wendt@arizona.edu (Alan Lee Wendt) (01/23/88)
Is it possible to build an amplifier just like you would build a switching power supply? Except that instead of feedback circuitry to maintain level dc, change the feedback so that the output is maintained at whatever the input is, times 1000. What would such a beast be good for? Just curious, Alan Wendt
flaig@cit-vlsi.Caltech.Edu (Charles M. Flaig) (01/24/88)
In article <3539@megaron.arizona.edu> wendt@arizona.edu (Alan Lee Wendt) writes: >Is it possible to build an amplifier just like you would build a >switching power supply? Except that instead of feedback circuitry >to maintain level dc, change the feedback so that the output is >maintained at whatever the input is, times 1000. What would such >a beast be good for? > >Just curious, >Alan Wendt I took a class a couple years ago on switch-mode power supplies, and was interested in building a high power switching audio power amplifier. The class texts were authored by Middlebrook and Cuk, and published by Tesla Inc. (or something similar). There is a series of three books, and at least one of them had details on using bidirectional Cuk switching circuits for such an audio amplifier. I built half of a single channel for the lab part of the course and encountered no problems, but never seemed to get around to building the complete amplifier. :-( In general, such a switching amplifier can be used whenever high efficiency and high output power is needed. They are excellent for low frequency amplification, but you have to be careful with high frequencies (such as audio) since the response depends on the switching frequency and the filtering circuits, among other things.... --Charles Flaig flaig@csvax.caltech.edu
wtm@neoucom.UUCP (Bill Mayhew) (01/25/88)
Switching amps are much like swtiching voltage regulators, except that the signal being amplified serves as the reference voltage. Some care has to be taken to get sufficient bandwidth for audio applications. Most uses are for motor control. Somebody once mentioned that a football stadium used a several KW switching amp in the PA system. --Bill
hes@ecsvax.UUCP (Henry Schaffer) (01/25/88)
and, as the last article pointed out, it can be very efficient. --henry schaffer n c state univ
mbe@dde.uucp (Martin Berg) (01/26/88)
In article <3539@megaron.arizona.edu>, wendt@arizona.edu (Alan Lee Wendt) writes: > Is it possible to build an amplifier just like you would build a > switching power supply? Except that instead of feedback circuitry > to maintain level dc, change the feedback so that the output is > maintained at whatever the input is, times 1000. What would such > a beast be good for? Some years ago, Sony made an amplifier (type identification ?) where the output transistors where driven in on/off mode (i.e. a switching output stage). I think they called it 'Class D' operation. The main idea was to minimize the power loss in the amplifier (just as in a switching power supply). The result was (as far as I can remember) that the ratio between output power and input power (messured from the 220V (110V :-) ) AC input) was as high as 63 %. Normal amplifiers (domestic) has a ratio about 50 %. Kind regards Martin Berg (Dansk Data Elektronik A/S) ..mcvax!diku!dde!mbe or mbe@dde.UUCP
gene@cooper.cooper.EDU (Gene (the Spook) ) (02/03/88)
in article <144@Giraf.dde.uucp>, mbe@dde.uucp (Martin Berg) says: > > In article <3539@megaron.arizona.edu>, wendt@arizona.edu (Alan Lee Wendt) writes: >> Is it possible to build an amplifier just like you would build a >> switching power supply? Except that instead of feedback circuitry >> to maintain level dc, change the feedback so that the output is >> maintained at whatever the input is, times 1000. What would such >> a beast be good for? > Some years ago, Sony made an amplifier (type identification ?) where > the output transistors where driven in on/off mode (i.e. a switching > output stage). > I think they called it 'Class D' operation. The circuit (amp) you're referring to is either a class D, E, F, G, or H model. Most of them are similar, except with a few unique features which were patented by the company who developed it first. In this case, I *think* Sony did the Class G amp. This sucker acted like a variable- output SMPS (switch mode power supply), and the switching frequency was near or actually in the MHz range. Also, that beastie had to be fully RF shielded to keep from killing any other RF stuff that happened to be near. Class D amps are great for motor controller circuits; the natural inductance of the motor acts as a low pass filter. As for speakers, I'm not sure the coil inductance is enough to filter out high frequency components (as if anyone could hear them ;^) ), but these components may just leak out through the speaker wires enough to cause trouble. The Sony version, if I'm not mistaken, uses two power supply voltages of each polarity, for example, V+, V++, V-, and V--. The lower-in- magnitude supplies are for low power outputs. This keeps the P(out)/P(in) ratio as low as possible. When extra power is needed, the higher-in- magnitude supply kicks in through a blocking diode to provide the needed voltage. (Forgive the wording, but I guess you know what I mean.) A good simple reference might be _Oscillators_Simplified_ by Delton Horn. There is a chapter which describes some of these classes. (By the way, if anyone has a more technical reference to the different amplifier classes, could he/she email me a listing? Thanx in advance!) Basically, Class D's started things off. Different variations and improvements became different classes of amplifiers. At the very least, it sure is an interesting subject. Spookfully yours, Gene ...!ihnp4!philabs!phri!cooper!gene "If you think I'll sit around as the world goes by, You're thinkin' like a fool 'cause it's case of do or die. Out there is a fortune waitin' to be had. You think I'll let it go? You're mad! You got another thing comin'!" - Robert John Aurthur Halford