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How to deal with 24v->3.3V LDO circuit?

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vvsvv

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24v to 3.3v

How to deal with 24v->3.3V LDO circuit?
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Goal : input : +24V~~+30V
output: 3.3V , 80mA
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I plan to use "LM317" .
If I input the 24V directly to LM317's input,
then the efficiency is too low ( efficiency = Vout/vin = 3.3/24 =13.75% ),
So I want to use a pre-regulator circuit , which as




May the circuit work well ?
And how to calculate the Value of R ??

Thanks.
 

Davood Amerion

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ldo circuit

Use cheap switching regulator MC34063 from motorola. it is better (for your purpose)
 

harrytrinh

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ldo 24v input

If you realy want to use LDO at last stage for better performance you can you a pre-regulator- a switching regulator to step down from 24V/30V to 3.6V or 4.2V then use a LDO to get 3.3V.
 

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