Using cheap audio DACs as light dimmers

Wouldn't that generate a lot of heat and waste a lot of energy?

Doug

Seems like a lot of work to create what amounts to a $10 X10 Lamp Module.

Key to understanding your question is in the two letters "DC".

You do mean to control Direct Current, not AC, right?

Next important questions would be:

1) What voltage? 2) What current 3) How many devices?

First additional reaction is that:

1) 8 bits are satisfactory 2) Check out DMX (aka DMX512 aka DMX-512a )

And then to ask whether you want to control LEDs. Them's a different kettle of fish than incandescent lamps so it would be better to know that from the git-go.

But yes, what you seem to be asking is eminently doable if you don't need to worry about the National Electrical Code and other regulatory concerns

Let us know ... Marc

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Marc_F_Hult

the OP writes " (DC)".

An X-10 amp module will not control DC (direct current).

To the best of my knowledge, there are no commercially available X-10 dimmers for DC. ACT had some modules that might have been modified for such. (I don't remember any more.) All the X-10 dimmers I've ever taken apart or read about use TRIACS for phase-control of an AC load and will/do not control a DC load

HTH ... Marc

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Marc_F_Hult

Yes, it would be if bipolar transistors were used as the OP seems to describe.

But PWM control of MOSFET devices to control DC c/would be more efficient than AC control using TRIACS.

... Marc Visit my ongoing Home Automation and Electronics Internet Porch Sale at

Marc_F_Hult

And would jam every radio within, oh, maybe a one block radius -- unless the person doing it was pretty doggoned skilled.

Also, why do you think it would be "more efficient"?

Isaac

"Every Radio within ... one block radius" ? That Hippospeak is premature IMO ;-) Last I knew, we didn't even know what voltage or current rating the OP was interested in ...

And, seems to me, assuming that the DAC already exists (see Subject title) fewer, and especially smaller components are needed to limit dv/dt (and hence emissions) using a PWM MOSFET design than with a simple TRIAC design.

The power loss in TRIACS (or inverse-parallel SCRs) is due primarily to the

0.65 volt/junction loss. There are 3 PN junctions in a TRIAC so power loss ~= 3 * 0.65 volts rms * # of amps through the device. A 115 watt bulb draws ~ one amp at 115VRMS and so a TRIAC dissipates about 2VRMS x 1 amp = 2 watts RMS when fully on. A 230 watt bulb watts and so on.

The power loss in a MOSFET is due both to I*R loss during conduction and loss during switching but the sum can be less than that for TRIACs or SCRs. The device R resistance depends not on the fundamental physics (an intrinsic property) of (eg) silicon band gap as with TRIACs, but rather on how the device is made (eg thickness; = extensive property) So the amount of loss depends on the device you chose which depends on the circuit needs (voltage and current) -- which we don't know cause the OP hasn't told us ;-)

Even if you contrived to switch the MOSFET at the same frequency and dv/dt as a TRIAC (partially mimicking the waveform of a TRIAC-based dimmer) the MOSFET could (typically, depending on current and voltage specifics) have a bit higher efficiency and so -- of a more immediate practical design issue -- produce less heat than the TRIAC-based design.

Clear as mud ;-) ?

.. Marc

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Marc_F_Hult

An overdriven transistor can have a collector-to-emitter voltage drop that is somewhat less than the base-emitter drop that I assume you are referring to.

An SCR looks sort of like cross-coupled NPN and PNP transistors. When it turns on, both are heavily overdriven by feedback, and so the forward conduction drop can be lower than that of a single bipolar transistor. That is one of the reasons for their popularity in high power circuits

-- less heat is generated because of the smaller forward conduction drop. another is that the feedback results in very fast switching times, again giving higher efficiency.

Triacs, with 5 junctions, are not quite so good, and that's why back-to-back SCRs are favored at higher powers -- again, less heat.

True, but in both cases that low loss is partly dependent on the device being in the linear region for as short a time as possible, and that's why both need to have proper RF suppression.

Isaac