Nine ways to drive a MOSFET Number 1, direct drive This is the direct drive method. Just send a voltage straight from your logic
to the gate of the MOSFET. You can control it manually by sending an
ON or an OFF pulse. Or send a PWM signal. Since this is an low side MOSFET, the source
of the MOSFET is always equal to ground. When connecting the gate to our positive rail,
the gate to source voltage is also the signal voltage, and if it is more than your MOSFET’s
threshold, it will turn on. And to turn it off you simply connect it to
ground. What are the pros? It is simple
Can be always on Can do PWM What are the cons? Only low side switching Number 2, low side driver IC This is a low side gate driver IC circuit. You can control it with a high or low signal. Or you can give it a PWM signal. It can take a 3.3 or 5 volt signal as an input. And depending on whether the signal is high
or low… ..it will either send the drivers supply voltage
to the gate to turn it on… … or it will connect the gate to ground
to turn it off. What are the pros? Can handle logic level
Fast switching What are the cons? You need an IC Number 3, push-pull This is a push pull circuit. You can not use a pulse to turn it on or off,
it needs a constant signal. Like a PWM signal. This circuit amplifies the current send to
the gate, this allows for faster switching. Your microcontroller will thank you for this. When the signal coming in is high, the NPN
transistor allows a larger current to come through from the supply, which is led to the
gate. Then when the incoming signal goes low, the
PNP transistor starts to let current through. From the gate to the ground, and turns the
MOSFET off. What are the pros? Faster switching
PWM Can be always on
It is cheap What are the cons? It needs a constant signal Number 4, inverted level shifter This is the inverted level shifter circuit. It allows us to send a voltage higher than
the signal is, to the gate. It is controlled by two separate pulse signals,
and it can not run on PWM When we pull the first signal to ground, the
second PNP transistor will start conducting… …and discharges the gate into ground, turning
the MOSFET off. And if we pull the second signal to the ground,
the first transistor will start to conduct… And the supply voltage is able to reach the
gate of the MOSFET, turning it on. What are to pros? Higher voltage to gate
Can be always on What are the cons? No PWM Number 5, high side driver IC This is the high side driver IC circuit. It can not be controlled by manual signals,
only PWM will work. This is a safety feature. When a low signal enters the input pin, it
connect the gate to the source of the MOSFET, turning it off. The source is then at ground level, and also
the capacitor that is connected to it. This capacitor then gets charged by the supply
voltage through the diode. And when the incoming signal is high, the
positive side of the capacitor gets connected to the gate of the MOSFET, and since its negative
side is always connected to the source, the voltage applied to the gate is always relative
to the source. What are the pros? It's fast
It's safe What are the cons? No manual signaling
No always on capability Number 6, bootstrap circuit This is a bootstrap driver circuit, it works
similar to the driver IC, but without the safety features. It can accept manual signaling. When the second signal is pulled low, the
gate-transistor starts to conduct. And the gate pin of the MOSFET gets discharged
to the source pin. This turns the MOSFET off and causes the source
pin to be at ground level. The capacitors negative pin connected to it
now also is at ground level, The capacitor can now charge through the diode connected
to its positive pin. If the other signal is pulled to the ground,
then the second PNP transistor conducts and the capacitor now charges the gate, turning
the MOSFET on. The capacitor is still connected to the source
so the voltage applied to the gate stays relative to the source. What are to pros? It's cheap
It's fast What are the cons? No always on
No PWM Number 7, floating gate driver This is a floating gate driver. It works by using an isolated supply for signaling
and driving, and connecting its ground to the MOSFETs source pin. It can do manual signaling. And it can also do PWM. What are the pros? It's simple
Can do always on What are the cons? Needs a separate supply Number 8, opto-coupler The is the opto-coupler driver. This circuit uses a second supply connected
to the source of the MOSFET. The signals however can share the same ground
with either supply. It can do manual signaling, but no PWM. When the first signal is pulled high, it powers
the diode in the first opto-coupler. This causes the transistor to conduct and
through the red jumper wires it connects the separate supply voltage to the gate. The ground of that supply is connected to
the source pin, so the voltage is always relative and the MOSFET turns on. The other signal, when high, activates the
second opto-coupler. This then uses the two black jumper wires
to connect the gate to the source, turning the MOSFET off. What are the pros? Can do always on What are the cons? Needs a separate supply Number 9, charge pump This is the charge-pump circuit, it works
a lot like the bootstrap circuit. It has a classic charge pump, that charges
a capacitor eight volts above the MOSFETs supply voltage. When the first signal is pulled low, a PNP
transistor conducts and allows the capacitor to charge the gate to an absolute voltage
of supply plus eight, turning it on. The second signal, when pulled low, controls
the gate-transistor we have seen before. When this PNP transistor conducts it discharges
the gate to the source of the MOSFET. What are the pros? Can do always on What are the cons? Needs relatively stable supply voltage.
