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Class D Switching Power Amplifiers and Power D/A conversion

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Old 1st February 2010, 07:13 AM   #151
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Originally Posted by Baldin View Post
Ok, tried it out in real life ... just kept R3=2k2 and R5=2k7 for startes.
Both MAX913 output and Level Shifter output looks much better.
Speed is faster also, caused the switching freq to shift from 270 kHz to around 290 kHz.

Will sim a little to find lower values for R3 and R5, which will not burn, to get even better and faster shifting
Resistor value should be reduced and also use sanyo pnp high speed video transistor TO-126 pack for helping in dissipation or get it in D-PAK.
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Old 1st February 2010, 09:18 AM   #152
bicikle is offline bicikle  Macedonia
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i have seen this " http://datasheet4u.com/download.php?id=595690 " and the reansistors are 330W, so if we use 12 transistor (btl) we have max 3960w....
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Old 1st February 2010, 12:16 PM   #153
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Default discrete driver

Driving Large-Die and Paralleled Power MOSFETs Is Easy with the Right Techniques
In this paper, mosfet totem pole (inverting) seems better than bipolar totem pole (non-inverting).
But why this mosfet totem pole is less popular than bipolar one?
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Old 1st February 2010, 12:19 PM   #154
Eva is offline Eva  Spain
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Originally Posted by bicikle View Post
i have seen this " http://datasheet4u.com/download.php?id=595690 " and the reansistors are 330W, so if we use 12 transistor (btl) we have max 3960w....
Wow, I always thought that the power had to be dissipated in the load, not in the amplifier
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Old 1st February 2010, 12:28 PM   #155
Eva is offline Eva  Spain
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Quote:
Originally Posted by lumanauw View Post
Driving Large-Die and Paralleled Power MOSFETs Is Easy with the Right Techniques
In this paper, mosfet totem pole (inverting) seems better than bipolar totem pole (non-inverting).
But why this mosfet totem pole is less popular than bipolar one?
Quote from that paper:
"Unlike the bipolar design, the MOSFET totem pole is inverting and offers voltage gain to improve on the pre-driver rise and fall times. This driver suffers from shoot-through current caused by the threshold voltage overlap during on and off transitions resulting in increased drive power requirements. Because of the inverting nature of the driver, it may cause false turn-on of the power device during power up and power down, requiring under voltage detection and hold-off circuitry."

More reasons:

-Every high and low side gate driver IC is non inverting
-Almost every gate driver IC puts its outputs in a low state during shutdown
-With bipolars you can get close to 10A peak from a SOT-23
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Old 1st February 2010, 12:42 PM   #156
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Hi, EVA,

How hot it is (when you touch the transistors), the totem pole with SOT23 transistors?
If price is not a problem, drivers like IXDD430CI seems good for driving difficult gates.
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Old 1st February 2010, 01:31 PM   #157
Eva is offline Eva  Spain
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Driving one IRFB4227 at 4A peak (turn off) and 125khz, not substantiaally hotter than the PCB.
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Old 1st March 2010, 07:02 PM   #158
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in my circuit is around 20V/ns for turn off and around 15V/ns after reverse recovery.

Of course, for high end I would probably be using pulse transformers to produce isolated high side supplies, and one regulator for each gate driver, but in this amplifier there is no room for that. I would probably be using separate optocouplers or transistors for level shifting too, for minimum skew and delay, but optos can't whitstand as high dv/dt as IR drivers (10-15V/ns vs 50V/ns).
Hi Eva,
I have to thank you for this discussion. It helped to find a design flaw in theory, before getting headache with the real thing.
Today was the first day I found time again for my hobby after my move
Remembering our discussion, I started to analyse the switching conditions in my circuit more detailed and I am coming to the conclusion that also my di/dt limiter cannot avoid fast dv/dt under all conditions.
I found load situations which exceed the the allowed dv/dt of HCPL9030 (15kV/us) isolators and especially during heavy load conditions it is not really convincing to rely on components that are hopefully better than their spec...

I am considering to use IR half bridge drivers and pay the price of reduced timing precision.
In fact the IRS20124S is looking not so bad. Low propagation delay and a clever overcurrent protection. In combination with simple bipolar buffers it might serve my design needs.

Anybody out there who has already real life experience with the IRS20124S?
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Old 2nd March 2010, 04:41 AM   #159
Eva is offline Eva  Spain
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I have seen full-range class D amplifier modules that use them, with bipolar buffers and IRFB4227. I'm not allowed to tell more, but they will work for sure

I'm considering IRS2011 and IRS20124 for my next projects. IR2110 is very reliable and produces consistent timing, but with bipolar buffers the lower output impedance is not really required, the propagation delay is high and the package is a bit bulky too.
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Last edited by Eva; 2nd March 2010 at 04:45 AM.
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Old 2nd March 2010, 04:25 PM   #160
Baldin is offline Baldin  Denmark
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Hi Choco and Eva

My thoughts exctly. I'm going for IRS20124 next.
IR2110 works great, but IRS20124 will give both dead time delay adjustment and current protection for free. Worth considering I think

I was actually hoping to skip the buffers, though it is only 4 small transistors. How bad would it be to drive e.g. IRFB4227 at say +- 60V?? ..... You have probably already made such calculations

Using buffers would maybe also allow for smaller gate resistors ... or skipping them all together for higher switching speeds

Why not use IRS20957S .... that would also save the levelshifting at the input ... but I guess you can do that much faster with a good high speed transistor (as Workhorse suggested) ......
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Last edited by Baldin; 2nd March 2010 at 04:44 PM.
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