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0-30 Vdc Stabilized Power Supply


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Guest liquibyte

I've been doing this circuit in Eagle and I have another question.  What is the purpose of R2 and C2?  I don't understand why this connects to the AC.  I'm not sure I've seen anything like this before.

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What is the purpose of R2 and C2?  I don't understand why this connects to the AC.  I'm not sure I've seen anything like this before.

R2 and C2 couple the AC from the transformer to D5 and D6 so these rectifiers can make the -1.3V negative supply. Sometimes the output of opamp U3 needs to be -0.7V so U3 uses the negative supply.
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Guest liquibyte

I just meant that I'm used to Eagle schematics.  I'm in the process of rearranging this one now with all of the off board parts having pads.  Pay no attention to the TLC080P, I haven't found a TLE2141 yet and I think the pinout on this is the same.  I may have to make the part from this one.  I've also renumbered the parts to be more consistent.

post-107142-14279144596865_thumb.png

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The revised and improved circuit WILL NOT WORK with TL080 opamps because their inputs do not work when their voltage is close to the negative supply. Also their maximum allowed supply voltage is too low so they will not be reliable and might fail immediately. Also a TL080 opamp needs a compensation capacitor that is inside all modern opamps.

Why can you not purchase Texas Instruments TLE2141 opamps? 

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Guest liquibyte

I just meant that I'm used to Eagle schematics.  I'm in the process of rearranging this one now with all of the off board parts having pads.  Pay no attention to the TLC080P, I haven't found a TLE2141 yet and I think the pinout on this is the same.  I may have to make the part from this one.  I've also renumbered the parts to be more consistent.


I meant the part in Eagle, not the actual part.
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  • 2 months later...
Guest pascacio

Buenas noches

tengo una consulta , estoy construyendo la fuente de voltaje 0-30v
ya he adelantado bastante me parece muy interesante este proyecto
CONSULTA tendrán los datos de estos componentes  ya que la descargue de esta pagina pero  al empezar a poner los componentes no logro ver bien los datos (matricula) de los componentes , la lista esta bien clara  . la pregunta es en donde sale el PCB y los componentes esa impresión no la logro ver .
espero me puedan colaborar .

saludos. 

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  • 4 weeks later...
Guest xwasx

Hi,

Why is collector of Q1 connected to output of opamp U2, why not to base of Q2 ?


As I see when Q1 turns on it will turn off Q2 and Q4, then output of opamp U2 will go to max voltage, and maximum current od U2-output will go trough Q2. If Q1 collector is conected to base of Q2 then much less curent will go trough U2-output and  Q1. ???

bye

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Why is collector of Q1 connected to output of opamp U2, why not to base of Q2?

That is another problem with the original circuit. I agree that Q1 should short the base of Q2 to ground (not the output of U2) when the power is turned off.

The TL081 opamp has the problem called "Opamp Phase Inversion" where the output suddenly goes high when an input voltage gets too close to its negative supply voltage (within a few volts) which occurs when the power to this project is turned off and the negative supply collapses before the positive supply. You do not want the output voltage to suddenly go as high as it can when the power is turned off so Q1 shorts the output of U2 to prevent it. The modified improved circuit uses opamps that do not have this problem so it does not have Q1.

Here is a 'scope-photo of the output of a TL081 suddently going high when its input voltage becomes low:

post-1706-14279144649084_thumb.png

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Guest xwasx

Hi.

I have read last 20 pages of this forum so I read your post about this inversion problem. I have also tried to reproduced that and I't happens on my tl082 but only when inverting is 0.5 volts under negative rail.
Anyways I have made this PS about 10 years ago but only for 0-20V (because I had only 20v transformer).

Now I have made another one based on xristos 3rd schematics. I't can regulate from 0-25 (because of transformer, and low supply voltage on tl082, it's   -4v / 30v ). I have put -4V to negativ rail  avoid possibility of having inversion.

Also he is using 3k+2xZener for reference which is OK if current trough Zener is constant. But current trough zener is constant only if positiv rail is stable.  My new PS have some voltage drop on positive rail when I put 2A load, so current trough Zener changes. When current trough Zener changes it also change reference voltage by little ( couple of mV). So I added jfet BF256 as current source instead of 3k resistor and now it's stable by 1mV under load.

Also I have looked at NE5532,  maximum supply is +-22, that 44v, so if we subtract -4v for negative supply we are left with 40v, that sould be enough to regulate from 0-30 ???


Bye

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But current through zener is constant only if positiv rail is stable.  My new PS have some voltage drop on positive rail when I put 2A load, so current trough Zener changes. When current trough Zener changes it also change reference voltage by little ( couple of mV). So I added jfet BF256 as current source instead of 3k resistor and now it's stable by 1mV under load.

Redwire recommends using a voltage regulator IC instead of this pile of parts that use a zener plus an opamp.

I have looked at NE5532,  maximum supply is +-22, that 44v, so if we subtract -4v for negative supply we are left with 40v, that sould be enough to regulate from 0-30 ???

We are using modern TLE2141 opamps that also have a max supply of 44V and inputs that work all the way down to the negative supply so we do not need a negative supply for opamp U2 (but opamp U3 needs its output to go to about -1V so it has a -1.3V negative supply and a 10V zener to reduce its positive supply.

Calculate all the voltage losses and you will see than a supply of about 37.5V is needed to guarantee good regulation at +30V/3A. The modified and improved circuit uses a 30VAC transformer that produces +40.4V when the output is +30V/3A. With no load the 30V transformer produces 31.0VAC which makes the positive unregulated supply +42.4V so the 44V opamps are fine.


Bye
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Guest xwasx

Hi,

I have tried folowing for voltage reference
1) opamp+5v6 zener
2) tl431 (set to 10v reference with 2 resistors)
3) 3k resistor + zener6v2 + zener3v3
4) bf256 + zener6v2 + zener3v3

The test was that I set output to 5.000v and I measured voltage with and without load (load was about 2.5A)
1), 2) and 4) where OK, i didn't noticed any change (my instrument has 3 decimal places)
3) like I said it have voltage drop of about 20mV, but that depends on positive rail (probably with stronger transformer there would be much less drop)

Than I have done temperature stability.
I have heated board from 20 deg. Celsius to about 60-70 deg. Celsius (I used electric fan heater)
4) was most stable, +-10mV change below 50 deg., and +20mV from 50-70 deg. (first was -5mV, than it started to rise to 5mV, and after 50 deg. it strated to rise  to +25mV)
2)  20-30mV change (I think it was +30mV)
1) 40mV
3) I haven't tried because of load voltage drop problem.

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A 5.6V zener diode (a low current 5mA one should be used) was selected because a 5.6V to 6.8V zener diode has a stable voltage when the temperature changes. A lower voltage zener diode has a voltage decrease as the temperature rises and a higher voltage one has a voltage increase when the temperature rises.
Maybe the opamp was used to double the zener diode voltage so that the output amplifier has a low the effect from input offset voltage.

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xwasx,  What is the capacity of your transformer?  2.5 A is a healthy load.    I'm curious about the effects when the current is lower.

Do you have a sketch of how you set up option  4) bf256 + zener6v2 + zener3v3. 

It seems you measuring output of the PS but what was happening at the output of the different voltage references?

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Guest xwasx

Hi,

It's like this, but instead of LED it's 6v2+3v3.




Transformer is from junk,  but its about 24-25V 3A i think.

Xristos in his 3rd version of supply is using 3k+6v6+3v3 which is probably ok if positiv rail is stable under load. If for example you set output of PS to 10V, and you put 2A load, if there is voltage drop on positiv rail (for example from 35v -> 34), current trough zener changes, and than there is change in reference voltage of zeners. With bf256 I'm geting about 10mA constant current no mater of positiv rail voltage.

I'll try to attach picture. In picture it's some other fet because I havent had time to find model for bf256B

btw: I think that vref4 configuration should give best reference voltage (by simulation). I found in local store 1n827 6v2 (temp compensated) zener for 4$, so maby in summer I'll try whit that diode and vref4 configuration. 1n827 needs 7.5mA for best result.

post-93121-14279144649236_thumb.gif

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Xwasx,
You are asking for your project to fail because you have a tiny low power 2N3904 transistor for Q2 and only a single 2N3055 for Q1.

The datasheet for a 2N3055 shows that with an output of 4A its minimum hFE is 20. A graph shows that its hFE is typically 35 at 2.5A but is typically 55 at 2.5A which is a difference of 55/35= 1.57 times. Then the minimum hFE at 2.5A is 20 x 1.57= 31.4. Then its base current (the output current of Q2) is 2.5A/31.4= 79.6mA. 

Your unregulated positive supply is probably 32VDC.
If the output current is 2.5A and the output voltage is set low or is shorted then the 2N3055 heats with 32V x 2.5A= 80W which is a lot of heat to remove. That is why the modified and improved circuit uses two 2N3055 transistors to share the heat.

The 2N3904 will have 31V x 79.6mA= 2.47W but its absolute maximum power dissipation is only 0.625W so it will fry. That is why a little power transistor with a heatsink is used. 



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Guest xwasx

Hi,

I know that, this i'm only simulating to see how voltage reference behaves, and i put 2n3904 and one 2n3055 because was first on list. In real circuit I'm using bd139 instead of 2n3904 and bd249 instead of 2n3055 at output. For now one bd249, probably two when I'll put everything in box.

2n3904 will not die in LTspice, and 2n3055 is OK too :)

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Hi,

I have tried folowing for voltage reference
1) opamp+5v6 zener
2) tl431 (set to 10v reference with 2 resistors)
3) 3k resistor + zener6v2 + zener3v3
4) bf256 + zener6v2 + zener3v3

The test was that I set output to 5.000v and I measured voltage with and without load (load was about 2.5A)
1), 2) and 4) where OK, i didn't noticed any change (my instrument has 3 decimal places)
3) like I said it have voltage drop of about 20mV, but that depends on positive rail (probably with stronger transformer there would be much less drop)

Than I have done temperature stability.
I have heated board from 20 deg. Celsius to about 60-70 deg. Celsius (I used electric fan heater)
4) was most stable, +-10mV change below 50 deg., and +20mV from 50-70 deg. (first was -5mV, than it started to rise to 5mV, and after 50 deg. it strated to rise  to +25mV)
2)  20-30mV change (I think it was +30mV)
1) 40mV
3) I haven't tried because of load voltage drop problem.




Hi, in my variant I use resistor+ 2 zeners, because voltage is already regulated with LM317, so there will be no voltage drop (if supply voltage is high enough).
It's interesting to compare yet another solution for voltage reference - LM317L with resistors 270/1.8k. This will produce 9.58V. According to datasheet line regulation is 0.02%/V. If input voltage change with 1V, output will change with only 0.2mV.
Temperature stability is 0.65% which is 8mV in entire temperature range.
I think it's worth to try.

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Guest xwasx

Hi.

I haven't try LM78xx but i tried TL431, and it's OK, only it's little more sensitive on temp. change.

real is in attachment. (I'm using bd249 instead of 2n3005).

Changed 10uF to 47uF (had oscillations)
Currently negative rail is -4 and positive +31. (changed resistor around LM3x7)
Also I'll change 3v3 zener on negative rail to 3.9 or 4.x.
TL082 are inside now, but when I get time to play I'll try with NE5532.

NOTE : schematics is from xristos i think.


post-93121-14279144653351_thumb.gif

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xwasx,  I don't see the benefit in adding a bunch of parts (LM317, LM337 and resistors necessary to set the voltage) to increase the  precision of the upper and lower rails of the op-amps when most of the PS's life will be well within those ranges .  It seems controlling  the voltage to the non-inverting pins of U2 and U3 would be more critical and would provide bang for the buck.  In this area you are utilizing a 6.2 and 3.3 Zener to get 9.5V.  Why aren't you using 2- 5.6v zeners which are less affected by  temperature change than the 3.3V zener or one part- a 7812.    If you have to have a negative rail of approx -4 then why not use a single 3.3 zener here similar to the 5.6 in the original design?
Because you are only supplying 9.5v to U2, you had to increase the gain in U2  from about 2.6  to about 3.5. As you increase the gain, the op-amp becomes more sensitive to change in your opamp inputs resulting in diminishing returns.  In the end are you really ending up with a meaningful improvement with the LM317 and 337?

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Guest xwasx

redwire, I have made xristos version because I didnt know that I'll have voltage drop because of week transformer, his PCB is realy good, and I had tl082 and all parts in my junk box.

This are some numbers numbers I have on real PS:
No load V+ = 36.8V,  LM317=31.45, LM337=-4.25
23V out 3A load -> V+ = 29.3

So on 23V/3A I have drop which effects curent trough zener. So solutionfor my problem  was to put BF256 as current source.
As you see I have 37V on positive rail so I must have some regulation to stay within spec. of opamp.
Of course that other type of regulation can be used (zeners or zeners+transistor) but xristos PCB is for LM3xx so I dont see any problems exept of aditional 1$ cost.

Temp coef of zener as I'm seeing in datasheet is: (min, typ,max) in mV
5v1 : -2,7,-0.8,1.2
5v6 : -2.0, 1.2, 2.5
3v3: -3.5, -2.4, 0
6v2: 0.4, 2.3, 3.7

So like xristos said 6v2+3v3 is about -0.1mV temp.coef.
Also datasheets for zener diodes are stating that temp. coef is also function of working current. (see attachment)
So by datasheet best cheap zener for reference is 5v1 with current of 10mA. (if we are talking about temp coef. problem)

I'll try with 1n827 which is special zener (5v6zener + regular diode in one package) which have 0.001%/C temp.coef. and its 4$

Normal LM317 have 0.02%/C, so if we have +20C change on 10V reference we get 40mV change in output.

post-93121-14279144653842_thumb.gif

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