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'[EE]: Voltage Regulation using diodes'
2002\11\05@223019 by ards, Justin P

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Hello Piclist,

I wanted to be sure that I can use 3 diodes to drop the voltage from a 5v
rail down to around 3v to drive an EPROM requiring 1.8v - 3.6.  I was using
an LM317T but seems a little overboard as the EPROM uses very little power.

It 'seems' to work ok, just wandered if there were any pitfalls and if I
should use a particular sized resistor to provide a load to get the diodes
to do their thing and perhaps a capacitor to smooth things out a little.

Regards Justin

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2002\11\05@230215 by Rick C.

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Not necessarily voltage regulation, but voltage dropping. I've used this method
and have seen it used in commercial products. Just watch the power dissipation.

Rick

"Richards, Justin P" wrote:

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2002\11\06@003625 by Russell McMahon

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> I wanted to be sure that I can use 3 diodes to drop the voltage from a 5v
> rail down to around 3v to drive an EPROM requiring 1.8v - 3.6.  I was
using
> an LM317T but seems a little overboard as the EPROM uses very little
power.
>
> It 'seems' to work ok, just wandered if there were any pitfalls and if I
> should use a particular sized resistor to provide a load to get the diodes
> to do their thing and perhaps a capacitor to smooth things out a little.

- Aways use same diodes once you have it right.
- Don't go too light on current (say mA's at least.)
- Check EPROM allowable voltage range spec.
- Do use filter cap
- Rail will vary if 5V rail does.
- A zener and resistpr would probably be as good.
   (Either through Z with R to gtound or through R with z to ground !
:-) )(different Z in each case though)
- If EPROM doesn't mind what supply is then aim for middle of range to
ensure lots of margin.
- Many 3v regs available at lowish cost. As one offs why not use them?. In
volume they may be cheaper.


       RM





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2002\11\06@073944 by Olin Lathrop

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> I wanted to be sure that I can use 3 diodes to drop the voltage from a
5v
> rail down to around 3v to drive an EPROM requiring 1.8v - 3.6.  I was
using
> an LM317T but seems a little overboard as the EPROM uses very little
power.
>
> It 'seems' to work ok, just wandered if there were any pitfalls and if I
> should use a particular sized resistor to provide a load to get the
diodes
> to do their thing and perhaps a capacitor to smooth things out a little.

It seems you have a handle on this.  Three of the cheapest jellybean
diodes you can find with 500uA thru them and a 100nF cap should be fine.


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