Exceeding Gate-Source Voltage Ratings

ysfherdem

Hi,

I am using QA123C-1504R3 to drive C3M0045065D but the gate voltages exceed 15V and -4V because of the tolerances of the converter module. Should I use an additional LDO regulator or something? The converter module's voltages are 16.7V and -4.6V at 10% load.

Cannot I drive this MOSFET at 100% duty cycle with these voltage levels?

Also why the static gate voltages are so sharp?

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Veera

Hello there,

From the QA123C-1504R3 modules datasheet, the output voltages should not exceed 15.75V/-4V. Can you check if your input voltage is higher than the recommended +12V?

The first Gate-source voltage ratings mentioned in the datasheet (+19V/-8) are the absolute maximum values, allowing for ringing and overshoot. Whereas, +15V/-4V are the recommended Vgs voltages. For safe operation and long-term reliability, it is recommended to turn-on the device with +15V with +/-5% tolerance (+15.75V to 14.25V).

ysfherdem

Hello,

I think these values are for just 100% load. But I am loading this supply between 10% to 30% in this project.

In the datasheet, there are some graphs about output voltages. As we can see from these graphs, they have high tolerances. I am not sure about the negative supply. I measured -4.6V, probably I didn't load the negative side enough.

Also, I tested this device with a regulated power supply so I am sure the supply voltage is exactly 12V.

So these voltage levels are exceeding the recommended value and I should use external LDO, right?

Thanks

Veera

Hello,

From the Output voltage regulation curves, the module needs to be at least 40% loaded in order to maintain the gate voltage with in 15V+/-5% voltage range. If you are planning for a continuous operating application with lighter load on power module (lower switching frequency operation), we would recommend the use of Zener diodes which will add another layer of protection for long term reliability.

May we know the frequency at which the devices are being operated. As you might already be aware of, the load on the power module is a function of switching frequency and not the duty % of the device.

Thanks and best regards,

ysfherdem

Hello,

I am sorry for the missing information. I want to switch the MOSFET at 200kHz but sometimes I won't switch the MOSFET and the gate driver will give negative voltage(-4.6) to the gate continuously or I will work with 100% duty cycle so the gate driver will give 16.7V to the gate of MOSFET.

Probably I will use zener diodes to load the power module. Or maybe I should use another power module as an effective solution.

Thanks for your interest.

Veera

Hello,

From the datasheet, Qg=63nC. Therefore, gate drive power consumption would be 63nC*19V*200kHz= 239mW=>12V, 20mA. Hence, ideally the module should draw an additional 20mA on top of the no-load current.

In this manner, you can estimate the load on the power module. This will also help in selecting the power rating of the Zener diodes.

Thankyou for working with our devices.

Best regards,

TBhatia

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.