Question: What is the limitation on the output of the 555 timer with respect to the requirements of the input of the BDW42G? Can the 555 provide enough current at 5 volts to trigger (sufficiently) the input (base) of the BDW42G?

I am using a 555 timer to generate the pwm signal and would like to drive a power Darlington transistor like the BDW42G.

The Hfe of the BDW42G is 250 for 10amp Collector Emitter

Darlington output requirements: 90volts DC at 10Amps (max)

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    \$\begingroup\$ What does the 555 data sheet tell you about output drive capabilities? \$\endgroup\$ – Andy aka Mar 29 '19 at 13:37

You've got a circuit like this


simulate this circuit – Schematic created using CircuitLab

Ratings of components do not tell us how to design the circuit.

Here, if the 555 can provide a HIGH output into 100 ohms in series with 1.5 or 2.0 volts of the Darlington two-diode base input, then this circuit will work.

However, the TI 555 datasheet, (if powered with +5v) promises only 2.75 volts output with NO current promised. At +12 volts, you can pull 0.2 amps.


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