Re: plus4 power supply

From: Gerrit Heitsch <>
Date: Fri, 21 Sep 2012 08:45:21 +0200
Message-ID: <>
On 09/20/2012 11:16 PM, Hegedűs István wrote:
> Would it be possible to replace only the 7805 regulator with this RECOM
> R-78B5.0-1.5 ? (suppose that I can remove it from the resin)

The RECOM doesn't run very hot, so it wouldn't be a good idea to hook it 
up to the old heatsink since that will be heated by the transformer. 
Besides, the old regulator is riveted to it, so it will be hard to remove.

If I wanted to go that route, I'd make a new PCB and use that instead 
with the regulator and rectifier apart from each other.

The problem with the RECOM is another one. It has a max current of 1.5A 
while the original regulator is a 78S05 which will give you up to 2A 
(unless the thermal protection kicks in). Since a transformer can take a 
certain overload, especially if the other output is not fully loaded, 
that makes the 1.5A written on the PSU a rather soft limit. Using a 
RECOM there will transform that into a hard limit. That's fine as long 
as you never exceed the 1.5A.

> Would it work with the resistor voltage divider on the output side?

No, that will have to go. The typical switching regulator needs a low 
resistance path to ground.

See here:

Not so much for the IC itself but for D1, but the RECOM has only one GND 

Also, if anyone here wants to put a RECOM in a C16 or C116, you HAVE TO 
remove R10 (the large white resistor).

> That would maybe easier than to mount this DC-DC step down regulator...

I'd do some free wiring... Not pretty, but you can get to everything.


       Message was sent through the cbm-hackers mailing list
Received on 2012-09-21 07:00:14

Archive generated by hypermail 2.2.0.