The resistor used on the base of the transistor is typically around 1K ohm. PNP, NPN, or MOS transistors can also be used. The transistor primarily provides current gain. On mbed, any GPIO pin could be used for the logic control input to the circuit with DigitalOut.īasic driver circuit using a BJT transistor A discrete BJT is sometimes used instead of a newer MOSFET transistor especially on older or low voltage circuits as shown below. When voltage and current levels are in the correct range, the transistor acts like a high-current switch controlled by the lower current digital logic signal. To control smaller devices that use DC, a transistor-based driver circuit can be used to boost the current to the levels needed for the device. Larger devices might even need several amps. Even though they might require the same voltage levels, small external devices such as high-power LEDs, motors, speakers, light bulbs, buzzers, solenoids, and relays can require hundreds of MA. BJT, drivers, IGBT, MOSFET, MOV, optical isolation, optoisolator, relays, snubber diode, solid state relays, ssr, transorb, triac, tvs diode, varistor Driver circuitsĪ typical digital logic output pin can only supply tens of MA of current.
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