Zener Regulator Calculator: Resistor, Current and Power
Size the series resistor of a Zener shunt regulator and check worst-case current and power dissipation. The calculation includes \(V_Z\) tolerance, the input-voltage range, and minimum/maximum load current.
Design inputs
Results
Zener current versus Vin
The curves use nominal Vz; resistor sizing and the worst-case table include the entered Zener tolerance.
Worst-case corner check
| Condition | Iz with Vz tolerance | Worst Pz | Worst PRs | Status |
|---|
Equations used
The current through the series resistor is \(I_R=(V_{IN}-V_Z)/R_S\), while the Zener current is \(I_Z=I_R-I_L\).
To maintain regulation at minimum input voltage and maximum load:
\[R_{S,max}=\frac{V_{IN,min}-V_{Z,max}}{I_{L,max}+I_{Z,min}}\]
The lower limit for \(R_S\) is found by requiring, across the full \(V_Z\) tolerance range:
\[P_Z=V_Z\left(\frac{V_{IN,max}-V_Z}{R_S}-I_{L,min}\right)\le P_{Z,rated}\]
Series-resistor dissipation is checked using both equivalent forms \(P_R=I_R^2R_S\) and \(P_R=I_R(V_{IN}-V_Z)\).
Model limitations
The Zener diode is treated as an ideal voltage source bounded by minimum and maximum Vz. Dynamic resistance, the real knee region, temperature coefficient, self-heating, and the variation of Vz with Iz are not modeled. For a final design, use the component datasheet and apply the specified power derating at the actual operating temperature.