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Boost power supply problem

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when i ran my circuit last it was rapidly gaining tempurature. It got very hot in less than a minute and it was using anbout 0.9A. Why could this be then?

You should use a PNP/NPN transistor pair to drive a MOSFET. When you use a mosfet it will have much less on resistance than a NPN transistor, and it will then have much less heat dissipation.

0.9A from 5V is only 4.5W. The fan probably used most of it.

And as I said you will need over an amp of input current to get like 200mA of 12v on the output, and as far as I know, most 12volt fans use about 2.4 watts, so you would expect maybe a power draw of around 5 watts at 5volts.

-Ben
 
when i ran my circuit last it was rapidly gaining tempurature. It got very hot in less than a minute and it was using anbout 0.9A. Why could this be then?


Do you have the new inductor already? If the inductor is too small it will destroy the transistor because after a short time the transistor will be forced out of saturation and yet still have full current through it so that will cause a very large amount of heat in the transistor. You really need an inductor with a higher value for this to work. We calculated 310uH as the min, but that's the minimum value so you could go higher like 400uH. I wouldnt argue with 500uH either as Mr RB pointed out earlier.
 
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