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Simple Adjustable Zener Diode Circuit

Think like small switch which controls how much voltage go through.

Normal Zener diode is like one fixed switch which let electricity pass only when voltage goes above certain level.

But this Simple Adjustable Zener Diode Circuit is like fancy dimmer switch.

We can change voltage level using some parts like mostly one thing called potentiometer.

This help us to control how much electricity move in our circuit, as this type of circuits are good for many kind of project.

But still the normal Zener diode is more common as the adjustable one are not used so much.

Circuit Working:

Parts List:

Component TypeComponent DetailsQuantity
Resistors680Ω 1/4 watt1
Preset 5k1
SemiconductorsTransistor 2N22221
Zener diode 4.7V1

Adjustable Zener diode circuit works like normal Zener but we can change breakdown voltage from small to big range.

The current going through voltage divider from resistors R1 and R2 must be more than current going to transistor base.

This current come only from R1 and we set it to 8 mA.

In this circuit Zener breakdown voltage can change from 5V to 40V.

Circuit keep stable when current is 15 mA.

If using Zener with 4.7V and 250mW then the max current will be around 50 mA.

When we want stable voltage more than 15V then better to put heatsink on transistor.

This is important if circuit use 40 to 50 mA current.

Formulas:

This formula help to find output voltage of adjustable zener diode circuit:

Vout = Vz × (1 + R2 / R1)

where:

We can change output voltage by changing R2 and R1 ratio using the preset.

To find maximum output voltage use this formula:

Voutmax = Vz × (1 + R2max / R1)

where:

To find minimum output voltage we can use:

Voutmin = Vz × (1 + R2min / R1)

where:

So how high or low voltage goes depends on Zener voltage, resistor R1 and preset values R2max and R2min.

How to Build:

To build a Simple Adjustable Zener Diode Circuit we need to follow the below mentioned steps:

Note:

Conclusion:

To conclude Simple Adjustable Zener Diode Circuit let us change breakdown voltage of Zener like diode in some range.

This gives us more flexibility for using in voltage reference jobs.

References:

Method of making zener diodes with selectively variable breakdown voltages

Zener diode

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