# Can somebody explain the principle beind making a dimmer switch which can manipulate voltage while keeping a consistent current?

### 6 Answers

- 8 months ago
Decades ago the most efficient light dimmers were variable transformers or variable inductors.

These days household dimmers use heavy duty transistor circuits which prevent current flow in the first part of each half-cycle. The switch on time in each cycle is determined by the voltage from a high resistance variable resistor. The large resistance draws very little power, and there is minimal loss in the transistors which are either on or off. The current is AC and at each instant, when flowing, is determined by the voltage and the resistance of the bulb. (This type of dimmer may not work well with florescent or LED bulbs.)

If you want to dim a bulb in a DC circuit, the simplest method would be to us a variable resistor which can tolerate heat comparable to that produced by the bulb. (A dimmed bulb receives less voltage and current.)

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- VamanLv 78 months ago
The best method is to control the current. This can be done volume control switches. But the resistances in bulbs is low may be 100 to 1000 ohms. Your volume control switch should have max 2000 ohms and lower can be 0. I forgot the name of these variable resistors used in the electronic departments.

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- Andrew SmithLv 78 months ago
In comments to Bill Russell's answer you ask "why can't I"

The power given to a resistance is i^2 R Which means that IF you could control the current to keep it constant and if R remains fixed then the power remains fixed.

Now we DO have controllers that do what you ask but they are no use for a fixed resistance.

In a traction motor for an elevator the electric motor USED to have a very high current and torque at starting.

Your feet left the floor when it started down. Your knees crushed when it went up.

By keeping the current constant it keeps the torque constant ( or at least approximately so ) and you get a steady increase in speed WITHOUT losing your lunch.

Now as the motor speeds up it needs MORE volts to maintain the constant current ( more work is being done as the speed increases ).

So you do use a controller to increase the volts with increasing load while maintaining the current to a selected level.

But this is not a simple resistance. It is a variable load and the controller is altering to match the load.

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- PhilomelLv 78 months ago
If you use a constant current source and manipulate the resistance the voltage will respond according to ohms law.

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- DixonLv 78 months ago
It is inductive smoothing, kinda of the complement to capacitive smoothing so it's all "opposite", ie series inductance rather than parallel capacitance.

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- billrussell42Lv 78 months ago
That is impossible. You cannot regulate (manipulate) both voltage and current. The best you can do is regulate one and let the load determine the other.

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- Flesh8 months agoReport
I read your answer wrong and actually it said what I wanted

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