This configuration can be used as a reference voltage source and if the used operational amplifier is a high power type, as a high power zener. The circuit is shown in figure bellow and the formula given bellow can be used in practical applications.
Formula:
Voltage source:
Vout = - Vz x (R2/R1)
Where:
Vout is the output voltage in volts (V)
Vz is the zener voltage
R1 and R2 are the resistances in ohm (Ω)
Note: Rz is calculated according the formulas described in the Diode Zener section (formulas 87.x).
Application example:
Determine the value for R2 when desiring a reference output voltage of 7 V from a 3 V zener diode in the circuit shown in figure 134. Given R1= 500 Ω.
Data:
Vz = 3 V
Vout = 7 V
R1 = 500 Ω
R2 = ?
Using formula:
7 = 3 x (R2 / 500)
7 = (3 x R2) / 500
Isolating R2:
R2 = (7 x 500) / 3
R2 = 3500 / 3
R2 = 1166 Ω
