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pusink
12-28-2009, 08:32 PM
I·make the RFID·project using parallax product with propeller chip. The question is why my IC regulator 5v·become hot...how to solve my problem??

Peter Jakacki
12-28-2009, 08:43 PM
Ice?
Looking at your other posts I see you are running motors, I hope it is not from the +5V rail that you are trying to do this. Remember power = volts*current and the volts that the +5V regulator is dropping times the current it is supplying equates to heat. If you are trying to feed +12V into the regulator then it is dropping +7V and even at 500ma this equates to 3.5W which is very hot unless you have good heat sinking. Of course you could use a switching regulator instead or you could power your motors off the +12V supply instead and PWM will still work.

Of course I could be wrong and you are not using motors but the same rules still apply. Try feeding the regulator with the bare minimum voltage needed for regulation, say 7.5V.

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*Peter*

Drone
12-28-2009, 09:57 PM
You could put a series power resistor between the input voltage and the 5V (assumed) linear regulator and dissipate "excess" power in the resistor instead of in the regulator. Typically you would not use a wire-wound resistor in this application as it may introduce unwanted parasitic inductance. There are pros-and-cons with this technique, but without more information on exactly what you're trying to do it is difficult to say more. The preferred method as described by Peter is to use a lower input voltage or change to a switching regulator, but switchers can introduce noise in RF circuits if you're not careful.

Regards, David