Bypass diode inside the junction box

AN3432

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Doc ID 019041 Rev 1

2

Bypass diode inside the junction box

2.1

Bypass function

The bypass diode principle is to use a diode in reverse paralleling with several solar cells

(see Figure 5). The bypass diode is blocked when all cells are illuminated, and conducts

when one or several cells are shadowed.

Figure 5.

Bypass diode working phases

2.2

Junction box

Bypass diodes are rarely mounted directly on the solar panel. They are soldered in a so

called junction box that is placed at the rear of the solar panel. Most of the time, it contains

three diodes in series as explained in paragraph 2.3.1. The junction box design has a

significant impact on the thermal diode performance. When qualified without solar module,

the junction box has to meet DIN V VDE V 0126-5:2008 standard requirements. When

qualified with its solar module, the standard is EN61215.

V cell

Vbypass =-n·Vcell

Vbypass =VF

Bypass OFF

Bypass ON

n= number of cells

per bypass diode

V cell

V cell

V cell

cell

s

F

V

n

V

V)·

1

(-

-

=

V cell

V cell

V s

V cell