Yesterday, a physical experiment instrument was dismantled, and the EDM timer was used. The error mark on the instrument label was the electromagnetic dot timer. After dismantling and analyzing from the structure diagram, it can be seen that there is an electronic circuit inside, and the working power source is 220 volt AC, which is obviously an electric spark dot timer. First look at the appearance of the picture, mainly intercepting the label part.

After powering on the instrument, turn on the power switch, the LED indicator lights up, you can hear the sound of high-voltage discharge and ignition, which further proves that this is a genuine electric spark timer. The circuit board and the coil can be seen by disassembling the inside, and the coil connected to the circuit board can be extracted, which is the primary coil, and the enameled wire is thickly wound on the magnetic bar. On the right is the insulating paper wrapped around the surface of the primary coil.

The analysis board found an electronic component, model BT1690, which was found to be a unidirectional thyristor. Let’s take a quick look at the thyristor. The thyristor referred to as SCR, also known as thyristor, has many advantages such as small size, high efficiency, and long life. The thyristor can be divided into a unidirectional thyristor and a bidirectional thyristor according to the current flow direction during operation. This article describes the one-way thyristor in the timer. The unidirectional thyristor circuit diagram is as follows, there are three electrodes, namely: anode A, cathode K, and gate G.

In the figure, a pulse control voltage is applied to the gate G, and the thyristor changes from closed to conductive, and current flows from the anode A to the cathode K. Control the pulse signal of the thyristor, the current is small, the voltage is low, so the thyristor is an electronic component that uses a small current and a low voltage to control a large current, which is equivalent to an electronic switch. As an electronic switch, the thyristor has a very fast on-time and no sparks from traditional mechanical switches. It is stable and reliable for long-term use. The other one is energized, once the thyristor is turned on, the control voltage is removed, and the conduction is still turned on unless the A to G circuit is disconnected. The controlled conduction characteristics of the thyristor can be applied to various circuits, such as the previous speed control fan, dimming table lamp, and the like.