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I am trying to simulate an IR21094 based half-bridge inverter on LTSpice. The design follows the recommended design on the datasheet by the manufacturer (https://www.infineon.com/dgdl/Infineon-ir2109-DS-v01_00-EN.pdf?fileId=5546d462533600a4015355c7e85b1679).

The issue? The low side NMOS switches on and conducts. Also, the LO signal can be seen as switching. However, the high side NMOS does not appear to be turning on. This can also be seen from the HO waveform. Basically, my output inverted waveform does not reach the supplied bus voltage (as in I would like it to reach 50 V, but it only reaches the Vcc).

I have placed screencaps of the HO and LO outputs.enter image description here

Here is a screencap of my schematic: enter image description here

And lastly, here is a screencap of the voltage across my resistor.enter image description here

Any and all help with fixing this would be greatly appreciated!

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  • \$\begingroup\$ 100k cannot supply enough current to VB. Reducing this value with raise clamp and hold Cap C1 voltage to VB so Vgs on high side will conduct better \$\endgroup\$
    – D.A.S.
    Commented Apr 18, 2021 at 1:10

1 Answer 1

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The high side relies on the boost converter to generate the gate voltage. The boost converter uses the switched output to charge the boost capacitor - your circuit has a load of 100k which does not provide enough current for this. Reduce the resistance to 1k or less - a value that represents the expected load. As well, your pwm frequency has to be high enough and the duty cycle > 0 and < 100% in order for the boost capacitor to gain adequate charge. In reality, do not use a 1N4007 diode - way too slow. Something like a UF4007 is more suitable.

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