sine wave inverter

[aamir shabbir]

Hi guyz im making a sine wave inverter of about 100W power using ir2110 for sine wave pwm generation but the output is generated in several milli volts only although ive given 312Vdc on drain of mosfets what could be the mistake ive attached the cicruit also plz guide someone in detail. The Pwm frequency from microcontroller is 15Khz im using a avr microcontroller to generate two waves of 15Khz with 180 degree offset and applying both waves on HIN and LIN.

The circuit is attached for reference.

 

[ChrisP58]

What do your waveforms look like?

 

[aamir shabbir]

Very small amplitude of sine wave comes at output i think its just noise or something like that

 

[alec_t]

We don't know what your IN1 and IN2 signal timings/phasing are, nor the FET ratings.
Have you allowed adequate dead-time to prevent shoot-through?
What load are you driving with the H-bridge?

 

[aamir shabbir]

dear alec the IN1 and IN2 are fed with 15Khz Pwm signal on IN1 and inverted PWM signal on IN2 and the Mosfets im using are irf740

Both signals on IN1 and IN2 are 180 degree out of phsae

 

[alec_t]

What load are you driving with the H-bridge? With no load the bootstrap caps won't get charged. With an inductive load and no back-emf protection a voltage spike may have killed one or more FETs.

 

[aamir shabbir]

i am using it as an inverter i will connect a 50Hz R-C filter on output and drive load on the output of capacitor. The H bridge is driven by 15 Khz PWM so a first order filter is enough for 50Hz sine wave filtering after that i will connect the load across the capacitor

this is the circuit i will use for that is this correct?

 

[alec_t]

Without knowing what the load is we can't tell if that is correct. The 318Ω resistor will restrict the load current, and the load impedance will affect the filter response.
In most H-bridge circuits the load would be connected directly between OutputA and OutputB.

 

[aamir shabbir]

if i connect the load directly how can i get a filtered wave on load ?

And the circuit of IR2110 which i posted is that correct will it work properly if proper load is connected

 

[alec_t]

If the load is a motor it's winding inductance will act as a filter to suppress the 15kHz component of the winding current.
As for whether the circuit will work properly, you still haven't specified the load. Any load with an inductive property may well need RC snubbers or other spike-suppression components to prevent damage to the FETS arising from back-emf effects. You may need to experiment. I suggest you google for typical H-bridge protection arrangements.

 

[aamir shabbir]

and if the load is resistive then will the circuit work ?

 

[alec_t]

It should do.

 

[ChrisP58]

and if the load is resistive then will the circuit work ?

That depends on what you want it to do.

If a 50/60Hz modulated 15KHz square wave output is acceptable, then yes.

But if you want only 50/60 Hz power to the load, then you'll need an LC filter to block the 15 KHz PWM frequency.

 

[aamir shabbir]

but the problem over here is that that the mosfet does not turn on properly what could be the problm

 

[moffy]

What load are you driving with the H-bridge? With no load the bootstrap caps won't get charged.

The Bootstrap caps C1, C2 are charged when Q2 goes low through D1 from Vcc. No load required.

 

[aamir shabbir]

plz tell me one more thing will the ground of 312V side be short with 5V and 12V of the circuit or both will be isolated?

 

[alec_t]

The Bootstrap caps C1, C2 are charged when Q2 goes low through D1 from Vcc. No load required.

Quite right, Moffy. My bad.

will the ground of 312V side be short with 5V and 12V of the circuit or both will be isolated?

The 312V, 5V and 12V supplies share a common ground. There is no galvanic isolation.

 

[moffy]

I would suggest that you do your fault finding at a much lower and safer voltage than the 312v. You could use 30v as the supply and be able to debug your hardware with greater safety.

 

[aamir shabbir]

yes im doing the same but the problem is that the ckt does not work either plz suggest some thing is the ckt correct or not and if not what is the problem with the ckt?

 

[moffy]

Cannot give suggestions if you don't provide information. What do your waveforms look like? Post pics.