New Dashboard

[GeoffSmith]

Ok, electronic whizzes.

Looks to me (from the diagram) that a rheostat is a glorified transistor?

If so, why not just have a transistor?

Or, just have a pot?

The problem of having a linear regulator like a true rheostat is that the power dissipation is high and worst case at half full scale, when the power dissipated is the same as that dissipated in the lamps. I suspect that the box shown driving the transistor in the rheostat module is a variable mark/space ratio oscillator with the m/s ration set by the potentiometer centre tap; this is essentially a class D amplifier (as used in laptops etc. to prolong battery life) and significantly reduces losses and power dissipation.

Geoff

[ailwyn]

The problem of having a linear regulator like a true rheostat is that the power dissipation is high and worst case at half full scale, when the power dissipated is the same as that dissipated in the lamps. I suspect that the box shown driving the transistor in the rheostat module is a variable mark/space ratio oscillator with the m/s ration set by the potentiometer centre tap; this is essentially a class D amplifier (as used in laptops etc. to prolong battery life) and significantly reduces losses and power dissipation.

Ok, I can accept that...... now does anyone know how to convey this in english?

Now back to my question.... why can't you relace the whole lot with a single pot, if memory serves, and Mr J. Walker is trying his best to confuse the issue, you can get pots which operate on a log(?) basis as opposed to linear... can't you just use one of these?

[GeoffSmith]

Refraining from a technical explanation, the answer is NO.

[GeoffSmith]

You can always read up on it in this information on class D amplifiers or this information on the different classes of amplifier (Note: linear = class A)

Geoff