ir2110 .. shoud we use same ground for VDD , VCC and DC bus bar ..

[Rinson]

Hi.. i am working on an inverter circuit and for switching i use ir2110 as gate driver for each half bridge..
when i done it , i found that the circuit is working properly only when common ground point ( grounds are all connected together even if the sources are different ) is used for VCC , VDD and DC bus bar..


is it necessary ?

and i found that my lower power mosfet in half bridge is getting abnormally heated ?

is the common ground has anything to do with it ?

 

[eem2am]

Are you giving the lower fet enough drive voltage?

Lok at the switching edge....is it too long in duration = high switching loss

 

[kabiru]

Can you cheak the gate voltage with refrence to ground and reply back?

 

[Rinson]

Are you giving the lower fet enough drive voltage?

Lok at the switching edge....is it too long in duration = high switching loss

i have provided 12V vcc.. and the switching frequency is 1 Khz and the bootstrap and lower capacitor for lower mosfet are both 1 uF electrolytic ones...
if it is due to switching loss as you mentioned why it is not coming in upper mosfet ?

---------- Post added at 23:32 ---------- Previous post was at 23:30 ----------

Can you cheak the gate voltage with refrence to ground and reply back?

yes.. for the lower mosfet the gate to source switching voltage is same as vcc and the shape is perfect as pwm with desired duty... for the upper mosfet the gate to source voltage is less than one volt compared to vcc..

 

[kabiru]

Then their is problem some were I dont think the lower side is swiching the way it should it should be 5volt and the Hi side should be 10-12v all refrence to ground.

 

[Rinson]

Then their is problem some were I dont think the lower side is swiching the way it should it should be 5volt and the Hi side should be 10-12v all refrence to ground.

No.. i don't think so... because the mosfet requires a switching voltage of amplitude at least 10 to completely turn on... the switching is ok i guess..

 

[kabiru]

your driver will not work in this condition,the high side gate voltage is always higher that the low side and you can cheak the signal with osciloscope and see also cheak the frequency and reply.

 

[Rinson]

your driver will not work in this condition,the high side gate voltage is always higher that the low side and you can cheak the signal with osciloscope and see also cheak the frequency and reply.

I think there is a misunderstanding .... what i have mentioned and what you have intended is both same... The gate to ground voltage of upper mosfet is much more than the gate to ground voltage of lower mosfet... but in both mosfets when the the gate to source switching voltage is measured it will show only the voltage difference due to the bootstrap diode drop only..

 

[kabiru]

That's how it should work, then what is the problem are you having now?

 

[Rinson]

That's how it should work, then what is the problem are you having now?

yea... in the application note an 978 .. the picture for three phase inverter is given .. in that one .. the vdd , vcc, and dc bus bar are different supplies and their neutral or grounds are not connected together... i made my first circuit according to it ... it didn't worked.. then after many attempts i interconnected the grounds all together and it worked ... but i doubt it is necessary or not .. and i used only single half bridge for trial and the result was that .. switching was ok ... but the lower mosfet got heated much...

 

[kabiru]

Can you upload the circute diagram?And let's see were the problem is.

 

[bobbywu]

i think two MOSFETs conduct at the same time..can u upload the result pwm Vgs high and low side? I have the same problem with u a month ago and now can the inverter can work