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Old 11th January 2011, 09:35 PM   #21
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Quote:
Originally Posted by Whortless View Post
Right, Are you sure you soldered the IC in correct way?
Best wishes,
The 2092 requires quite a few conditions to be right before it wil output pulses to the mosfets. VAA and VSS must be right, check with a scope or multimeter. Mine was about 7v and -7v respectively.

VCC must be very clean, I used a 12 volt regulator but still got spikes on VCC. So i put a 100uf close to the 2092 and a 47uf close to the regulator.
The mosfets need decoupling close by, 220nf from b+/gnd, b-/gnd and b+/b-.
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Old 11th January 2011, 09:40 PM   #22
tinitus is offline tinitus  Europe
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yeah, some of the 55V and 60v are down at 500pf, and very low "miller"
and even more so, the closest N and P devices seems to be fairly well matched
yeah, I vacuumed all the spec sheets a hundred times

reason I ask you guys is
some of the interesting higher voltage are recommended for classD("B" devices), and almost all of them have high transconductance
which means high gain, and efficiency, yes ?

so, wheres the hatch, whats the possible problem with such devices ?
instability issue maybe ?
and what may the advantages be ?
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Old 12th January 2011, 02:14 PM   #23
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Quote:
Originally Posted by Whortless View Post
Right, Are you sure you soldered the IC in correct way? Check the electrolytic caps polarities and be sure there is not short circuit. I also recommend to clean the board from solder paste with isoporpyl alcohol or thinner. After all these, first turn on the aux power to see whether you are getting the reference voltage from the IC and check its temperature as well (without output mosfets).
Best wishes,
That's an insult Yes they are all connected the right way around.
Quote:
Originally Posted by nigelwright7557 View Post
Which MOSFETs are you using ?
It definitely works with irfb4019's.
I have 4 on my setup.

Does the csd pin go up and down ? this would indicate something is wrong with the power supply or the mosfets.
I too am using the irfb4019's.
Quote:
Originally Posted by nigelwright7557 View Post
The 2092 requires quite a few conditions to be right before it wil output pulses to the mosfets. VAA and VSS must be right, check with a scope or multimeter. Mine was about 7v and -7v respectively.

VCC must be very clean, I used a 12 volt regulator but still got spikes on VCC. So i put a 100uf close to the 2092 and a 47uf close to the regulator.
The mosfets need decoupling close by, 220nf from b+/gnd, b-/gnd and b+/b-.
My VCC was very clean and can take the high current spikes if needed. I also added a lot of capacitors (like i said in my last post)
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Old 12th January 2011, 08:58 PM   #24
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hi people,

I have build a prototyp with irs2092 and irfb4212. Two things struck me.

-the amplifier have a strong noise, I can it hear till 50cm from the box.
-the amplifier disturb the the radio(HF-radiation).

Do you have similar experiences?
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Old 12th January 2011, 09:14 PM   #25
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I havent checked for RFI.

I did have trouble with a low frequency background noise and this turned out to be lack of decoupling on the 12 volt regulator. There were glitches on the VCC rail.
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Old 13th January 2011, 01:56 AM   #26
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Originally Posted by Boudemaniak View Post
That's an insult Yes they are all connected the right way around.
Solve your problem yourself then! Do not ask anyone anymore if you know it all!
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Old 13th January 2011, 04:47 AM   #27
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No Ground Plane and lack of knowledge of routing RF sensitive tracks is all i can see here in the modules shown by members, resulting in EMI.

Class-D is not your analogue linear amplifier in which you route the tracks as you wish.
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Old 13th January 2011, 07:57 PM   #28
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Quote:
Originally Posted by tinitus View Post
yeah, some of the 55V and 60v are down at 500pf, and very low "miller"
and even more so, the closest N and P devices seems to be fairly well matched
yeah, I vacuumed all the spec sheets a hundred times

reason I ask you guys is
some of the interesting higher voltage are recommended for classD("B" devices), and almost all of them have high transconductance
which means high gain, and efficiency, yes ?

so, wheres the hatch, whats the possible problem with such devices ?
instability issue maybe ?
and what may the advantages be ?
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Old 13th January 2011, 08:31 PM   #29
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Join Date: Dec 2003
Location: Munich
Quote:
Originally Posted by tinitus View Post

some of the interesting higher voltage are recommended for classD("B" devices), and almost all of them have high transconductance
which means high gain, and efficiency, yes ?

so, wheres the hatch, whats the possible problem with such devices ?
instability issue maybe ?
and what may the advantages be ?
Higher transconductance will lead to a faster change of the MosFet impedance in the moment of switching.
If you have a high transconductance device in a TO-220 package and some reasonable strong driver and reasonable layout, then the resulting di/dt will be dominated by the driver voltage, the voltage of the miller plateau (which sometimes is not a Miller plateau, but and an inductive caused plateau) and parasitic inductance of the TO-220 package.
High di/dt is desirable for low switching losses. On the other hand high di/dt is triggering high frequencies ringing more massive....(Everybody has to find his way of snubbering away resonances. Eva's RLC snubbering appears the most efficient to me so far.)
When playing around with the IRS20957 and IRFB4615, I settled the design at a reasonable di/dt around 700A/us - may be 800A/us.
I especially examined hard switching behavior, means the device which turns ON has to take over the load current and additionally has to deliver the reverse recovery charge of the body diode of the opposite MosFet.
At 31A load current this took slightly less than 70ns.
During these 70ns the MosFet has to handle increasing currents and is still operating at full rail voltage. Voltage sloping does not start before the load current is taken over + the reverse recovery charge has been removed.
==> Under this load conditions you are forcing losses !
At 400kHz already 30A are not really a reliable load for hard switching conditions with the IRFB4615 anymore. At 200-300kHz I could easily experiment with 35A, but at 400kHz 31A things touched the limits of the device. At 450kHz I already got defects at 27A....
Why looking for hard switching behavior? Because it is a typical load condition in class D amps, when driving load currents above the ripple current of the output filter.

Edit:
Rail voltage was +/-55V, well under heavy load dropping slightly below +/-50V....

Last edited by ChocoHolic; 13th January 2011 at 08:35 PM.
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Old 13th January 2011, 09:17 PM   #30
tinitus is offline tinitus  Europe
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ah, good explaining, thanks
even I can understand, almost

will use for small classA tho
and not the "B" devices
I was just curious what they are good at

anyway, I dont really fit in here
but fantastic to get expert info like this

good luck
cheers
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