# Multi PWM switch with mosfet

I have a Futaba radio with switch that can send 3 different PWM signals (1000, 1500, 200 multi state selection). I have been trying to use these signal for an on/off Video transmitter power source and gripper relay in the following manner:

1. ->1000, state 0, both parts are off
2. ->1500, state 1, Video transmitter power activate, gripper relay off
3. ->2000, state 2, Video transmitter power activate, gripper relay on

I used an Arduino RC filter (4.7K, 100nf) to make different level of voltage (.2,2.5,5), also used a pair of IRF540 N-Mosfet. I have noticed the mosfet will be on when the analog line voltage is greater than 1 volt which is equal to 1100 band wide, hence I used a voltage divider in the way that output voltage always equal to mosfet Vgs, so for 1500 band wide (2.5 volt) need a 1k and a 2.7k resistor.

My question is whether this configuration can run a 500 mA device.

• yes, mosfets can handle 500ma. well, all of them i've used at least... – dandavis Feb 6 '18 at 4:22

## 1 Answer

The IRF540 has a gate threshold voltage of 2-4 volts for a drain current of 250 uA, so depending on the part, you might not turn on the FET or might only turn it on partially. There is no reason to divide the gate voltage down. Look for a FET with "logic level" gate threshold voltage of less than 2 volts. Then put a 2.5 volt zener in series with the gripper.

simulate this circuit – Schematic created using CircuitLab

• thanks @john-birckhead for advise , however mentioned Schematic not worked for me , and if I directly connect the Arduino PWM signal to the gate (bypass filter )it will work whenever V signal is more than 0.5 volt , but it won't work even Vgate more than 2 volte . do you think either of voltage divider, polar capacitor or pull-down gate resistor cause any malfunction ? – Hamid s k Feb 6 '18 at 16:23