Protect power-LED strings from overcurrent

摘要

HA common method for driving multiple power LEDs is through two parallel strings. This inexpensive and less critical driver circuit can provide a lower voltage. However, the driver circuit must deliver twice the current of other methods and needs a circuit that halves the current in the two strings, regardless of the LEDs' forward voltages. The LEDs' forward-voltage tolerance is as high as 20%, and the voltages change with LED temperature and aging. A current mirror performs this task well. If an LED breaks, it can cause destructive overcurrent. The current mirror, however, can safely partially protect two parallel, connected strings of any number of 350-mA power LEDs from these overcurrents (Figure 1).