Contents
What makes a PNP a high side transistor?
High-Side Transistors (Note the FET has a Pull-Up resistor.) For a PNP BJT, the emitter connects to the voltage source, while the collector connects to the load’s positive side. Looking at the schematic drawing for an NPN and PNP, the PNP might look like it is upside down.
Which is the opposite of the low side switch?
The opposite of the low side switch is the high side switch. This transistor connects between +V and the load. Because of how transistors work, these can be a little more difficult to use in an Arduino or Raspberry Pi circuit. Typically these use a PNP BJT or P-Channel MOSFET.
What’s the difference between high side and low side transistor switch?
High-side transistor switch. The opposite of the low side switch is the high side switch. This transistor connects between +V and the load. Because of how transistors work, these can be a little more difficult to use in an Arduino or Raspberry Pi circuit.
Can a low voltage NPN be used safely?
I can tell you that the above configuration is not correct and can not be used safely. The low side switch is very simple as shown in Figure 1a. The low-voltage logic just has to feed sufficient current into the NPN transistor to turn it fully on.
When to use a NPN driver with a PNP MOSFET?
It is very common to use an NPN driver with a PNP BJT or P-Channel MOSFET, when the load voltage is higher than the signal voltage. Without a driver, the transistor may never turn-off. The driver, effectively, boosts the driving voltage high enough to unbias the Vbe or Vgs junction of the transistor.
When to use a high side transistor driver?
Until the FET is saturated, its Rds-ON can be relatively high, limiting the maximum current it can handle. It is very common to use an NPN driver with a PNP BJT or P-Channel MOSFET, when the load voltage is higher than the signal voltage. Without a driver, the transistor may never turn-off.
What is the base current of an NPN transistor?
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, the base current is 100/110 = 0.909mA.