IR2110 failure with a scope probe - diyAudio
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Old 23rd January 2010, 03:58 PM   #1
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Default IR2110 failure with a scope probe

Hello

i've made a PCB to build a amp (UCD topology ) with IR2110 as driver.

it starts to oscillate with a 6.8 ohms power load connected at output.

F=280 KHz,low side gate measurement is quite good,no ringing.
after 10 mn,i have try to check pre-filter signal with a digital scope (without ground )

i saw a little spark when the scope probe touch the Vs pin of IR2110.(ground clip was attached to star ground,far away from 0V onboard )

10 seconds after,output MOS (IRF540N ),fuses and driver blown.

maybe,this a problem with parasitic capacitor probe,i don't know..

if anyone got an idea,advice...to avoid IR2110 destruction.
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Old 24th January 2010, 07:35 AM   #2
AP2 is offline AP2  Italy
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Hi,

you put between pin 5 and pin 6, a pair of 100nF + polarized capacitors?
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Old 24th January 2010, 09:15 AM   #3
Eva is offline Eva  Spain
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Scope probe gound should never touch Vb, Vs or HO, these are floating nodes...
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Old 24th January 2010, 09:43 AM   #4
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but did not say that probe(gnd) has connected to vs or Ho driver.
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Old 24th January 2010, 01:46 PM   #5
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hello,

thanks for reply,

there is no capacitor (100nF ) as close as possible to the Vs-VB and Vcc-com pins.

only 1 uF plastic film,1.5 cm (0.7 inch ) from the pin to capacitor

ground clip was connected to 0V,on the capacitor bank.
the scope earth is disconnected.i can make measurement on floating voltage.

i will try to put 100nF between Vs-VB,Vcc-com,
maybe i have to discharge the probe (shorting ground clip and probe ) between each mesurement.

is it possible that the ground clip was to far from the measurement point,it makes a large loop ?


i saw IR application note,they talk about diode between Vs and COM (for undershooting voltage ),but in this case
this diode is connected in // with the low side MOS,it acts as a freewhelling diode !
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Last edited by thierry38efd; 24th January 2010 at 02:14 PM.
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Old 24th January 2010, 06:08 PM   #6
AP2 is offline AP2  Italy
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Hi,
Probe is original probe for oscilloscope or...simple wire?(in this case..destruction is ok)
only 1uF not polarized is..only theorical data.
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Old 24th January 2010, 06:30 PM   #7
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hello,

probe is tektronix 500 MHz.so it should be ok,(Cin 8pF).

do you mean 1uf is not a correct value,(at first,47 uF tantalum for HIGH side without bypass capacitor )

470 uf after the 12 V transistor supply.
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Old 24th January 2010, 09:18 PM   #8
Eva is offline Eva  Spain
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The oscilloscope is only floating at low frequencies, like 50/60Hz for line isolation, but nothing is floating at RF or even just at 10khz. Same applies to the power supply of your amplifier.

That's why you will be always creating an high frequency short circuit and destroying your amplifier every time you try to connect the ground of a conventional oscilloscope probe to a node being switched at high frequencies (or just with high dV/dt voltage slope).

You need a differential probe to do that, a special kind of active probe with one ground and two tips that senses the voltage difference between the tips.

And now, do you understand how dumb was the idea of connecting the ground of the probe to VB, VS or HO?
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Old 24th January 2010, 09:55 PM   #9
81bas is offline 81bas  Germany
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Why the oscilloscope probes must be floating to measure something between GND and testpoint? I understand, that it is required to measure the high side driver output voltage (connect between Vs and Ho), but the measure using normal GND does NOT require floating probes. And the sensing probe was connected to Vs - switching node with huge current capability - this would more probably destroy the oscilloscope input, rather than mosfets.

Please, notice the absence of the groundplane on input part in the photo. I think, the reason was in parasitics, which were produced by the osc probe (GND wire was connected far away from switching node with high inductance inbetween). These parasitics have turned the amp to be not an UcD, but to be a simple self osc amp with prefilter feedback... And such uncontrollable prefilter feedback can cause very high switching frequency, causing overheat of the mosftes (in few seconds). Also, experimenting with class D amp with output mosfets without any heatsink is pretty dangerous. Any uncotrollable behaviour will cause uncontrollable heating of them. I have also killed pair in such way
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Old 24th January 2010, 10:17 PM   #10
infinia is offline infinia  United States
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Hi
Some here above have hinted at the possible failure modes.
For the future when sensing high dV/dt low impedance source/s. Use an on board test point with a resistive voltage divider say at least 10-20 dB with a 50 ohm termination at the scope to keep the bandwidth. ( an old RF trick we call a sniffer probe)
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