PWM Motor speed contorller, MOSFET getting hot

Thread Starter

wstay90

Joined Mar 3, 2013
4
Hi,

I have a PIC16f877A controlling the DC speed motor.
The motor is basically 12V motor rating of 8W(around 600mA).Actually it is a submersible water pump which commonly used in Aquarium.
The mosfet that I'm using is K1300.
When i ask the electronic shop for IRLZ14, they didnt have, so they just find
a replacement part number from the book which is K1300.

When running the circuit,It takes few second for the motor to actually start pump the water and
the MOSFET get quite hot which is impossible for me
to touch after around 10 seconds. It is a T0-220 Package. Im running at 5Khz.

I'm from Malaysia, getting some other model MOSFET will be hard.
is it the wrong mosfet that im using ? or thats something wrong with my circuit I uploaded my schematic below. Or is it the gate-voltage(4.5V) for the K1300 is not enough and therefore produce so much heat.
Thanks and Appreciate
 

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Last edited:

antonv

Joined Nov 27, 2012
148
I haven't looked at the MOSFET data but for sure don't drive it through a 1k resistor. The MOSFET probably never gets time to turn on completely.

What is your PWM frequency? You may need to add a MOSFET driver circuit to make sure the transistor turns on and off completely.
 

tubeguy

Joined Nov 3, 2012
1,157
Hi,

I have a PIC16f877A controlling the DC speed motor.
The motor is basically 12V motor rating of 8W(around 600mA).Actually it is a submersible water pump which commonly used in Aquarium.
The mosfet that I'm using is K1300.
When i ask the electronic shop for IRLZ14, they didnt have, so they just find
a replacement part number from the book which is K1300.

When running the circuit,It takes few second for the motor to actually start pump the water and
the MOSFET get quite hot which is impossible for me
to touch after around 10 seconds. It is a T0-220 Package. Im running at 5Khz.

I'm from Malaysia, getting some other model MOSFET will be hard.
is it the wrong mosfet that im using ? or thats something wrong with my circuit I uploaded my schematic below. Or is it the gate-voltage(4.5V) for the K1300 is not enough and therefore produce so much heat.
Thanks and Appreciate
A 2SK1300 Mosfet looks like it's nearly fully on with 4.5 v gate drive.
So, try reducing the gate resistor to 10-47 ohms.
You could try reducing the PWM frequency. What is the duty cycle or the on time vs off time of the PWM signal?
 

antonv

Joined Nov 27, 2012
148
The issue may be that the 25mA that the PIC can source into the MOSFET gate is not enough current to turn it on fast enough.

Also, a small heat sink may be a good idea.

The transistor is probably a 2SK1300 MOSFET.

Do you have access to an oscilloscope?
 

Thread Starter

wstay90

Joined Mar 3, 2013
4
At that time i was running at 5Khz frequency;
setup_timer_2(T2_DIV_BY_16, 61,1) 20Mhz HS oscillator.
and set_pwm2_duty(61) which is 100%; correct?
so i might lower to 1.2Khz(Lowest) and trying lower and hopefully adding heatsink will help.

the gate resistor is the 1k or the 10k ?
Later i will try measure again using multimeter at the gate-source Voltage. see whether it is around 5V.
 
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