Simple Adjustable Zener Diode Circuit

Imagine a tiny switch that controls voltage.

A regular zener diode is like a fixed switch it only lets electricity flow past a certain voltage level.

An adjustable zener diode circuit is like a fancy dimmer switch for voltage.

It uses special parts often a potentiometer to change the voltage level that the switch allows through.

This way, you can control the amount of electricity flowing in your circuit, making it more flexible for different projects.

While adjustable zener diode circuits exist, they are less common than regular zener diodes.

Circuit Working:

Parts List:

The Adjustable Zener diode circuit functions similarly to a zener diode, with an adjustable breakdown voltage across a wide range.

The current passing through the voltage divider composed of resistors R1 and R2 should exceed the current through the transistors base.

This current is determined solely by R1 and is set to 8 mA.

The simulated zener diodes breakdown voltage can be adjusted between 5V and 40V.

The circuit stabilizes at a current of 15 mA.

The maximum current for a zener with a breakdown voltage of 4.7V 250mW is approximately 50 mA.

For stabilizing voltages above 15V, it is necessary to mount the transistor on a heatsink.

This precaution should be taken if the circuits current consumption reaches 40 to 50 mA.

Formulas:

The following formula is used to determine the above circuit diagram the adjustable zener diode circuits output voltage:

V_out = V_z * (1 + R2/R1)

where,

• V_out is the output voltage
• V_z is the diodes zener voltage
• R1 and R2 are the resistors resistances when connected to the zener diode and preset respectively.

You may change the R2/R1 ratio with the preset, which will change the output voltage.

You may use the following formula to get the maximum output voltage:

V_outmax = V_z * (1 + R2_max / R1)

where:

• V_outmax is the maximum output voltage
• R2_max is the maximum resistance of the preset.

You may use the following formula to get the minimum output voltage:

V_outmin = V_z * (1 + R2_min / R1)

where:

• V_outmin is the minimum output voltage
• R2_min is the minimum resistance of the preset

The values of the preset, resistors and zener diode voltage will determine the maximum and minimum output voltages.

How to Build:

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

• Connect one end of the preset R1 to the positive terminal of the power supply.
• Connect the other end of the preset R1 to the base of the T1 2N2222 transistor and one end of resistor R2.
• Connect the other end of resistor R2 to ground.
• Connect the collector of the NPN transistor to the positive terminal of the power supply.
• Connect resistor R2 between the base and emitter of the transistor 2N2222.
• Connect the zener diode to the emitter of the transistor 2N2222.
• Optionally, connect a capacitor in parallel with the zener diode for filtering.

Note:

• Ensure the transistor is mounted on a heatsink if stabilizing voltages above 15V and if the current consumption of the circuit reaches 40 to 50 mA.

Conclusion:

To conclude, an adjustable zener diode circuit allows for the breakdown voltage of the ‘zener like’ diode to be adjusted within a certain range providing flexibility in voltage reference applications.

References:

Method of making zener diodes with selectively variable breakdown voltages

Zener diode