simple buck switcher for LED drive from 9v?

[Dbowey]

John posted:

You'd need a special lamp: say 30 V 150 mA for 110 V or 120 V 50 mA for
220-240 V. It may have been done: it's the sort of thing Philips would
have looked seriously at. But I don't recall one in Britain.

I'm surprised Lucas didn't produce one. He is known by every US MG car owner
as the God of Darkness.

Don

 

[Walter Harley]

Presumably then the LED is there as a reminder to switch
off the amp when not in use. Couldn't this be done with a
short 'blip' every now and again, say about every 10S?

Quite possibly.

Simple RC charging [...]

Or, if I'm using an oscillator plus a divider to time the turnoff, I could
take an earlier output from the divider, through an R-C to shorten the
pulse.

But the LED, bezel, and connector right now cost me around $2, so if I could
eliminate it altogether, I could buy myself a few extra espressos per month
If I'm using a timer to automatically shut the thing off, there's no
need for a power indicator; the only remaining application is as a
low-battery indicator, and maybe that's not crucial.

(Let's see, if I used one of those little sampler chips in greeting cards, I
could just feed some audio into the headphones... "ALERT! YOUR BATTERY IS
DANGEROUSLY LOW!" But then I'd have to market different versions
internationally, and I actually do have a bunch of international customers.
Hmm.)

 

[Mac]

Presumably then the LED is there as a reminder to switch
off the amp when not in use. Couldn't this be done with a
short 'blip' every now and again, say about every 10S?

Quite possibly.

Simple RC charging [...]

Or, if I'm using an oscillator plus a divider to time the turnoff, I could
take an earlier output from the divider, through an R-C to shorten the
pulse.

But the LED, bezel, and connector right now cost me around $2, so if I could
eliminate it altogether, I could buy myself a few extra espressos per month
If I'm using a timer to automatically shut the thing off, there's no
need for a power indicator; the only remaining application is as a
low-battery indicator, and maybe that's not crucial.

(Let's see, if I used one of those little sampler chips in greeting cards, I
could just feed some audio into the headphones... "ALERT! YOUR BATTERY IS
DANGEROUSLY LOW!" But then I'd have to market different versions
internationally, and I actually do have a bunch of international customers.
Hmm.)

I'm not sure how they would do for you, but some devices use surface mount
LED's and snap-in plastic light pipes to bring the light out. This has a
convincing look. That is, the LED appears to be at the end of the light
pipe.

Also, I measured the current through an LED I have on a board at work. It
was around 5 mA, and the LED was quite bright. It was a tiny SOT surface
mount LED. Green, if that matters to you.

So I wonder if you are seriously over-estimating the current you need.

The other thing is that I think you are on the right track with having
this thing turn on and off automatically. You could have some very low
power circuitry that detects an input signal and resets a timer (which
also must be very low power, as in a digital watch) whenever an input
signal is present. If the timer ever runs out, the low-power cicruitry
shuts off the rest of the device (perhaps by way of a FET switch).

Anyway, it sounds like a fun project.

Mac
--

 

[N. Thornton]

On 31 Oct 2003 09:33:42 -0800, the renowned [email protected] (N.
Thornton) wrote:

How about making the world's first combination night-light and radio?
(Using the bulb as a dropping resistor) That would have been within
the technology then.

Hi Spehro. This kind of thing was done by amateurs in the 1920s, dont
think I've ever seen a commercial set do it tho, it wouldnt exactly
lend an air of whatever was the fashionable image of the time. Of
course dial lights in series with the heater chain were routine, but I
dont recall ever seeing them in the HT path. The surges could be quite
a problem.

But... the question still remains how you get the heat out of the box?
I suppose you're thinking radioation plus reflector? Clever.

Got it. Use your bulb dropper, complete with reflector, but add an IR
filter so that it doesnt light the place up. Then most of the heat is
directed out onto the wall, and it looks socially acceptable.

Or of course you could just use a bulb at half V so it only glows
dimly. I like that one. Creates a market for replacement bulbs too,
one per 10 years or so.


Regards, NT

 

[N. Thornton]

I read in sci.electronics.design that N. Thornton <[email protected]>
wrote (in <[email protected]>) about 'Does
this work?', on Fri, 31 Oct 2003:

The valve/tube heaters WERE connected in series. On 100 V mains, the B+
voltage needed to be as high as could be obtained, with a valve/tube
rectifier - about 120 V.

I'm not sure what you have in mind.

Hi John, I dont think I explained too well. The idea was to split the
_HT_ load into 2, and put the 2 HT loads in series. So effectively
there'd be 2 grounds, the rf one at real ground, and the af one at
half rectified mains V.

The af output stage is one of the 2 loads, and the rest of the stages
make up the other load. Put the 2 in series, with the audio
capacitor-coupled up to the output stage.

The more I think about this, the more it sounds like a bad idea.
Radios struggled a bit on 110v mains due to low HT, but they were
still quite workable. Thus in principle one could divide the 320v
supply in half, and run the circuitry at about 160v, with the 2x 160v
supplies effectively in series.

This doesnt touch heater dropper dissipation, but was intended to drop
HT diss, thus total diss... but on second thoughts maybe it wouldn't.

Time to ditch that idea.

Kolster-Brandes did make a radio
with the heaters in series with the B+ supply, but it was
unconventional.

Never seen one myself, but I seem to recall warnings about servicing
these: dont pull valves out and power up It sounds like a clever
idea, if the numbers matched OK.

That's quite a good idea. Go back to 1960 and propose it to me. (;-)

I wish I have a few ideas that would have been good in former
times, but are now about as useful as.... something useless.


Regards, NT

 

[Klave]

I have both a real application and a philosophical one. The real
application is a battery-powered headphone amplifier (used by electric
bassists when practicing) that I make and sell. I make 50-100 of them a
year - not exactly the big time but enough that manufacturing efficiency and
parts cost matter. Right now, the power LED is a big factor in the battery
life.

What about trying to make use of power being wasted elsewhere in the
circuit, for example, put the LED in series with some of the circuitry
that draws power. It might even be possible to use it in the bias
stage to replace a diode.

Depending on where it goes, it may be modulated by the sound - maybe
this will help keep everyone else in time.

GK