Connected in series or parallel

[rineheart25]

I am doing research on Zener diode and LEDs. I found a U.S. Patent #7518158.

http://www.google.com/patents?id=jlS_AAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

With respect to Fig. 4: Is the LED and Zener diode connected in parallel or series?
Thanks

[berkeman]

I am doing research on Zener diode and LEDs. I found a U.S. Patent #7518158.

http://www.google.com/patents?id=jlS_AAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

With respect to Fig. 4: Is the LED and Zener diode connected in parallel or series?
Thanks

It looks like the back-to-back zeners are connected in parallel with the LED. In the reverse direction they probably are for reverse breakdown protection. Do you know what function they would serve in the forward direction? I think I know (it may be in the patent also).

[rineheart25]

It looks like the back-to-back zeners are connected in parallel with the LED. In the reverse direction they probably are for reverse breakdown protection. Do you know what function they would serve in the forward direction? I think I know (it may be in the patent also).

I agree with you. It looks like the LED and back-to-back zener diodes are in parallel with the LED. They are connected in the reverse/antiparallel direction direction. In your question above, about the forward direction: I know of a two-way Zener diode that when connected in parallel with LED---the two-way Zener diode has two-way breakdown voltage and the diode can protect the LED from being damaged by electrostatic discharge (ESD). What are you getting at in the "forward direction"?

[berkeman]

I agree with you. It looks like the LED and back-to-back zener diodes are in parallel with the LED. They are connected in the reverse/antiparallel direction direction. In your question above, about the forward direction: I know of a two-way Zener diode that when connected in parallel with LED---the two-way Zener diode has two-way breakdown voltage and the diode can protect the LED from being damaged by electrostatic discharge (ESD). What are you getting at in the "forward direction"?

In LED lighting applications, well-matched LEDs are often connected in series. But if one LED fails open, that opens the whole series string. Having the zeners in there in the forward direction lets the series current keep flowing in the forward direction, even if the LED fails open. That adds robustness to LED lighting applications. Neat idea.