Zener diode tester 1V to 50V

Zener diode tester 1V to 50V

This section introduces a Zener diode tester for testing unknown Zener diode voltage values. A Zener diode, or diode voltage regulator, is a special type of diode. Unlike ordinary diodes, these diodes are designed to operate at their breakdown voltage and are an important component of voltage regulator circuits. These components maintain a constant voltage across their terminals, which varies even with large currents. Their connections are typically reverse-biased, and to operate at the Zener voltage, the source voltage Vs must be greater than the breakdown voltage Vz. A series resistor Rs is typically used to limit the current, ensuring it remains below the maximum power.

Different package types and power bases of Zener diodes.

For all electronics enthusiasts, finding the characteristics of certain components is a notoriously tedious task. Zener diodes, in particular, come in a wide variety of values. To find their Vz value, we must spend time searching for a component that is typically very small, requiring the aid of a magnifying glass, patience, and markings on the component itself. If the Vz value isn't printed on the component, we can look at its characteristics, but this often requires patience and courage.

Checking the condition of a Zener diode is typically done using the diode setting on a standard multimeter. This test provides an accurate understanding of the component's condition but does not give the Zener diode's Vz value. A Zener diode tester is very useful when we want to quickly find the Vz value of the Zener diode under test.

Zener tester

Photo of the assembled circuit boards of the prototype

characteristic

Prototype assembly board.

Battery-free, 230V.

Read the numerical value Vz

Zener diode tester 1V to 50V

Two measurement ranges: 5mA and 15mA testing.

Zener Test

As you can see, the circuit is very simple. It starts with a transformer with two 24V secondary windings, which is rectified and filtered to obtain a voltage of about 80V. Then, a voltage regulator circuit consisting of (R1, R2, D1, D2 and Q1) reduces the voltage to about 52V to avoid exceeding the maximum voltage limit of the LM317AHV integrated controller.

The LM317AHV is a high-voltage version of the LM317T, capable of reaching up to 57V. The LM317T, however, can only reach 37V. We must not confuse these components, otherwise the circuit may not be able to operate sustainably.

This setup is based on the LM317AHV constant current generator, with the addition of a switching circuit (S2) in series with a resistor (R4) to select two test ranges (5mA and 15mA) as the power of the Zener diode under test.

As is often the case in practical circuit design, all components can be easily assembled with standard components, and if they can be recycled from various devices, costs and environmental degradation can be minimized as much as possible.

Recycling electronic components is not difficult, but it is a bit tedious, yet very rewarding, and we can learn a lot from devices that attempt to recycle components.

Modified photo of the switch adapter used to power digital panel meters, changed from 12V to 9V.

I changed the voltage from 12V to 9V to power the panel meter using a small 0.2A switching adapter, which was really easy; I only needed to modify the voltage divider value of the TL431 pre-regulator.

The resistor to be replaced is the one that connects directly to the positive output terminal and the source of the TL431. I used a 100K LIN resistor because it's rare to calculate a new value for a resistor with a 9V output, so this is fair and ready.