Anybody For X Sub C?

PJAllen

Reactive power is imaginary. No "joule thief" this.
(see attached)

[BTW -- Quo vadis, Dang it? I really miss those buttons for super script and, even more, sub script, up there in the editor tools.

pjv

Hi P.J.

Discovered years ago that in the case of driving LED's, the parallel 1N400X diode is usually not needed as the LED will break over at some 10 ish volts when reverse biased. So a small cap is all you need, but at a high capable working voltage.

I use a somewhat similar scheme to power an SX circuit straight off 120 V mains, but the your diode is replaced by a very robust "surge zener diode". So the negative cycle reverse charges the cap through the zener in the forward direction, and on the positive cycle the cap is dumped into the zener which limits the voltage, and that is tapped off with another diode followed by a cap giving me Vcc. Very simple... no dropping resistor with its heat generation.

Caution of course on which is the Hot and Neutral lines!!

Cheers,

Peter (pjv)

PJAllen

I reckoned that at first, too, but after a few croaked on me I added the diode to divert the negative alternation's current (LEDs make lousy rectifiers.)

pjv

Hi P.J.

I must admit that after discovering the concept I have never used it in real life to drive LED's. I would agree that using the diode is a good idea as that is much more robust. Using the concept for driving (small) residential area lighting applications is intriguing.

Cheers,

Peter (pjv)

mctrivia

pjv wrote: »

Hi P.J.

Discovered years ago that in the case of driving LED's, the parallel 1N400X diode is usually not needed as the LED will break over at some 10 ish volts when reverse biased. So a small cap is all you need, but at a high capable working voltage.

I use a somewhat similar scheme to power an SX circuit straight off 120 V mains, but the your diode is replaced by a very robust "surge zener diode". So the negative cycle reverse charges the cap through the zener in the forward direction, and on the positive cycle the cap is dumped into the zener which limits the voltage, and that is tapped off with another diode followed by a cap giving me Vcc. Very simple... no dropping resistor with its heat generation.

Caution of course on which is the Hot and Neutral lines!!

Cheers,

Peter (pjv)

PJV wouldn't the zener get really hot?

pjv

Actually no, the SX is running on its internal RC oscillator, and draws only a couple or so milliamps, so the capacitor is selected to give the right level of current at 60 Hz, and not a lot goes through the zener. But it IS a very robust surge protection zener.

Cheers,

Peter (pjv)

PJAllen

Funny that you mention these "surge protection zeners". My experience with them has been their failing short. They knock fuses out that way and take systems down like that, it bugs me.