|
James,
I basically agree with you. A switching type drive makes sense when the power levels are large. The inefficiency of a linear drive becomes prohibitive at such levels. At 7A and 80V, a classic linear drive dissipates an unacceptable 560 Watts of heat in the power transistors.
At the other extreme, say 1A and 24V, the complexity of a switching type drive makes less sense. Heat dissipation then is a manageable 24 Watts and the simplicity and other advantages of a linear amplifier becomes appealing.
An interesting switching / linear hybrid out of favor these days is the bi-level drive. A high voltage supply (80VDC) is used as a "kicker" to rapidly inject current into the winding. Once current reaches the desired value, the high voltage is turned off and a low voltage (5VDC) "sustainer" power supply takes over to maintain the desired current The drive stays linear at all times while incurring almost no switching losses. The major drawback is two power supply voltages are needed.
Actually the "whine" of a chopper is caused by two free-running oscillators phase-locking and breaking phase-lock. This lock-break behavior creates beat frequencies that fall into the audible range to create the hissing, squealing, whistling and grunting associated with choppers. It is irritating but there is no inefficiency associated with that action. I personally cannot stand to listen to a constant off-time chopper drive; it's like fingernails on a chalkboard for me.:-)
Mariss
|