[sdiy] Best way to get a +3.3V rail from +15V?

[Tom Wiltshire]

A similar board I did on stripboard (the new one is getting a PCB) draws 101mA on the 3.3V rail. This board will have a 74HC594 driving some LEDs too, so I need perhaps 200mA. Does that change the picture any?

Thanks,
Tom


On 7 Mar 2013, at 14:26, blacet at blacet.com wrote:

> You can always use a series low value resistor to drop the 15V a bit and
> take some of the heat before the regulator. It depends on how much current
> you need and this will effect resistor value/wattage and regulator type/
> heatsink requirements.
> 
> 
>> Hi all,
>> 
>> I'm putting a little dsPIC prototype dev board together for mucking about
>> on. I've done such things before, but I've always had a +5V supply
>> available, so when I've needed a 3.3V rail for the dsPIC, I've stuck a
>> regulator on the 5V supply. Which was fine, but that's not the situation
>> this time.
>> 
>> If I've only got +/-15V available, what's the best way to derive a 3.3V
>> rail?
>> 
>> 
>> I've used 3.3V regulators on the 15V rail before and found they got hot,
>> which wasn't a surprise seeing how much voltage they've got to lose
>> somewhere. But perhaps I was doing something wrong?
>> 
>> Thanks,
>> Tom
>> 
>> 
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> 
> 
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