How do i control a n-channel mosfet with a tlc5940 sink PWM chip

Thread Starter


Joined Nov 7, 2012
Any help is very much appreciated, i am pretty desperate since i cannot find what i am doing wrong!


How do i control a n-channel IRL540A mosfet with a TLC5940 sink PWM chip, i want to control it with settings like half open, or open or closed!

What did i try?

Mosfet in series woth TLC chip out port and gate with resistor to VCC.
Problem: mosfet is fully open when chip does not give PWM valueQ

Mosfet controlled by transistor BC327 that can make a source from the sink by getting the VCC in.

Problem: minimal PWM value just put mosfet fully open

Used setup:

Used diagram (same as mine, used as an example):


Thread Starter


Joined Nov 7, 2012
I'll send a Dutch or Belgian beer for anyone helping me to get this right! I have IRL540A mosfets and want to control them, and being able to PWM them. Other PWM chips are welcome too if i can control them with an arduino (or something simular)


Joined Nov 12, 2008
Welcome to AAC.

I'm far from a MOSFET expert, but looking at your schematic, it appears you have the gate of the MOSFETs tied to pull-UP resistors. If the MOSFET is a IRL540, an N-Ch, then the MOSFETs will always be on whenever the output of the TLC5940 is high or simply not putting anything out.

I'd suggest connecting the resistors, RN1 and RN2, to GND making them pull-down resistors. In this way, the MOSFETs will be open (off) whenever the TLC5940 sends out a low signal or no signal at all.

Is this the problem you are having, i.e., the MOSFETs stay on when they are not supposed to?

I wasn't sure what you meant with the BC327 - I didn't see it in the schematic.


Joined Aug 23, 2012
1. What is the V,I of Load of MOSFET?
2. The TLC5940 output is a OD sink that the current is flowing into the output port from outside.
3. Most MOSFETs that it's Vgs >= 10V, when the DS is on(sat), unless you use a logic level MOSFET.
4. If you can change to P channel, it's better to drive the load, and the power of the load also raise to 12V, and the vgs can be >10V.