Re: LED Reverse Polarity Protection


"Dave.H" <the1930s@xxxxxxxxxxxxxx> wrote in message
news:dfcc9dd0-cbb2-4fa1-af88-a7fd4b1bacbe@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 10, 5:10 pm, "BobW" <nimby_NEEDS...@xxxxxxxxxxxxxx> wrote:
"Dave.H" <the19...@xxxxxxxxxxxxxx> wrote in message

news:227bac2d-4517-4cd5-8880-d8eaca9b7c4a@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Hi, I'm considering using a high brightness LED in an old incandescent
flashlight, in series with a 220 ohm resistor, for use with a 6 volt
lantern battery, but I also want some type of reverse polarity
protection for the led, as I'm putting the LED, resistor, etc. in a
regular flashlight lamp base. I assume this would most likely be done
with a diode, perhaps a 1N400x type, but how would I wire this up?

You're on the right track. You don't need a high-current diode like a
1N400x, however. A 1N4148 or 1N914 will work fine because the maximum
current will always be very low (6V/220ohm = okay for a small signal
diode).

Anyway, just put the diode across the led backwards. That is, put the
anode
of the diode to the cathode of the led, and the cathode of the diode to
the
anode of the led. That way, if your flashlight batteries are installed
backwards, the diode will conduct the current (I=6V/200ohms) and the
reverse
voltage across the led will be limited to under 1V.

Bob

Thanks, do I put the resistor before or after the diode?

One end of the resistor to one of the battery leads. The other end of the
resistor to one end of the paralleled diode/led. The other end of the
paralleled diode/led to the other battery lead.

I'm not too good at ascii art, but here's an attempt:

Batt+ ----resistor----|-----cathode(diode)anode-------|
|-----anode(led)cathode----------|

|
Batt- ---------------------------------------------------------|

Does this make sense?

Bob


.

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  • Re: LED Reverse Polarity Protection
    ... flashlight, in series with a 220 ohm resistor, for use with a 6 volt ... with a diode, perhaps a 1N400x type, but how would I wire this up? ... One end of the resistor to one of the battery leads. ...
    (sci.electronics.basics)
  • Re: LED Reverse Polarity Protection
    ... flashlight, in series with a 220 ohm resistor, for use with a 6 volt ... with a diode, perhaps a 1N400x type, but how would I wire this up? ... paralleled diode/led to the other battery lead. ...
    (sci.electronics.basics)
  • Re: LED Reverse Polarity Protection
    ... flashlight, in series with a 220 ohm resistor, for use with a 6 volt ... with a diode, perhaps a 1N400x type, but how would I wire this up? ... One end of the resistor to one of the battery leads. ...
    (sci.electronics.basics)
  • Re: LED Reverse Polarity Protection
    ... flashlight, in series with a 220 ohm resistor, for use with a 6 volt ... with a diode, perhaps a 1N400x type, but how would I wire this up? ... One end of the resistor to one of the battery leads. ...
    (sci.electronics.basics)