Zener diode check: how to check the stabilizer using a multimeter

Zener diode (Zener diode) resembles a diode in its external resemblance. However, its functions differ from the diode in terms of the current-voltage characteristic (VAC). The Zener diode has a high resistance, but when a certain voltage is applied to it, a breakdown occurs. Because of this, the current flowing through it increases. In the breakdown mode, the voltage across the Zener diode with a wide range of currents is maintained with the specified accuracy.

Checking the Zener diode with a multimeter

In order to check the zener diode with a multimeter, you must have certain knowledge.

Measuring with a multimeter is similar to testing a diode. The operating state of a zener diode can be characterized by its ability to pass current in only one direction.

On a measuring device, it might look like this:

1. If the measurements are carried out with a digital device, with the connection of the positive probe to the cathode terminal indicated by the strip, and the negative probe to the anode output, which means that the device should reflect the readings in the form of numbers (for example, checking the 5.1 V zener diode is displayed on the multimeter display 688 Ohm). If you swap the probes, then the device will display infinite resistance, which characteristically indicates a working radio element. When, when connected, infinite resistance is indicated on the multimeter in both directions, this indicates an open element. If the resistance in both directions is zero, then such an element is broken.
   instagram viewer
2. Similarly, the measurement can be carried out with a pointer device, where in one direction, instead of numbers, the arrow indicates resistance, and in the other, infinite resistance.

In semiconductor technology, double-sided zener diodes (KS175A), as well as precision (D818), can be used. They cannot be verified by the method described above, since their resistance is infinite in both directions. To check these elements, you can apply the method below.

Stabilizer measurement

This method allows you to measure the parameters of radioelements by including them in the circuit and the applied voltage of the power source. Depending on the stabilization voltage of the component under test, it is necessary to have a divider consisting of one or more resistors. The power supply connects directly to a pre-assembled wiring diagram with a common minus or common plus. This circuit is a parametric voltage regulator:

1. Consider the inclusion of a circuit in a common disadvantage. The positive wire of the power supply is connected to pin 1 of the divider, which is the resistor R, and the zener diode under test is connected by the cathode to pin 2 of the resistor R. The anode terminal of the zener diode is connected to the negative terminal of the power supply and is a common power bus. The divider resistor is selected so that the applied voltage from the power supply reaches such a level that will allow at pin 2 of the resistor to obtain the breakdown current of the zener diode, at which it will open.
2. The multimeter switches to the DC voltage measurement mode, after which the positive terminal of the voltmeter is connected to terminal 2 of the resistor, and the negative terminal is connected to the common bus, this is the minus of the power supply + the anode of the element under test. It is desirable to have a power supply with smooth regulation, which gives this method the ability to test a wide range of stabilized voltages.

For example, consider a Zener diode with 12 V stabilization.. To do this, it is necessary to apply a voltage so that at pin 1 of the divider it is about 11 V, with the resistance of the divider selected to be about 100 Ohm. Voltmeter at pin 2 of the resistor (no load). The voltage before and after the divider remains unchanged, depending on the selected resistance. If you apply above 12 V or higher to pin 1 of the divider, then at the output of the output divider, the second voltage should not exceed 12 V, which indicates its serviceability.

The divider R is chosen so that the source current at pin 2 does not exceed the maximum current of the zener diode, which is fraught with the failure of the latter.

If the element under investigation is broken or incorrectly included in the circuit, then the voltage on the voltmeter is zero, and the divider will also heat up. If the element is open, then the applied value at the input of the divider will be higher than 12 V, then the tested element can be considered faulty.

Precision and double-sided devices

Precision zener diodes are checked in a similar way. Double-sided zener diodes are connected to the terminals of the power supply without observing polarity.

To check the stabilizer, it is necessary to switch the multimeter to the DC current measurement mode, observing the polarity. Initially, the value of the supply power to the stabilizer is checked.

If the voltage is normal, then the multimeter is directly connected to the output of the stabilizer, measuring the voltage value already at the output.