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Old 23rd September 2007, 12:43 PM   #1
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Default Help... Meassure Signal perfect points to classd

Which are the points of measure of a ClassD using LM311 + 74AC00SC + IR2010 in Scope. I do not obtain measured of 74AC00SC. Some reference of aid?

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Old 28th September 2007, 01:00 PM   #2
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how is the wave form at lm311 output?
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Old 29th September 2007, 06:58 AM   #3
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See the circuit.
I don't get to do a reading in the pin 11 and 8 of the 74AC00.

Veja o circuito.
Não consigo fazer uma leitura no pino 11 e 8 do 74AC00.

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Old 29th September 2007, 07:42 AM   #4
Eva is offline Eva  Spain
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Have you noticed that this is a self oscillating circuit?

You could try to inject a 5Vpp square wave at pin 12 of U5 to see if the output stage works.
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Old 29th September 2007, 09:14 AM   #5
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But I am injecting 1Khz SineWave in 0.47 Capacitor of the Pin 3 in LM311.
But I don't get to do the reading regarding Ground and Pin 11 of the 74HC00.
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Old 29th September 2007, 11:49 AM   #6
IVX is offline IVX  Russian Federation
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lindomar, i guess you can have a troubles due to stupid manner of drawing circuit: GND graphic symbol (refered to base Q2) and GND node (refered to pin#7 of U5) aren't the same nodes at all! Actually, author of this "circuit" many times was catched in the act of falsifications, any of those circuits, that you can see at the russian forums, is mismatched with claimed specs and conditions. You can get confirmation of my opinion, if you would ask for Eva (or for others adequate diyaudio.com members) what she think about using irfb31n200 for 180V switching without any tricks around Trr body diode, or about full power frequency response when R1=1K, C6=4.7n, L1=50u, C16=.68u and 4ohm load..20khz -6db isn't it? Why 90VDC rail if 14A and less current limiting (4ohm load claimed)? Where is resistors for Q3,Q4 base current limiting? Why R21 only 2K? I'm sure 45mA input current is dangerously too much for 74AC00. R12 will dissipate 33W at 20Khz full power! Lindomar, i saw in the russian forums, that you many times asks mr.K-v -"why your circuit isn't work?", and now i want to help you understand, that mr.K-v just ignorant and agressive troll. He use SOA for choice mosfets for class D (!), and tell -"I see that php28nq15 will drop 5V at 30A -it's too much..", but simply 5V*30A=150W He thinks that half bridge class D is AD if dead time short enough, and BD if dead time is more! Trust me, you just spend your time for nothing if you seriously look to the such trolls.
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Old 29th September 2007, 12:41 PM   #7
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Hello IVX... thank you very much for the help...
Good... do you want to say that this circuit doesn't really work?

Lindomar.
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Old 29th September 2007, 01:48 PM   #8
IVX is offline IVX  Russian Federation
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Depends of what you mean when saying "work". OCP is completely wrong, but without OCP, or with corrected OCP, the circuit will have very low switching quality, hence bad THD, and shameful efficiency. BTW, if you'll add just one capacitor to the feedback network, it will markedly reduce output impedance.
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Old 29th September 2007, 05:57 PM   #9
Eva is offline Eva  Spain
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As IVX stated, this circuit has some pitfalls and is essentially a lower-part-count lower-performance higher-distortion adaptation of UcD, but it should work. The output devices can't be pushed too far in terms of switching speed because they don't have a fast body diode.

If you are feeding 1Khz to the input of the LM311 and the output does not toggle, thete is something wrong with the own LM311. Check supply rails, strobe pin at the right level, IN+ not floating, etc...

Also, as IVX stated, be careful with node naming in this schematic because "GND" and the "earth" simbol are not the same node.
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