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Topic: Why LED works but BC547 is not Working ? (Read 1 time) previous topic - next topic



Please help me out for my PIR Sensor example where i do make PIN 13 of Arduino Uno R3 HIGH when i get signal from PIR from Digital pin 2. LED works fine but when i attach BC547 with 4.7K registor to base pin of BC547, +V12 to Motor and Ground of Motor to Collector pin, and Emitter to Ground as per attached image and fritzing layout.

With same circuit, my LED get powered on but motor is not. I know i'm making something wrong but not able to find out where.

Please help me to make my DC motor run or energize my Relay ....

James C4S

Why 4k7?  You probably need something smaller.

What's the measured voltage of the battery when the motor should be "0n"?
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And I think you might have the collector and emitter back to front
Roy from ITCrowd: Have you tried turning it off an on again?
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when i connect power to pin 1, nothing to Base and ground of motor to pin 3 motor works does it mean that BC547 is shorted or not working ?


Feb 25, 2013, 05:06 pm Last Edit: Feb 25, 2013, 05:09 pm by xpleria Reason: 1
Well, how did you select the base resistor?

Refer to the datasheet. Check your transistor type (A, B, C). Probably your using type B with 220 hfe approx.

Connect your motor to the 9V battery directly via multimeter and measure the current. BC547 can't handle currents greater than 100mA.

The below calculations are based on the assumption that your motor uses 70mA.
IC = 70mA
IB = IC/hfe = 70/220 = 318 uA.
VBE (sat) = 0.8V
Hence voltage across resistor is 5 - 0.8 = 4.2V
R = 4.2/318u = 13kohm
with 10% overdrive, R=R/1.1 = 12kOhm

You probably burnt your transistor. Design your amplifier before you actually try it.

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