Induction Cooking Table : IGBT keeping to short !

[Jon Elson]

Phil Allison wrote:

"Jon Elson"

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.


** Switching PSUs in many high powered audio amps use IGBTs - often in
parallel groups. The topology is a driven, square wave inverter - no
feedback or regulation is needed.
OK, in the off-line DC power supply section, this makes perfect sense!

Not in the audio amp section. (You can probably tell I rarely get into
late-model consumer audio gear.)

Thanks,

Jon

 

[Phil Allison]

"Jon Elson"

Phil Allison wrote:
"Jon Elson"

IGBTs in an audio amp sounds really odd to me, I'll bet a set of
FETs could have been dropped into it perfectly.


** Switching PSUs in many high powered audio amps use IGBTs - often in
parallel groups. The topology is a driven, square wave inverter - no
feedback or regulation is needed.

OK, in the off-line DC power supply section, this makes perfect sense!
Not in the audio amp section.

** But no body said that they were used there, you misread Arthur's post.

" A while ago, I had the misfortune to work on a switcher that was
in a Yammy powered speaker."

The "switcher " is the PSU.

..... Phil

 

[Phil Allison]

<jurb6006@gmail.com>

I am not responding to you here Phil, but the whole bunch.

Everyone wants to get into all this esoteric shit here and really an
induction top doesn't run at microwave speeds. Simple RF. I mean television
SMPS RF.

The bottom keeps shorting, well lessee here, what can cause one transistor
in a totem type pole circuit to short ?


** An intermittent fault ( ie internal short) in the load.

That induction heating coil is a non- trivial device running at high voltage
& frequency.

The briefest short or arc between adjacent turns would take out one or both
IGBTs instantly.

BTW:

Stop being such a PITA jerk.



..... Phil

 

I am not responding to you here Phil, but the whole bunch.

Everyone wants to get into all this esoteric shit here and really an induction top doesn't run at microwave speeds. Simple RF. I mean television SMPS RF.

The bottom keeps shorting, well lessee here, what can cause one transistor in a totem type pole circuit to short ? This is a switcher. Can an imbalance cause a problem ?

First of all the drive. Now you might not be able to compare the drive to the top transistor without diff inputs or all that, but yuo should stil be able to tell. If the duty cycle is 50/50 then the E-B or S-G voltage will read the same on a voltmeter, which can be floated easily.

Once a 50 % duty cycle is conformed then the DC reading confirms equal drive. I ASSUME both transistors were changed at the same time. If not, shame on you.

There will be some snubber caps, and then there are the coupling caps. If it ain't drive it is load, PERIOD.

You got the bottom Xstr shorting, look at the TOP coupling cap. Leakage there would never bother the top Xstr. But the bottom might have a problem with it. The capacitor decides to be a resistor. C'mon you old folks, tell everyone about it.

Know what else ? If you can't get the same rating caps, so what ? Most likely they were chosen by price. Engineers might even make adjustments in the operating frequency to accomodate lower value caps, if it saves the company money.

You got 0.68uF and you are afraid to use 1uFs ? Just use them as long as the current capabilities are up to snuff. The value does not mean shit as long as it doesn't go too low.

Use whatever, within reason, just make them equal. They must be equal, otherwise the engineer would have just used one cap instead of two.

Kapeesh ? Think of it from their end.

J

 

To add;

The top snubber cap (or transistor) is just as likely to be a problem. This cap's value is a bit more critical. For snubbers I would use the original value. The couplers don't matter.

J

 

"An intermittent fault ( ie internal short) in the load. "

Of course it would. But not always the same transistor. As a matter of fact, if it is the final load doing it, both transistors would usually short. You saw the circuit. Or are you all talk and no analysis ? Can you REALLY read the fucking schematic to a basically clipping SASEPP audio circuit from the 1970s ?

Now if there is an imbalance in the coupling or snubbers or even the devices, the device on the good side will usually fail first. Do you disagree ?

I want to know if both devices were replaced. Don't you ? Before you battle with me that is. I would hate to find out later I was right. It's not all that fair because it has happened so much on my life.

You wouldn't believe, but I got witnesses all over the place. Now be nice.

Look Man, on a fucking TV I solved a greyscale problem by adjusting the vertical height. This is no bullshit I got witnesses. It involved a Sony, need I say more ? Want the technical details just ask, but I am sure you, nor anyone else on this forum would have been able to solve it. Anyone.

I will admit I am a PITA, but I recommend you do not engage me. You are good, but if you want to take me on, pack a lunch. I can design the shit you try to fix.

J U R B Yeah that's me. Back from the 1990s and shit. Think I been forgetting shit all this time ?

T

 

[cLx]

An intermittent fault ( ie internal short) in the load.

That induction heating coil is a non- trivial device running at high voltage
& frequency.

The briefest short or arc between adjacent turns would take out one or both
IGBTs instantly.

I've got a look at the coils, seem OK, not a trace of burn, and the
turns are isolated by section to distribute the voltage equally.


On 29/11/2012 07:45, jurb6006@gmail.com wrote:

I want to know if both devices were replaced. Don't you ? Before you
battle with me that is. I would hate to find out later I was right.
It's not all that fair because it has happened so much on my life.

On my first and only test, I've changed only the shorted IGBT, ie. the
bottom's one. Worked, but the top got tripping two or three times and
failed again. Now I've removed the both IGBT, the 3 polypropylenes caps,
and the both MKT snubbers for replacement. I've also inspected the
kapton isolation behind the IGBT, saw no damage here.

Now i'm stuck at finding the polypropylene caps. They are expensives,
and what i found can handle only 17 amps. Seem a bit underrated for such
that case.

Doing measurements is not easy as, without load or transistors, the
drive shuts itselfs (not detecting anything), just trying shorts pulses,
and i would not wasting my replacements parts.

 

[William Sommerwerck]

...I solved a greyscale problem by adjusting the vertical height.

When this issue has calmed down... I want to hear about that.

I grew up reading the "Model Garage" stories in Popular Science and the ones
about an electronics technician (Art Margolis?) in Radio-Electronics. These
usually revolved around a difficult problem that did not have an obvious
cause.

 

[Franc Zabkar]

On Wed, 28 Nov 2012 19:22:28 -0800 (PST), jurb6006@gmail.com put
finger to keyboard and composed:

You got 0.68uF and you are afraid to use 1uFs ? Just use them as long as the current capabilities are up to snuff. The value does not mean shit as long as it doesn't go too low.

Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy?

Also, wouldn't each capacitor take longer to charge, and if the
capacitor wasn't fully charged when the IGBT switched off, wouldn't
this result in an interruption of the current in the coils, with a
potentially damaging back-EMF? Or am I completely misunderstanding how
this appliance works?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Phil Allison]

<jurb6006@gmail.com

"An intermittent fault ( ie internal short) in the load. "

Of course it would. But not always the same transistor.

( snip loads of puerile shit )


** Bollocks.

You have thoroughly worn out you welcome here - pal.

Fuckwit GG posters are tolerable in small doses only.

Sooooo - YOU are now fair game.

Watch out.



..... Phil

 

[William Sommerwerck]

You have thoroughly worn out you welcome here - pal.
Fuckwit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game.
Watch out.

For what? You're going to throw a tub of spicy hummis at him?

 

[Phil Allison]

"William Sommerwerck"

You have thoroughly worn out you welcome here - pal.
Fuckwit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game.
Watch out.

For what? You're going to throw a tub of spicy hummis at him?

** That joke is tad obscure.

My remark is fair warning that the GG poster has crossed the line and needs
to pull his head in.

Or I will bite it off .....



.... Phil

 

[William Sommerwerck]

You have thoroughly worn out you welcome here - pal.
Fuckwit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game. Watch out.

For what? You're going to throw a tub of spicy hummis at him?

** That joke is tad obscure.

It is obscure. It's a line from a movie I haven't seen, "Paranorman".

My remark is fair warning that the GG poster has crossed the line
and needs to pull his head in. Or I will bite it off ...

If you mean figuratively... You won't be doing much actual damage.

 

[Michael A. Terrell]

William Sommerwerck wrote:

You have thoroughly worn out you welcome here - pal.
Fuckwit GG posters are tolerable in small doses only.
Sooooo - YOU are now fair game. Watch out.

For what? You're going to throw a tub of spicy hummis at him?

** That joke is tad obscure.

It is obscure. It's a line from a movie I haven't seen, "Paranorman".

My remark is fair warning that the GG poster has crossed the line
and needs to pull his head in. Or I will bite it off ...

If you mean figuratively... You won't be doing much actual damage.

All Phil will ever do, is bore people to tears with his juvenile
whining.

 

All Phil will ever do, is bore people to tears with his juvenile whining.

Internet Turet's syndrome maybe. But I am not going to dwell on that. The only real power Phil has is that every once in a while he has something to say so people don't completely ignore him YET. Whatever.

"Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy? "

No, that is a common misconception in the business. Do you remember the formula for capacitive reactance ? Apply it and just guess the frequency is over an octave above the sonic range.

The fact is that those caps are not being used as reactive components like in a tuned system, they are being used as coupling caps.

In that circuit they are effectively in parallel. Ground and the power supply rail are effectively at the same AC potential, so it's not 0.68, it's aready 1.36 uF. That is almost a piece of wire at 20 Khz. Almost, but we are dealing with a quite higher frequency here.

I got some pretty beefy 1 uF/400 V here but they are old and I can't be sure they can really handle the current. Actually I would like to use them in speaker crossovers someday.

Anyway, people also make this mistake working on SMPSes. Some use a coupling cap to keep DC off the transformer, OK, but that is a coupler. Think about it a sec., it LOWERS frequency to produce more output. Letting the capacitive reactance curve into that would fight against what you want to accomplish.

"Now i'm stuck at finding the polypropylene caps. "

Digikey doesn't have anything ?

What are you dealing with here, rectified 240 volts ? At 320, 17 amps is 5,440 watts. Four burners would add up to 68 amps. What size breaker does this thing take ?

It is possible that they are special caps of course. Manufacturers love using special parts.

Either way, lots of that type of cap fail by exhibiting leakage under stress. Same with the snubbers.

When you get a circuit like that, treat is like a bridge rectifier. Balance.. You change all four diodes in a bridge right ? You change both outputs in an audio amp right ? Same deal here.

Also everybody think about why SMPSes with the "totem pole" configuration usually use full wave rectification on the secondaries. Because balance is as important as it is in an audio amp. It may not seem so, but it is. If not they would save money on diodes.

 

[Franc Zabkar]

On Thu, 29 Nov 2012 09:31:06 -0800 (PST), jurb6006@gmail.com put
finger to keyboard and composed:

"Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy? "

No, that is a common misconception in the business. Do you remember the formula for capacitive reactance ? Apply it and just guess the frequency is over an octave above the sonic range.

The fact is that those caps are not being used as reactive components like in a tuned system, they are being used as coupling caps.

In that circuit they are effectively in parallel. Ground and the power supply rail are effectively at the same AC potential, so it's not 0.68, it's aready 1.36 uF. That is almost a piece of wire at 20 Khz. Almost, but we are dealing with a quite higher frequency here.

Here is an induction cooker design where the capacitors and coil are
said to form a "resonant tank":
http://beaversource.oregonstate.edu/projects/44x201103/wiki/IGBT%2BCoil

The second IGBT's body diode allows the coil current to decay
gracefully when the first IGBT switches off. I forgot about that.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Franc Zabkar]

On Fri, 30 Nov 2012 13:54:20 +1100, Franc Zabkar
<fzabkar@iinternode.on.net> put finger to keyboard and composed:

Here is an induction cooker design where the capacitors and coil are
said to form a "resonant tank":

http://beaversource.oregonstate.edu/projects/44x201103/wiki/IGBT%2BCoil

The above design references the following document:

Induction Heating System Topology Review:
http://www.fairchildsemi.com/an/AN/AN-9012.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[cLx]

On 29/11/2012 11:23, Franc Zabkar wrote:

On Wed, 28 Nov 2012 19:22:28 -0800 (PST), jurb6006@gmail.com put
finger to keyboard and composed:

You got 0.68uF and you are afraid to use 1uFs ? Just use them as long as the current capabilities are up to snuff. The value does not mean shit as long as it doesn't go too low.

Wouldn't increasing the capacitance from 0.68uF to 1uF result in a 50%
increase in cooking energy?

Also, wouldn't each capacitor take longer to charge, and if the
capacitor wasn't fully charged when the IGBT switched off, wouldn't
this result in an interruption of the current in the coils, with a
potentially damaging back-EMF? Or am I completely misunderstanding how
this appliance works?

It's a serie LC resonnance driven by a half bridge switcher, if I'm correct.

 

"The second IGBT's body diode allows the coil current to decay
gracefully when the first IGBT switches off."

No. Don't you understand that ground is a human thing, not an electronic thing ? There is no up and down.

The only possible difference is if one side of the coil has more capacitance to ground, which would make an inbalance. This COULD happen, but if it did, the bottom Xsistr failing would be such a common failure mode it would be on Fox fucking news. Switching the leads to the inductor could prove it, because then the top Xsistr would fail first.

We are talking about a ground fault condition here, without that, no anomality in the load could be imbalanced after it is running. Failing on startup is a different story, and this ain't it.

Get a grip, or a firm base of theory. Somehting. I'm surprised people can tie their shoes,,,, oh wait, they can't.

So much for that.

 

[William Sommerwerck]

I've been following this with curiosity and amusement.

I suspect this product is a marginal design that fails more-often than it
should, but not often enough to be considered outright "defective". (The
NuWave product advertised on late-night TV seems to be plagued with similar
problems.) There is probably no way to "fix" it, short (hmmm) of a complete
bottom-up redesign. It's a shame, because a counter-top induction "burner"
is a good idea. (I almost ordered the NuWave until I learned how unreliable
it -- and its seller -- are.)

The Infinity "SWAMP" switching amplifier from the late '70s is an example of
such a marginal design. It blew its output transistors far too often. The
designer later found the problem, and admitted that adding two cheap diodes
per channel would have prevented it.