[Coco] Converting CoCo 3 to USB power

[Patrick Ulland]

The CoCo supply is more complex than you’d think. Starts easy, a 
transformer rated 8 volts either side of center tap. Runs about 10 volts 
under light load. Those 3 to connector.

The two (+/-) are rectified and sent to the SALT (or pepper 
replacement). The salt internally regulates these to become the +/- 
power rail for analog and zero crossing work – cassette, bitbanger, 
joysticks. Low current supply done.

  The raw +8VDC also goes to pass transistor Q1 – what many call a 
‘voltage regulator’. SALT has the 5v reference, and switches Q1 at the 
right speed to keep the + side of C15 a perfect 5v, which feeds the main 
5v rail.

I don’t see from this video what Bob’s done with Q1, maybe hidden under 
tipped over c29? Else there are more secrets;-)

  -ricku

CoNect

On 1/27/2024 6:21 PM, Lee via Coco wrote:
> I watched this video (https://www.youtube.com/watch?v=tTwTgGR-jSU&t=867s)
> on converting the CoCo 3 to USB-C PD power, and would really like to do
> this.  However I have some questions.  He mentions the two of the 3-pin
> connectors going to 12v and the 3rd pin going to ground, yet the Googling
> I've done seems to indicate the original power supply output 5v and 8v
> (NTSC model) to those two wires.  Am I missing something? Is it fine to
> supply 12v (or even 9) to both?  USB-C PD can negotiate 5v, 9v, 12v, ...
> from the power source.  Is it safe to provide the same voltage where the
> CoCo is expecting +5v and +8v?
>
> -----
> Lee
>