0-30 Vdc Stabilized Power Supply

[audioguru2]

I changed output transistors and it works. I get maximum 24V on output. Is this ok?

If you use a 28VAC or 30VAC transformer at 4.2A then the max output should be higher than 30VDC at 3.5A and the calibration trimpots should reduce the max output to 30VDC at 3.0A.

 

[fikic]

No, I have 3A version with 24V AC toroid transformer.

 

[audioguru2]

No, I have 3A version with 24V AC toroid transformer.

Didn't you see the latest parts list?

To have a 30V DC output then the transformer must be 28V AC or 30V AC.
Since your transformer is only 24V AC then the max output will be only 24V DC or 25V DC.

The transformer must have a currenty rating of 4.2A AC for the output of the project to be 3A DC.
Since your transformer is only 3A then the max continuous output current is only 2.1A DC.

 

[fikic]

My transformer is 250VA, so current isn't the problem. So 24V output is just fine?

 

[audioguru2]

My transformer is 250VA, so current isn't the problem. So 24V output is just fine?

Your transformer has an output voltage too low so I don't know if the maximum output voltage from the project at a current of 3A is 24V DC or 25V DC. It might have excellent voltage regulation at 24V DC but produce a lot of hum riding on 25V DC.

 

[fikic]

With this hum, you mean just noise, or it has impact on quality of output?

 

[audioguru2]

With this hum, you mean just noise, or it has impact on quality of output?

When the output of a "regulated" power supply has hum (100Hz in Europe or 120Hz in North America) then it indicates that the output is saturated and is not regulating the voltage.
The voltage changes of the AC input (including noise) and the ripple of the filtered rectifier are simply passed to the output. The output voltage will also change with load current changes.

 

[fikic]

So, I need at least 28V 120VA transformer? But output with 28V or 30V transformer has also hum at maximum output voltage, yes?

 

[audioguru2]

So, I need at least 28V 120VA transformer? But output with 28V or 30V transformer has also hum at maximum output voltage, yes?

No.
When a 28V AC or 30V AC 120VA transformer is used then the output at 30.0V and 3A will be regulated perfectly with no hum.

There is hum when the transformer voltage is too low which causes the output transistors, driver transistor and opamp U2 to be saturated.

 

[iliaskr]

i had the original pcb from ages ago so i modified it (at least i tried) with audioguru's changes.
however i am having the following problems:

voltage regulation seems to work, but when the current goes over 1 amp, i have oscillation on the 3055s and c7 gets very hot
u1 gets a bit warm
the current limiter works in a weird way, i mean, it limits current up to the middle position of the potentiometer then it allows current again. the led has a constant dim light and when the current limit kicks in it lights fully

now, i should mention that i could not find tle2141 so i used ca3140, the closest i could find here
also, i tried a higher value for c7, it reduced the oscillation, but it's still there
i replaced the d13,d14 with the original 5.6v zener, before, the led burned up

i am suspecting i have done something wrong modifying the old pcb, or the ca3140 is not proper for this i might try this on a stripboard if i have the time..

any suggestions?..

 

[audioguru2]

The very old CA3140 is completly different to a modern TLE2141 opamp:
1) Its maximum allowed supply voltage is too low.
2) It is very noisy.
3) Its datasheet talks about it oscillating.

 

[iliaskr]

ok...i will try to find a tle2141..

funny thing is that in every shop i asked about it they either never heard of it, or thought it was obsolete. especially with the crisis here in Greece it is very hard to find components in stock anymore, maybe online..
i'll get the 2141 somehow and will check again the circuit
thanks

 

[srecenvid]

hey.

Thanks for fast replay. My 3A supply is working perfect, now i will try 5A. i did scheme for 5a, as u said, can u check scheme and tell if everything is ok?

thanks alot!

P.S. sorry for 2 posts did not know which is more active

 

[srecenvid]

hello. i am new in forum. i checked yesterday almost all 118 pages and i have to admit that you are all amazing. Audioguru you are doing really good job. I already built today 3A version (will upload pictures after testing it). I found also picmaster's Schematic and i am interested to build 5A version also. Can u point me where to find picmaster posts and part list. is there any forum where can i read about 5A project?

thanks alot for answers

 

[audioguru2]

Hi Srecenvid,
The 5A version has only a few changes from the 3A version:
1) More powerful transformer, 28VAC/200VA or 30VAC/212VA.
2) Medium size heatsink for the 10A rectifier bridge module.
3) R7 changed to 0.27 ohms/10W.
4) Three output transistors on a huge heatsink with fan and a 0.33 ohm/2W emitter resistor for each output treansistor.

I didn't save the design by PicMaster. I think he changed the calibration trimpot positions and changed all the parts designation numbers which makes talking about it difficult (R7 is now his different number etc).

 

[srecenvid]

why i cant see 118 page when i am logged in, but if i log off i see?

 

[mixos1]

why i cant see 118 page when i am logged in, but if i log off i see?

This topic is fixed.. thanks for notifying me..

Mike

 

[tjille]

Hi,

I can't adjust output voltage down to 0V. Instead i get aprox 30 mV. No big issue but it would be nice to fix if possible. Is this something that could be solved by changing trimpot or resistor at offset inputs or is it a leakage i have to live with?

Output goes down to 0 volt when current pot is in its "closed" position.

Regards

 

[fikic]

Somewhere in this topic, somebody said, that some capacitor must be changed from electrolytic to tantal or something. Try to browse a little.

 

[audioguru2]

I can't adjust output voltage down to 0V. Instead i get aprox 30 mV.