mosfetmosfet-driverpwm
I am using this mosfet driver Intersil HIP2101. I have soldered a bootstrap capacitor to HB and HS of 100nF, a standard 100nF for supply stabilization and a 100kOhm resistor to HS and VSS. Now If I apply a PWM signal of 3.3Vp-p 200khz 50% duty cycle this is my signal:
Why is the voltage from t(0-ton) decreasing? The IC is meant for operating as a half bridge driver but I only have one PWM generator. Is this the problem or does it have another cause?
Schematic:
The analysis is correct. The main period of the duty cycle is higher than the reaction time of the motor mechanic, so the motor reacts only on the average voltage applied by the PWM output signal.
Vo(average)= Vsupply * DutyCycle
Basically it works like a low pass filter.
IN pin should not be pulled high continuously , this driver is a bootstrap driver , which means it needs to recharge the bootstrap capacitor through the low side mosfet when the high side mosfet is off.
buttom line , IN pin should be PWM from 0 to around 95% but never to 100%.
if you want 100% , ( for some applications you do ) there is solutions like adding a charge pump ... etc
check out this app note from Texas instruments Providing Continuous Gate Drive Using a Charge
EDIT:
After checking the datasheet it seems you have another mistake , that is powering the IR2104 from 5v , the IR2104 accepts 3.3v and 5v and 12v logic inputs at IN and SD , but its supply (aka VCC ) should be above between 10v to 20v. the IGBT voltage can be 5v no problem .
Best Answer
You should read up on how the bootstrap circuit works in order to understand if it is causing problems in your design. Obviously you suspect this already...
Typically you need to be alternately energizing and grounding that bootstrap capacitor to push the charge through the diodes in the bootstrap circuit. By removing the low-side switch, you are not providing a prompt switch transition that goes through Cboot and draws current from the input...
Story short, you need a high-side MOSFET switch that can provide its own bootstrap bias voltage without needing to be connected to the output switching node.