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2n2222 resistor value

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eplanet

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2n2222 resistor value
« on: February 15, 2012, 12:56:07 PM »
hi friends
please show me how can i calculate resistor value  connected to base of 2n2222?
thanks

Hero999

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Re: 2n2222 resistor value
« Reply #1 on: February 15, 2012, 01:35:51 PM »
Assuming Vcc is the same as the voltage powering the MCU, as a general turle of thumb, make the base resistor 10 times the value of the relay's coil resistance.

eplanet

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Re: 2n2222 resistor value
« Reply #2 on: February 15, 2012, 01:57:02 PM »
thanks hero999
is there any formula for this issue?
my coil is 57ohm