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Old 30th March 2014, 03:45 PM   #11
kaip is offline kaip  Netherlands
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Old 30th March 2014, 04:29 PM   #12
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The 2092 wont drive an irfb4227.
You need lower capacitance gate mosfets. irfb4019 is OK.

However I am not sure if that is the whole problem as I used irfb4227 and the amplifier run but wouldn't work at high volumes it just kept resetting when I turned it up.
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Old 31st March 2014, 04:58 AM   #13
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Kaip:
Nice compact layout!

I think decoupling caps should be ceramic type and as close as possible to pins of 2092. Also maybe add some 1uf X7R at pins of MOSFETS.

May also help to add damping network at MOSFETS.

I am curious about your aux +12 supply. Why not just use a transistor and zener diode? It looks like it may not be properly referenced, but I did not study too closely yet.

Again nice work on layout.
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Old 31st March 2014, 11:00 AM   #14
kaip is offline kaip  Netherlands
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spare_parts:
Thanks for the compliment.
The 12V is because the 7812 only allows for a 37V input. I use the 24V to raise that a bit. Nw it should be able to regulate about 35-50V to 12V
Works well.
I just tried a transistor and zener , as a I am becoming paranoid by now, but that didnt help.
Which decoupling caps do you mean ?
The PCB is small so just about everything is close to the 2092
And all traces are minimal.

nigelwright:
Wouldnt the 2092 start regardless of used mosfets ?
If not can I disconnect the mosfets to see if the chip will then start up ?

It is still resetting every second or so.
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Old 31st March 2014, 10:15 PM   #15
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Quote:
Originally Posted by kaip View Post
nigelwright:
Wouldnt the 2092 start regardless of used mosfets ?
If not can I disconnect the mosfets to see if the chip will then start up ?

It is still resetting every second or so.
What happens is the 2092 sends out a pulse to the lower mosfet.
Due to high capacitance the mosfet doesn't switch on soon enough and the 2092 thinks there is a current overload so immediately resets itself.

Without gate driver buffers you can just about get away with a pair of irfb4019's
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Old 31st March 2014, 10:30 PM   #16
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NigelWright is correct, try MOSFETS with lower gate capacitance.

Regarding decoupling caps, they work most effectively when connected directly to the pins on the chip because of PCB trace resistance/ inductance, but that is probably not causing your resetting.

just for testing, you could try some IRF540N (usually easy to find and low C) at up to about +/- 45V supply rails.
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Old 2nd April 2014, 11:13 AM   #17
kaip is offline kaip  Netherlands
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I tried with some IRF520s. Good enough for testing and with low input capacitance.
Now it starts up. Ok the Mosfets get quite hot but that could be fixed.

I will try some IRF540's later but plan a revision to the circuit with some totem drivers
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Will this be ok , or do you have suggestions ?
I am limited to through hole components and the size of this board so have to keep component count low.
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Old 2nd April 2014, 09:48 PM   #18
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I suggest using the IRFB4019 for 4 ohm loads, and the "4020 for 8 ohm loads with higher voltage rails.

The "2092 can drive these fine, see datasheet for info and a power table.

If you add totem pole drivers, I think you lose some of the functionality and attractive features of the "2092, like current sensing of the drivers' and rise/ fall time probably suffers.

Seems like going to totem pole drivers gets you closer to going fully discrete, which in my opinion is more attractive anyway. (like phillips/ hypex/ Putzey's UCD) which is post- filter feedback, another attractive feature.
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Old 4th April 2014, 03:57 PM   #19
kaip is offline kaip  Netherlands
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Thanks guys

Now will have to try IRFB4019/4020
The IRF540s were an improvement over the IRF520s.
They run much cooler. You can just feel them warming up from room temperature.

I agree about the totem poles.
And less is more.
My ClassD knowledge is too limited to attempt anything discrete now.
But you have to start somewhere...

One more "problem" : when switching off you hear a load thud.
I remember reading something about that but cannot find it anymore.

Any idea ?
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Old 5th April 2014, 01:18 PM   #20
ungie is offline ungie  Canada
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Quote:
Originally Posted by spare_parts View Post
If you add totem pole drivers, I think you lose some of the functionality and attractive features of the "2092, like current sensing of the drivers' and rise/ fall time probably suffers.
Not at all true.
See IRAUDAMP9 reference design.
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