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Old 12th January 2012, 12:18 PM   #1
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Default Level shifting with half brige

Hi all

I'm designing a simple half bridge class-d amplifier from a +/- 12v supply source my design uses a LM311 powered from the +/- 12v source,the comparator is outputting a PWM signal and modulating to the music source signal (no feedback yet)..

My question is how do i design the next block in the signal path to do level shifting to feed a IR2011 gate driver also i have X2 IRF640 at my disposable.

Do i need to level shift if the comparator is already swinging between (-v) and (+v) dont i just need a pulse phase splitter such as a xor gate and feed it directly to the IR gate driver ?


Ive searched other threads and don't seem to get a clear enough example how to level shift so that the IR gate drive can work correctly.

Help and Patience will be really appreciated.

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Old 12th January 2012, 12:39 PM   #2
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Anyone ?
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Old 12th January 2012, 12:44 PM   #3
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can you try a Ac coupled (capacitively) plus a DC restorer. I had done something similar, and it worked pretty fine.

I´d used a HCF4047 oscillating at 250KHz, a TS274 (four CMOS opamps) working as differential integrator, a TS3402 (a version of double LM311 with push pull output), a HCF4049 driving a couple of 3A MOSFET´s, which in turn driver the output pair. All MOSFET´s Stage!!! Capacitively coupling had the advantage that the output transistor both automatically go off under no PWM signal, or driver failure.

Good luck !!!
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Old 12th January 2012, 12:51 PM   #4
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Sorry for the double post.

No, i don't think that will work im using a IR2011 and its able to drive the mosfets without any issues, my confusion is why cant i just drive the HIN, LIN from a xor phase splitter without a level shifter.

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Old 12th January 2012, 01:08 PM   #5
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Can be a common base/gate transistor/fet, an quick photocoupler like TLP504, or a transformer???
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Old 12th January 2012, 01:31 PM   #6
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Sounds like a job for an IRS20957.
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Old 12th January 2012, 01:42 PM   #7
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Quote:
Originally Posted by gmarsh View Post
Sounds like a job for an IRS20957.
IRS20957 has no educational value and it cost more im using components straight from my junk box at the cost of a steeper learning curve.
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Old 12th January 2012, 02:08 PM   #8
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Well then... use two gates from a 4030 XOR gate, powered from 0V and -12V rails, to give inverted/non-inverted drive signals to the IR2110. If you don't have a 4030, you could use a 74x86 logic gate, but you'll have to add a 7805 regulator or similar to power it. I wouldn't use a simple inverter circuit as the time delay might cause cross-conduction on turn-on or turn-off.

I still think you're better off using a "single input" H-bridge driver, preferably with adjustable dead time. It'll make this project a lot easier and likely save you some frustration.
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Old 12th January 2012, 05:19 PM   #9
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Quote:
Originally Posted by gmarsh View Post
Well then... use two gates from a 4030 XOR gate, powered from 0V and -12V rails, to give inverted/non-inverted drive signals to the IR2110. If you don't have a 4030, you could use a 74x86 logic gate, but you'll have to add a 7805 regulator or similar to power it. I wouldn't use a simple inverter circuit as the time delay might cause cross-conduction on turn-on or turn-off.

I still think you're better off using a "single input" H-bridge driver, preferably with adjustable dead time. It'll make this project a lot easier and likely save you some frustration.
Thanks for the tip gmarsh!

Here is a very minor version of the my circuit nothing special many blocks are missing example: feedback, gate driver, MOSFET and LPF i will continue exploring until i feel confidant enough to configure each signal block, (This why i used a low voltage power supply )

BTW I am using a CD4030 XOR as a phase splitter, i do feel i need to introduce a transistor buffer stage to buffer between the gate drive and comparator i don't think the Logic hi/low voltages from the comparator are a driving hard enough the pulses.

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Old 12th January 2012, 05:30 PM   #10
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The output from the XOR phase splitter outputs a phase split with some strange dv/dt results.

Strange behavior not sure but the difference in XOR phase output A and B are

OUTPUT A: V-MAX=720mv and V-MIN=-4.00V
OUTPUT B: V-MAX=400mv and V-MIN=-8.00V

why are they not matched.

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