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Old 21st January 2010, 03:27 PM   #1
vogor is offline vogor  Russian Federation
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Default Selfoscillating class D amplifier

Hi Guys!

I wont to build my first class D amplifier, in attachment the cirquit example that i make, and i wont to now it workable? Maybe some one show me my mistakes.

PS Sorry for my English.
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Old 21st January 2010, 05:19 PM   #2
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Which stage is intended to work as a comparator?
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Old 22nd January 2010, 12:53 AM   #3
vogor is offline vogor  Russian Federation
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Quote:
Originally Posted by darkfenriz View Post
Which stage is intended to work as a comparator?
DA2 CD4070 is comparator stage, in original (iraudioamp) was used another logic.
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Old 23rd January 2010, 06:11 AM   #4
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Quote:
Originally Posted by vogor View Post
DA2 CD4070 is comparator stage, in original (iraudioamp) was used another logic.
its not a comparator stage
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Old 24th January 2010, 11:18 PM   #5
81bas is offline 81bas  Germany
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Originally Posted by Workhorse View Post
its not a comparator stage
Comparator can be represented as a usual hi-speed opamp, even with not very high amplification coefficient. And we have here the stage T1 plus one XOR element, providing relatively high amplification coefficient. So it will work similar to comparator without any problems. Sure, input offset voltage of T1+XOR is 'not ideal', but this will be compensated by input integrator easily.

I think this schematic will work...

Also, be careful, the switching freq can be too high, because delay producing by DA2 is not so big. Maybe I would inlcude one more free XOR element of DA2 into the path to produce more delay, even more helping DA2 to act as a comparator

I will only say, that the UcD topology is more preferable, if it is not a commercial development. UcD will give more stable switching frequency and better performance results... Simply replace DA1 with a comparator IC (T1+XOR will be not enough here ), replace your feedback with a UcD style feedback and it will be a UcD amp!

Last edited by 81bas; 24th January 2010 at 11:30 PM.
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Old 25th January 2010, 06:21 AM   #6
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Quote:
Originally Posted by 81bas View Post
Comparator can be represented as a usual hi-speed opamp, even with not very high amplification coefficient. And we have here the stage T1 plus one XOR element, providing relatively high amplification coefficient. So it will work similar to comparator without any problems. Sure, input offset voltage of T1+XOR is 'not ideal', but this will be compensated by input integrator easily.

I think this schematic will work...

Also, be careful, the switching freq can be too high, because delay producing by DA2 is not so big. Maybe I would inlcude one more free XOR element of DA2 into the path to produce more delay, even more helping DA2 to act as a comparator

I will only say, that the UcD topology is more preferable, if it is not a commercial development. UcD will give more stable switching frequency and better performance results... Simply replace DA1 with a comparator IC (T1+XOR will be not enough here ), replace your feedback with a UcD style feedback and it will be a UcD amp!
Do you even know what comparator does?
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Old 25th January 2010, 11:36 PM   #7
81bas is offline 81bas  Germany
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Originally Posted by Workhorse View Post
Do you even know what comparator does?
yes, and you?
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Old 26th January 2010, 06:37 AM   #8
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Quote:
Originally Posted by 81bas View Post
Comparator can be represented as a usual hi-speed opamp, even with not very high amplification coefficient. And we have here the stage T1 plus one XOR element, providing relatively high amplification coefficient. So it will work similar to comparator without any problems. Sure, input offset voltage of T1+XOR is 'not ideal', but this will be compensated by input integrator easily.

I think this schematic will work...

Also, be careful, the switching freq can be too high, because delay producing by DA2 is not so big. Maybe I would inlcude one more free XOR element of DA2 into the path to produce more delay, even more helping DA2 to act as a comparator


Quote:
Originally Posted by 81bas View Post
yes, and you?


CD4070 XOR is used as PHASE SPLITTER OF PUSLES [for driving the gate driver chip]not a comparator, opamp is already acting as integrator and comparator simuntaneously
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Old 26th January 2010, 05:10 PM   #9
Baldin is offline Baldin  Denmark
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Hi vogor

I hope you do not intend to start it up with +-100V as a first!!!

A good advice is to go for someting smaller sa +-20V or so. Also put in a polyfuse of 1 A in each rail ..... this will spare you for a lot tears
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Old 26th January 2010, 05:38 PM   #10
Eva is offline Eva  Spain
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I have only blown my output stage once with an high supply voltage around 190V (and 13200uF of low ESR caps). I was doing power testing and I was in another room with two closed doors and two concrete walls inbetween, yet I could hear the bang in detail.

The result was a lot of vapourized PCB (thick polygons, not just tracks), exploded TO-220 cases, vapourized TO-220 leads, and some small SMD parts disappeared.

And this happened with a quite mature design, not just the first prototype.

In other words, be careful

btw: Your design lacks many important things.

btw2: An high-speed op amp can't do the work as a hi speed comparator, and vice-versa. A comparator is a one bit analog to digital converter. An op-amp is intended to produce an analog output. Comparators exhibit very high gain and slew rates at the expense of the inability to make them work in a NFB loop. 5mV of overdrive are enough to change the state of the outputs completely within a few dozen nanoseconds.
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Last edited by Eva; 26th January 2010 at 05:44 PM.
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