bench power supply

[gmw666]

Hi all
i am a complete newbie to electronics  and have a question. I built a bench power supply (modular) and it works fine, however although it is cc cv there is no indicator led to tell me when it has gone in to cc mode. is it possible to add one and if so what would be involved. the unit consists of a 240v AC to 36V DC unit and a 36v dc to dc buck converter  with a smaller buck converter 2A to supply the meter and fan.
any help or advice would be much appreciated
Graeme

[aheid]

You've not told us how the thing works, so how can we tell you how to modify it?

Show us some schematics of your circuit.

[gmw666]

hi Aheid
sorry as i said i am new to this as i explained it is a modular unit so the design is not mine i found it on utube and followed the video on how to make it i have attached some pictures so you can see what i have done what i am trying to do is wire in an LED to let me know when the unit has gone in to CC mode hope the pics help
thanks
Graeme

[xavier60]

CC indication needs to come from the Buck regulator's control circuitry. To do it with minimum risk, a schematic is needed.
Look for pins or unoccupied holes that might be for an optional CC LED.

[gmw666]

here are a few close ups of the modules i used purchased from ebay of course

The buck module is marked as an SZBK07 and the control chip on the back is an LM25116 i have tried to find a schematic for the module  but the closest i got was a schematic for the control chip from the datasheet

[xavier60]

The 5 pin IC is likely to be the CS op-amp. Only if you are confident that you can take measurements without any probe slips, look for a pin that that has a large voltage swing as the regulator goes in and out of CC mode. Your probes need to be needle sharp. I use Silver Steel probes.

[gmw666]

I believe you are spot on the 5 pin IC is marked as an A63A which appears to be an LM321 op amp Am i looking for an increase in voltage when it goes in to cc mod eand a drop when it resorts back to cv mode

[xavier60]

Just look for a large voltage swing for now.

[gmw666]

ok will do
i will get back to you with what i find. Also for info the small 3 pin IC above the op amp is a 5V regulator supplying the op amp and  the inverting input of the op amp appears to be connected to the centre pin of the cc pot