![]() If you are doing a high side switch (pulls the load high or positive to turn it on) a P-channel device would be chosen. For discussion we will assume a 10V system (keeps the gate circuit simple). since the input to output voltage differential is so great.!!!Ī simple rule but definitely not inclusive is P is for Positive N is for negative switching. ? I think possibly the saturated N-channel circuit would be better. with the collector tied to 37 volts.? so that the GATE of the MOSFET is hard driven ON.!! by the MC34063…? Please advise. driven by the emitter output of the MC34063. Which circuit would you suggest rather.? using this P-channel. MC34063 is switched off… the GATE voltage will become almost 37 volts.!!! and the MOSFET should be turned off.!!! and hopefully when this happens the RDs of the MOSFET is very low.!!! and so heat dissipation in the MOSFET is very low.? so basically there will be almost 37 volts across the 220 ohm 10 watt resistor.!!! DOES THIS VOLTAGE ADVERSELY AFFECT THE VGS LIMIT OF THE MOSFET.? Hopefully when the “bottoming”. is dropped to about 0 volts.!! This should totally enable the MOSFET. !! So that when the MC34063 output transistor is turned on. there is a 10 ohm resistor from GATE to the open collector of the MC34063. the circuit is basically described above. using the MC34063… I want to know what value resistor I should be using across from DRAIN to GATE…? I hope that a 220 ohm 10 watt resistor should work. I using IRF4905… so the output of the MOSFET. the problem I have is the resistor I need across the DRAIN to GATE of the power P-channel MOSFET. to be driven by the output transistor of a MC34063. I believe that I have to use a P-channel FET. Thank you for a very good little explanation…!!! NOW… I have a 37 volt power supply. We just have to get over the myth that they work with “negative voltages.” ![]() Using a P-Channel with positive voltages is easy when connected to the circuit correctly. ![]() If your load voltage is higher, like 12 or 24V, then you might want to use an N-Channel MOSFET in a “low side” configuration. In this case, use a P-Channel MOSFET to turn the relay on from the Arduino’s I/O pin. The current necessary for the relay coil is too high for an I/O pin, but the coil needs 5V to work. For example, if you’re trying to turn on a 5-volt relay with an Arduino. An excellent use for P-Channel is in a circuit where your load’s voltage is the same as your logic’s voltage levels. We would need to dedicate a tutorial on when to use an n-channel and p-channel MOSFET. See what just happened there? We got a “negative” voltage using only positive voltage supplies… Why use N-Channel over P-Channel If you take the GATE voltage minus the SOURCE, you get 0V – 5V = -5V. However, now the GATE is at ground which means it is 0V.
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