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Class D Switching Power Amplifiers and Power D/A conversion

level shifters and mosfet drivers
level shifters and mosfet drivers
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Old 30th April 2006, 01:15 PM   #1
Tekko is offline Tekko
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Question level shifters and mosfet drivers

If i use a MAX628 mosfet driver to a class d amp project, do i still need a level shifter on the high side input ?

If so, how is a level shifter made ?
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Old 30th April 2006, 01:46 PM   #2
fredos is offline fredos  Canada
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Simply use a 6N137 optocoupler, but you will need a mosfet driver for each mosfet..

Fredos

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Old 30th April 2006, 02:18 PM   #3
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The MAX628 is a dual mosfet driver, one inverting and one non inverting.

Could i use optocouplers from like a smps ?
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Old 30th April 2006, 02:20 PM   #4
fredos is offline fredos  Canada
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Bad move with your IC...Use and inverting with the 6N137 and non-inverting with the lower side..

Fred

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Old 30th April 2006, 02:26 PM   #5
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Hum ?

I donīt fully undterstand what you mean ?

What was a bad move ? Atleast the MAX628CPA ICīs are free samples.
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Old 30th April 2006, 02:33 PM   #6
fredos is offline fredos  Canada
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You cannot drive upper and lower mosfet with that single chip, you will need 1 for upper mosfet and 1 for lower...If I understand that you was planning to use this chip for high side and lo side driver..

Fredos
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Old 30th April 2006, 02:42 PM   #7
Eva is offline Eva  Spain
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As the datasheet makes obvious at first look, the ICs of that family (MAX626/627/628) are plain dual gate drivers, with both halves sharing the same power supply pins. Thus, there is no way in which you could drive a half-bridge-like class D output stage with one of these ICs.

Not only level shifting is required, but also independent or floating gate buffers are. You can either design a discrete solution, or use an IC having all those features built in, like IR2112, IR2110 or IR2113.

Also, there are standard and fast optocouplers like 6N137 whose practical propagation delay is in the range of 50ns. However, be very careful when using optocouplers because they don't provide perfect AC isolation but only DC isolation. There are internal capacitances between the input and the output sections of the IC that will disturb the state of the output if a certain common-mode dV/dt slope is exceeded during switching transients. You will find those dV/dt inmunity ratings on datasheets, and even in the best optocouplers from Avago (formerly Agilent or HP) the rated dV/dt (up to 15KV/us) may become quite short considering the fast rise and fall times involved in class D (expect something like 100V in 40ns or less). Indeed, I can tell that simple optocouplers like 4N25 are extremely easy to disturb.

I feel that you should learn more about switching circuits before starting class D experimentation, otherwise plenty of component blowing disasters may arise.
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Old 30th April 2006, 03:30 PM   #8
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Bah

Is it possible to cancel a samples order ?
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Old 30th April 2006, 03:37 PM   #9
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What about SC1205CS for mosfet drivers ?

Will they work ? The datasheet does say class d amplifiers.

Tho i have not found any place that sells them

Anyone have a few ?
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Old 1st May 2006, 02:47 AM   #10
fredos is offline fredos  Canada
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Look good, but power supply limted to abou 18V if you use 12V bootstrap voltage...Good for experimentation!

fred

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