power supply circuit help

Thread Starter

hemuz

Joined Mar 7, 2010
14
hi all
i need to design power supply that`s used in powering micro-controller chip, the required circuit can operate from 4.5V AC source to 40 AC source to provide 3.4 to 1.9 V to power up the micro-controller chip , i tried to design it but the problem in case of 40 V is the massive heat , and in case of 4.5v source the circuit output is lower than 1.9 v that`s needed to power the controller

note that i need only 15 mA to be supplied from this power supply load

thanks
 

rjenkins

Joined Nov 6, 2005
1,013
Look at the LM2574HV series, either the adjustable or 3.3V versions.

This is a 'Simple Switcher' device, it takes anything from 4.5V to 60V DC in for 3.3V out.

You may need to add a simple resistor and zener diode to limit the DC to under 60V after rectification, but the current will be so low that heat should not be a problem.

That's probably the nearest you will get to the range you are after in a simple design.

Datasheet:
http://www.national.com/ds/LM/LM2574.pdf
 

Wendy

Joined Mar 24, 2008
23,408
Show us what you've done schematic wise. It might be possible to drop this voltage with a switching setup, maybe even one chip.
 

Thread Starter

hemuz

Joined Mar 7, 2010
14
thanks all, to the post i think the LM2574HV a solution but i need to implement the circuit by simple discrete components , the attached picture contain the circuit i make, the voltage drop across the 7812 regulator makes the voltage on the load lower than 1.5v i need to modify this value to more than 1.9v , noted that all diodes after 7812 regulator i need, and all diodes is .4v forward .

thanks
 

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rjenkins

Joined Nov 6, 2005
1,013
You are using two integrated circuits, so hardly descrete components ;)

If you want to do it that way, either find a low drop out equivalent of the 7812 or use a lower voltage reg (7809?) to feed the shunt stage so you can do away with the series diodes.
 
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