[Coco] CoCo 3 Voltage Regulator heat sink

[jdaggett at gate.net]

On 9 Apr 2009 at 9:34, Stephen Adolph wrote:

> I'm sure everyone knows this, but the +5 supply in the COCO3 looks to
> be a linear regulator..no wonder it is so hot.
> 
> I'm thinking about a 512k upgrade, but this power issue is pushing me
> towards my "sram version" as opposed to a "dram version".
> 
> Also, a good argument for the 63C09 (or B).
> 

Not really. The average current differences between the two is marginal compared to the 
overall current demand of the system. 


  
> I wonder if there is a nice little switchmode supply, like a PC VRM,
> that could be dropped in there.  I don't know of any "common" VRMs for
> 5V (something I could find in my scrap electronics pile for example).
> 
> Anyone know of a nice tidy solution, that can work as an upgrade to
> the standard COCO3?
> 
> ..Steve
> 

Be careful. The Coco3 also supplies voltage to an 8 volt regulator for the video 
modulator. Even if you replace the transformer with an external switcher it should be 
about 12VDC. That will increase the heat dissapation of the 5 volt regulator pass 
transistor that is wired to the SALT chip.  You will also have to remove an electrolytic cap 
and a diode to the 7808 regulator for the video modulator. C62 will have to be replaced 
with a short and diode D13 removed. These in combination with D14 form a voltage 
doubler. You could also short D14 but it can remain inline to act as a reverse polarity 
protection. 

james