Re: plus4 power supply

From: Hegedűs István <>
Date: Thu, 20 Sep 2012 21:35:06 +0200
Message-ID: <>
Thanks for the information!
Very valuable! I have already purchased 2 of those DC-DC step down 
regulators (LM2956) from china but soldering quality was not the best... I 
had to resolder the adjustable resistor.
I will think on how to install it inside the PSU cage while the old PCB with 
the graetz and Elko Cap is installed.


-----Original Message----- 
From: Gerrit Heitsch
Sent: Thursday, September 20, 2012 5:31 PM
Subject: Re: plus4 power supply

On 09/20/2012 01:39 PM, Hegedűs István wrote:
> Hi Gerrit,
> That is strange because I have measured an old C64 power supply and
> other plus4 power supplies which provide 5.4v. The plus4 power supply
> schematic diagram says 5.2v though.
> I have checked the CPU datasheet and it says max voltage is 7v but of
> course the other components might not like it.

Usually the voltage is supposed to be 5V +/-5% which comes out to 4.75
to 5.25V. So even if the PSU supplies 5.2V and they all make it to the
ICs, that's still fine.

> I know the regulator you linked here but that still needs the diode
> bridges and the 4700uF capacitor (I believe).

Yes, those you still need. Also, it can't hurt to have 100nF ceramic
parallel to the 4700µF.

> The heat is generated by
> the 7805 regulator so you are right it will be cooler (and maybe more
> stable).

It should be as stable but a bit more noisy with the switching
regulator. And the rectifier will also generate some heat. About 1.3W
per Amp. But there will be less current drawn through it with the
switching regulator, so even that will run cooler.

When I replaced the 7805 in my C16 with a switching regulator (*) and
removed R10, the current before the regulator went down to 380mA when
supplied with regulated 9V, with the original supply, it was 280mA since
that is about 11V. This meant a LOT less heat in the box. Combined with
CMOS-EPROMs instead of NMOS-ROMs and heatsinks on CPU, TED and PLA, I
hope to have extended the livespan a fair bit.

(*) RECOM R-78B5.0-1.5  drop in for a 7805.


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Received on 2012-09-20 20:00:12

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