[sdiy] Multiple Voltage Power Supply / design problem!

[Seb Francis]

I'd seriously consider using a PC power supply with some additional 
filtering.  Can pick them up for next to nothing (free if you can find 
an old computer to cannibalise), and they'll give you all you need 
current and voltage-wise, with the exception of +9V which you'd easily 
get using +12V and a 7809 regulator (but aren't you saying you don't 
need this anyway?)

Seb


Rutger Vlek wrote:
> Hi everyone,
>
> I'm working on a nice 8xSID synth based on the works of Thorsten Klose 
> (www.ucapps.de), but with the addition of 8 seperate Moog filters (one 
> for each "voice"), controlled by 4 PIC's. This design has quite 
> complicated power requirements, so I started designing my own PSU, but 
> I think I need some help with it...
>
> First lets make a list of the power lines I need and the current 
> requirements for each of them:
>
> +5V    (for digital stuff, estimated max. 700mA)
> +5V/1 (for analog stuff, estimated max. 800mA)
> +9V   (for SID's, estimated max. 320mA)
> +12V  (for SID's and filters/op-amps, estimated max. 640mA)
> -12V   (for filters/op-amps, estimated max. 320mA)
> AGND  (analog ground)
> GND    (digital ground)
>
> The design is meant to be used with either 8580 or 6581 SID's. They 
> use different types of voltages to run so a jumper is added to select 
> the voltage on the SID's power pins. This means that EITHER 320mA is 
> drawn from the 9V line or 320mA is drawn from the 12V line. The above 
> list takes shows the needed 320mA on both rails...
>
> This is the schematic I made:
> http://members.home.nl/r.j.vlek/psu.jpg
>
> A big issue in the design of a PSU for this project is the amount of 
> current needed on the +5V rail (both +5V's are joined at the PSU). 
> Regulating this down from a high voltage results in alot of heat 
> production at the regulator, so my idea was to use a seperate 
> transformer with a lower output voltage for the +5V regulation 
> circuit. The second transformer is a center tapped 2x15V transformer 
> that drives the +12/-12V regulation circuit. The 9V is regulated down 
> from the +12V line.
>
> Two questions came up, during the design that I do not know the answer 
> to. I hope someone here can help out with it...
>
> 1. Is it alright to join the grounds of the normal and the center 
> tapped transformer and the earth pin on the 230V power inlet. 
> Something tells me that there will be a difference in potential 
> between the grounds of the regulation circuit from the two 
> transformers. Is there a solution to this problem?
>
> 2. What type of transformers should I use? I'd like to keep down the 
> heat on the regulators, but I think that 2x15V is the minimum for the 
> +12/-12V circuit and 9V is the minimum for the +5V circuit. Is that 
> correct?
>
> Greetings,
>
> Rutger
>
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