R U sure you have drawn it right ?
One possible solution can be found on IR's website (some charge pump using a 555).
Another one would be the use of a simple current-source from your elevated rail. You wouldn't need much current supplied by this (in the range of 350 uA IIRC).
Regards
Charles
One possible solution can be found on IR's website (some charge pump using a 555).
Another one would be the use of a simple current-source from your elevated rail. You wouldn't need much current supplied by this (in the range of 350 uA IIRC).
Regards
Charles
Mine isnot a current source, its a voltage source type of 15V floating and is referenced to the source....I have tested the amp with DC at input also and the output easily delivers it without any damage in continuous load....
BWRX said:
When you want to drive low frequency signals, the charge in bootstrap caps decays and the Mosfet enters linear conduction mode and would get damage,but using this elevated rail of VCC+15V the cap always remains charged, even if DC signal is used at the input of amp[provided DC coupling]...
Workhorse said:
I realized that after I posted, and edited my previous post
Your scheme makes sense but if you don't plan on amplifying DC wouldn't it be easier to just increase the value of the bootstrap cap?
The base voltage must be higher than the emitter voltage to turn on the transistor. So I think you have drawn the circuit differently than you actually implemented.
This wouldn't help since it wouldn't allow sustained turn-on of the upper MOSFET which is what is intended here. The idea is to allow driving the amp heavily into clipping without causing latchup or worse.
Not that heavy clipping should be a usual mode of operation of any amp - but it is always good practice to design things such that they survive any type of misuse.
Regards
Charles
This wouldn't help since it wouldn't allow sustained turn-on of the upper MOSFET which is what is intended here. The idea is to allow driving the amp heavily into clipping without causing latchup or worse.
Not that heavy clipping should be a usual mode of operation of any amp - but it is always good practice to design things such that they survive any type of misuse.
Regards
Charles
0-100% duty cycle could be realized,no smoking of amp during continuous clipping of low frequency signals at output....
Yes,phase_accurate said:
Actually
The elevated Rail voltage is 25V
The Zener voltage is 16V and thus the floating bootstrapping voltage is around 15V[including losses]....perfect to drive the mosfet during heavy clipping
Now I am happy driving any type of abusive clipped program continuously...
Do you like this technique Charles?🙂
Do you like this technique Charles?🙂
phase_accurate said:
Workhorse said:
DC and heavy clipping are two different conditions. You don't think you could get away with using a much larger bootstrap capcitance for the heavy clipping condition? Obviously it won't work for DC...
BWRX said:
I have tried 220uFD cap also, but encountered a failure during driving subsonic clipping signals around 18Hz.....
So I developed this technique and now quite happy with the results so far
Yes I do. A disadvantage might be the third rail. But this voltage can be generated on board as well if necessary. You know I am fond of topologies that are easy to use like the UcD modules for instance where you only need ground and two rail voltages. This is of coarse a non-issue for complete amps.
I was once thinking about some charge-pump technique to charge the bootstrap capacitor.
Regards
Charles
Its party time for me Charles, cheers
Thanks!
I think generating third rail from additional windings of regular transformer[or from on board DC-DC converter] isnot difficult, when the amp under consideration is designed for power output in Kilowatt levels and with pro world abusive conditions survival...
Atlast I feel relief from the clipping headaches...they are gone forever...
regards,
Kanwar
phase_accurate said:
Thanks!
I think generating third rail from additional windings of regular transformer[or from on board DC-DC converter] isnot difficult, when the amp under consideration is designed for power output in Kilowatt levels and with pro world abusive conditions survival...
Atlast I feel relief from the clipping headaches...they are gone forever...
regards,
Kanwar
Workhorse said:
That's a huge bootstrap cap! Hard to believe it couldn't hold the voltage up long enough. What voltage is it being used at and how much current does the cap have to supply?
BWRX said:
I onced used it with subwoofer class-D amp with SW 75Khz, the Bootstrap voltage was 15V, cap rated at 25V, The IR2110 was used to drive 2 pairs of IRFP460[as their gate charge was high thats why the cap wasnot charging enough during massive 12dB signal overdrive conditions]....
The input signal was 18Hz and the rail voltage was +-130V[open load] , load was 2 X 18" woofers @4ohm total
The input capacitance should have nothing to do with the current drawn while being on. The static current is only drawn by the driver circuit.
The turn-on is of course drawing charge from the bootstrap cap but this should be the same per switching event wheter the amp is overdriven or not. So your trouble might have been caused by something else than the high input capacitance.
Regards
Charles
The turn-on is of course drawing charge from the bootstrap cap but this should be the same per switching event wheter the amp is overdriven or not. So your trouble might have been caused by something else than the high input capacitance.
Regards
Charles
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