Re: power supply 2

Ken O wrote:

John

You mentionned earlier that I would need a circuit to supply the timer. I was going to use the LM317, but that has a maximum of 36 v. Now the transformer is given me 44v, that do not matter, Should I be just using resistors for a voltage divider and feed my timer directly with that? would there be any problem ?


This has to be designed, just like anything else.

Start with the voltage and current your 555 circuit requires. What current is it supplying to the base of the power switch? You have to get rid of all the extra voltage and still supply that total current. I would be thinking of a several watt resistor and a 15 volt zener to lower the voltage. The resistor would have to be sized to carry the peak circuit load current, and the zener would have to burn that additional current when the circuit was in the low current phase of its operation. If you wanted more precise regulation than that, you could add the LM317 downstream of that.
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