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Old 19th November 2005, 04:03 PM   #1
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Default switching class d amp

http://www.angelfire.com/indie/jcnoe.../switching.pdf




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Old 19th November 2005, 04:43 PM   #2
Pierre is offline Pierre  France
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It seem quite a classic and not very hi-tech Class-D amp (P/N mosfets, etc), but has anyone had a look at the power supply? It seems to use the 117VAC input to produce +/-51V rails, with no transformer!!!

For apps. where the user can't touch any terminal, such as active speakers, etc, where safety is not a problem (this supply is not galvanically isolated!), it can be useful.

Mmm, I wonder if that design can be modified for 230VAC mains and any output voltage with proper component values... I will have a deeper look at it but it is, at least, interesting.
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Old 19th November 2005, 04:53 PM   #3
john65b is offline john65b  United States
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Default Huh?

I don't get it. You rectify 117AC and you get +/- 81V (not including diode losses)

How do they get 51V?? Is my math wrong??
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Old 19th November 2005, 05:21 PM   #4
Pierre is offline Pierre  France
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The triac cuts the output during a variable time, depending on the output voltage, that is sensed and compared to a reference. This way the caps are charged to the correct voltage. It is similar to a lamp dimmer, but I hadn't seen something like this, operating from a _rectified_ mains and then filtered to get DC.

the center point (GND) is obtained by a voltage divider made by caps. I don't know how stable this will be...
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Old 19th November 2005, 05:22 PM   #5
mzzj is offline mzzj  Finland
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Quote:
Originally posted by Pierre:
It seem quite a classic and not very hi-tech
Not very high-tech is not right word, stone-age low-tech is proper for this!



Triac "regulated" power supply. TL074 used as a comparator. Not isolated from mains. 50khz modulation frequency. No output coils/chokes. Collection of ideas how not to do d-class.
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Old 19th November 2005, 05:30 PM   #6
Pierre is offline Pierre  France
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Yes, Class-D has been improved a little bit since them, hasn't it?
But you cannot say that the supply is not, at least, original and worths the pain being studied a bit more...
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Old 19th November 2005, 08:10 PM   #7
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Default class d amp articles

I have only put these here because they work but know they are old and can be improved.Class d is still not as easy to build for the diy as gainclone chip amps,also there are not many schematics around.Both of these circuits could use a vco or maybe a tl494 as the osc and also use a high/low mosfet driver chip to drive better fets or maybe IGBTs.Sometimes the best thing to do is use something that works and make it better


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Old 19th November 2005, 08:12 PM   #8
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Default class d schematics

I would not recommend using the power supply circuit,very dangerous,better off with standard transformer setup.


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Old 19th November 2005, 08:17 PM   #9
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Default class d schematics

I would welcome anyone who has schematics for class d amps to post them here maybe we all can pitch in and redesign something or get a better understanding of what can be built in the diy community


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Old 19th November 2005, 10:22 PM   #10
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Default class d amp article

Good article


http://power.ece.uiuc.edu/blueboxes/PWM_amp/PWM_amp.htm
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