## What's the max voltage over R3?

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I have difficulty to choose the right resistor. Can I use the SMD part which is rated to 150V or do I have to use the normal resistor which is rated over 400V?

Datasheet: IR2103S

Regards
heguli

Heguli, I haven't used that driver. But, the voltage across the resistor will be equal to the current multiplied by the resistance, of course. One advantage of FET, like R3 will be driving, is that its gate has teraohms of impedance, so they'll be basically no current across R3 except when charging the gate capacitance. I think that's why resistors like R3 are often used, to prevent a significant current flow to source/sink the gate capacitance. Other reason for R3 is if the rise times of HO are fast compared to the transmission length, R3 can be used as a series terminator to prevent reflections causing overshoot/undershoot. I think you'll be quite fine with the SMD resistor.

There are TWO potential issues, and I don't think EITHER is a real issue.

First is power dissipation. The next is voltage drop. Power dissipation is an average measure; voltate is an instantaneous measure.

R3 is going to have a voltage drop larger than 0.7V only when the gate voltage is rising. When the gate voltage is falling, the diode limits the voltage to 0.7V. There is no static voltage. This voltage arises due to the gate charge current. Thus, it is in narrow spikes. It can never be more than the peak voltage delivered by "HO". The maximum gate current can be no larger than the peak that can be delivered from "HO".

Suppose that the peak current is 500ma. That would generate a voltage of 17V across R3 (IF there is sufficient voltage swing available from HO to do it). That makes an instaneous power dissipation of 8,5W. If this peak arises 1% of the time, then the AVERAGE poser dissipation is 85mW.

This is only an example, You have to plug in real numbers from the IR2103 to figure out your sitation.

Jim

Until Black Lives Matter, we do not have "All Lives Matter"!

New deal:

I'm planing to drive washing machine motor(5Amp x 230VAC motor), maybe 1kW would be the maximum load. Fet's can handle 7A/500V.

Drive method is mainly changing frequency from 10Hz to 400Hz and torque is PMW controlled. I have no exact knowledge what the pulse wide should be? I imagine it's the same as commercial frequency driver works, 1500Hz? As you can see, I'm in the beginning.

Regards
heguli

Quote:

I'm planing to drive washing machine motor(5Amp x 230VAC motor), maybe 1kW would be the maximum load. Fet's can handle 7A/500V.

Make sure you have plenty of heatsinking

IR2103 has not INVRTED HIN ! Only /LIN