Rick Hughes wrote:
Hi Andrew ... in the post below you asked me for data on the LED
Standard W10 Silicon Bridge Rectifiers ...

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Can you point to the datasheet for your LEDs?
My calculation assumed 40mA non-repetitive peak current.

What design constraints have you got (such as max power
dissipation per indicator)?


Here is datasheet on Br Rectifiers ...
http://pdf.datasheetcatalog.com/data...y/mXyzsrux.pdf

LED are standard 5mm LED (100mcd) ... forward Voltage 1.8-2.2V
20mA nominal current, 40mA maximum.

Capacitor are X2 rated, Polypropylene MPX 0.47uF
Withstand Voltage 275V AC
Rating Voltage 250V AC

No specific design constraint on display, just something that will
illuminate them.

I have purchased the capacitors, Br Rectifiers & LED so keen not to
waste these ...


Were you able to take a look at cct to see if there is suitable a
resistor or modification that allows use of these components, while
reducing the risk you (thankfully ) pointed out of blowing the LED's

One suggestion was to increase resistor to 680R

Welcome your advice.




Thought a bit more about this. If these are low efficiency red leds,
then the Vf will be about 2V---roughly. This is about twice the level of
a 4148 diode which will withstand 1A for 1 second (data sheet).
This indicates that the leds will probably withstand 300mA for 1 second
so, I'd guess that 1A at 10mS would be survived. So personally, I'd go
with 4(400V) resistors to make up 1K and survive any transient voltages.
I'd also reduce the capacitor to 0.1uF. Over run leds don't last long,
as the chinese are proving in lamps. My rule of thumb for capacitative
droppers is 80mA/uF, so peak running currents of 12mA should be
adequate. These are off the cuff thoughts, others may differ. I've seen
1500V transients on our house mains supply and I would normally scope
this circuit to make sure that things are behaving as expected.