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dear all,

i build a full hbridge cct with 4 mosfet and 2 IR2110 mosfet driver and test it yesteday.

i supply 5V to Vcc, 12V to Vcc and give signal with 5V to Hin or Lin continuously to switching the 4 mosfet continuously at 40Hz like usual.

i connect Vb to Vs with cap 1uF, a diode FR103 from Vcc to Vb, SD and Vss to GND, cap 22uF from Vdd to Vss,cap 22uF from Vcc to com. HO to gate of high side mosfet through 22ohm and its Source to Vs. Lo to gate of mosfet low side through 22ohm and its source to com.

after that i supply 5V to Vdd and 12 V to Vcc and 0V to my load. i found that Vbs=11.0V, and Vgate of high and low mosfet or Vho and Vlo are around 4.0V.

then i increase the load voltage (middle of hbridge like usual) slowly.everthing looks find and the output is ok. but when i keep increase the voltage, i found that the Vho or gate voltage decrease and finally both high side mosfet turn off when the load voltage exceed 3.0V but both low side mosfet still on.

then i increase the Vcc to 15V, the load output voltage can reach only 6.0V. after that both the high side mosfet off again. i check Vbs, it show more than 10V so i think it is ok.

(1) so what problem?? why Vgate of high side mosfet or Vho keep decrease when i increase the load voltage? i need to apply high voltage later, may be up to 200V and 10A to my motor(load) so what can i do to my cct.

thanks..

from kim