I have used a very small MOASFET like a 2N7000A. Any small "logic level" mosfet. The 2n700a had a gate turn on voltage of 2.5V max.
S=gnd, G to micro. D to IR2117 in put and a pull up resistor to 15V. Burn 1/4 watt in the resistor.
Problem: this will invert the signal! Can you fix that in software?
If you can't, I can think of another way.
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Is your micro at 3.3V or 5.0V?
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With out inversion:
Gate to micro's supply (3.3 ro 5.0V)
Drain to resistor and resistor to 15V (10 to 20V)
Source to micro.
When the PWM pin of micro is high there will be 0 volts (G-D) on the little mosfet and thus the transistor will be off. The (S) will be at 15V.
When the PWM pin is at 0V there will be more than 2.5V (G-D) and the little mosfet will be on and pull the (S) down. Warning the micro will have to handle all the current that is going through the resistor. Maybe 10mA.