Re: SSgap Diagrams

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Marco,

At 09:42 AM 4/4/2001 +0300, you wrote:
>Hi Terry (again),
>
>Tesla list wrote:
>> 
>> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>> 
>> Hi Marco,
>> 
>> Thanks for the great tip about the gate resistance.  I now think high speed
>> switching noise is what killed IGBT #2.  I setup to look for noise and it
>> was not hard to find!  Very high frequency (~4MHz) bad stuff was going on
>> in the turn off and on times.  
>
>You didn't mention *where* you measured that noise.

Mostly radiated through the ground system ;-))

>
>>I now have ended up with 680 ohms in the
>> gate.  
>
>This is a very high value (too high). Again, something must be wrong.

I agree...

>
>>This will probably be tweaked further but it eliminates all the
>> noise and does not seem to hurt operation.  The IGBT remains cool.  A scope
>> picture of the noises are at:
>> 
>> http://hot-streamer-dot-com/temp/GateR.jpg
>> 
>> The R1 (white) trance is with no gate resistance. R2 is with 100 ohms and
>> the top yellow trace is with 680.  The noise was not bad at low voltage but
>> it got super bad at higher voltages and was causing some false switching
>> (really bad for H bridge SMPSs ;-)) and general loss of control.  With the
>> 680 ohm in there things are much more stable and I don't see little noise
>> burst in things I shouldn't.  I am sure I will have to work on this more
>> but you probably save me a bunch of IGBTs :-))
>>
>
>A sad fact you have to accept is that with a breadboard assembly you
>probably can't get any further. Noise, glitches and nasty transients
>will make your life an hell. It makes an enormous difference to use a
>PCB, even a prototyping PCB with your own (short) wirings.

I have started up my little 0.01 inch PCB basement shop again!  Those proto
boards are cute but when you go above 1MHz they start to get real bad
transients.  A big problem now in my case... 

>
>I suggest that you:
>
>- abandon the breadboard

Agreed!

>- use a small prototyping PCB (say 3 x 3 cm) where you SOLDER the
>IR2118, bootstrap cap and diode, and some good 0.1uF + 10 uF filter
>capacitors
>- on one side of the PCB solder DIRECTLY the IGBT, which is properly
>fixed to its heatsink
>- mount the *heasink* somewhere, with screws: the PCB is so light that
>can simply hang from the IGBT.
>- drive this thing with several cm long wires (as you need) feeding
>power and drive (to the IR2118, this time).
>- use series termination at the drive side for the IR2118 inputs: use
>star topology (NOT bus), use resistor for each star "leg"

I need to make all the stuff really small and low inductance and low
capacitance...

>
>I hope you got the idea. It shouldn't take you more than 1/2 hour to get
>that little PCB done.

I will take me a few hours ;-))  But well worth the time now that it is
going so well.  The voltage limiting was working tonight to protect the
IGBT and other good stuff was happening so the great SSgap is on it's way!!

Cheers,

	Terry


>
>Cheers
>
>-- 
>_____________________________________________________________
>
> Marco Denicolai           Senior Design Engineer 
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