On Fri, 29 Jan 2010 17:37:28 -0800,
wrote:

On Sun, 17 Jan 2010 10:23:00 -0800, John Larkin wrote:

On 17 Jan 2010 16:54:58 GMT, mick wrote:

On Sun, 17 Jan 2010 08:35:12 -0800, John Larkin wrote:

On 17 Jan 2010 16:01:35 GMT, mick wrote:

On Fri, 15 Jan 2010 23:02:08 -0800, John Larkin wrote:

snip

There's a pot on the linear regulator; it's in plain sight. And that's
all this thing needs. The PWM accomplishes nothing.



PWM dimming is more efficient than linear dimming - by a long way. It
all depends on how much heat the OP is willing to let the dimmer
dissipate.

PWM is no more efficient than resistive dimming the way he did it. There
are no inductors in his circuit. All this sort of PWM can do is move the
heat around.



I couldn't see his circuit on my server, but I assumed that he was
varying the mark/space ratio. In that case power dissipation in the
output device is always low, depending on Vsat.

That just moves the heat into the series resistors. Overall efficiency
is always the same for a dissipative (inductor-free) regulator.

I don't believe you. Foe a given diode plus resistor at the same supply
voltage load the power dissipation varies closely with % on time.
Lower % on time = less power.

Sure. And lower linear regulator output current pulls less supply
power, too.


You could always LTspice it to see what it says, or you could build an
example circuit and measure it. Or you could blow me off.

Without inductors, using PWM to adjust LED brightness is just as
efficient as using a variable linear regulator. Or just a series
rheostat.

You could get higher efficiency using a rather complex inductorless
charge pump, but that wouldn't be worth the effort.

A linear regulator driving multiple paralleled LED strings, each a
resistor and two or maybe three LEDs, is clearly the easiest way to do
this.

John