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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Thank you... posted by real_jj on April 26, 2006 at 10:20:35:
These things can vary with load, too, and audio equipment, unlike industrial convertors, runs with a very wide load range, from maybe 5% to 100% of load, depending on the input signal and the level adjustment.
Which also explain why PFC'ed switching power supplies are quite not used in power amps, despite their big advantages.
It is not easy to design an excellent switching power supply with such a large span of loads.
In technical terms, we want to make the switching transistors commute exactly:
- when the voltage between their pins is null (condition called ZVS, zero voltage switching), or
- when the current through them is null (condition called ZVS, zero voltage switching).
Doing so is called soft swiching, since it avoids high dV/dt and dI/dt when switching.
Those dV/dt and dI/dt are evils since they are the source of strong EMI/RFI in the stray components of wiring (they excite them).
Without them, EMI/RFI is easily managed as long as the board is well laid out.
Another big advantage of soft switching is that less heat is generated since energy stored in parasitic elements is not changed into heat, but rather into another form of energy (for example, energy stored in the drain-source capacitance of the power transistors, instead of being flatly shorted, is transfered to some inductance in the design, for example the stray inductance from storage caps).
Since less heat is generated, you can make the PS run faster (500KHz is state of the art for less than one KW), make it smaller too.
So, the aim is to have ZVS condition when the transistors are closing, and ZCS when opening.
For technical reasons above what I have currently the courage to write down, these conditions are very difficult to keep on a large span of load current like seen in a PA, as notes real_jj.
In fact, it is a hot topic in current industrial research and development: I don't know of any IEEE Transactions on Power Electronics since circa 2000 without at least 2 or 3 papers about soft switching.
Many solutions do exist, we are at the time when most of these solutions are yet known, but the best ones have still to emerge from the pool.
enough for today
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Follow Ups
- About the very wide load range of PA and switching PS - Jacques 12:42:00 04/26/06 (2)
- Reread and found a typo - Jacques 03:00:14 04/29/06 (1)
- Very minor... - real_jj 12:40:58 04/29/06 (0)
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