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Class D Switching Power Amplifiers and Power D/A conversion

Class D amp with 300v mosfets
Class D amp with 300v mosfets
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Old 20th January 2018, 12:41 AM   #91
kASD is offline kASD
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Class D amp with 300v mosfets
Evita check this unfriendly version IRS2452AM, it has got +/-200V capability with symmetric current sensing.

Last edited by kASD; 20th January 2018 at 12:44 AM.
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Old 22nd January 2018, 12:26 PM   #92
Eva is offline Eva  Spain
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- Td-on is 385ns typ. Tdoff is 340ns typ. Slow chip. I got fast with IR2110 and opto.
- The current limiting of both channels is hardwired together regardless of BTL. There is a single CSD line. If ch.1 has a bad load, ch.2 does not produce sound. This is not good for 2ch rack amplifier, unless both channel are BTL.
- I suppose external comparator is tolerated by driving COMP pins with logic signal.
- PWM may not be mandatory, but there is no explanation of PWM mechanism.
- Pricing seems adequate.

In the end this is a magnified LF boombox chip. The high propagation delay prevents good amplifier performance at high frequencies. Imagine Behringer or the Chinese relasing an ultra-long excursion subwoofer with ultra high power amplifier, and using this chip and some 600V IGBTs or 300V FET. And maybe non-isolated PSU with speacial speaker driver.
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Last edited by Eva; 22nd January 2018 at 12:29 PM.
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Old 25th May 2018, 01:03 AM   #93
endryc1 is offline endryc1  Cuba
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Sorry, i can`t see the pictures. Please can you put in other site. Sorry for my english. Thanks a lot.
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Old 11th November 2018, 12:59 AM   #94
ViennaTom is offline ViennaTom
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Hello all, is the confusion about strange ROHM -4V abs max rating already solved?
I am trying to simulate a self oscillating class D full bridge using 350V bus voltage and SCT3030, UCC21521C plus bootstrapping hi supply.
I am trying to get some negative gate "for free" by zener diode plus cap in series to gate, maybe -1.5V at the gate, but dependent on duty cycle and no negative voltage at startup. Not sure if the -4V is a mandatory limit. But anyway, I think the ROHMS are good at ~-1V and plus 16 ... 19V (depending on load current).
(I built a simulation using LTSPICE incl. the models of driver and SIC, but no chance to get the simulator to show anything. Just convergence issues, "time step too small", def con... etc...)
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Old 11th July 2019, 06:56 AM   #95
kASD is offline kASD
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Class D amp with 300v mosfets
Quote:
Originally Posted by ViennaTom View Post
Hello all, is the confusion about strange ROHM -4V abs max rating already solved?
I am trying to simulate a self oscillating class D full bridge using 350V bus voltage and SCT3030, UCC21521C plus bootstrapping hi supply.
I am trying to get some negative gate "for free" by zener diode plus cap in series to gate, maybe -1.5V at the gate, but dependent on duty cycle and no negative voltage at startup. Not sure if the -4V is a mandatory limit. But anyway, I think the ROHMS are good at ~-1V and plus 16 ... 19V (depending on load current).
In my application and as per ROHM technical team suggestion, unipolar gate drive serves the purpose. They are recommending +18V/0V gate drive. Which I have also found to be adequate. In case if you want to have negative gate drive, it should not increase beyond -4V at any cost, otherwise traps will form in the die and impact the reliability.


Whereas the real issue with CREE and ROHM SIC is as follows:

1. The Rthjc junction to case is very high when compared to other same package mosfets/Igbts. For example Rohm SCT3060AL specifies Rthjc as 0.91C/W vs 0.27C/W of IXGH100N30C3 IGBT.

This severely hampers the operation at high frequencies >250khz at higher currents >25A.

As per CREE and ROHM, they are Trench SIC mosfets whose DIE area is smaller as compared to other mosfets and hence higher Rthjc and higher RDS ON [compared with equivalent VCES drop of IGBT]

Hence the Fmax2 limit suffers severely, even if you have lower Total switching loss.

2. The Body Diode drop is very high 3-4V, which means you have high voltage drop during third quadrant switching or during deadtime. To keep this low, one has to keep the deadtime low or have to use external high voltage schottky barrier diode to keep the dissipation at minimum by bypassing the internal body diode voltage drop, though RDS based current path shunting does help but not much.. Again this conduction loss of diode increases the case temperature and further creates reliability problems.


IMHO these SIC mosfets are more suitable for use at high rail voltages , low current and lower frequencies.

See the attached graph based on data provided by ROHM itself.
Attached Images
File Type: jpg thumbnail_image005.jpg (46.2 KB, 95 views)

Last edited by kASD; 11th July 2019 at 07:04 AM.
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