[sdiy] re re power supply pain

[Doug Tymofichuk]

Hello, Gavin,

> thanks for all the responses on this question,  Is it 
> possible to take the voltage coming off the filter caps 
> (after the bridge rectifier) and split it off so it goes 
> through all the neccessary regs but not in series?  
> (does this sentence make sense?)

Yes, this is the BEST way to do it, IMHO.

  Basically, to use one 3A 
> 25VCT transformer to drive three separate + and three 
> separate - voltage regulators?  Some responses to my 
> original power supply question seemed to suggest yes, others
> no.  I put together a schematic on how it would look (using 
> 220uF elec caps to filter the output of each of the regs 
> and tapping off the voltage across the 1000uF elec filter 
> caps from the bridge rectifier as I said to in put to the 
> regs)  possible problems occuring to me are 1. too much 
> draw on the transformer 

This depends on your total load to the power supply, not 
really on the regulator configuration.

 2. too much voltage going into the 
> 7805 

This may be a problem, if the wattage that the 5V regulator 
has to dissipate is too high, that will cause the regulator 
to overheat. This wattage is basically the current draw X 
the voltage drop (input voltage minus output voltage) 
across the regulator. This is why the 5V is sometimes 
derived from another lower regulated voltage, such as +15. 
But it all depends on the current draw on the 5V rail, if 
it is too high then it can pull down the +15V supply.
 
3. some signal interaction problem resulting from all 
> the voltage sources being connected together

No, actually this method minimises interaction. Because all 
regulators get their power right from the source (power 
transformer), there is less chance of interaction between 
supplies.

Take care,
Doug

----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca