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The role and measurement method of unidirectional thyristor and triac thyristor conduction conditions:
First, a forward voltage must be applied between the thyristor anode and the cathode, and the control pole must also be supplied with a forward voltage. The above two conditions of the unidirectional thyristor working principle diagram [1] must be at the same time, the thyristor will be in the conduction state. In addition, once the thyristor is turned on, the thyristor is turned on even if the gate voltage is lowered or the gate voltage is removed. Thyristor shutdown conditions: reduce or remove the forward voltage applied between the thyristor anode and the cathode so that the anode current is less than the minimum holding current.
Two-way thyristor:
The thyristor has the characteristics of being turned on and off in two directions. The triac is essentially two anti-parallel unidirectional thyristors, and is a semiconductor device formed of four PN structures and three electrodes by an NNPPN five-layer semiconductor. Since the structure of the main electrode is symmetrical (both drawn from the N layer), its electrodes are not called anodes and cathodes, respectively, like unidirectional thyristors, but are called first electrode A1, and the other is similar to the control electrode. It is called the second electrode A2. The main disadvantage of two-way thyristors is their low ability to withstand voltage rise rates. This is because when the two-way thyristor is turned on in one direction, the carriers of the silicon wafer in each layer have not returned to the off-state position, and corresponding protection measures must be taken. Two-way thyristor components are mainly used in AC control circuits, such as temperature control, lighting control, explosion-proof AC switches, and DC motor speed regulation and commutation.
The two compare the unidirectional thyristor and the triac, which are all three electrodes. The unidirectional thyristor has a cathode (K), an anode (A), and a gate (G). The two-way thyristor is equivalent to the reverse parallel connection of two single thyristors. That is, one of the unidirectional silicon anodes is connected to the other cathode, and the leading end is called the T1 pole. One of the unidirectional silicon cathodes is connected to the other anode, and the leading end is called the T2 pole, and the remaining is controlled. Extreme (G).
The discrimination between single and two-way thyristors is measured first. If the positive and negative indicators are not moving (R×1 block), it may be A, K or G, A pole (for unidirectional thyristor). It is T2, T1 or T2, G pole (for two-way thyristor). If one of the measurement indications is tens to hundreds of ohms, it must be a unidirectional thyristor. And the red pen is connected to the K pole, the black pen is connected to the G pole, and the rest is the A pole. If the positive and negative measurement instructions are tens to hundreds of ohms, it must be a two-way thyristor. Then turn the knob to R×1 or R×10, and the resistance must be slightly larger. The slightly larger red pen is connected to the G pole, the black pen is connected to the T1 pole, and the rest is the T2 pole. .
The difference in performance is to turn the knob to R×1 block. For 1~6A one-way thyristor, the red pen is connected to K pole, and the black pen is connected to G and A poles at the same time, and disconnected while keeping the black pen from the A pole. G pole, the pointer should indicate tens of ohms to one hundred ohms, at this time the thyristor has been triggered, and the trigger voltage is low (or the trigger current is small). Then, the A pole is turned off and then turned on again, and the pointer should be returned to the ∞ position, indicating that the thyristor is good.
For 1~6A two-way thyristor, the red pen is connected to the T1 pole, and the black pen is connected to the G and T2 poles at the same time. When the black pen is not separated from the T2 pole, the G pole is disconnected, and the pointer should be indicated as tens to more than one hundred. Europe (depending on the size of the thyristor and the manufacturer). Then, the two strokes are reversed, and the above steps are repeated once. The pointer indication is slightly larger than the previous one by a few ten to several tens of ohms, indicating that the thyristor is good and the trigger voltage (or current) is small.
If the G pole is turned off while the A or T2 pole is turned on, the pointer immediately returns to the ∞ position, indicating that the thyristor trigger current is too large or damaged. It can be further measured according to the method of Fig. 2. For the unidirectional thyristor, the switch K should be closed, the lamp should be bright, and the K lamp will not be extinguished, otherwise the thyristor is damaged.
For the two-way thyristor, close the switch K, the lamp should be lit, disconnect K, the lamp should not be extinguished. Then reverse the battery and repeat the above steps, all of which should be the same result, which is good. Otherwise the device is damaged.
