Shunt or series, current and voltage protection, what is best ?

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howdoesthatworkguy

Joined Jul 23, 2007
39
With the most limited of parts I want to be able to create a circuit that can power my PIC, but also protect it and the other components. I require my circuit to operate as far down as 7v, be able to bad connections for a slipt second without the PIC resetting, current and voltage protection. 7805 was what I was first using but found this limiting and not ideal. I am working with small SMD devices and small is the word :)

The supply voltage is from 0v to 17v, spikes can go up to 27v, then a zener will clamp it. I had been looking at using a transistor with a zener on the base to control the voltage for the PIC. I don't require much power to run the PIC, most of the other circuit will run off the high voltage rail of 9 to 17v.

I had seen some use of a mosfet, with the ability to turn off if the polls are reveresed thus protecting the circuit which I thought was good, as well as acting as a current limiting device.

Any ideas anyone ? I don't want to look at exspensive IC solutions, I feel there must be a way of using a few discrets to do the same job.
 

bloguetronica

Joined Apr 27, 2007
1,372
With the most limited of parts I want to be able to create a circuit that can power my PIC, but also protect it and the other components. I require my circuit to operate as far down as 7v, be able to bad connections for a slipt second without the PIC resetting, current and voltage protection. 7805 was what I was first using but found this limiting and not ideal. I am working with small SMD devices and small is the word :).
Try using a LM78L05 regulator. It looks like a transistor. It only supplies 100mA although (can't perform miracles there).
 

SgtWookie

Joined Jul 17, 2007
22,220
Take a look at the LM117 / LM317 series of regulators.

National Semiconductor has datasheets available on their site.

Click: http://www.national.com/mpf/LM/LM317.html

The SOT-223 package is small footprint, capable of 1.0A output; needs minimum of two resistors to set the output voltage. Input and output filter caps required depending on length of leads.

Don't forget that you will need proper heat-sinking in order to dissipate that much power.
 
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