Microcontroller 18f4550 gets hot

Discussion in 'General Electronics Chat' started by scorca, Jan 20, 2009.

  1. scorca

    Thread Starter Active Member

    Oct 31, 2008
    36
    0
    Dear Forum,

    I have a problem with the microcontroller 18f4550.
    I use its PWM for controlling a driver mosfet, and it goes to the boost converter mosfet. The output of the PIC should be 5Volt DC 150kHz 70% Dutycycle. I tested the output (without connecting it to the driver and the boost converter) and it is running well..

    I connect the converter with the microcontroller, it worked well and in a short time it became very hot, the driver did not give any output and offcourse the mosfet waas not switching. I dont know the reason for that.

    Anyone knows something about this?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Can you post up a schematic?
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    First, did you put a resistor between the gate of the MOS and the output of the PIC with a value of at least 200 ohms?
    Second, at such high frequency the current a PIC can provide (25mA max for each I/O) is not enough to turn on the MOS fast. You need to use a BJT at the output of the PIC to drive the MOS. Also, you will need to put a 500 ohm resistor between the gate and the source of the MOS as to turn it off.
    I think the PIC is gone, so replace it.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    10kHz is about the limit for a PIC to directly drive the gate of a logic-level MOSFET, unless the total gate charge is extremely low (as in the case with a 2N7000).

    As Mik3 mentions, you must use a 200 Ohm resistor between the gate and the PIC to limit the maximum current to 25mA. However, the 500 Ohms from gate to source is much too low; it should be 5k-10k.

    If you really want to drive your MOSFET in the 150kHz range, you should use a MOSFET driver IC. Microchip makes a variety of such driver ICs. Consult the applications notes before ordering.
     
  5. scorca

    Thread Starter Active Member

    Oct 31, 2008
    36
    0
    I use IR2301 driver IC. so PWM signal comes from microcontroller, this signal will get into the driver and then the driver controls the mosfet.
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Can you post a schematic of the circuit? Maybe the PIC is getting hot due a short on the pcb tracks. Check it.
     
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