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What's the best way to dim a lamp, and why? Also, which method is typically used in most typical residential dimmers? I originally thought it was as simple as wiring a potentiometer between the source and load, like this: enter image description here Or this: enter image description here Apparently not. I guess potentiometers are prone to overheating.


I notice a lot of schematics online simply add a transistor (BJT or FET): enter image description here enter image description here Slightly different configuration: enter image description here I don't really understand how that's supposed to be any better, but it's relatively simple and I see it a lot.


Here's a (kind of confusing) monostable 555 PWM circuit: enter image description here


Here's a 240VAC pulsing circuit that uses a diode bridge rectifier, capacitor and potentiometer: enter image description here Slightly more complicated: enter image description here Two capacitors: enter image description here


And an unusual one with a transformer: enter image description here


I'm sure there's probably more, but these are the schematics that I've simulated, and have on hand.

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closed as too broad by old_timer, pipe, Voltage Spike, Harry Svensson, winny Nov 20 '17 at 14:55

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ you've given this a lot of thought. Most wall dimmers are just triacs with a couple discrete parts unless they are the digital ones with ramp dim, and pause with touch sequence for rapid off. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 18 '17 at 9:26
  • \$\begingroup\$ @TonyStewart.EEsince'75 Yeah, I've been accused of not doing any research before asking (hastily written) questions, so I tried to be thorough. Plus I thought publishing them together might be helpful to someone. Thanks for writing in. \$\endgroup\$ – voices Nov 18 '17 at 9:49
  • \$\begingroup\$ i find that n-chan mosfets to PWM a DC source dims LEDs the best \$\endgroup\$ – dandavis Nov 18 '17 at 12:15
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In general for dimming a lamp following is applicable.

  1. Make the amount of power going into the lamp variable
  2. Prevent as much as possible the loss of power in the controller

In many domestic dimmers using mains this is done with a triac or IGBT controller. enter image description here

The triac controller makes that an adjustable part of the incomming mains voltage is transfered to the lamp. Leading edge phase cutting. An IBGT controller can operate with leading edge and trailing edge phase cutting.

Now if you replace the lamp with an LED device than the preferred methode of dimming is to rectify the incomming voltage and feed the DC voltage to the LED device in a chopped manner. This is called Pulse width modulation.

In some expensive dimmers one can preset the methode of dimming making such a dimmer suitable for Halogen lamps, LED Lamps with buildin electronics both trailing and leading edge modulation, CFL lamps and so on.

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  • \$\begingroup\$ Cool. So is this applicable to (incandescent lamp) circuits with an AC power source only? \$\endgroup\$ – voices Nov 18 '17 at 9:57
  • \$\begingroup\$ @HarrySvensson DIACs and TRIACs are new to me. They look like a pair of diodes back to back. I'll have to read up on them. So are there substitutes compatible with DC circuits? \$\endgroup\$ – voices Nov 18 '17 at 10:10
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    \$\begingroup\$ The substitutes compatible with DC circuits are using transistor circuits. An IGBT controller is such a device. In transistor circuits the switching is fully controlled. Meaning that both on and off are controlled. A triac controller in combination with AC shuts off when the voltage passes zero or when the hold current becomes to low. \$\endgroup\$ – Decapod Nov 18 '17 at 10:23
  • \$\begingroup\$ Whats the disadvantage of using a simple series resistor to dim ? What is the functionality of diac and triac and capacitor here? Don't know ...simply asking \$\endgroup\$ – Mitu Raj Nov 18 '17 at 10:28
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    \$\begingroup\$ @MITURAJ You need to study the use of a diac and triac first. If you get stuck ask again in a question. The use of a series resistor works only with incandescent lamps and does produce wasted energy. \$\endgroup\$ – Decapod Nov 18 '17 at 10:55

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