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Variable Zener Diode ~Super Zener~

2017-12-22 03:06  
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super zener diode variable zener diode


Variable Zener Diode-SUPER ZENER

This circuit is intended primarily to produce a stable reference voltage in battery operated equipment designed for minimum current consumption. Despite the fact that only 1mA flows through the zener the output voltage showed a fluctuation of less than 1mV for supply voltage variations of 10 to 30 volts.

super zener variable zener diode circuit using 741 op amp

PARTS LIST
R12.2kΩ
R2100kΩ
R3220kΩ
D15.6V 400mW zener
IC1741? op amp

The reference voltage from the zener is applied to the non-inverting input of a 741 op-amp, and the output voltage is the zener voltage multiplied by the op-amp gain.

Vo=Vz×(R2R3)/R3

Vo=5.6V×(100KΩ 220KΩ)/220

Vo=5.6V×1.45=8.14V


Vo=OUTPUT VOLTAGE

Vz=ZENER VOLTAGE


This approach has two advantages. Firstly, a low temperature coefficient zener (5.6V) can be used to provide any desired reference voltage simply by altering the op-amp gain. Secondly, since no since no significant current is ‘robbed’ from the zener by the op-amp input, the need only be fed by a small current. So that the resistance the of? zener does not affect the output voltage the zener current must be fairly constant. This is achieved by feeding the zener via R1 from the output of the op-amp. The zener current is,

1mA=V0-Vz/R1

so R1 should be chosen to give a zener current of about 1mA. The reference voltage obtained from the op-amp output can supply currents of up to 15mA.

One point to note when using? this circuit is that the supply voltage must be at least 2V greater than the output voltage of the circuit.


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