DC Power supply question...duh...

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sat Jul 3 23:07:28 1999

<In this bridge circuit with a 12 volt supply:
<
<+12 -------
< A B
< .LOAD..
< C D
<return-----

The last design I did in the analog realm was a 500w per channel
that could be bridged for 1000W. (for studios and theatures) I am
acutely aware of the topology of bridge amps and power measurement.

<(A, B, C, D) are switches, either A, D or B, C on,
<The 4 Ohm load sees a maximum current of 3 Amps in either direction.

or 24V PP with 6a. Keep in mind it takes 6A to move the coil through the
full range it will travel with this 24VPP signal. It will move forward
3A(12v) worth from the resting position and it will move rearward the
same distance with the reverse polarity but it will take 24v6a to make
it transverse the same path in a continious cyclic way.

<That is 1.5 Amps for each of two 8 Ohm speakers in parallel.
<The maximum (peak) power is 36 watts, 4x that of a non-bridged amplifier.
<"peak to peak power" is just a marketroid term. Actually I don't even use
<the term "RMS power", as IMHO, "RMS" applies to voltage or current, not pow

Oh boy... RMS WATTS are measured using real RMS Amps and real RMS Volts
across a real (non inductive load). A real 500w amplifier heats a 4ohm
resistive load the same as pluging it into a ~45V RMS AC source. As long
as you know what is meant all the terms are valid. One of the problems
with small amplifers is the power supply is tepid to weak and often they
can actually supply full load power for one or two cycles until the PS
voltages fade due to lack of iron and copper in the core. I have a 35W
(continous RMS) stereo amplifer I built and due to the transformer (not
enough core) but plenty of Capacitor it can in short bursts deliver 55W
(10 cycle pulses of 400Hz _at_<.1%). There are far more dynamics than discussed
though some of the numbers are really meaningless.

Most of those wall cubes are very limited and 30-40W is about the limit,
often less. There are a few switchmode designs for wall cubes at will pack
70-80w output into something 4x1x2 but those don't go cheap.

Allison
Received on Sat Jul 03 1999 - 23:07:28 BST