Class-D Amp with Discrete Gate Drivers - diyAudio
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Old 13th January 2004, 12:38 AM   #1
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Arrow Class-D Amp with Discrete Gate Drivers

Here is the schematic layout of my recently completed Class-D amp with using discrete Gate drivers using MJE350/340 transistors.
The Frontend includes
LM3524D Pulse Width Modulator
Nand Gate with deadtime insertion
Gate drivers
Output half bridge stage
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Old 14th January 2004, 08:41 AM   #2
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I wanted to increase the switching frequency @ 300KHz using LM3524D ,could it will give better results.
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Old 14th January 2004, 09:10 AM   #3
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What sort of audio frequency range do you get?
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Old 14th January 2004, 09:44 AM   #4
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you really shouldn't have connected wires INSIDE the schematic for the IC.. it gets really confusing.. :S
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Old 14th January 2004, 09:54 AM   #5
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What about using an IC?

HIP4080, 4081, 4082 from Harris. Good IC's for driving H-bridges. You can also adjust deadtime. These IC's are aslo rather fast.
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Old 14th January 2004, 10:41 AM   #6
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Those Harris ICs have indeed many advantages but they have a rather lowish suply voltage.
The IR21xx types are better in this respect but need additional circuitry like comparators etc.

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Charles
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Old 14th January 2004, 10:44 AM   #7
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The frequency response i get is 10Hz To 18Khz
Secondly
The HIP4081 or HIP4080 are meant to operate only at 80Volts maximum supply voltage.
What If some wants a AMP with supply Rails of an order of +-95VDC
Thirdly I am in INDIA and discreteness is my destiny thats why i have choosen the discrete gate drive for simplicity and cost effective ness
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Old 14th January 2004, 10:58 AM   #8
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Exclamation Blow-up for certain.

Replace the IN4007 with an ultra-fast diode like BYV26C or similar. But even more important, the floating rail that this diode pumps will get jolted to 56 volts when the lower fet turns on!!! WAY too much for the upper fet gate. Perhaps run the top of the diode to a ~15 volt or so ground referenced supply, and use 100uF across the floating driver rail in addition to what is there now. (can't see it while writing this).

Other than that, Good Man!

Edit -> Oh yeah, I see. The upper fet gate at most is only going to get as high as the +56v rail. The fet will never fully turn on, unlike the lower one. Spells even-harmonic distortion.
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Old 14th January 2004, 11:06 AM   #9
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Extreme THANX to CIRCLOTRON

PLZ CARIFY BY MEANS of a diagram what u wanna say!
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Old 14th January 2004, 11:08 AM   #10
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I understand your concerns about using "standard" discrete components. But I have some doubts about the performance of your high-side driver:

You don't limit the supply voltage of this driver which could in turn be dangerous for the driven Mosfet.
I don't know how fast the upper Mosfet can be turned on with this "VAS" using a mosfet and a pullup resistor.

Why do you use modulators that work with a sawtooth instead of a triangle ? Didi you ever attempt a switching amp that takes feedback from the output filter ?

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Charles
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