MOSFET driver killed with no particular reason

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
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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

can you post the schematic to sci.electronics.schematics , or upload to a web site and post the link to it? Might help us understand what you're doing.

--
Al, the usual
Reply to
Usual Suspect

In addition to the schematic, a photograph of your breadboard is needed. You may have wiring issues.

=== mark

Reply to
qrk

Read ALL the application notes carefully. Sounds like latchup (probably from poor layout).

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

This picture shows what I did:

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(NOTE: bootstrap diode is built in)

Plus what Spehro said as latchup really fall into my mind, as I have a "feel" that chip internal logic crashed somehow. As I'm already using decoupling cap, can you explain a bit more on that thx.

Reply to
w2kwong

......

Avoid drivers - :-) Hrmph!

My first guess is that the driver is way too fast for it's own good so you get ground bounce and probably a latchup. Or the chip oscillates. Both problems are due to the layout and decoupling - if there is an application note on how capacitors should be placed and wires routed then I.M.E. this should be followed without fail - because this will be the only way that *beeep* chip ever worked (once, in the lab).

The second guess is that the MOSFET is oscillating, overvolting and killing the gate then blowing the driver. This is sort-of a layout thing but not always. Usually I stick a resistor between 10 and 47 Ohms in series with the gate to preempt any oscillation.

PS: A discrete bipolar driver curcuit is not more expensive, it is much more tolerant of abuse and layout and the circuit itself is more robust too. Them sales people like to boast the biggest slew rates on their powerpoint slides - while most of the real power electronics applications do not need kV/nsec at the driver level it at all.

Reply to
frithiof.jensen

Hello, What kind of de-coupling cap are you using? You need something with a very low impedance, in order to supply the current spike for the gate of the MOSFET.

The other thing is, what is your PWM frequency? You might be buggering the chip because it's power will be similar to f*c*v^2, as a direct reflection.

Cheers, Rob.

Reply to
brushhead

I'm using electrolytic plus a green cap for decoupling. A fairchild application note

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suggests the gate resistor to be 4.7ohms. So for 10 to 50 ohms of Rg suggested by frithiof, would it be too large that may slow down rise and fall time by too much?

Also it sounds good idea to buy discrete high and low side drivers as it debugging isolated devices will be easier. Thankyou

Reply to
w2kwong

I would have though that that would be OK. Increasing the value of tge gate resistor will increase the switching losses in the FET, but will reduce the peak current required from the driver; simple Ohm's law that one.

I would not have though that adding discreets will help you though. Herpahs understanding the current in the FET would be more beneficial. Have you scoped what the gate drive waveform looks like yet? That might tell you all you need to know. Also what does the D-S voltage look like. Is there a lot of overshoot because of a bad layout? Is the voltage source (CD?) properly de-coupled?

There are loads of things to look at, but one thing my experiences have taught me is that gate drive is everything to a circuit. You may be ringing the gate-source capacitance like hell which is causing enourmous losses int he FET and then killing it.

Cheers,

Rob.

Reply to
brushhead

I saw the other thread in s.e.misc. If you would have cross posted this (instead of multiposting) it would have been easier to keep it all straight. :-)

At any rate, is that 100uF cap your Cboot? If so, shouldn't it be more like .1uF (100nF)?

Reply to
Anthony Fremont

the

I'm curious Frithiof, what sort of bipolar driver do you prefer? Something like this?:

. Vcc . --- . | . | . |/ . +----| . | |>. . | | . >-+--R1--+--R2--> to FET . | | . | |

Reply to
James Arthur

Are you saying that you manually moved the driver input wires by hand while the power was on?

Mark

Reply to
Mark

Wow, you really mean breadboard. Superstrips are unsuitable for these types of circuits due to the fast switching speeds. The long interconnection wires can have enough inductance to produce voltage spikes that exceed the ratings of your devices. This sort of layout frequently causes gate punch-through on the FETs.

I notice you have a lack of bypass capacitors. You need good quality bypass at the driver chip and the FETs. These capacitors need to have shortest possible leads to reduce the lead inductance. You can get circuits like your present breadboard layout to work if you bypass properly. Don't expect to drive much of a load with this setup.

This sort of circuit could benefit using much better breadboard layout practices. Use perf board and copper tape for your ground and power. Use SMT bypass capacitors in the range of 100nF to 1uF around the driver and the FETs. You also need bulk capacitance from an electrolytic capacitor (use a low esr type for switching power supplies). Your bootstrap capacitor is generally in the range of

100nF.

Try make your interconnections as short as possible. That could help.

--
Mark
Reply to
qrk

Sorry I'm newbie of using google group, how might I do cross post instead?

Reply to
w2kwong

YES!!!

Reply to
w2kwong

Please ignore this question, I just found out how, and sorry for my previous multiposting

Reply to
w2kwong

Well it's how you learn. I don't cross post, simply for avoiding encurring the wrath of the Usenet community.

Cheers,

Rob.

Reply to
brushhead

A plug-in breadboard?

Dont't use these for power control circuits.

RL

Reply to
legg

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