[Michael Mc]

Simple Zener Regulator
A Zener diode is a type of diode that, when connected in its reverse bias configuration (see below), begins to “break down” or conduct at a specific voltage, called its Zener voltage. Once it starts conducting, there is no stopping the current, so a resistor (R1 shown below) needs to limit the current to a safe value.

In the simple regulator above, Vin is 12V, and Vout is 5V, and I is 10mA. Without the Zener R1, then it would be R=V/I = 12-5/0.01 = 700Ω. However, there would be no regulation, as the Zener would not be conducting. Using the rule of thumb, the Zener needs to be conducting two to five times the load current, say 50mA. Given that, it should be I = 50 + 10 = 60mA, so R1 = 7/0.06 = 116Ω.

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