0-30 Vdc Stabilized Power Supply

[kankki]

Thanks for the reply! :) I fiddled around with my board a  bit and lo and behold- the hysteresis thing just disappeared. Hope it ain't intermittent. The LED is still acting weird. Gonna do more research on that tomorrow.

One thing though. Is there supposed to be a ~2v drop across the pass transistors when they are fully open? I measured the base voltage when they are supposed to be fully open and it was around 1.1v.

Is the On-resistance that high on the TIP3055's that I'm using  :o

Anyways thanks for the help so far :)

[audioguru]

I fiddled around with my board a  bit and lo and behold- the hysteresis thing just disappeared.

Good. you fixed it.

Is there supposed to be a ~2v drop across the pass transistors when they are fully open? I measured the base voltage when they are supposed to be fully open and it was around 1.1v.

Doors and windows open and close. But transistors turn on and turn off.

The output transistors are not fully turned on in this circuit because the opamp U2 cannot drive its output voltage high enough. U2, Q2 and the output transistors have a combined voltage loss of as high as 5V.

Is the On-resistance that high on the TIP3055's that I'm using  :o?

A Mosfet has an on-resistance but a transistor has a voltage loss.
The datasheet for the 2N3055 transistor shows a max voltage loss of about 1.7V. The driver transistor Q2 has an additional voltage loss, opamp U2 has an additional voltage loss and current-sensing resistor R7 also has an additional voltage loss. Extra voltage must be provided when the mains electricity voltage is a little low.
So for an unregulated positive supply of typically 37.6VDC, the max regulated output is only 30.0VDC.

[kankki]

Thanks a lot for the help!  :)

[redwire]

gogo2520,  

I would not have an objection if you labled this thread "old"  and the other one "new"  or part 1 and part 2.     I started the other  tread when this one was  lost.  It was meant to be a continuation of the original thread.  Having 2 out there  is confusing to new posters.   The this one could be available for viewing but closed for posting.

[gogo2520]

hello
 about renaming the threads. They both have some valuable information and I don't want to mess either thread up. and that is what could happen, so the best for now is just to leave them alone. Think one of the other moderators with more experience should handle this.
  have fun
gogo  

[Guest]

Is there any reason why there's a 2 year gap between reply 1445 and 1446? I downloaded a schematic from 24 April 2008 which is within that gap. Can't seem to find the discussions for that version.
http://www.electronics-lab.com/forum/index.php?topic=7317.msg62464#msg62464

[audioguru]

Is there any reason why there's a 2 year gap between reply 1445 and 1446? I downloaded a schematic from 24 April 2008 which is within that gap. Can't seem to find the discussions for that version.
http://www.electronics-lab.com/forum/index.php?topic=7317.msg62464#msg62464

What are you asking talking about?
1445 was 556 years ago.

[Guest]

Just trying to look for an old schematic from 2008 (before there were 3 calibration trimpots).

[audioguru]

Just trying to look for an old schematic from 2008 (before there were 3 calibration trimpots).

There were never 3 calibration trimpots. Only two were added, one for max voltage and one for max current.
I think the latest schematic is the same as the one in 2008 except two calibration trimpots were added. Simply remove them if you don't want them.

[Guest]

Thanks for the clarification, I can finally finish this project after 2 years in the drawer.

[kankki]

Hi! I have had great success with this circuit  :D

But I have a problem. I'm trying to use relays to change the transformer taps from 24v to 12v. ( Series to parallell :) ). It works great in CV mode, regulation is fine.

But when I have it in CC mode the current limiting turns off a good five seconds or so, when the relays switch. There seems to be some capacitor holding a charge for a while.. I've tried to disconnect and connect all the caps, but still the same fault. Some parts that work together perhaps?

Is there any way I can modify this circuit to take the tap switching better?  :)

Help is greatly appreciated! :)

[Waldo]

I have a little predicament that I could use a second opinion on.

Problem

Yesterday I was charging a 12v battery (13.4v @ 1amp) and everything was great until I turned off the power supply and switched it back on without disconnecting the load. I ended up burning out my 2n2219. In hind sight, I've burned out 2 previous 2n2219 transistors under similar circumstances.

Proposed Causality

I speculate that this occurs because... while under load with the power supply off, the load is leaking back through my circuit. I have verified the function of D10 and R16 and they are in good working order.

Is it possible that the current from the load is leaking back into my circuit through the power transistors (2n3055) and causing U2 to overdrive the base of my 2n2219? If so would a protection diode (like D10) placed between the emitter and collector of my power transistors solve the problem?

I may be very much mistaken, I could use a second opinion.

I've got one 2n2219 left (more are on the way) and I would love to find a fix before I burn out anymore :)

Thanks

[audioguru]

Problem
.....
I ended up burning out my 2n2219. In hind sight, I've burned out 2 previous 2n2219 transistors under similar circumstances.

Then you built the original project that has problems with many parts being overloaded and it is not reliable. That is why we fixed and improved it in the forum for the last 6 or 7 years.
The tiny little 2N2219 was an old video amplifier transistor that cannot use a good modern heatsink.
We replaced it with a real little power transistor, a BD139 with a real heatsink.

It is a bad idea to have a powerful battery feed power backwards into the output of a power supply that is turned off.

[Waldo]

audioguru,

Thanks for the quick response.

I was able to navigate to one of your previous posts (page 55) and download your parts list (rev3) and schematic (rev2 11/09). I assume these are the most current based upon previous posts?

thanks for your help, I'll post a picture when my rebuild is complete.

[audioguru]

Hi Waldo,
Yes, you found the latest revision of the project.

[Guest zeraphine]

Hey Guys, I'm building this power Supply, using the Excellent PCB designed by PICMASTER (3-5A version), Can any one please tell me or point me to a post that describe what the Trim Pots RV1,2,3 does, thanks a lot.

[audioguru]

I can't find Picmaster's schematic. Maybe he changed all the parts designation numbers.

The trimpot connected to pin 1 and pin 5 of the output opamp nulls its input offset voltage so that the project has a 0.0V output when the voltage setting pot is at minimum.

The trimpot near the voltage setting pot calibrates the output voltage to be exactly 30.0V when the voltage setting pot is at maximum.

The trimpot near the current regulating opamp calibrates the current to be exactly 3.0A or 5.0A when the current setting pot is at maximum and the load current is very high. 

[Guest zeraphine]

Thank you very much audioguru, I'm waiting for the opamp samples from TI, I couldn't find either of the Opamps from where I live (Sri Lanka), I have attached the picmaster's Schematic and the PCB to this post, :)

EL3-_5A_PSU.pdf

[audioguru]

In Picmaster's circuit, RV3 adjusts 0.0V, RV2 calibrates 30.0V max and RV1 calibrates 5.0A max.

[PicMaster]

Hey Guys, I'm building this power Supply, using the Excellent PCB designed by PICMASTER (3-5A version), Can any one please tell me or point me to a post that describe what the Trim Pots RV1,2,3 does, thanks a lot.

Thanks for the comment,

[einstein0]

Hi

Yes, you have to use a Diode either in serie to the Battery, or as a Bypass to your Transistor...

Einstein0

I have a little predicament that I could use a second opinion on.

Problem

Yesterday I was charging a 12v battery (13.4v @ 1amp) and everything was great until I turned off the power supply and switched it back on without disconnecting the load. I ended up burning out my 2n2219. In hind sight, I've burned out 2 previous 2n2219 transistors under similar circumstances.

Proposed Causality

I speculate that this occurs because... while under load with the power supply off, the load is leaking back through my circuit. I have verified the function of D10 and R16 and they are in good working order.

Is it possible that the current from the load is leaking back into my circuit through the power transistors (2n3055) and causing U2 to overdrive the base of my 2n2219? If so would a protection diode (like D10) placed between the emitter and collector of my power transistors solve the problem?

I may be very much mistaken, I could use a second opinion.

I've got one 2n2219 left (more are on the way) and I would love to find a fix before I burn out anymore :)

Thanks

[gutoski]

I build this project, and i'm having some troubles, i have changed the 2N2219 for a TIP41C, it works fine, but the short-circuit protection doesn't works, the voltage regulator is less than 1/4 turn of pot, after 1/4 turn gives me around 27V and don't changes, when shorted gives me around 27V 1.5A, my transformer is 24V 5A.  ???

Thanks for help.  ;D

[audioguru]

I build this project, and i'm having some trouble, I have changed the 2N2219 for a TIP41C

Then you built the original version instead of the fixed and improved version that uses a BD139 driver transistor.

it works fine, but the short-circuit protection doesn't work

It has current regulation, not short-circuit protection. If you build the latest version that has calibration trimpots then when the current is set to 3.0A and the output is shorted then the output voltage will be 0V with a current of 3.0A. Then the driver and output transistors (two paralleled output transistors are needed) get very hot and will need a big heatsink.

the voltage regulator is less than 1/4 turn of pot, after 1/4 turn gives me around 27V and doesn't change

Then maybe your voltage reference (the output voltage of U1) is much higher than 11.2V or your output amplifier has wrong value resistors that cause its output voltage to be mostly too high.

when shorted gives me around 27V 1.5A, my transformer is 24V 5A.  ???

A 24V transformer is too low. It needs to be 28V to 30V for the output DC voltage to be 30.0V.
The setting of the current setting pot determines the max output current from a few mA to 3.0A.
I don't know which wrong parts or wrong connections are reducing your max output current.

[jrhodes]

can anyone help me i ve built a dual power supply. i did picmasters version and im having trouble ive got my 11.2 volts out of u1 so i know my reference voltage is right. my current limiter was working before  but i found a bad trace to ground and my voltage out of u2 was always 17 volts now when i fixed the bad trace i can adjust up to 17 volts only and current limiter light dont come on. i get a max voltage of 34 volts between ground and positive rails i get a max at pin6 of u2 of 34 volts but only get 17 at output havent tryed second power supply cause im waiting ing .33ohm resisters does a heatsink on transisters have to be grounded

[audioguru]

my voltage out of u2 was always 17 volts now when i fixed the bad trace i can adjust up to 17 volts only. i get a max voltage of 34 volts between ground and positive rails i get a max at pin6 of u2 of 34 volts but only get 17 at output.

The driver and output transistors are simple emitter-followers so their output voltage should be 1.2V to 2V less than the voltage at the output pin 6 of U2. Since your output voltage is much too low then either your transistors are connected backwards or they are blown up.

does a heatsnk on transisters have to be grounded?

The collectors of the driver and output transistors are both connected to +34VDC. They are also connected to their metal case so they must be insulated with thermally-conductive insulators from the heatsink or the heatsink must be insulated from 0V.