Help for PWM controlling MOSFET for High Current LED

[crutschow]

The IRF9540 has an on resistance of 0.11Ω, ten times the MOSFET I used in the simulation. When I substituted a MOSFET with a 0.105Ω on resistance the simulated dissipation was about 12W, which would warm things up a bit. So you need a MOSFET with a lower ON resistance.

I used a sense resistor of 0.01Ω which is a lot smaller than the 0.22Ω you used. 0.22Ω will waste a lot of power at high currents.

It sounds like it's significantly different than what I simulated.
What's a "high grade transistor"?
What's a "matrix PCB"?
What is the heat sink you are using?
Can the choke carry 10A without saturating? If the choke saturates, the transistor power dissipation will become very high.
Do you have an oscilloscope to observe the waveforms?

Certainly theory isn't going to work well if the actual circuit has arbitrary differences from the simulated circuit.

Post a circuit diagram of what you did, if you can.

 

[MrAl]

Mr.Al
can you give me a suggestion circuit too for my project that i can assembly it ? better if i can't meet difficult IC/P-MOSFET that in my country is hard to find. thank a lot.. because lot of peoples outside there that asking same question to this project but can find the efficient circuit..
regard.

Hello again,

Yes, the LM2576 for example or the LM2596. Just look for the data sheets and they give the circuits, and they are simple.
One circuit uses one inductor, one diode, two capacitors, two small resistors.
If you still want a more discrete component circuit let me know and i'll draw something up or recommend something here or somewhere else.

Also, do not test these circuits with your expensive LED. When you first build one there can be any number of things wrong which blows the LED ranging from bad circuit design to just something soldered wrong. Instead, wire up 4 or 5 diodes in series and use them as the test LED. They have a similar forward characteristic so the circuit will work almost the same with the diodes. Once you have it tested and working properly, only then use the real LED for the final tests.
Typical diodes are 1N4001 that will take up to 1 amp, and 1N5400 type which will take up to 3 amps like your current LED. Any diode 1N4001 though 1N4007 or 1N5400 through 1N5408 or similar will work, although the 1N5400 family have higher current of 3 amps.
Blowing out 4 1N5400 type LED's is a *lot* cheaper than blowing out 1 Cree XML T6 LED.

One of the tests you should do with the diodes is to check the current surge during turn on. If it is too high you'll have to incorporate some sort of slow start mechanism.