Single synchronous three-phase digital trigger circuit TC790A

TC790A is a single synchronous three-phase digital trigger circuit, suitable for three-phase half-controlled and fully-controlled bridge thyristor rectifier triggering and three-phase AC voltage regulation anti-parallel and bidirectional thyristor triggering. TC790A uses crystal oscillator and digital design methods to improve accuracy and three-phase balance, while the phase shift part still uses sawtooth wave. TC790A has the advantages of high precision, ease of use, high reliability, few peripheral components and excellent performance. At the same time, due to the use of single synchronous sampling, its application is as convenient as single-phase trigger circuit, and it is also more convenient for the design and application of trigger board. In addition, TC790A also has the following characteristics:

◇Single power supply, working voltage 9~15V.

◇Use single synchronous sine wave signal input.

◇The phase imbalance when using crystal oscillator as time base is less than 3°.

◇Using single sawtooth wave phase modulation, the phase shift voltage can be phase shifted according to the height of the sawtooth wave, and the phase modulation angle is 0~175°.

◇The device is designed with an interlocking circuit inside, so it has strong anti-interference ability.

◇The output can be modulated or duty cycle.

◇The output can be selected between full-control double pulse mode and half-control single pulse mode.

◇When synchronizing with A, you can choose positive phase sequence output or reverse phase sequence output.

◇ The output prohibition mode can be selected as locked or unlocked mode. The locked mode allows output only after reset.

2 Internal Principle of TC790A

The circuit principle of TC790A is to use one phase of the three-phase electricity as A synchronous voltage after being stepped down by a transformer, and then enter the 18th foot of the circuit through a resistor network. The peak value of the synchronous voltage is not greater than the power supply voltage. The zero point and polarity of the synchronous voltage can be detected by the zero detection and polarity discrimination circuit. Figure 1 shows the internal principle block diagram of TC790A.

The crystal oscillator circuit will form oscillation on the crystal and RC at pins 16 and 15 of the circuit, then divide the signal as the time base, and then count the synchronous zero point to form a sawtooth charge and discharge pulse, and at the same time form a sawtooth wave on the capacitor at pin 17.

3 Pin Function

The pin arrangement of TC790A is shown in Figure 2. In fact, the sawtooth wave and the given voltage of pin 1 can give the +A phase shift angle in the positive half cycle through the comparator, and then give the -C phase and +B phase phase shift angle through two 60° frequency division counts; then give the -A phase shift angle in the negative half cycle, and then give the +C phase and -B phase phase shift angle through two 60° frequency division counts. There is a 30° count after the phase shift point of each phase to determine the trigger width.

Pin 2 of TC790A is used to determine whether the output is a modulated pulse or a duty cycle pulse. When pin 2 is left unconnected or at a high level, there are 8 modulated pulses at a trigger width of 30°. When pin 2 is at a low level, the trigger is a 30° duty cycle pulse.

Pin 3 of TC790A is the disable terminal, and pin 4 is the reset terminal. There are two ways to connect pin 4: locked and unlocked. In the locked mode, when pin 4 is suspended or connected to a high level, pin 3 is also at a high level, the output is disabled, and then when pin 3 is at a low level, the output does not recover. Only when pin 4 is connected to a low level can the output recover; in the unlocked mode, pin 4 is connected to a low level. At this time, if pin 3 is at a high level, the output is disabled, and when pin 3 is at a low level, the output recovers.

The circuit pin 5 is the single or double pulse output selection terminal. When pin 5 is suspended or connected to a high level, the output is a double pulse mode. At this time, the output pins from pins 12 to 7 (in positive sequence) are +A, -C, -C, +B, +B, -A, -A, +C, +C, -B, -B, +A. When pin 5 is at a low level, the output is a single pulse mode. At this time, the output from pins 12 to 7 (in positive sequence) is +A, -C, +B, -A, +C, -B.

The circuit pin 14 is the phase sequence selection terminal. When it is suspended or at a high level, the output is in positive sequence (as above); when pin 14 is at a low level, the output is in reverse sequence. When pin 5 is a double pulse, the output pins from pins 12 to 7 are +A, -B, -B, +C, +C, -A, -A, +B, +B, -C, -C, +A. When pin 5 is at a low level, the output is in single pulse mode. At this time, the output pins from pins 12 to 7 are +A, -B, +C, -A, +B, -C.

The pin functions of TC790A are listed in Table 1. Table 2 lists the main parameters and operating conditions of TC790A.