capacitortransformerlessvoltage
I am going to make a transformerless power supply.
Here I am using a 105J 400V polyester capacitor to drop the voltage.
I connected the capacitor and AC main in series, but when I measure the voltage across the capacitor using a multimeter, it shows same as 220 to 230V AC and no voltage drop there.
What can I do for that? Has the capacitor gone mad?
Have a look at the image on this page. It's one of the representations which are clearer on how the IC works. I'll reproduce the image here:
You can clearly see that the voltage divider is independent for any pin of the circuit (well, except Vcc and Gnd). So the 1/3 and 2/3 voltages are just derived from there, but the actual comparison is done by two comparators, which take the pin 2 and 6 voltages to set and reset the F/F (flip.flop)
EDIT: Just found this diagram from the Texas Instruments LM555 data sheet, which is also quite neat:
Okay, I think somewhere in here one of these matches your verbal description. I ran the simulation with the built-in circuit simulator and the voltages are correct for the type of LED used.
simulate this circuit – Schematic created using CircuitLab
R7 just simulates the input resistance of your meter, so the emitter is open.
In cases 1 and 3 the transistor is saturated and has < 0.1V across it (collector to emitter).
In case 2 the transistor has about 0.5V across it (less than the usually quoted 0.6 or 0.7V because the meter draws almost no current).
I don't see anything that resembles 1.2V there. If it's an IR LED then you could get 1.2V and then V1 would be 1.2V but the other voltages should be the same as shown above.
Best Answer
The capacitor will form a voltage divider with the impedance it's feeding. If that impedance is solely that of your meter, which is very high, then the resulting voltage drop will be very small.
Once loaded with the output load, there will be a significant voltage drop.
Be warned that if your load consists of a bridge rectifier, then a reservoir capacitor, then a DC load, that the rectifier and reservoir cap must be rated for full mains voltage. If the DC load ever gets removed or fails open, then the series capacitor will no longer drop your design voltage, and the reservoir cap will charge up to full peak mains voltage, 340 V in 240 V rms land.