1. Home
  2. General Robotics Forum
  3. MOSFET driver killed mysteriously and need help

MOSFET driver killed mysteriously and need help

hi to everyone. I mysteriously killed 5 MOSFET half bridge drivers and wish to see if anyone can help.

I'm making a N-MOSFET H bridge circuit that switch a sine wave output using unipolar PWM for an inverter project. The gate driver I choose was IR21834 and I began testing half of the bridge on breadboard according to the datasheet circuit. Connecting input lines manually to V+ or GND to produce the output, the lower MOSFET would first work, but it always happened that somehow after changing the circuit such as connecting driver input here and there or switching the value of boostrap capacitor, at a random time the chip would go crazy . The chip would feel hot touch, followed by increase in current drawn, all of which signifying an internal short circuit. It seems the hide side circuit is causing problem, since the low side output would usually still functioning afterwards.

I believe such short circuit behavior can only be caused by shorting high side output to ground or to V+, and I swear I didn't, nor did I connect bootstrap diode and capacitor wrongly (I redid the circuit several times and same error can't happen over and over again). I thought it might be chip design problem but as I tried chip from other manufacture, L6388 from ST, the same happened. Now I'm really threatened as I don't want to kill any more chips. Although I might find out the reason myself but that would probably take another 10 chips dedicated to destroy, and this is why I ask for help here.

While not expecting a direct reason to the problem, I am REALLY REALLY glad if someone who have killed MOSFET driver before (for whatever reasons) to share his/her story, and also tell me what to avoid when working with drivers, thousands thanks in advance!

Reply to
w2kwong
Loading thread data ...
  1. Connecting the input manually to vcc actually should not work. The driver you describe is a bootstrap-only type (as opposed to hybrid bootstrap+chargepump) and so the output line must periodically go to ground to recharge the bootstrap capacitor.

  1. Are you just connecting HIN and /LIN? Many IRF datasheets for single-input drivers discuss having specific circuitry to prevent shoot-through. You should install a protective resistor on the rail and use an oscilloscope to see if there are current spikes during switching. If there are, you must redesign your drive circuit to have a deadband where both mosfets are open between high and low.

  2. High-side drivers usually have a Vbs threshold to prevent destroying mosfets by applying an insufficient drive voltage. To some extent this is more of a sanity check -- depending on your mosfets and load, this threshold may not be high enough to fully protect your circuit. Verify that Vbs never goes below the (practical) "full-on" Vds of your mosfet.

-chris.

Reply to
e c kern

First of all, let me say that an H-bridge PWM driver should not be driven by a sine wave. These circuits are designed to switch a square wave PWM signal. This may be the cause of your problem.

I will, however, assume that you meant square wave and typed sine wave.

In my experience, here are a couple causes of MOSFET driver death. Improperly sized gate resistor (the resistor connected between the driver and the gate lead). This is typically about 51 ohms. Undersizing will overheat your driver. Oversizing will overheat your MOSFETs. No 15V zener diode connected between the gate and the MOSFET source lead. This diode protects the driver. Good drivers like the HIP4081A have these built in. Supply voltage sag - do not go below the minimum driver voltage from a dying battery, power supply overload, etc.

Other words of advice: I probably don't need to say this, but you must have flyback suppression diodes across your MOSFET Drain/Source. Many MOSFETs have these built in. Use about 100 uF per amp capacitor across your load supply lines. This helps suppress flyback.

Overall, improper flyback suppression has been the biggest killer of MOSFETs and drivers for me when I was new to this. I recommend looking at your driver output on a scope to make sure the signal is clean. You can expect some ringing and spikes of about 6V or so, but no big spikes should be seen.

Hope this helps. I know how frustrating H-bridges can be.

BRW

Reply to
BRW

Sorry for my bad English and indeed it is square wave modulated with sine signal @40kHz

An app note from fairchild suggested use of 4.7ohm as gate resistor, and value too high will undermine efficiency.

formatting link
51 ohm being too high as it will slow down rise/fall time by too much?

The gate is insulated from D and S and can be considered as floating and there should not be any current flowing back to driver from gate. why is it necessary to have zener diode in place?

I suppose low voltage may cause insufficient Vgs that result in MOSFET overheat, but this should only kill the MOSFET not the driver.

I hadn't used freewheel diode as I haven't yet connect the bridge with inductive load, for decoupling cap I used 10uF. Since I'm not loading it with large current I think the cap value should be enough.

I thought driver+MOSFET bridge is pretty straight forward stuff. Although I've heard a lot how ppl blowed MOSFET, but very few mentioned destroying the driver. As this is the 6th chip I killed, I'm really frustrated. Thanks for your kind help!!!

Reply to
w2kwong

yes I know. and that's why I first played around with low side output, then pump in a low frequency square wave to test high side with multimeter. Because of low frequency I used bootstrap cap 100uF. At

12V supply I checked HG output voltage is 20V when is high justfying bootstrap was working, but then somehow it failed.

I thought the internal anti shoot through circuit which generates

500uS dead time is a bullet proof. Even if cross conduction occurs the one who dies should be MOSFET, not driver.

If Vbs goes low, at most the chip shut down and deactivate MOSFET, but this should not kill driver itself.

Thanks for your helping. This is the circuit I test with breadboard:

formatting link

Reply to
w2kwong

efficiency.http://www.fairchildsemi.com/an/AB/AB-9.pdf> Would 51 ohm being too high as it will slow down rise/fall time by too

That's right. Use the recommended resistor for your component selection.

Current is not the problem. High voltages are the problem. Don't confuse theory and the real world. It is highly recommended to use

15V zeners.

I think that about everything until I actually try to do it. Golf seems pretty straightforward, too :-)

BTW, how much current are you supplying? If it's 3A or less you can just use the LM18201 H-bridge. They work great.

BRW

Reply to
BRW

A couple of things:

HBridge circuits with MOSFETS are liable to fail when breadboarded the way you have done, --> way to much lead inductance for the high switching speeds/currents involved.

Also 100 uF is too big for the bootstrap, this by itself could destroy the driver on the first negative output swing if the Hbridge output voltage is high enough

Peter Wallace

Reply to
Peter Wallace

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.