Mystery Strange issue (class D amplifier)

Thread Starter

Joined Mar 29, 2016
Hi folks,

I've just built this and i was very satisfied with the results, just amazing HIFI !!! Yes -> HIFI.
It was very comparable to quality AB amplifier, absolutely same !
My ears said 0.000000% distortion. :D I know class d distort varies ~0.1% but im not hearing that much :)

I was testing with 16v output capacitor and it boomed.
It was loud and beautyful. Now its quiet when I changed the capacitor with new ???

The sound is good again and everything is working well.

I measured everything 1000 times, perfect squares, 12V ones (one side little more - dont know why), output full range 0-12V before the filter,
duty cycle good range, everything fine, but quiet signal :O


Whats the catch here, any suggestions ? What do you think ?


Now i will explain the sch because its low quality camera..(laptop) -> starting from the input @ first -> 12k to ground -> 2.2uF -> 560 ohm to 2nd pin of TL494,
3.3k from 3rd pin to the 2nd. (fb network) . 1st pin to trimmer (one side to ground, one to 5v ref - 14pin) (this one adjusts standby duty cycle at 50%). 1,2,3,.. 4pin -> ground,.. 5 to ground via 1nF for clocking, 6th to ground via 12k, clocking too,.. 7th to ground ; 8th to 12v rail via 220ohm. A point between 8th and the 220R goes to IR2111's input clock. 9pin to gnd, 10 to ground via 220ohm (not used just inverting signal here), 11 to the 12v rail. 12 too ; 13 to ground (allowing wide range duty, not only 0-50%), 14 to the trimmer as mentioned and to 15 via 10k resistor. 16 to ground.

Now -> IR2111 -> 1 to 12v ; 2 input as mentioned ; 3 - ground ; 4 - to lower mosfet via 22ohm gate stopper ; 5 - not used ; 6 - to mosfets out. ; 7 to 1st gate via 22 ohm stopper again ; 8 to 12v rail via fast diode (i use 1n5817) and to 6th pin via 1uF (+ upside - down).

Next -> Fets and output filter -> two irfz44n first drain connected to 36V rail (boosted from the 12v one) -> 1uF decoupling (this blowed) -> 22uH (im having and using 100uH) aand 220n to ground.

UUh it was a weird ride :D Please computer dont get mi BSOD (blue screen of death) right now :D


and the big great speaker =>

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Thread Starter

Joined Mar 29, 2016
Aand is this correct?

From this forum i know that -> C bootstrap capacitor > (Qg + Dmax*Tsw*Idrv ) / ?V

i am having 50khz => T = 1/50000 = 0.00002 ( 100khz with these values i explained :D )
i am having Qg = 63nC
i am having 100% duty cycle
i am having ir2111 with 250 ma typical current for the one side and 500ma for the other (average -> 0.375)
i dont know what is the optimal value for the ripple, i am using 0.1v here

C boot (nF) > (63 + 100*0.00002*0.375 ) / 0.1
C boot (nF) > (63 + 100*0.0000075 ) / 0.1
C boot (nF) > (63 + 0,00075 ) / 0.1
630,0075 => 1uF

Thread Starter

Joined Mar 29, 2016
Well, i tried a few thing & no progress at all.

-> new TL494 -> equals to -> same
-> not using IR2111, just voltage divider to divide the voltage by 2 (the cross point goes below Vth while saturation is still good). -> equals to -> same
-> using complementary fets irf530+9530 -> equals to -> same
-> tried with diodes too -> same
-> tried with one irfz44n and one irf530 :D
-> tried everything

-> its not the driver
-> its not the TL
-> and yes there's no sense, capacitor only destroys itself blowing like a fuse (worst case short circuit but what ? no problem in this case )
-> not fets
-> what else ? the filter ? :D
->checked for loose connections too, i am not hallucinating it was very heavy bass and very loud amp, now its quite quiet and distorting when i higher the volume :(
no bass @ all ..

same, same, same, wtf what i am missing ?
here's nothing to check, checked everything :??

you know i feel strange right now
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Joined Feb 5, 2010
The output coupling cap should not be a standard polarized aluminum electrolytic.

Try to find non polarized caps for that. Or use two polarized caps hooked up neg to neg and the positive ends are now the input and output ends.

Thread Starter

Joined Mar 29, 2016
Ok, then i'll use two 470n in paralell, i thinked the reason was the voltage rating of the blown cap but i found it on the ground and it was 50v one.
I didn't understanded this -> "Or use two polarized caps hooked up neg to neg and the positive ends are now the input and output ends."

do i need to use 100v cap due to back EMF or 50 is sufficient ?

i have an idea -> to connect a HF ATX transformer @ the out before the LPF filter (after HPF), put 50hz sine @ the input and get powerful 220v sine after the filter, maybe i'll need 1kv capacitor for the LPF. And ill connect the trafo where are the 5V windings.

This makes an inverter with small transformer. I've seen this but it was used different -> get HV first and then PWM that..
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