Using cheap audio DACs as light dimmers

Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
comment on the feasability of using something like the TDA1543 as a
home-brew (DC) light dimmer?

My idea was to couple it to a 10-bit DIP switch and some TTL and
support stuff, so I can "address" the device, then send a 16bit
setting to configure brightness - assuming the output of these things
is suitable for driving a matched transister for the expect load...

cnd <abuse.bot@gmail.com> wrote:

>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
>comment on the feasability of using something like the TDA1543 as a
>home-brew (DC) light dimmer?
>
>My idea was to couple it to a 10-bit DIP switch and some TTL and
>support stuff, so I can "address" the device, then send a 16bit
>setting to configure brightness - assuming the output of these things
>is suitable for driving a matched transister for the expect load...

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

Doug

"cnd" <abuse.bot@gmail.com> wrote in message
news:5d5b0042-1bc8-45d2-b8a3-7dd6c61e5206@h17g2000prg.googlegroups.com...
> Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
> comment on the feasability of using something like the TDA1543 as a
> home-brew (DC) light dimmer?
>
> My idea was to couple it to a 10-bit DIP switch and some TTL and
> support stuff, so I can "address" the device, then send a 16bit
> setting to configure brightness - assuming the output of these things
> is suitable for driving a matched transister for the expect load...

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

On Sun, 10 Aug 2008 06:34:13 -0700 (PDT), cnd <abuse.bot@gmail.com> wrote in
message <5d5b0042-1bc8-45d2-b8a3-7dd6c61e5206@h17g2000prg.googlegroups.com>:

>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
>comment on the feasability of using something like the TDA1543 as a
>home-brew (DC) light dimmer?
>
>My idea was to couple it to a 10-bit DIP switch and some TTL and
>support stuff, so I can "address" the device, then send a 16bit
>setting to configure brightness - assuming the output of these things
>is suitable for driving a matched transister for the expect load...


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

Visit my ongoing Home Automation and Electronics Internet Porch Sale at
www.ECOntrol.org/porch_sale.htm

Marc_F_Hult
www.ECOntrol.org

On Tue, 12 Aug 2008 10:49:25 -0500, "BruceR" <NoSpAm@NoHoW.com> wrote in
message <Zaidney6s_yULDzVnZ2dnUVZ_qHinZ2d@comcast.com>:
>"cnd" <abuse.bot@gmail.com> wrote in message
>news:5d5b0042-1bc8-45d2-b8a3-7dd6c61e5206@h17g2000prg.googlegroups.com...
>> Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
>> comment on the feasability of using something like the TDA1543 as a
>> home-brew (DC) light dimmer?
>>
>> My idea was to couple it to a 10-bit DIP switch and some TTL and
>> support stuff, so I can "address" the device, then send a 16bit
>> setting to configure brightness - assuming the output of these things
>> is suitable for driving a matched transister for the expect load...
>
>Seems like a lot of work to create what amounts to a $10 X10 Lamp
>Module.

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

Visit my ongoing Home Automation and Electronics Internet Porch Sale at
www.ECOntrol.org/porch_sale.htm

Marc_F_Hult
www.ECOntrol.org

On Tue, 12 Aug 2008 12:11:53 -0300, Doug Meredith <doug.meredith@hotmail.com>
wrote in message <vv93a4p3dcsunetludo66n7cj0v687c6t3@4ax.com>:

>cnd <abuse.bot@gmail.com> wrote:
>
>>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
>>comment on the feasability of using something like the TDA1543 as a
>>home-brew (DC) light dimmer?
>>
>>My idea was to couple it to a 10-bit DIP switch and some TTL and
>>support stuff, so I can "address" the device, then send a 16bit
>>setting to configure brightness - assuming the output of these things
>>is suitable for driving a matched transister for the expect load...
>
>Wouldn't that generate a lot of heat and waste a lot of energy?

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
www.ECOntrol.org/porch_sale.htm

Marc_F_Hult
www.ECOntrol.org

In article <6hk3a4p92vcor55pk06ml8bg4408ptp5ag@4ax.com>,
Marc_F_Hult <MFHult@nothydrologistnot.com> wrote:

> On Tue, 12 Aug 2008 12:11:53 -0300, Doug Meredith <doug.meredith@hotmail.com>
> wrote in message <vv93a4p3dcsunetludo66n7cj0v687c6t3@4ax.com>:
>
> >cnd <abuse.bot@gmail.com> wrote:
> >
> >>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
> >>comment on the feasability of using something like the TDA1543 as a
> >>home-brew (DC) light dimmer?
> >>
> >>My idea was to couple it to a 10-bit DIP switch and some TTL and
> >>support stuff, so I can "address" the device, then send a 16bit
> >>setting to configure brightness - assuming the output of these things
> >>is suitable for driving a matched transister for the expect load...
> >
> >Wouldn't that generate a lot of heat and waste a lot of energy?
>
> 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.

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

On Tue, 12 Aug 2008 20:16:53 -0700, isw <isw@witzend.com> wrote in message
<isw-69BAB7.20165312082008@newsgroups.comcast.net>:

>In article <6hk3a4p92vcor55pk06ml8bg4408ptp5ag@4ax.com>,
> Marc_F_Hult <MFHult@nothydrologistnot.com> wrote:
>
>> On Tue, 12 Aug 2008 12:11:53 -0300, Doug Meredith
<doug.meredith@hotmail.com>
>> wrote in message <vv93a4p3dcsunetludo66n7cj0v687c6t3@4ax.com>:
>>
>> >cnd <abuse.bot@gmail.com> wrote:
>> >
>> >>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
>> >>comment on the feasability of using something like the TDA1543 as a
>> >>home-brew (DC) light dimmer?
>> >>
>> >>My idea was to couple it to a 10-bit DIP switch and some TTL and
>> >>support stuff, so I can "address" the device, then send a 16bit
>> >>setting to configure brightness - assuming the output of these things
>> >>is suitable for driving a matched transister for the expect load...
>> >
>> >Wouldn't that generate a lot of heat and waste a lot of energy?
>>
>> 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.
>
>And would jam every radio within, oh, maybe a one block radius -- unless
>the person doing it was pretty doggoned skilled.

"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.

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

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

Visit my ongoing Home Automation and Electronics Internet Porch Sale at
www.ECOntrol.org/porch_sale.htm

Marc_F_Hult
www.ECOntrol.org

In article <su86a4dbpq2g216spkcju827318aspft4h@4ax.com>,
Marc_F_Hult <MFHult@nothydrologistnot.com> wrote:

> On Tue, 12 Aug 2008 20:16:53 -0700, isw <isw@witzend.com> wrote in message
> <isw-69BAB7.20165312082008@newsgroups.comcast.net>:
>
> >In article <6hk3a4p92vcor55pk06ml8bg4408ptp5ag@4ax.com>,
> > Marc_F_Hult <MFHult@nothydrologistnot.com> wrote:
> >
> >> On Tue, 12 Aug 2008 12:11:53 -0300, Doug Meredith
> <doug.meredith@hotmail.com>
> >> wrote in message <vv93a4p3dcsunetludo66n7cj0v687c6t3@4ax.com>:
> >>
> >> >cnd <abuse.bot@gmail.com> wrote:
> >> >
> >> >>Hi all, my electroncis knowhow is a bit dated nowdays... can anyone
> >> >>comment on the feasability of using something like the TDA1543 as a
> >> >>home-brew (DC) light dimmer?
> >> >>
> >> >>My idea was to couple it to a 10-bit DIP switch and some TTL and
> >> >>support stuff, so I can "address" the device, then send a 16bit
> >> >>setting to configure brightness - assuming the output of these things
> >> >>is suitable for driving a matched transister for the expect load...
> >> >
> >> >Wouldn't that generate a lot of heat and waste a lot of energy?
> >>
> >> 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.
> >
> >And would jam every radio within, oh, maybe a one block radius -- unless
> >the person doing it was pretty doggoned skilled.
>
> "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.
>
> >Also, why do you think it would be "more efficient"?
>
> The power loss in TRIACS (or inverse-parallel SCRs) is due primarily to the
> 0.65 volt/junction loss.

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.

> 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.

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