0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Elecrofreak,
If you used the original value of 1k for R15, it would smoke with about 16V across it. Maybe the pins of Q2 are incorrect, or maybe Q2's collector isn't connected.

About the only thing that would kill D11 is if it was shorted or connected backwards, and the current was set high. ;D

 

[ElectroFreak]

Thanks, Audioguru...

I used the 100 Ohm resistor for R15...
Q2's pins seems to be OK.
But I still can't figure it out how D11 burned.
So, I'm going to change R15 & D11...
Maybe it will work...  ;D

 

[audioguru2]

Hi Electrofreak,
U2's max output current is about only 30mA. With 30mA through a 100 ohm resistor it dissipates only 90mW. Didn't you use an OPA445 high power supply voltage opamp for U2? 

 

[ElectroFreak]

Hmmm....

I used TL081 ... OP445 not availabile in my area...
But something is strange here ... to me ...
I dont know....

 

[audioguru2]

Hmmm....

I used TL081 ... OP445 not availabile in my area...
But something is strange here ... to me ...
I dont know....

Hi Electrofreak,
Your positive unregulated voltage is probably about 41V (across C1) and your negative supply is about 5.2V (across D7). It is strange that the TL081 opamp survives with the resulting total voltage of more than 46V across it since its absolute max rating is only 36V!

I don't know what happens to an opamp with way too much supply voltage since I haven't tried it. I would feel foolish to ask the manufacturer. :

What did you use for Q2? Maybe it breaksdown from overvoltage too. 

 

[FireFly3]

I started collecting the parts for this project quite some time ago and then got sidetracked with other things.

 

[audioguru2]

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.

 

[audioguru2]

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?

 

[audioguru2]

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?  ??? :-\ ???

 

[audioguru2]

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 

 

[Tedy1]

Hi
I today have completed this PSU and it is working.
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.

 

[audioguru2]

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.  

View attachment 37292

 

[Tedy1]

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?

 

[audioguru2]

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?

 

[audioguru2]

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