it during the pulse and stash the result. That's
pretty much it.

Hi Joerg,

I cant quite picture it, would you care to cough up an ascii
schematic? didnt unitrode make a chipset that did prettty much this?

The Unitrode UC1901 does something similar but not to the precision that
my designs usually need:

http://focus.ti.com/lit/ds/symlink/uc1901.pdf

yeah, thats the one I was thinking of.

Possibly this chip is heading for lalaland. Found it only at Arrow and
IMHO outrageously expensive. Maybe because guys like me always roll
their own ;-)

Can't draw in ASCII but in a nutshell it works like this:

The goal is to obtain an AM signal. A square wave, but a bit bandlimited
so the Federales won't come after you. Its amplitude has to become
proportional to the voltage to be measured on the isolated side.

One way to do that is to generate a clock, let's call it SENSECLK and
transfer that over to the isolated side via XFMR1. On the iso side you
use SENSECLK to switch a MUX such as a 74HC4051. SENSECLK low -> switch
to ISOGND. SENSECLK high -> Switch to the voltage node to be measured.
Might have to buffer first it it's a hi-Z node. Send the MUX output to a
buffer amp and then to another iso transformer called XFMR2.

At the other end (the system side) you can restore the measured value
with its DC component in many ways. The good news is that you have
SENSECLK right there because it is generated on the system side. One
method: Couple to XFMR2 with a small capacitor and connect the other end
to a high input impedance amp. Pull that side to SYSGND whenever
SENSECLK is low. Let go when SENSECLK is high. The output of that buffer
gets a track-and-hold and will now track the signal that was measured on
the isolated side. Including DC even though it has to be transported
over via an iso transformer.

Hope this helps. At the end of the day those circuits look quite busy on
a schematic but it's all mundane jelly-bean stuff, meaning it costs a
lot less in production than all those fancy single-source chips. And you
don't have to worry about parts obsolescence. I still remember that poor
Burr-Brown sales rep 20 years ago. He wanted to sell me on a
dielectrically isolated "super-duper iso amp". Nice product idea. I
asked him what it costs. "Oh, these are a bargain, less than $75". When
I told him that my discrete version was about five bucks including the
transformers he walked away with a sad face.

gotcha. bung a clock over, scale it proportional to Vout, then feed it
back & synchronously rectify it. the key of course is generating the
clock on the primary side, which allows for synchronous detection. that
beer must have addled my brain (I'm onto the chocolate milk now)

Right, back to my voltage-mode controller PFC thingy

Cheers
Terry

 

[MooseFET]

MooseFET wrote: [...]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr,

[....]

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

 

[Jamie Morken]

MooseFET wrote: [...]
To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr,

[....]

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.jpg
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform1.jpg

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.asc

cheers,
Jamie

 

[Terry Given]

Joerg wrote:

MooseFET wrote:
[...]

To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr,
[....]

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.jpg

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform1.jpg


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.asc


cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Cheers
Terry

 

[MooseFET]

MooseFET wrote:

Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Yes, that is it.

The CD4053 used like this in a decoder:

---/\/\--
! !
AC in --+----/\/\--+--!-\ !
! ! >---+------ Decoded out
--0 ---!+/ to filter
<------
GND---O
4053

If you are using a micro and an ADC, you can just digitize the two
voltages of the AC-feedback signal and subtract.

 

[Jamie Morken]

Joerg wrote:

MooseFET wrote:

[...]

To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,

[....]

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.jpg

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform1.jpg


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.asc


cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2.jpg

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.

So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?

here's the corrected circuit:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.jpg

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.asc

cheers,
Jamie

 

[Jamie Morken]

Joerg wrote:

MooseFET wrote:

[...]

To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,

[....]

I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.jpg

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform1.jpg


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.asc


cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2.jpg

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.

So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?

here's the corrected circuit:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.jpg

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.asc

cheers,
Jamie

 

[Terry Given]

MooseFET wrote:


Joerg wrote:

MooseFET wrote:


[...]

To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,


[....]

I cant quite picture it, would you care to cough up an ascii
schematic?
didnt unitrode make a chipset that did prettty much this?


Here's what was rattling through my mind while I was thinking about
how to do this.



ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------


This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.




Hi,

I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?

Heres the circuit and waveform:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.jpg

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform1.jpg


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit1.asc


cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3)
(roughly). What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2.jpg


V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.

So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?

here's the corrected circuit:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.jpg


ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.asc


cheers,
Jamie

Dude, work on your reading comprehension - its a little rusty. Your V1
should be THE DC VOLTAGE YOU WANT TO MEASURE. RE-READ THAT SENTENCE.

then probe across winding L4

 

[MooseFET]

MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie

Hi Jamie,

Vout is the DC output voltage to be sensed.

V2 is the drive to the AM chopper transistors

where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.

http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.

So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?

here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V2 should be a square wave.

The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1

The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.

 

[Jamie Morken]

Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.

http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.

So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?

here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V2 should be a square wave.

The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1

The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.

Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.

Here are the L4, L5 and L6 waveforms:

http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2-I(L4).jpg
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2-I(L5).jpg
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform2-I(L6).jpg

The overall circuit:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit2.jpg

I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

cheers,
Jamie

 

[MooseFET]

Terry Given wrote:
Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.
Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?
here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V2 should be a square wave.

The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1

The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.

Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.

Here are the L4, L5 and L6 waveforms:

http://rocketresearch.nekrom.com/ne...h.nekrom.com/new/transformer chopper voltage%...

The overall circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

 

[Jamie Morken]

Terry Given wrote:
Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.
Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?
here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V2 should be a square wave.
The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1
The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.

Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.

Here are the L4, L5 and L6 waveforms:

http://rocketresearch.nekrom.com/ne...h.nekrom.com/new/transformer chopper voltage%...

The overall circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

I checked the coupling, and changed the L5 and L6 coil winding (dots)
to have both dots on the centertap, and the primary current looks better
now, (no spikes) but the secondary is still just current spikes on the
rising and falling edges of the primary pulses.

If I change the winding of the L2/L3 coils to be opposite winds (dots
together towards the centertap), then the L5/L6 currents are in phase,
otherwise they are out of phase, either way the L4 secondary is still
current spikes on the rising and falling edges of the L5/L6 primary
pulses, but the L4 waveform looks more balanced when all coils have
dots towards the centertaps

I probably just need to add the demodulation circuitry to the L4
secondary to translate the spikes back into the voltages?

cheers,
Jamie

 

[Jamie Morken]

MooseFET wrote:
Terry Given wrote:
Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii
schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the
voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work,
the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC
input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is
AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3)
(roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.
Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"? Also
what
about FM would that work too, or is this AM method the way to go?
here's the corrected
circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice
file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V2 should be a square wave.
The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1
The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.
Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.

Here are the L4, L5 and L6 waveforms:

http://rocketresearch.nekrom.com/ne...h.nekrom.com/new/transformer chopper voltage%...


The overall
circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...


I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

here's the waveforms and circuit:


schematic:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit3.jpg

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/circuit3.asc

output L4 current:
http://rocketresearch.nekrom.com/new/transformer chopper voltage measurement/waveform3-I(L4).jpg

L5 and L6 currents (in phase and no spikes now):
http://rocketresearch.nekrom.com/ne... voltage measurement/waveform3-I(L5andL6).jpg


cheers,
Jamie

 

[MooseFET]

MooseFET wrote:
Terry Given wrote:
Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.
Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?
here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V2 should be a square wave.
The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1
The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.
Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.
Here are the L4, L5 and L6 waveforms:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%......
The overall circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

I checked the coupling, and changed the L5 and L6 coil winding (dots)
to have both dots on the centertap,

Both transformers should look like this:

0
))))))
==============
))))) ))))
0 0

Note where the dots are

 

[Jamie Morken]

MooseFET wrote:
Terry Given wrote:
Jamie Morken wrote:
MooseFET wrote:
Joerg wrote:
MooseFET wrote:
[...]
To monitor the waveform? Why not just sample it? Send sampling
pulse
through toroid xfmr,
[....]
I cant quite picture it, would you care to cough up an ascii schematic?
didnt unitrode make a chipset that did prettty much this?
Here's what was rattling through my mind while I was thinking about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/---- +Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+----------- -Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.
Hi,
I put this schematic into ltspice and it seems to kind of work, the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
cheers,
Jamie
Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3) (roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or Joergs
suggestion which is even simpler.
Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"? Also what
about FM would that work too, or is this AM method the way to go?
here's the corrected circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
ltspice file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
V2 should be a square wave.
The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1
The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.
Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.
Here are the L4, L5 and L6 waveforms:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%......
The overall circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...
I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.
Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

I checked the coupling, and changed the L5 and L6 coil winding (dots)
to have both dots on the centertap,

Both transformers should look like this:

0
))))))
==============
))))) ))))
0 0

Note where the dots are

hmm, the two primary coils are 180 degrees out of phase, with nice
looking waveforms but the secondary has just a few fA and pV on it
now!

cheers,
Jamie

 

[Terry Given]

MooseFET wrote:


MooseFET wrote:


Terry Given wrote:

Jamie Morken wrote:

MooseFET wrote:


Joerg wrote:

MooseFET wrote:

[...]

To monitor the waveform? Why not just sample it? Send
sampling
pulse
through toroid xfmr,

[....]

I cant quite picture it, would you care to cough up an ascii
schematic?
didnt unitrode make a chipset that did prettty much this?

Here's what was rattling through my mind while I was thinking
about
how to do this.
ACFB+ ! ! ACFB-
+-/\/\--+
! !
(((((((
=======
(((((((
! ! !
! -- ! ---------+--/\/\/----
+Vout
! ! !
!/ \! \
!! ----------! !---- /
Drive ---- !! ( !\e e/! ! \
) !! ( ! ! ! !
) !! ------------+-------+----- ! --+-----------
-Vout
) !! ( !
GND ------ !! ( !
!! ---------------------------
This works even in the AC case if the resistors bring the
voltage low
enough that the EB junctions aren't breaking down while the
transistors trade off conducting.

Hi,
I put this schematic into ltspice and it seems to kind of work,
the AC
voltage is being chopped by the Drive signal to Vout, but it is 90
degrees out of phase with the input AC signal, and also very low
amplitude. Any ideas how to get the output phase to match the
AC input?
Heres the circuit and waveform:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice file:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

cheers,
Jamie

Hi Jamie,
Vout is the DC output voltage to be sensed.
V2 is the drive to the AM chopper transistors
where you have V1 is actually the output of the circuit - it is
AC, at
the same freqency as V2, but the amplitude is Vout*R2/(R2+R3)
(roughly).
What Joerg & MooseFET are talking about is then using V2 to
synchronously demodulate this AC output - e.g. with a 4066, or
Joergs
suggestion which is even simpler.

Ok I hooked it up right now I think, I am not sure if the waveforms
are correct, it looks like it would be pretty hard to sample the
voltages as the peaks are very fast.
http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

V(n001) the green trace is the output voltage of L4 on the R1 side,
and V(n003) is the voltage at the common node of R3 and R2 (the
divided voltage from 120VAC.
So do these traces look correct for doing the "demodulation"?
Also what
about FM would that work too, or is this AM method the way to go?
here's the corrected
circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

ltspice
file:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...


V2 should be a square wave.
The L4, L5, L6 transformer should end up with a near squarewave on it
That is V2 times the voltage from V1
The L4, L5, L6 transformer may need a load resistance on the L4
section. A small capacitor may also be needed to kill the spikes.

Checked V2, it is a squarewave, gives similar results whether it is
AC or DC squarewave current.
Here are the L4, L5 and L6 waveforms:
http://rocketresearch.nekrom.com/new/transformer chopper voltage%......

The overall
circuit:http://rocketresearch.nekrom.com/new/transformer chopper voltage%...

I changed the V1 source to DC and got the same output spikes in
L4 as when it is AC.

Those currents look not too far from right. Carefully recheck stuff
including the dots on the inductors. Try dropping the K value of the
coupling to perhaps 0.25 to see that the inductors work right when
they are not coupled.

I checked the coupling, and changed the L5 and L6 coil winding (dots)
to have both dots on the centertap,

Both transformers should look like this:

0
))))))
==============
))))) ))))
0 0

Note where the dots are

hmm, the two primary coils are 180 degrees out of phase, with nice
looking waveforms but the secondary has just a few fA and pV on it
now!

cheers,
Jamie

operator error.

to think of it another way: its a very low power push-pull converter.
being very low power, you can feed the center-tap of the "primary" via a
voltage divider. if you get no secondary voltage, your sim is wrong.

to start with, throw away L1 - L3, and just drive ideal switches with a
complementary square wave. all L1-L3 does is allow the non-isolated
primary to provide the drive signals to the isolated voltage sampling
circuit (Qn, L4-L6). this is only necessary so you can then easily
synchronously rectify the output of L4.

personally, I like to use ideal components in my sims, to get the basic
concepts up and running. once you have proved the concept, *then* toss
in FETs/bipolars/leakage inductance etc. until you become an expert at
your particular sim package, this is a good approach.

Cheers
Terry