This is actually a very common configuration where an extra NPN transistor is used to drive the PNP transistor. However, if the load voltage is higher than that, it’s extremely risky to try high-side driver configuration.īelow you can see an improved version of the PNP transistor based high-side driver. When using the PNP transistor based circuit similar to the one provided below on a load voltage that is the same voltage level of the GPIO of the microcontroller, it works fine (ofcourse the logic-level is inverted). Just note that the dc current per GPIO (aka I/O) pin of an Arduino (5VDC) is 40mA. The opposite of this is the “high-side driver” where the transistor is wired between Vcc and the load. resting on the low side of the load, this configuration is called as a “low-side driver”. Since the transistor is switching the path to ground i.e. Here, the load is between Vcc and the transistor, and the transistor is wired to ground. If the circuit is used to drive inductive loads such as coils or motors, it must be equipped with a diode to damp the inductive driver-off back-emf. For such a feeble current and small voltage, one 4.7KΩ ¼ W resistor is fine. Since the output voltage of an Arduino GPIO is 5V in logic-high state, the base resistor (RB in the above schematic) value is 5 – 0.7/0.909= 4730Ω. Well, just assume that the load (incandescent bulb) in this circuit requires 100mA of current, and the NPN transistor picked out has a typical gain (hFE) of 110. Then you can calculate the base current (Ib) to find the right base resistor. To use a BJT as a driver, you need to know several things to be successful – for example, current requirement of the load (Ic), and gain of the transistor (hFE). As a driver, the BJT (bipolar junction transistor) operates in saturation mode, means there’s enough base current to turn on the transistor fully. 7 MOSFET Driver IC – Why & When? Driver based on a BJTĪ common task for a transistor is switching a device on and off.
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