250W resistor?

[mneary]

Don't forget the 1N914/4148 is only a 100V diode. It will work as the antiparallel or bridge, but not as a blocking diode.

 

[revans]

Don't forget the 1N914/4148 is only a 100V diode. It will work as the antiparallel or bridge, but not as a blocking diode.

Ummmm....... I'm not 100% on what you meant, but I have no intention of swapping the diodes around. I'm just following the schematic to the letter.

 

[vne147]

Ummmm....... I'm not 100% on what you meant, but I have no intention of swapping the diodes around. I'm just following the schematic to the letter.

What is being said here I think is that the 1N914/4148 has a maximum reverse voltage of 100V. So that means you can only apply 100V to it the "wrong" way before it breaks down and starts conducting anyway and essentially, no longer acts as a diode. In the upper circuit, the one with the cap and resistor it is OK to use these diodes because most of the voltage drop occurs across the capacitor and the resistor. The actual reverse voltage seen by the diode will not be nearly as high as 100V and so the diodes should never break down and conduct in reverse.

However, the other circuit with the single diode and two resistors is different. The diode in that circuit sees a much higher reverse voltage and care needs to be taken to select the correct diode with a high enough reverse voltage rating.

That's all.

 

[revans]

Oh ok, I see. Well I used the same 1A 1kV diode in the schematic so I think it was alright.

Anyway though, I'm using the other circuit, so not to worry.

 

[MrAl]

Hi there,


First off, the W is sometimes used because although the upper case Greek letter 'omega' looks like an upside down horse shoe, the lower case Greek letter 'omega' looks almost like a lower case English w.

Second, the design of the line driven LED is partly about powering the LED during normal operation and partly about protecting it against transients that might come about on a typical power mains line. To get both and keep the power consumption down to below 1/2 watt it's a good idea to use a 220 ohm resistor for transient suppression along with a zener rather than a higher value resistor which might consume 1w all by itself during normal operation.

Here is a circuit i designed many years ago and recently updated it for 230vac operation. You'll note there are more parts than you normally see in a circuit like that, and that is to accomplish all goals while keeping power under 1/2 watt.
The 120vac version was built and tested for about a year or two of constant operation. The circuit should last quite a while without any problems.
It's not a bad idea to use a 500v capacitor for 230vac operation.