Voltage testing and display appts. - has two antiparallel LED between its terminals, with series circuits in parallel, each with Zener diode

摘要

The appts. has two test terminals with two antiparallel light emitting diodes between them, with current limiting series resistors. Each LED (19, 16) has its own series resistor (12, 18). Series circuits are connected in parallel with the LED (16), with each circuit comprising a Zener diode (201-207), a further LED (161-167) of the same polarity as the original LED (16) and a current limiting resistor (181-187). Breakdown voltages of the Zener diodes increase from one circuit to the next, and the current limiting resistors (18, 181-187) have falling current-voltage characteristics.