0-30 Vdc Stabilized Power Supply

[audioguru]

Hi Firefly,
Your 25V/5A transformer would allow the modified project to provide 25V or 26VDC at 3A.

With only 18VAC, many resistor values must be changed to make it work.

You cannot parallel regulated supplies easily without using isolating resistors that ruin the voltage regulation. You will have lots of problems trying to set them the same.

If you connect two of these regulated supplies together in parallel with isolating resistors or connect them in series, each one must have a completely isolated transformer winding or transformer. ;D

[ta03]

Hi all!I am planning to build this psu with the modified parts list.I managed to get 3
opa445ap as samples from TI (they came fron the us to greece in only 2 days at my door! wow!).I will use the original pcb.Is it correct?Also in the modified partslist C5 is 220nf and in the original 200.Why c5 is changed?D7 and D8 low current diodes are common parts?If i dont find them can i use the original diodes??I am using a 24V 5A transformer.

[audioguru]

Hi Ta,
Welcome to our forum. ;D
TI shipped your samples very quickly! ;D
The original pcb is fine except you must mount the rectifier bridge and Q2 externally on their own heatsinks. You might have difficulty fitting the larger R1, R2, R7 and C1.

C5 is only a supply bypass capacitor and its actual value doesn't matter. 220nF is a standard value.

BZX79C5V6 are common European low-current zener diodes that regulate much better in this circuit than higher-current ones. The original project didn't spec a part number.

Since your transformer is only 24V, the project will have mains hum on its output if it is loaded to 3A and you try to adjust its voltage above about 25V. :(

[ta03]

Thanks for your reply and i am glad that i am a member here! ;D ;D ;D  Indeed i was amazed with TI and FEDEX.

If i use any 5.6V 1/2W zener will it be ok?Also i contacted a local electronics shop and they have tip31c insted of tip31a. Is it ok?

[audioguru]

Hi Ta,
1/2W zener diodes are available spec'd at different operating currents. The project originally used 4.7k for R4, that set the current through zener diode D8 at only 1.2mA.
If you use a 1/2W zener diode spec'd at 40mA, it won't work very well. I use a 1N5231 1/2W 5.1V zener diode in series with an LED and current limiting resistor as a low battery voltage indicator for 9V batteries. With only 1mA through it, it regulates so poorly that it has only 4.2V volts across it, a good indication that the 9V battery is at 6V. It is spec'd at 20mA.

If you modify the project and use 1k for R4, then the zener's current is 5.6mA, perfect for a zener spec'd at 5mA.
5mA zeners are the BZX79C5V6, BZX55C5V6 and 1N5994. I hope you can get some. ;D

The TIP31A is rated at 60V and is cheap. The TIP31C is rated at 100V and costs a little more. Both are fine in this project. ;D

[ta03]

I will try to find one of BZX79C5V6, BZX55C5V6 or 1N5994.Lets hope that i will find one of them!Sorry for my ignorance about zeners, i do not know much about them(I study physics, not electronics  :-\ :-\ :-\ ). When someone says the eg. 5V zener spec'd at 10mA means that with a current of 10mA or more the voltage drop across the diode is 5v ?  ???
About tip31 the same told me the sales-person-something-whatsoever...I just wanted comfirmation(i dont want to blow anything especially the opa445ap's!).

[ta03]

Anyone please?  ??? :-\ ???

[audioguru]

Hi Ta,
The original project used 4.7k for R4 and a 5.6V zener diode without a part number for D8.
Therefore the current in both was only 1.2mA.
If you used a 1W 1N4734 5.6V zener diode that is made to operate at 45mA, then it probably won't regulate and have a voltage in the original circuit of only a couple of volts.
If you used a 1/2W 1N5232 5.6V zener diode that is made to operate at 20mA, then it might regulate a little but its voltage in the original circuit will still be low.

I have chosen 5.6V zener diodes that are made to operate at 5mA, and changed the value of R4 to 1k to provide a current of 5.6mA to match them. Since D8 is the main voltage reference in this project then it is best to have it regulate voltage very well. ;D 

[Tedy]

Hi
I today have completed this PSU and it is working. :D
I have 30V 4A transformer and TLE2141 now. Max voltage output is 34V without load,
but minimum is 4mV. Is that normal that minimum is 4mV?
Adjusting RV1 didnt change anything.
:P

[audioguru]

Hi Tedy,
It is great to hear you say that your project works well! ;D
Did you build the modified version?

In order for the offset voltage adjust trimpot to work with the TLE2141 opamp, the value of RV1 must be changed from 100k in the parts list to 5k, and the value of R10 must be changed from 270k in the parts list to 1k as shown on the datasheet for the TLE2141.

With your 30VAC transformer, the unregulated positive supply voltage for the opamps is about 43.8V, plus the 5.6V negative supply puts a total of 49.5V or more (if your mains voltage increases) across the opamps when your project has little loading. Their absolute maximum voltage is only 44V. :( 

[Tedy]

Thanks, Ill change trimpot and R10.
It it possible that I have damaged TLE2141? (I havent put any load on it?
And what transformer do you suggest, what should be output voltage of it?

[audioguru]

Hi Tedy,
Who knows how long your 44V-rated opamps will last with excessive supply voltage? ???
If you can't get the high-supply-voltage-rated OPA445AP opamps that I recommend, then the transformer should have an unloaded voltage of no more than 28V, which would be about 26V when fully loaded and its rating. Then the project's max output voltage would be only about 25V to 26VDC when fully loaded and your TLE2141 opamps will be operating at their absolute max supply voltage when the project has little loading. :(

[ta03]

I constructed the psu but there is a problem.when i alter
the output voltage it varies from 19v to 31v and its jumps rappidly
from 19 to 31 not proportionally.Also the current regulator does not
function,the led turns on only when the amps pot is on its end.Any opinions?
which components should i check?

[audioguru]

when i alter the output voltage it varies from 19v to 31v and its jumps rappidly
from 19 to 31 not proportionally.

Hi Ta,
It sounds like you have a bad pot. Measure the voltage on its slider when you turn it. The voltage should change smoothly and proportionately from zero to about 11.2V.

Also the current regulator does not function, the led turns on only when the amps pot is on its end.

Another bad pot?

Maybe your pots are from the same bad batch. Try another manufacturer. ;D

[Sallala]

Hi all!

I'm, who start this topic some years earlyer.
My parts are in a box one years ago, now  there is the time to build the PSU. :-)
I think, I visit the topic, before start building. It was a good idea ;)

I readed through the topic. Thank you everybody, who help to correct the circuit, especially audioguru! I updated the parts list, TI shipped the three free OPA445 today.
(I ordered it July 5 evening, and FedEx knocked the dor July 8 in the morning Whoaa. (I'am in Europe/Hungary)

Maybe I will finish it the end of the next week. (I will busy in the weekend) I will post my experience.

Gabor Salamon

[ta03]

I measured the volt pot and it is ok.the other pot varies from 0v to 1.6v .
When i connect a 30 ohm load the out put voltage drops (without current limitation)
and varies from 0.5 to 0.8v . ??? ??? ??? :-\Current limiting also seems erratic.

[audioguru]

Hi Sallala,
Welcome back! ;D
You are going to end up with a power supply that works very well.

[audioguru]

I measured the volt pot and it is ok.the other pot varies from 0v to 1.6v.

Then your pots are OK.

When i connect a 30 ohm load the out put voltage drops (without current limitation)
and varies from 0.5 to 0.8v . ??? ??? ???

If you have the output voltage adjusted for 30V without a load then with a 30 ohm load (1A) what voltage does it drop down to when the current pot is set to max?

With a 30 ohm load, when you adjust the output voltage upwards, is there a point where the voltage doesn't increase any more when the voltage pot continues to be turned up?
Then measure the voltage at pin 6 of U2. If it doesn't increase to about 34V then your transformer can't supply enough power.
What is the rating of your transformer?

Current limiting also seems erratic.

With the output voltage adjusted to 30V with a 30 ohm load, doesn't it drop to 15V when the current pot is set to about 17%?

[ta03]

with 30ohm load and pot set to 30v the output voltage is 0.81V(without  load it is 31V)  .With the volt pot set at min output voltage(with load) is 0.5V(without  load it is 19V) .By turning a bit the volt pot it jumps instantly at 0.81v and stays there independently from the pot(without load jumps from 19 to 31v the same way) .Pin 6 of u2 is at 31V  and i use a 24V 5A transformer. With the output voltage adjusted to 30V with a 30 ohm load,  it doesn't drop to 15V when the current pot is set to about 17%

[audioguru]

Hi Ta,
Your project has a few problems. Maybe its -5.6V supply section isn't working. Isn't the voltage of pin 4 of U2 -5.6V with and without a load?

with 30ohm load and pot set to 30v the output voltage is 0.81V(without

[ta03]

The voltage of pin 4 of U2 is -5.58V without load and with load, with current limiting on it is -4.35V.should i measure the voltage at the transistors?

[audioguru]

Hi Ta,
Your negative supply is fine.
Let's fix the output voltage without a load when it is 19V instead of zero:
1) With the voltage pot turnsd down to zero, the slider's voltage is 0V, isn't it?
2) Then the input pin 3 of U2 is also 0V, isn't it?
3) Since the output voltage is 19V, then the emitter of Q2 is about 19.6V, isn't it?
4) Then the output pin 6 of U2 is about 20.2V, isn't it?
5) The voltage divider of 56k R12 and 27k R11 from the 19V output results in 6.18V on pin 2 of U2, doesn't it?

[ta03]

Audioguru thanks a lot but before i do anything i just discovered that the 2 2n3055
are probably burned and they need replacement(strange they didn't smell bad...LOL).The collector of 2n3055 is its case right?I will check what you have told me right after.Thanks again for your patience.

[audioguru]

I just discovered that the 2 2n3055 are probably burned and they need replacement(strange they didn't smell bad...LOL).

If you have a big heatsink and the current regulator works, they shouldn't burn in this modified circuit. I never smelled a burnt metal one. Aren't you using transistors with the metal TO-3 case?

The collector of 2n3055 is its case right?

Yes.

[ta03]

I replaced the 2n3055.Now the its varies fron18.1 to 31 volts but now it is proportional to the volt pot.By turning the volt pot from max output to minimum,the voltage drops until halfway of the pots turning ability,and after halfway it remains steady at 18V.Now to your questions:
1)Yes
2)It varies from 0V to 10.7volts if i turn the volt pot from one end to the other.
3)Emmiter of q2 is 31.8V, base 18.6,collector 18.4 with output voltage at minimum
4)31,2V at max output ,14.4 at minimum
5)5.85 at minimum and 9.88 at maximum