Hello,
I am working on a circuit for some heating elements and I am trying to control them in order to limit the amount of heat they produce. To do so I am using a bunch of N-Channel MOSFETs that I control using a teensy 3.5's PWM signal (488 Hz). The teensy cannot produce a high enough voltage to be able to run the nmos effectively and as such I am using a 3.3V to 5V level shifter to provide a high enough gate voltage to reduce Rds,on. I am powering the heaters with a 24V power supply and I am using a 5V DC-DC converter to provide power to the teensy and to provide a reference voltage to the level shifter. I have a 100 Ohm resistor from level shifter output to gate to limit current and a 10kOhm resistor from gate to source to allow the mosfet to discharge.
3.3V to 5V level shifter: http://www.mouser.com/ProductDetail/SparkFun-Electronics/BOB-12009/?qs=WyAARYrbSnb%2bGYLWggQnjQ==&gclid=Cj0KCQjwi97NBRD1ARIsAPXVWWBRT5mQV-07DzXEsrCvUHC7szT0kbg3AMQUTV_p-2UGTRVs6k0LoRkaAlPpEALw_wcB
MOSFET datasheet: http://www.vishay.com/docs/91300/91300.pdf
What I found is that the MOSFETs get really hot when I run them. I was expecting them to warm up but this exceeds what I calculated. At 5V, Rds,on is supposed to be 77mOhm and since I am passing at most 2 amps I should get at most a 19C temperature increase for a thermal resistance of 62C/W. I even added TO220 heatsinks to help them stay at room temperature. I am kind of stumped and not sure of what the problem is. The only solution I can currently think of is to add more MOSFETs to spread the current. Is possible that the level shifter is the problem and it is not sending a high enough voltage to gate? What is a good way to troubleshoot this?
I am working on a circuit for some heating elements and I am trying to control them in order to limit the amount of heat they produce. To do so I am using a bunch of N-Channel MOSFETs that I control using a teensy 3.5's PWM signal (488 Hz). The teensy cannot produce a high enough voltage to be able to run the nmos effectively and as such I am using a 3.3V to 5V level shifter to provide a high enough gate voltage to reduce Rds,on. I am powering the heaters with a 24V power supply and I am using a 5V DC-DC converter to provide power to the teensy and to provide a reference voltage to the level shifter. I have a 100 Ohm resistor from level shifter output to gate to limit current and a 10kOhm resistor from gate to source to allow the mosfet to discharge.
3.3V to 5V level shifter: http://www.mouser.com/ProductDetail/SparkFun-Electronics/BOB-12009/?qs=WyAARYrbSnb%2bGYLWggQnjQ==&gclid=Cj0KCQjwi97NBRD1ARIsAPXVWWBRT5mQV-07DzXEsrCvUHC7szT0kbg3AMQUTV_p-2UGTRVs6k0LoRkaAlPpEALw_wcB
MOSFET datasheet: http://www.vishay.com/docs/91300/91300.pdf
What I found is that the MOSFETs get really hot when I run them. I was expecting them to warm up but this exceeds what I calculated. At 5V, Rds,on is supposed to be 77mOhm and since I am passing at most 2 amps I should get at most a 19C temperature increase for a thermal resistance of 62C/W. I even added TO220 heatsinks to help them stay at room temperature. I am kind of stumped and not sure of what the problem is. The only solution I can currently think of is to add more MOSFETs to spread the current. Is possible that the level shifter is the problem and it is not sending a high enough voltage to gate? What is a good way to troubleshoot this?