phase loss protection circuit HM231 is a special thick film circuit, it can automatically and quickly detect the phase loss of the three-phase power supply, and quickly send out a protection signal to avoid the lack of three-phase AC power supply Unnecessary losses caused by the phase. This circuit can be widely used in mines, petroleum, machinery, electricity, coal, tourism and other applications where three-phase AC power is applied.
The thick film circuit HM231 is small in size and easy to use, with a few external components and no debugging. It is only used to detect whether the three-phase AC power supply is missing phase, but it cannot determine the phase sequence of the three-phase power supply, so it has no phase sequence detection and phase sequence error protection functions.
1. Pin arrangement, each pin name, function and usage
HM231 adopts 13-pin single in-line standard package, and its package form is shown in Figure 1. The name, function and usage of each pin are listed in Table 1.
Figure 1 Pin arrangement of HM231
Table 1 Pin description of HM231
2. Internal structure and working principle
The internal structure and working principle diagram of HM231 is shown in Figure 2. It can be seen from the figure that the circuit is composed of three unit links: sampling link, phase discrimination link and power amplification link. Its working principle can be divided into three parts to analyze.
(1) Sampling circuit
The composition and principle of the sampling circuit are exactly the same as those of TH221A, so I won¨t repeat them here.
(2) Phase discrimination circuit
The phase discrimination circuit is composed of a dedicated integrated circuit. It can detect whether there is zero voltage in the voltage output by the sampling circuit. If it is an ideal DC voltage, the 9# terminal outputs a current of about 10mA to make the green light-emitting diode light up, indicating three-phase voltage Normal, no lack of phase occurred. If there is zero voltage in the voltage provided by the sampling circuit, the output voltage of terminal 9# is zero, and the green light-emitting diode is extinguished. At the same time, the 11# terminal outputs about 10mA current to make the red light-emitting diode light up, indicating that there is a lack of phase. At the same time, the phase discrimination circuit outputs a signal voltage to the power amplifier circuit.
(3) Power amplifier circuit
The power amplifying circuit is composed of power amplifying transistors and other components. It takes the phase failure signal provided by the phase discriminating circuit, and the external capacitor 47μF connected to the 10# terminal
The 25V is maintained and amplified to the current that can drive the relay J to act. When the phase is missing, the relay J is activated, and the action signal of the relay J contact is provided to the subsequent protection circuit.
Figure 2 Diagram of the internal structure and working principle of HM231
3. Typical applications and main parameter restrictions
(1) Restrictions on main parameters
1) Working power supply voltage: VDD1 +12゛+15V, VDD2 +12゛+24V;
2) Power supply current: ＋10mA;
3) Input the effective value of the three-phase AC line voltage: 30V (direct input), 380V (1MΩ resistor in series for each phase, power 1/2W);
4) The low-level signal at the 8# terminal after protection: <4V.
(2) Typical application wiring
HM231 can be used in all occasions that need to monitor the lack of phase fault of the three-phase power supply. Figure 3 shows the principle diagram of HM231 used in three-phase direct 380V input transformer power supply and distribution power electronic equipment for lack of phase monitoring. In the figure, the resistance R can be 1MΩ/(1/2)W. This circuit can ensure the no-phase operation of the power supply grid.
Figure 4 shows the principle diagram of HM231 used in a three-phase transformer step-down isolation system. Once a phase loss occurs in the figure, the HM231 protection circuit will act and output a control pulse to block the chopper for phase loss protection.
Figure 3 Schematic diagram of HM231 used in three-phase direct 380V input three-phase grid power supply system
Figure 4 Principle diagram of HM231 used in three-phase transformer step-down isolation protection system