Zener Diode Shunt Regulator Calculator

Sizing a zener shunt regulator

A zener shunt regulator holds a node at V_z by letting a series resistor drop the rest of the supply and forcing the zener to sink whatever current the load isn't using. The resistor must supply the zener's own regulating current plus the load current: R = (V_in − V_z) / (I_z + I_load). Set I_load = 0 for a simple voltage reference with nothing but the zener drawing current.

Two checks after you pick R: the resistor's power dissipation, P_R = (V_in − V_z)·(I_z + I_load), and the zener's own dissipation, P_z = V_z·I_z — both must stay under the component's rated power with margin. This simple version assumes a fixed I_z; a robust design also re-checks R against the zener's minimum current (a few mA, needed to stay in the regulating knee of its I-V curve) at worst-case low V_in and maximum I_load, and against the zener's maximum current at worst-case high V_in and zero load.

Shunt regulators are simple and cheap but wasteful (the resistor burns power continuously) and have poor load regulation compared to a linear regulator IC — fine for low-current references and simple protection clamps, not for powering a real load efficiently.