Re: Need ideas for 8-channel output
- From: Jan Panteltje <pNaonStpealmtje@xxxxxxxxx>
- Date: Wed, 01 Jul 2009 17:18:46 GMT
On a sunny day (Wed, 1 Jul 2009 09:21:55 -0700 (PDT)) it happened "Doug B."
<c.difficile@xxxxxxxxx> wrote in
<d3e05cc8-ef8a-4bc7-8aee-562694657050@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
Hello all,
I am getting started in electronics and would like some design advice
for a circuit that I have built, but am trying to improve.
This project involves a simple, 8-channel power amplifier. The input
will be a 1-10 Hz, audio-level control signal that will be either a
pure sine wave or something very close to it. The output stage will
drive a mainly resistive load (NOT audio at all, just driving lamps,
solenoids or similar). My current design and prototype uses IRF-511
power MOSFETs, driven in switching mode from a 13.2 V regulated power
supply.
The client is a artist friend of mine who uses sub-audio range signals
to control a bunch of different gadgets he has built. Currently he
amplifies these with a stack of car stereo amps that are hard to
transport and only provide four mono channels each. I believe we can
get all eight channels of amplification into a small box, as long as
the output stage is driven PWM-like. I am basically looking for a way
to provide reasonable dynamic range on the output, given the audio-
level inputs.
My current prototype uses an LM124 op amp with > 100db gain to
transform the input into a square wave, directly into the gate of the
IRF-511. This "on or off" amplification is not flexible enough.
My current thinking is that PWM is the way to go on the output, but
how to do that for 8 channels? I have looked into Class D amps, but
workable designs seem over my head in complexity and would require
absurdly large output filters for the low frequencies involved.
I have thought of using an analog Mux and microcontroller with ADC to
sample the levels on the 8 input channels. Given the low frequencies
this should be fairly straightforward.
I'm not sure how to handle the output, however. I could create a PWM
signal in the uController and analog Mux it out to an op amp buffer/
gate driver, but I would only get 1/8 of the PWM cycle on each
channel.
Ideas, anyone?
Thanks,
doug beeson
Stndard way is use 2 quad opamps as 8 comparators,
audio into one input of each, the other inputs conneted together to a
sawtooth wave that you make with an other opamp integrator perhaps.
The output will then be 8 PWM channels with 50% duty cycle for zero
audio.
ch 1 input ---- -
out -------- PWM
ramp --- +
8 x
.. .
.. . .
.. . .
.. . . . ---- 0V
.. . . .
..-.------- . .-------- slice level if audio a bit negative
.. .
_______ ______
|__| |__| PWM out
Do you know how to make a ramp waveform?
The opamp output can directly drive a suitable MOSFET.
No micro needed.
.
- References:
- Need ideas for 8-channel output
- From: Doug B.
- Need ideas for 8-channel output
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