Resistor instead of a step-down transformer

[Frenemy90210]

As a quick and dirty/cheap solution, can a resistor be used instead of a step-down transformer ( stepping down from 230V AC mains to 3 V AC) to drive some simple electronic circuit such as a few LEDs or transistor radio etc ?

 

[NFuller]

Technically yes but it would be impractical for most circuits. The big issue is that the device would need to draw constant current while operating and any change in the load will change how much voltage is dropped across the resistor.

 

[G Bonn]

If you are dropping AC voltage you will want to use a capacitor to drop most of the voltage as it will not dissipate any power. But you also may want to keep a resistor to drop some of the voltage so it will limit current from noise that is at a higher frequency than the main AC. That noise will be blocked less by the capacitor as the noise frequency increases.

And if your driving more than cheap LED's you may need to include some active electronics to limit current and voltage to your circuit.

 

[Asymptotic]

What you propose can work, but is inadvisable from a safety perspective.

• The galvanic isolation a step-down transformer provides between primary and secondary reduces the possibility of electrocution.
• Short circuit current is limited by winding impedance and core saturation in the transformer. The consequences of a direct mains short are more severe.

 

[Svein]

 

[Guineafowl]

View attachment 211629

I’m willing to be corrected by those with more knowledge, but...
1. CX should be rated at least 400V as the peak voltage will be 330V or so.
2. If the output is open circuit, C1 could well be charged to more than its 50V rating. Bleeder resistor?
3. An inrush (fusible?) current-limiting resistor is usually added for powering LEDs.