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

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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.

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Hi Heguli,

Is there something missing from the schematic? I can see the mosfets' Gate drive, but I cannot see the mosfets' Source return path.
I am afraid that the IR2103 mosfet driver cannot function without:
1. Connecting Vs (Pin 6) to LSP2 junction (Q2 Source pin), and
2. Connecting GND to Q1 Source pin (even through R5, since R5 is only 20mOhm and its current is kept reasonably low).

With this setup suggested, R3 and R4 will never see more than +/- volts across their ends, and the Q1 & Q2 Vgs will be kept in safe levels: 0..15V.

-George

I hope for nothing; I fear nothing; I am free. (Nikos Kazantzakis)

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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

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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First, thanks for your reply's guys. Very valuable info!

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

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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

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IR2103 has not INVRTED HIN ! Only /LIN

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That was over 2 years ago! I doubt that it is still an issue.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net