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.

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.

With a linear regulator and properly chosen series resistors, you can
balance the regulator heat distribution versus dimming level.
Regulator power dissipation versus output voltage is sort of
parabolic... low at low illumination, low at max illumination, peaking
somewhere between.

It's easier to heatsink a voltage regulator than a lot of small
resistors.

Another advantage of a voltage regulator is that it regulates.

John