Re: Clamping to Linear regulators

AJ wrote:

Hi,

I have a 3.3V linear regulator that I want to use to clamp 24V to via a 100K resistor and a diode. Im pretty sure this is ok but just wanted to double check. Does anyone have any feedback?



Most power supply type regulators (i.e. 3-terminal ones) are 1-quadrant devices -- they supply current in one direction from a voltage at one polarity. If you just had a 3-terminal regulator, a 24V supply and your resistor the voltage at the output of your regulator would rise, possibly not to 24V but probably well above 3.3V.

If you just want a shunt regulator look for a 'precision zener'. These are IC's that behave like zener diodes, but with much better regulation. If you don't mind wasting a bit of power in your system make sure that you're drawing more current from 3.3V than the maximum that can be delivered from your '24V' rail and resistor, possibly with a simple load resistor on the regulator output.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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