Shunt Reg… need help

[apassgear]

This is a simple mono shunt reg using TL431 as the shunt control over a transistor.
It works as is but when I join grounds from each rail I have a short and can’t figure out the reason.
Attached is the layout of component over the PCB and a picture of the real thing.
Can someone point which is the problem?
Thanks, Tony

 

[Zen Mod]

catch must be in schematic

 

[apassgear]

SCHEMATIC

I did draw a quick schematic for this reg which is almost from the spec sheet.
Sorry for the representation of inductors.

Thanks, Tony

 

[Zen Mod]

with quick look , I can't see anything wrong with schematic

regarding pcb , I traced so much of them in everyday's work , so I'm simply not having enough concentration for doing that

 

[Elvee]

You cannot use this circuit with a center tap transformer: you need two completely separate (uncommitted, floating) windings (or transformers)

 

[aparatusonitus]

I think the problem is that you have CT transformer, so you have to connect transformer CT tab to ground as well, or just split transformers secondaries if you can. Moreover, if your inductors are common mode type, you can make CLC filter after each diode bridges, but if they are differential type, wire them as a LC filter in each power supply line only, they are not needed in ground rail.

 

[RJM1]

The problem is that you are using two bridge rectifiers; this would be fine if it was not a center tapped transformer but two isolated windings. With two bridge rectifiers your power supply grounds are not isolated from each other. If you use one bridge rectifier and the transformer center tap as ground you will be fine.

 

[Zen Mod]

yup , usual problem with ZM prior to first morning coffee

I didn't noticed gnd issue , being concentrated on TL and bjts orientation

 

[apassgear]

Guys, thanks for your answers, I'll test suggestions tonight and report the findings.

 

[apassgear]

Did try both suggestion and it only worked correctly with a transformer with double secondaries but most probably I will end using two trafos for this application.

Great help from you all, appreciated.
Cheers, Tony
🙂

 

[Salas]

CT to ground takes one bridge only.

 

[apassgear]

Thanks Salas, fortunately the problem was solved.