View Full Version : IRS2186SPBF output pulses sometimes disappears

Mar 21st, 2019, 06:29 AM
We have Problems with IR driver circuit IRS2186SPBF

We use the IRS2186SPBF in a buck stepdown converter from 310V to 270V. The switching frequency is 200 kHz. Ref attached picture:

Red color shows the output voltage from the stepdown converter.
Yellow is the switching output voltage in front of the output filter.
Green is the gate source voltage of the upper transistor (corresponding to the output signal from the IRS2186 driver).
Blue is the input voltage to the upper side (same) driver.

As we can see from the picture, the output signal (green) disappears occasionally in the driver. This is our problem and we wonder why this is happening.
The Vcc voltage is 12V. We have tried to increase this to 15V, without it helping.
We would very much appreciate comments/help on this matter.

BR Terje B°hler

Mar 22nd, 2019, 10:22 AM
Hi Terje,

welcome to the forum.
at first glance, it looks like your boostrap capacitor is discharging and cannot handle such a long pulse.

Bootstrapping is a great way to avoid using a second power supply for the upper side but care has to be taken when dimensioning it and in your control algorithm.
The capacitor size and pulse width have to be designed such that the voltage across the capacitor always stays above 9V (this is the undervoltage lockout of this gate driver, see figure 17 & 18 in datasheet).

could you please have a look at the voltage across the bootstrap capacitor during the switching and include it in your next waveform capture image?

Please let me know if this has solved you problem.
Best regards,