More complex but less EMI than the Triac dimmer.

A little (9 components instead of 7), but accurate. It doesn’t need an output filter, and a phase fired dimmer would.
I would not recommend this circuit if it were driving a transformer

 

That will generate several amps of average DC current, which the main's power transformer may object to by saturating.

I have a toaster that uses this cheap principal and not my favorite. But it seems quite common.

 

I have a toaster that uses this cheap principal and not my favorite. But it seems quite common.

It's only allowable under harmonic-current standards for items that run for a very shortperiod of time, another being hair dryers

 

Please explain how a 100 watt load on a 120 volt system will produce " generate several amps of average DC current, ". I see a bit of confusion at that point.

 

Please explain how a 100 watt load on a 120 volt system will produce " generate several amps of average DC current, ". I see a bit of confusion at that point.

That's only when a half-wave rectifier is used to reduce the power.

 

A common (although obviously not widely known) trick is to put a reasonably sized capacitor in series with the kettle (aka heating resistor)
If "somebody" would use LTSpice to find out how many microfarads would be required to create a drop of eg. 20 V ?
Voltage rating of the capacitor: 200 V would be fine. (You can get away with less if you're using a self-healing type (metallized paper or metallized foil) and are not shy occasionally hearing sparkovers

 

A common (although obviously not widely known) trick is to put a reasonably sized capacitor in series with the kettle (aka heating resistor)

It requires about 160uF, which could perhaps be provided by a motor run (not start) type capacitor (but they likely aren't cheap).
LTspice sim below showing a voltage at the load of 99.7Vrms:

 

@crutschow
Thanks for the math. So an EPCOS-TDK B32361A2157J050 (CAP FILM 150UF 5% 250VAC RADIAL) might work. It's a real bargain (ca. 30 € for single pieces @ digikey) as you get a lot of capacitor for your money: 63,5 (dia) x 123 mm, 500 g Heavy, bulky - maybe not very fancy.

Alternative:
An inductor in series. If my math holds, this would require 40 mH with a current rating of >4 A (more would be better in terms of resistive losses). These are even bulkier and heavier (basically look like a transformer with a single winding) - an example (32 mH) would be:
https://www.digikey.com/en/products/detail/triad-magnetics/C-49U/4915195
To avoid voltage spikes during switchoff, I'd add an RC and/or a transzorb diode parallel to the choke.

An autotransformer will be about the same size and weight as the choke, but even more expensive.
Example: https://www.hammfg.com/electronics/transformers/line/168
This one at least wouldn't raise concerns about voltage spikes during switchoff.

 

@crutschow
Thanks for the math. So an EPCOS-TDK B32361A2157J050 (CAP FILM 150UF 5% 250VAC RADIAL) might work. It's a real bargain (ca. 30 € for single pieces @ digikey) as you get a lot of capacitor for your money: 63,5 (dia) x 123 mm, 500 g Heavy, bulky - maybe not very fancy.

But still bigger and more expensive the transformer suggested in post #2

 

But still bigger and more expensive the transformer suggested in post #2

Yep (Do you mean post #9 ?)
An appropriate autotransformer is > $100 (and should be > 400 W)

 

Yep (Do you mean post #9 ?)
An appropriate autotransformer is > $100 (and should be > 400 W)

No.I mean post #2.

 

I find 150uF motor run capacitors for about $10.

 

No.I mean post #2.

Ah - I begin to understand your idea.
While I'd expect such a transformer to be somewhat smaller (it's only 100 W), your idea relies on the secondary voltage being perfectly in phase with the primary - either 0° or 180°. Might require some phase shifting (best done on the primary side where the current is lower).
Did you ever try this trick?

 

I find 150uF motor run capacitors for about $10.

What voltage rating? Or is this from some surplus outlet?

 

Ah - I begin to understand your idea.
While I'd expect such a transformer to be somewhat smaller (it's only 100 W), your idea relies on the secondary voltage being perfectly in phase with the primary - either 0° or 180°. Might require some phase shifting (best done on the primary side where the current is lower).
Did you ever try this trick?

I have used the "autotransformer" scheme successfully in industrial applications, and it works quite well.

 

Ah - I begin to understand your idea.
While I'd expect such a transformer to be somewhat smaller (it's only 100 W), your idea relies on the secondary voltage being perfectly in phase with the primary - either 0° or 180°. Might require some phase shifting (best done on the primary side where the current is lower).
Did you ever try this trick?

It is well known, and the voltages ARE in phase. The result is almost identical to an autotransformer.

 

I have used the "autotransformer" scheme successfully in industrial applications, and it works quite well.

You mean the "fake autotransformer" according to post #2?

 

your idea relies on the secondary voltage being perfectly in phase with the primary - either 0° or 180°

Yes, but power transformers introduce negligible phase-shift.
Why do you think they do?

 

Yes, but power transformers introduce negligible phase-shift.
Why do you think they do?

Murphy's law (adapted): you get ample of everything you didn't call for

 

I find 150uF motor run capacitors for about $10.

For 120Vac, 60Hz that would give a heater voltage of 97.7Vrms and heater power of 382W