Switching Regulator for Audio Amplifier

[Phil Allison]

"Eeysore Congenital Fuckwit "

You don't understand semiconductors in that case.

** Go get fucked - you pile of vacuous pommy shit.

It's either 84V or 94V, maybe a misprint somewhere.

** Read the FUCKING data sheet -

you blind as a fucking bat POMMY ASSHOLE.


IT COULD NOT BE CLEARER !!




......... Phil

 

[Eeyore]

Anyways, in audio the average loading is much less (unless you want to play continuous sine waves),
and 30% power rating would be safe perhaps for the transformer for music use.

LOL !

Try rave DJ music. It has a dynamic range after being compressed (which it will be ) of about 2 dB !

That's what I use for my amplifier 'tortutre test'. Few pass it. Some even catch fire. It's aslo
another reason I know how to design very efficent heatsinking.

Graham

 

[Phil Allison]

"Eeysore".

I don't know the tolerances on your supplies ( I assume it's the USA) so
design
for 94V with a 126V supply or whatever is typical high line.

** Read the fucking data -

you RIDICULOUS STUPID **** !!





...... Phil

 

[Bob Eld]

** Read the fucking data -

you RIDICULOUS STUPID **** !!

** Go get fucked - you pile of vacuous pommy shit.

you blind as a fucking bat POMMY ASSHOLE

..... Phil

I see Phyllis is getting "technical" again. Maybe we can all learn from her
erudite scientific discussion.

 

[Fred]

LOL !

Try rave DJ music. It has a dynamic range after being compressed (which it will be ) of about 2 dB !

That's what I use for my amplifier 'tortutre test'. Few pass it. Some even catch fire. It's aslo
another reason I know how to design very efficent heatsinking.

Graham

That's the music I destroyed the chips with. I originally put all
that capacitance on the rail to power all the bass in that stuff.

Fred

 

[Fred]

Thats transformer is really really bad.
I do admit I use a 200W toroid (once I wanted to make a stereo amp),
but, for a fraction of what this home build did cost me, I also bought a 2 x 180 W in 4 Ohm
19inch stereo amp ...... You cannot beat German design manufactured by a Chinese company
where they work for peanuts, or maybe M&Ms.
Lookup PA3000 at conrad.nl...

I work the other way around,
If 42V is max, then subtract 10% for mains variation makes 37.8V DC nominal peak.
This is 'top of the ripple'.

You drop 1.4V in a bridge, so 39.2V peak out of the transformer.

At 50 W into 8 Ohm you need a voltage swing of P = U^2 / R so
U^2 = 50 * 8 = 400, that makes U = 20V eff.
The peak would be 20 x sqrt(2) = 28.28 V.

How much does the chip drop of this? I dunno. but say 4V (just for the example).
So that makes 28.28 + 4 = 32.28.

We have 37.8 - 32.28 = 5.52V for the ripple.
At 50 W the peak current into 8 Ohm is 28.8 / 8 = 2.54 A
At 50 Hz mains, and a full bridge you have 10 mS between mains tops,
Q = C . I = U . t
So 5.52 V at 2.54 A in 10 mS makes C = (5.52 x .01) / 2.54 = .022 F or 22 mF or
22 000 uF for the filter caps.

Interesting, they omitted any mention of those last two equations in
the data sheet. I just looked at it again and apparently I had
17,670uF on each rail rather than what I said before. When I was
listening to it loud, I thought I could hear it completely bottom out
that reserve in spots.

I was using 4 ohm load.

Maybe I give this one more try with a transformer large enough to
supply both stereo channels. That would be about 500VA. A toroidal
that size should have a regulation of like 3%.

Also the transformers I used before were rated 115:24 @ 8A. The power
here runs about 120-121. So, that was an additional 4%-5% rise.

And yes, I did want this thing to be capable of outputting 50W rms
sine wave all day long...

Thanks,

Fred

 

[Fred]

Thats transformer is really really bad.
I do admit I use a 200W toroid (once I wanted to make a stereo amp),
but, for a fraction of what this home build did cost me, I also bought a 2 x 180 W in 4 Ohm
19inch stereo amp ...... You cannot beat German design manufactured by a Chinese company
where they work for peanuts, or maybe M&Ms.
Lookup PA3000 at conrad.nl...

I work the other way around,
If 42V is max, then subtract 10% for mains variation makes 37.8V DC nominal peak.
This is 'top of the ripple'.

You drop 1.4V in a bridge, so 39.2V peak out of the transformer.

At 50 W into 8 Ohm you need a voltage swing of P = U^2 / R so
U^2 = 50 * 8 = 400, that makes U = 20V eff.
The peak would be 20 x sqrt(2) = 28.28 V.

How much does the chip drop of this? I dunno. but say 4V (just for the example).
So that makes 28.28 + 4 = 32.28.

We have 37.8 - 32.28 = 5.52V for the ripple.
At 50 W the peak current into 8 Ohm is 28.8 / 8 = 2.54 A
At 50 Hz mains, and a full bridge you have 10 mS between mains tops,
Q = C . I = U . t
So 5.52 V at 2.54 A in 10 mS makes C = (5.52 x .01) / 2.54 = .022 F or 22 mF or
22 000 uF for the filter caps.

Not counting any internal resistance of the transformer.
I'd say: You cannot even do 50 W into 8 Ohm with a 'perfect' transformer with that chip.

Maybe I messed up the math....

Anyways, in audio the average loading is much less (unless you want to play continuous sine waves),
and 30% power rating would be safe perhaps for the transformer for music use.
Then you run into the larger internal resistance (thinner wire) of that transformer again...
And somebody WILL do sinewaves for hours on end (I know somebody that did, but IIRC they
told him to move his workshop after that).

I see my Chinese amp simply uses a _huge_ torroid, 250W? ...... and normal transistors,
a temp controlled fan, stereo, all in a nice 19 inch rack, with separate volume controls
for left and right, with clipping warning indicator LEDs, with power switch, cinch AND XLR
connectors on the back....
And I payed 65 Euro (about 91 dollars) for it..... some years ago, see they are now 87.95 Euro...
with more LEDs
Lookup 'PA3000' atwww.conrad.nl

That is the absolute maximum limit of the chip. I

37.8VDCpk nominal - Good
39.2Vpk out of the transformer - Good

50W into 4ohms = 20Vpk and 5Apk
DropoutV 4 - Good

So, 37.8 - ( 20 + 4 ) = 13.8V ripple

120Hz mains = 8.33ms between peaks.

Accordingly, 13.8V * 0.00833s / 5A = ~23,000uF

National told me that all the reserve I put on the on the rails,
beyond the 0.1uf and 470uf bypass caps, was unnecessary. I mentioned
that I failed to understand how the chip could handle large transients
without it, and they just left it at that.

In any case, I guess I'll buy a 115 to 2 x (50 @ 5A ) 4% transformer
and give this another shot.

That should give me 38.4 out of the transformer with a 120 at the
mains.

Thanks again,

Fred

 

[Eeyore]

I see Phyllis is getting "technical" again. Maybe we can all learn from her
erudite scientific discussion.

I'd like to know why Nat Semi quote 94V (no signal) and 84V with signal. Since
signal level isn't specified, are they saying 1mV of input @ 94V will kill it ?

Someone at Nat Semi needs to be shot.

Anyway, I suggested a better option, also from National.

Graham

 

[Eeyore]

waves), and 30% power rating would be safe perhaps for the transformer for music use.

That's the music I destroyed the chips with. I originally put all
that capacitance on the rail to power all the bass in that stuff.

No surprise. DJs can kill most equipment without even trying. You really need to understand your thermal
calculations to make amps that'll survive that. Oh, never mind the speakers too !

Graham

 

[Eeyore]

I was using 4 ohm load.

Do you know how to calculate the heat dissipated in the amp ?

It'll need a biggish heat sink. I've done 1600W amps that have TWO fans in them and huge heatsinks.

Graham

 

[Eeyore]

National told me that all the reserve I put on the on the rails,
beyond the 0.1uf and 470uf bypass caps, was unnecessary.

Are these local bypass caps in addition to the PSU reservoir caps ?

You'd need no more than that for sure.

Graham

 

[Eeyore]

In any case, I guess I'll buy a 115 to 2 x (50 @ 5A ) 4% transformer
and give this another shot.

That should give me 38.4 out of the transformer with a 120 at the
mains.

BEWARE. Transformers may or may not be rated loaded. When rated loaded it will invariably be with a
RESISTIVE load, not a rectifier and capacitor inpur PSU.

Ask for the *turns ratio*. That's the only way to find the 'no-load' DC voltage.

Graham

 

[Jan Panteltje]

37.8VDCpk nominal - Good
39.2Vpk out of the transformer - Good

That makes 27.7 V effective secondairy.

50W into 4ohms = 20Vpk and 5Apk
correct.


DropoutV 4 - Good
So, 37.8 - ( 20 + 4 ) = 13.8V ripple

120Hz mains = 8.33ms between peaks.

Accordingly, 13.8V * 0.00833s / 5A = ~23,000uF
Yep.

National told me that all the reserve I put on the on the rails,
beyond the 0.1uf and 470uf bypass caps, was unnecessary.

I dunno, these numbers are from the worst case, of course the top, tha tcharges the C,
is part of the 8.3 ms, so in reality you neeed a bit les C,
also 4 V is really bad for a drop in a good output stage, if it is some MOS then it
could be close to zero (with bootstrap C).

I mentioned
that I failed to understand how the chip could handle large transients
without it, and they just left it at that.

470 uF is way to small.

In any case, I guess I'll buy a 115 to 2 x (50 @ 5A ) 4% transformer
and give this another shot.

I think you mean 2 x 27 V secondary, and a bridge configuration?

 

[Fred]

That makes 27.7 V effective secondairy.




I dunno, these numbers are from the worst case, of course the top, tha tcharges the C,
is part of the 8.3 ms, so in reality you neeed a bit les C,
also 4 V is really bad for a drop in a good output stage, if it is some MOS then it
could be close to zero (with bootstrap C).


470 uF is way to small.


I think you mean 2 x 27 V secondary, and a bridge configuration?

 

[Fred]

That makes 27.7 V effective secondairy.




I dunno, these numbers are from the worst case, of course the top, tha tcharges the C,
is part of the 8.3 ms, so in reality you neeed a bit les C,
also 4 V is really bad for a drop in a good output stage, if it is some MOS then it
could be close to zero (with bootstrap C).


470 uF is way to small.


I think you mean 2 x 27 V secondary, and a bridge configuration?

Bridge yes. 1/2 the transformer feeds both rails for one channel.

50Vrms * 1.414pk * 1.04 regulation * 1.043 for 120 local voltage =
~78Vpk

That gives 39Vpk before the bridge. Right?

 

[Fred]

BEWARE. Transformers may or may not be rated loaded. When rated loaded it will invariably be with a
RESISTIVE load, not a rectifier and capacitor inpur PSU.

Ask for the *turns ratio*. That's the only way to find the 'no-load' DC voltage.

Graham

Hey Graham,

Let me see if I can address these in order:

I did the thermal calculations. I used a 3C/W heat sink, and directed
a 40mmx40mm fan at during testing because it got hot when at full
load.

The 0.1uf and the 470uf were local bypass close as possible to the
pins of the device. In the gain clones, its those caps, a bridge, and
the tranny. Absolutely minimalistic.

My uinderstanding of transformer ratings is that the regulation is
drived from the voltage rise from load to no-load, and they deliver
the stated VA when resistively loaded.

I'm unsure about what difference a bridge and cap filters would do to
the output of the PS besides lower the VA a bit due to the diode drop
and the caps ESR

Fred.

 

[Fred]

That makes 27.7 V effective secondairy.




I dunno, these numbers are from the worst case, of course the top, tha tcharges the C,
is part of the 8.3 ms, so in reality you neeed a bit les C,
also 4 V is really bad for a drop in a good output stage, if it is some MOS then it
could be close to zero (with bootstrap C).


470 uF is way to small.


I think you mean 2 x 27 V secondary, and a bridge configuration?

I could has said that clearer. The bridge differential, it supplies
both rails directly.

 

[Jan Panteltje]

Bridge yes. 1/2 the transformer feeds both rails for one channel.

50Vrms * 1.414pk * 1.04 regulation * 1.043 for 120 local voltage =
~78Vpk

That gives 39Vpk before the bridge. Right?

____________________ + (27 . sqrt(2) - .7) = 37.48V
| k |k
D1 D2
| |
--------------------| |
| 27V | |
T1 | |
|------ GND 0V | |
T2 | |
| 27V | |
-----------------------------------|
|k |k
D3 D4
| |
-------------------- - 37.48 V

So, 2 windings of 27V?

 

[Fred]

____________________ + (27 . sqrt(2) - .7) = 37.48V
| k |k
D1 D2
| |
--------------------| |
| 27V | |
T1 | |
|------ GND 0V | |
T2 | |
| 27V | |
-----------------------------------|
|k |k
D3 D4
| |
-------------------- - 37.48 V

So, 2 windings of 27V?

Are you trying to obfuscate?

27 volts would be too high, you omitted the transformer no load rise
and adjustment for local mains voltage.

I'm thinkin'

_____ ___ +( 50 * sqrt2 * 1.04 regulation * 1.043 local
mains )/2
| k |k - 0.7 = aprox +38V
D1 D3
| |
-------------| |
| | |
| | | 0
| t1 50Vrms | | |
| | | |
| | | |
-------------------| \\\
|k |k
D2 D4
| |
--------- aprox -38V

 

[Jan Panteltje]

Are you trying to obfuscate?

No, this is a real circuit.
I am also assumimng you will run both left and right channel from the same supply,
needing 2x value of caps and current.

27 volts would be too high, you omitted the transformer no load rise
and adjustment for local mains voltage.

Ok, use a lower voltage then, but the issue was about the type of rectifier configuration.

I get the strange feeling you have ground floating in your diagram, this is not true now is it?
that 50V has a middle tap I hope?

There are actually a standard range of torioid transformers for amplifiers in the shops,
I dunno if 50V (or 2 x 25 what it should be) is a standard value.