1N4742A 12V 1W Zener Diode DO-41

A Zener diode is a special kind of diode which allows current to flow in the forward direction like a regular diode, but also allows it to flow in the reverse direction when the voltage is above a certain value. This is known as the 'breakdown voltage'. That means you apply voltage across them, and when a preset voltage is reached, they start conducting. A common analogy is a 'pressure relief valve'. They have lots of uses, especially in safety circuits where you want to make sure a voltage signal doesn't exceed a limit that might damage the circuit.
This 1N4742A zener diode is set at 12V, making it ideal for protecting the inputs of a 12V circuit.
Zener diodes are often used to stabilize and clip circuits.
The 1N4742A is a 12V Zener Diode, meaning it has a breakdown voltage of 12V.

Charactiristics 1N4742A Zener Diode
Nominal Zener Voltage: 12 V
Zener Voltage Tolerance is ± 5 %
Maximum Zener Impendace at 21 mA: 9 Ohm
Power Dissipation: 1 W
Maximum Forward Voltage at 200 mA: 1.2 V
Package - DO-41
Weight: 0.35 grams
Operating and Storage Temperature Range: -65 to +175 °C