power supply - senior moment

We all start somewhere
Post Reply
User avatar
ed
retired
Posts: 5433
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:
Contact ed

#1 power supply - senior moment

Unread post by ed »

I've built a number of power supplies like the one shown, at least I think I have.
This one doesn't work. The rail voltages are as shown on the diagram. The Tx is 2 x15v.
it's supposed to supply + and - 12v but the negative rail comes out at -20v ish.

At first I thought I'd got a dodgy 7912 so I bought some more and replaced the one in the circuit....same result, -20v
I've double,triple checked the connections because the pin outs on 78 and 79 regs are not the same...all is good.
Can anybody suggest what I'm doing wrong?
ps.jpeg
ps.jpeg (34.36 KiB) Viewed 1037401 times
There's nowhere you can be that isn't where you're meant to be
Top
User avatar
Nick
Site Admin
Posts: 16462
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2 Re: power supply - senior moment

Unread post by Nick »

Try adding a small load, not sure the reg will work with no current being drawn.
I think the main reason why Europeans no longer want to travel to the USA is the big time difference. For me, it's now 7pm. In the USA it's now 1933.
Top
User avatar
ed
retired
Posts: 5433
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:
Contact ed

#3 Re: power supply - senior moment

Unread post by ed »

thankyou...12.2 and -11.9
There's nowhere you can be that isn't where you're meant to be
Top
Post Reply

Return to “Beginners”