Help on my h-bridge configuration circuit

Thread Starter

GERY

Joined Dec 4, 2009
2
Hello Kkazem I have been following your post and came to the believe that you can help me out of my pressing problem.
I have been trying to design a pure sine wave inverter using PWM, I have succesfully completed all the circuit stages needed, but, I was badly disappointed when I completed the circuit for H-bridge configuration stage, using an IR2110 driver and IRF3205. I wanted to test its behavior by powering it on with no load connected to it. I expected to have no bad result, but, I was surprised when the circuit sparked and killed one out of the two Mosfet from either side and the two drivers used.

I powered the circuit with a 24V supply, 18khz pwm to have an out put of 50hz sine wave, 100 ohm gate resistor.

Please I will like you to explain to me what could cause the problem and how I could go about the successful design of this circuit.

Please u can mail me to <snip> or post the answers here.

thanks so much I shall be very grateful.

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Hi,
You came to the right guy. This is what I do for a living, I design power inverters in the 100 watt up to 10KW power level. In this case you have two good choices for H-Bridge switches: 1) Power MOSFETs, and 2) IGBTs. Either would work well, and for the MOSFETs, you may need to parallel a few for each leg of the H-Bridge whereas for IGBTs, usually one will do for each of the 4 switches. You would not use a D/A converter as such, you would use PWM (Pulse-width modulation) from an analog chip or from a DSP. However, a 240 VDC source is not enough for transformerless operation. You need 240V*Sqrt[2] = 339V and that really isn't enough to compensate for drops in the circuit. You really need about 375 VDC to make a 240 VAC Sine wave from a PWM circuit. You'll also need an output LC filter to remove the switching frequency and the best choice is usually about 20 KHz to 25 KHz. This type of design requires the best breadboarding technique. Actually, I wouldn't make it without a PC Board for at least the most critical parts of the circuit, which are the gate drive and the power H-Bridge layout.

Gate drive, for either a MOSFET or IGBT are both very similar and it requires the proper drive circuit. You can't just drive it from the logic or DSP output. If you reallly are set on building this, then I highly recommend the IR2110 half-bridge gate driver. For a full H-Bridge, you'll need two of them and a 12V to 15V DC supply to run the chips. It's critical to keep the layout as short as possible and you must use a series gate drive resistor between each Drive output from the 2110's and the gates that they drive (that's 4 equal valued resistors of between 10 Ohms and 50 Ohms each). These help prevent ringing in the drain (FET) or Collector (IGBT) circuit. Selecting the proper MOSFETs or IGBTs is also critical. Use a breakdown voltage of at least 500 VDC to 600 VDC. THe battery power supply must be well bypassed as close to each 1/2-bridge section as possible between the upper fet drain and the lower fet source or its equivalent for an IGBT. You'll need a fairly high value low esr aluminum electrolytic cap in parallel with a couple of polypropylene film caps of at least 500 VDC each. One at about 2.2uF and another at about 0.47uF, both in parallel with a 10,000uF to 20,000uF, 500VDC Low ESR aluminum elytic cap for bulk storage. The impedance coming out of the batteries is way too high to use directly with the H-Bridge without all the bypassing I just discussed above.

Don't forget safety! It is critical to keep in mind that the potentials you'll be working with are very lethal and won't give you a second chance if you put your body across the 375VDC supply. Always use a fuse in series with the battery positive. For a 20A RMS output, your battery drain will be in the area of about 20ADC or a bit above, so use a 25A to 30A fast-blow fuse, or better yet, a superfast blow semiconductor type fuse. This may save you a lot of money on blown FETs and drivers, and may save your life as well. Be sure to put test points on your breadboard or PWB for easy hookup of scopes and DVMs. This is also a good safety practice.

Be sure and read the manufacturer's datasheets completely for the FETs, IGBTs, Gate Driver ICs, etc and do not exceed their ratings. In fact, make sure you have at least a 20% derating below the breakdown voltage and below the max current ratings, the derating should be more like 50%.

Good luck and reply if you have any specific questions for me.
Regards,
Kamran Kazem
 
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SgtWookie

Joined Jul 17, 2007
22,221
Hello Kkazem I have been following your post and came to the believe that you can help me out of my pressing problem.
If someone is not specifically addressing you in a thread it is better off to not request help directly from them, as they may not ever see it - and it may discourage other knowledgeable people from replying to your inquiry.

Starting a new thread for a new inquiry is a good idea, unless it is a continuation of another extremely similar inquiry that YOU have made.

If there are threads started by others that are similar, just include a link to them.

I have been trying to design a pure sine wave inverter using PWM, I have succesfully completed all the circuit stages needed, but, I was badly disappointed when I completed the circuit for H-bridge configuration stage, using an IR2110 driver and IRF3205. I wanted to test its behavior by powering it on with no load connected to it. I expected to have no bad result, but, I was surprised when the circuit sparked and killed one out of the two Mosfet from either side and the two drivers used.
Success is when the design works. Since it does not appear to work, it is not yet a success.

It sounds like you tried to use 24v for the IR2110 supply. If your MOSFET Vgs exceeds +/-20V, you will immediately destroy the MOSFET, and likely the driver as well. 15v is a good compromise supply voltage between fast charging of the boost caps, exceeding the low voltage shutoff, yet staying several volts away from the maximums.

The IRF3205 has a Qg of 146nC, which is quite large. You are attempting to charge/discharge that gate via a 100 Ohm resistor. You will have slow turn on and turn off times as a result, and fried MOSFETs once they have a load on them.

I powered the circuit with a 24V supply, 18khz pwm to have an out put of 50hz sine wave, 100 ohm gate resistor.
You really need to post BOTH your schematic, and your board layout.
 
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