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Please help me in Hbridge with BJT

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Ramesh_maharjan

Ramesh_maharjan

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h bridge bjt

I have designed the Hbridge with the BJT BC108 to drive the motor which draws 400mA current. But it does nothing when I connect the motor in the terminals of H bridge. When I remove the motor and check with LED it worked fine but not when motor is connected.
Datasheet of BC108 specified that it can withstand up to 500mA of current. So I think it is not a problem.
 

BC108 is rated for 100mA, not for 500mA ..
Select BJTs with Ic (Continuous Collector Current) of at least 1A, for example, BC639, BD135 ..

Regards,
IanP
 

IanP is right.

However, as your transistors do not have gone away after connecting the motor (it still can light up the LED then), it means that you do not give the transistors the proper bias (base currents).

With your motor, and the re-selected transistors, you have to calculate the base currents in order to make them saturated when opened.

nguyennam
 

The 100mA Ic for BC108 is not enough to spin the motor initially.
Check this circuit which commonly used in H-bridge configuration.

Added after 4 minutes:

The circuit.
 
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