| 摘要 |
<p>Zener diodes Z1, Z2 are connected in parallel with sets 201a, 201b of series - connected light emitting diodes L1-L4 with a reverse forward bias orientatio n. The threshold voltage of the zener diodes Z1, Z2 is matched to equal, or be just slightly greater than, the forward voltage drops for the light emitting diodes L1-L4 at maximum current. During normal operation, therefore, the zen er diodes Z1, Z2 draw virtually no current. Upon failure of one of the light emitting diodes L1-L4, the associated zener diode Z1 or Z2 conducts without increase in the applied voltage, providing an alternate current path maintaining circuit integrity so that other set 201a or 201b of light emitti ng diodes L1-L2 or L3-L4 connected in series within the circuit 200 continues t o illuminate.</p> |
