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Old 21st January 2010, 06:59 AM   #131
Sing is offline Sing  Thailand
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All.
Can I have PCB and top view componemt for 6KW class"D" please

Thanks for your help
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Old 21st January 2010, 12:37 PM   #132
Eva is offline Eva  Spain
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Quote:
Originally Posted by Baldin View Post
From what I read in your post Eva, you are only introducing delay between driver and gate. Is that correct?

I'm using a 74HC86 at the input of the IR2110 driver, but would like to get rid of it all together, as it takes up space / adds complexity.
I was thinking of just skipping the 74HC86 but still use two separate RCDs on the two input pins .....
Any suggestions here???
I'm using some logic before the IR driver too, both for preventing too short pulses in either direction and for splitting the H/L signals. I use RCD directly at the inputs of the IR drivers to fine tune pulse widths and get almost no dead time equally on all transitions, which in my circuit requires pulse extension rather than shortening (IR2110 delays are not always matched, it depends on supply voltages, but they seem to be very consistent from part to part). The inputs of IR2110 are schmitt triggers and seem to have quite consistent thresholds so no additional buffering is needed.

Concerning the diodes, HO should be clamped to VB and VS with schottkys, LO should be similarly clamped to COM and Vcc, and finally VS should be clamped to COM. For HO and LO clamping 1A 20V schottkys are ok, I use low inductance SOD-323 packages. For the later purpose I use a bigger 3A 200V schottky in SMB package (consider figuring out the part numbers as some homweork ).

These diodes may not be always required, it depends on di/dt and layout parasitics. My layout is good, but I also use insane turn-off di/dt close to 4KA/us resulting in negative Vs spikes of more than 5V at high output currents and also negative spikes on HO and LO, so the diodes are almost required for reliability. At some point in the development I added buffer transistors to the outputs of the IR2110, which greatly reduces the need for diodes on HO and LO because the chances for negative or positive spikes are reduced, but I dediced to keep the diodes.

On your schematic the value of C2 is way too high and the connection seems quite strange, I have not tried to simulate it in detail but I think it's calling for trouble.

Concerning XOR gates, you may find 74AHC1G86 (74LVC1G86) single ones in SOT23-6 (and smaller ones too) to be quite useful. 74LVC1G57 and 74LVC1G58 are also quite versatile. LVC seems to have higher output current than AHC.
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Last edited by Eva; 21st January 2010 at 12:46 PM.
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Old 28th January 2010, 07:00 PM   #133
Baldin is offline Baldin  Denmark
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Hi Eva

Hmmm, had not seen this reply before now? ....

Thanks for the tips. Well it's an awful lot of diodes to find room for, but I think I might be experiensing the lack of these at the moment. Funny things are happening when either I remove the load or I try to start up without (shoot through instability).
Have tried to mount a 10k resistor from com to Vs as suggesed in IR DT 99-7, which at least prevent shoot through when starting up with no load ... but it the IF2110 dosen't start switching either ..... I'm scratching my head, and it must be something with the working of the IR2110 in the un loaded state ....

Home work: 1A/20V could be On's NSR1020MW2T1G and the 3A/200V could be MBRS3201T3G

Haven't any schottkys at the moment, but will try with some ES1D

As to the size of C2. Yes it's too big, but was only for the first trials to make sure there was enough dead time.
Now running with 100pF, on FETs without heat sink. With a little alu on the FETs I could probably go down to 10-33pF.
The connection is right I belive, and it's running without any problem. You culd use two caps going to GND, but this connection saves one and works as well.
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Old 29th January 2010, 07:26 AM   #134
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Quote:
Originally Posted by Eva View Post
Concerning the diodes, HO should be clamped to VB and VS with schottkys, LO should be similarly clamped to COM and Vcc, and finally VS should be clamped to COM. For HO and LO clamping 1A 20V schottkys are ok, I use low inductance SOD-323 packages. For the later purpose I use a bigger 3A 200V schottky in SMB package (consider figuring out the part numbers as some homweork ).

These diodes may not be always required, it depends on di/dt and layout parasitics. My layout is good, but I also use insane turn-off di/dt close to 4KA/us resulting in negative Vs spikes of more than 5V at high output currents and also negative spikes on HO and LO, so the diodes are almost required for reliability. At some point in the development I added buffer transistors to the outputs of the IR2110, which greatly reduces the need for diodes on HO and LO because the chances for negative or positive spikes are reduced, but I dediced to keep the diodes.

.
The new series of IRS2110 & IRS2113 gate drivers address some of these failure modes and therefore they now come with INBUILT CLAMPING diodes except VS to COM diode.


http://www.irf.com/technical-info/appnotes/an-1100.pdf

Last edited by Workhorse; 29th January 2010 at 07:37 AM.
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Old 29th January 2010, 03:20 PM   #135
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Default workhorse

dear sir
greetings which city in india do you live in
thanking you
andrew lebon
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Old 29th January 2010, 04:36 PM   #136
Baldin is offline Baldin  Denmark
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Quote:
Originally Posted by Workhorse View Post
The new series of IRS2110 & IRS2113 gate drivers address some of these failure modes and therefore they now come with INBUILT CLAMPING diodes except VS to COM diode.
Yeah, that would have been my next question ... why didn't they built it in .... makes sense
But thanks for the heads up ... will bye the IRS version next time
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Old 29th January 2010, 04:48 PM   #137
Baldin is offline Baldin  Denmark
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Default Clamping the output

I just tried to clamp the output (just after the filter) with 2 diodes (ES1D).
I will still try all the other clamps, but I was actually wondering what would happen to the stored energy in the filter, when the load is just removed. It might not be much in idel mode or just playing softly, but otherwise a large current would give rise to a very high voltage on the output ....

It did help; removing the load, it still keep oscillating, but nor stable, and there are still some shoot through ....

Eva and Workhorse, do you also use clamping dirodes on the output??
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Old 29th January 2010, 05:21 PM   #138
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Quote:
Originally Posted by Baldin View Post
Workhorse, do you also use clamping diodes on the output??
Clamping diodes at output in class-d after the filter helps when amps are working in bridge mode especially when the speaker load is highly reactive.
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Old 29th January 2010, 05:26 PM   #139
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Quote:
Originally Posted by Baldin View Post
but I was actually wondering what would happen to the stored energy in the filter, when the load is just removed.
Remember we have body diodes in mosfets also
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Old 29th January 2010, 06:22 PM   #140
Baldin is offline Baldin  Denmark
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Ok, did the clamping:
COM to LO to VCC, and VS to HO to VB.
Did it with 4 x 1N4148 as this was what I had.
No improvement what so ever

VS is already clamped to COM through lower bodydiode and external ES1D in parallel.

Don't know what is wrong
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