PWM and logic mosfet problem

[aqustic206]

Hello guys,
I am driving 15a lamp via MOSFETs without Heat sink .
How I can protect MOSFETs from burning??
is necessary pull down resistor?
Mosfets are very hot.Also ı used logic level ırlz44 mosfet.

 

[FvM]

Slow switching and risk of damaging the PIC output driver by driving four parallel MOSFETs. Use a gate driver circuit.

Static conduction losses with 15A load are about 0.5W per MOSFET, results in about 30K overtemperature, warm but not very hot. Switching losses can play a role.

 

[aqustic206]

@Fvm
I want to doing dimmer with pwm

Gate driver:A transistor,two resistor and ırfz44 are enough??

 

[KlausST]

Hi,

There are dedicated mosfet driver ICs.
And there are proven circuits.
No need to reinvent the wheel. All has been discussed before. Search the forum.

Besides what already mentioned:
GND wiring is critical. Especially the path from FET_source to PIC and/or driver.
Avoid load current to flow in this path. Make it short and wide...or a plane..

Klaus

 

[FvM]

For fast switching, you need a push-pull gate driver. A complementary emitter follower might do.

 

[aqustic206]

@Fvm
Thanks
Also Can ı this circuit without heatsink?Mosfets are ırfz44

 

[FvM]

Switching losses due to large gate voltage rise/fall time are one of several explanations for getting excessive losses. There are other possible reasons like self oscillation caused by bad circuit layout as KlausST explained. In so far we can't guarantee that a better driver solves the problem. Your TLP250 circuit misses a power supply. Did you notice that TLP250 has 10V minimal supply voltage?

I would go for a non-inverting low-side driver like TC427.

 

[aqustic206]

Sorry;
TLP250 pin8 minimal 12v

 

[KlausST]

Hi,

I don´t see a benefit in optical isolation (like your TLP...)
TC427 or similar is sufficient.

Klaus

 

[Audioguru]

Did you know that an incandescent light bulb that draws 15A when it is white-hot draws almost 150A when it is cool?
Is the PIC powered from 5V?

 

[aqustic206]

@KlausST
@FvM
pin 5 is hpwm 12f683 and 1khz
For example %100 duty mosfets are heating.Why?What is the problem ırlz44?irlz44 are logic levels mosfet
I want not to use heatsink

 

[KlausST]

Hi,

in post#2 FvM explained power dissipation.

What ambient temperature do you have?
And what MOSFET temperature do you have?

Klaus

BTW: I recommend to use a solid GND plane.