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Bench PSU 0-30v 0-5A Circuit question

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albert22

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0-30v power supply circuit

I have been looking for a good circuit of a "laboratory" power supply. I finally found this one. That looks fairly good. It features a floating regulator that could be scalable to more voltage. And selects diferent secondaries to keep down the power dissipation at the series regulator.

Specs:
https://www.radios4you.com/mastech-hy3005-LG.html
Schematics:
https://www.technica.ru/objects/images/scheme/50.gif

I dont understand something:
Please see the the N1 op amp (741C)
As far as I understand this is the voltage comparator
The Inverting input (Pin 2) is connected to the emitter of transistor V26A
This transistor drives relay K2A that switches secondary windings.The base is driven but what it seems a schmitt trigger.
Does this make sense ? I think that there is to be a sample of the output
voltage on this pin. Could this circuit work ? Or may be the schematic is drawn wrong in purpose?

May be this circuit would be useful for others, like me, wanting to build a bench power. If it works.

Regards
 

happy2005

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0-30v 5a power supply schematic

I think N2 current regulator and N1 voltage regulator. But i didn't understand the feedback loop of N1 and how the transistor V26A is working. V26A emitter is open circuited at DC, it can be wrong shematic.

It is very complex design and not suitable for bench supply for hobbiest. a 2x15V/1A simple linear regulator with short circuit protection will be ok. You can make it by using LM723 type regulators with output voltage range between 1-20V easily.

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IanP

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mastech hy3005

This circuit looks rather suspicious ..
If I were you I would try something else: what about classic power supply based on the unforgetable 723 voltage regulator?
Have a look at this project:
https://www.uoguelph.ca/~antoon/circ/ps3010/ps3010a.html
And I am pretty sure this one will work ..
Regards,
IanP
 

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albert22

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ps3010a.html

Thanks for your replys. I have seen some circuits based on the 723 but I am oriented towards a floating regulator. Ill probably use this one as a base modifiying the voltage feedback.
I pretend to build a small supply to test it. And as I have another bigger xformer, go for a 40V 10A, supply with triac preregulator on the primary. Surely with a PIC to control the firing angle. If it ever works Ill post the schematics.

I still have another interesting link:
https://members.shaw.ca/novotill/
specifically the 0-50v 1A supply at:
https://members.shaw.ca/novotill/LabSupply50V1A/index.htm

Again it looks as if there is something wrong here on the circuit compossed by the power transistors 2N6059 and 2N3055.
Note that says: "Do not build this circuit".
Anyhow I am learning a lot with this project. Getting new ideas on the various circuits

Regards
 

snovotill

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laboratory power supply 50v 5a schematic

Novotill here regaring:

https://members.shaw.ca/novotill/LabSupply50V1A/index.htm

The 2N6059/2N3055 circuit is actually correct. The reason for the strange setup is to increase the efficiency of the power supply at output voltages below 30 volts. When the supply is outputing low voltages, the current comes from the center tap of the transformer via 2N3055. At higher voltages the current comes only from the 2N6059. Very very clever. It says do not build because I don't want anyone getting a shock or burning down the house.

Stepan
 

albert22

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bench psu

Novotil,
I agree that when at low output voltage the 2N3055 supplies the current. But there is a 100ohm resistor in the emitter of the 2N6059. Then the output current from the 2N6059 goes thru the Base Emitter junction of the 2N3055 ( that is 1 Amp max). However the datasheet says that this transistor can handle up to 7 Amp on its base. I am wondering if working the transistor in this mode is correct.
Anyhow. Now that you say that the circuit is right Ill give it a try.
Thanks for your answer and for sharing the info that you have in your site.

Happy New Year
 

snovotill

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building a bench power supply

I have seen power transistors operated in this way on a couple of ocasions before. Not to worry, this is a good power supply which was originally made by Anatek. I like it because it's easy to fix with off the shelf parts in you accidentally feed 120VAC into the DC output or discharge a high voltage capacitor into it or some other such nonsense! I have 3 commercial units at home and they work great. Stepan
 

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