what do u mean by measuring? 15 vdc is the optimum voltage that is measured many times before applying it as Vdc

I mean measure it while it's operating.

 

I mean measure it while it's operating.

yes, i have measure its being operated the voltage remains constant

 

Not sure if I understand the circuit, but isn't a Vgs of 2-3V asking for trouble? The threshold for that MOSFET is anywhere from 2-4V so you might be making it sweat.

 

D1 is 1n4048, VGS IS 2-3Volts.
vs-com is not measured.
any further advices

I don´t see anything called D1 in the schematic from post #15. Did you change it?

 

I don´t see anything called D1 in the schematic from post #15. Did you change it?

i think he is referring to the original schematic

 

Not sure if I understand the circuit, but isn't a Vgs of 2-3V asking for trouble? The threshold for that MOSFET is anywhere from 2-4V so you might be making it sweat.

yes it is very less according to the datasheet to provide enough current, that is the reason i cannot find out what could be the problem...i have never driven the mosfet with a driver like ir2110 always used a resistive network wich always worked,,,but now for buck converter controlling i require it.

 

Do you have a load on the output of your power supply. There needs to be a path to ground to charge the boost cap. It might be helpful to know the values you are using in your circuit for all the parts.

 

According to http://www.irf.com/technical-info/designtp/dt98-2.pdf the bootstrap capacitor value calculated from the formula it gives should be multiplied by a factor of 15 to prevent "overcharging which could in turn damage the IC". A too low capacitor also means that the voltage ripple from VB to VS could be high, meaning that the voltage on the gate of the MOSFET could fall below the threshold voltage and make it get hot too.

Making an assumption or two about your circuit I got a value of 42uF which multiplied by 15 gives 630uF. Perhaps this is why your IC is getting hot.

Other than that you might already have damaged it, have you checked the output transistors?

 

................
Making an assumption or two about your circuit I got a value of 42uF which multiplied by 15 gives 630uF. Perhaps this is why your IC is getting hot.
.....................

That value sounds way to high. That's likely nF not uF. I think you need to redo your calculations.

 

@crutschow, you're right, thank you. The correct value for the values I entered was 27nF which is multiplied by 15 to get 405nF.

That is still much more than 100nF (if I read correctly) that is being used on the circuit. Looking back at my calculations some of the values on the denominator were conservative (e.g. diode drop = 0.7V) so it might be even more than that. Perhaps the UF4004 reverse leakage is causing problems as well since the frequency is not that high and the capacitor has to hold charge for some time.

Bottom line is I would change the bootstrap capacitor from 100nf (if I read correctly) to >1uf and see if the MOSFET Vgs goes up.

 

D1 is 1n4048, VGS IS 2-3Volts.
vs-com is not measured.
any further advices

D1 from the original schematic, 1st post , is supposed to conduct when Q1 turns off. That's the only way to charge the bootstrap caps to the correct voltage. Measure with a scope the voltage on D1 and VGS and post the result here.

What do you mean by 2 to 3 V VGS? Negative transients or positive voltage? If positive that would mean the boostrap cap is only charged to 3V?

I was asking for measuring negative (prohibited) transients. What do have NEGATIVE going measured directly at the output of the IR2110 :

- VG to VS
- VS to COM

?