Benefit for a beginner ham: check thyristor

A thyristor is a semiconductor element made on the basis of a semiconductor single crystal having three or more pn junctions and two stable states: a low-conductivity state, which is called closed; And the state of high conductivity is open.

A novice ham radio can ask the question: "How is the thyristor checked?" In this article, we will look at a technique for testing this semiconductor element. Also, we will analyze what kind of device is needed to check thyristors.

There are several methods for testing semiconductor devices. A preliminary check of the thyristor can be performed using the following instruments: a digital multimeter, a tester or an ohmmeter. The multimeter must be switched on to the "continuity" mode of the diodes, and the tester must be in the resistance measurement mode . With the help of these devices it is possible to check thyristor transitions between the control electrode and the cathode, and also between the anode and the cathode. The resistance of the transition of the semiconductor element between the control electrode and the cathode should be 50-500 ohms. The value of this resistance is approximately the same for both forward and reverse measurements. The higher the resistance value, the more sensitive the semiconductor thyristor is. In other words, the device needs a small current value on the control electrode to go from closed to open. A good thyristor has the value of the resistance between the anode-cathode electrodes for both forward and reverse metering tending to infinity.

A preliminary check of the thyristor gives the probability that a used semiconductor element may contain a burnt cathode-anode transition. With measuring devices such a malfunction can not be determined.

The basic thyristor check is carried out using additional power supplies. This operation completely eliminates the failure of the semiconductor device. The thyristor goes into an open state, if through the cathode - the control electrode - to pass the short-time pulse necessary to open the element. For this purpose, a circuit is constructed for checking the thyristors. Such schemes can be assembled set, we consider the most elementary. To do this, we will use the power source, indicator light, two switches and a resistor. The circuit can be assembled on a test board, or mounted mounting. We collect the scheme: minus the power supply (5-25 V), we feed it to the cathode of the thyristor. Plus source through the normally closed button K1 and through the indicator lamp to the anode of the device. To the output of the control electrode, we attach a resistor, the second contact of which through the normally open button K2 is connected between the lamp and the button K1. The value of the resistance is selected so that the flowing current is sufficient to turn on the device. Everything, the scheme is ready, we begin the verification. To do this, we close button K2, the control current goes along the chain: from the plus, through the buttons K1 and K2, through the resistor, through the control electrode, to the cathode and to the minus of the source. The thyristor opens. Release the button K2. The indicator light comes on. Press the normally closed button K1, the load current circuit through the thyristor breaks off and it closes. The lamp goes out, the circuit returns to its original state.