Practical Electrical Limiter: Traditional Chinese Circuit Design Guide

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Limited electrical appliancesElectricity is an essential energy source for industrial and agricultural production and people's lives. Nowadays, there is a widespread phenomenon of insufficient power resources, which brings great inconvenience to production and life. If people's excessive use of electricity can be restricted, it will undoubtedly not only ensure the normal use of electricity for production and people's lives, but also avoid waste and achieve electricity conservation.Electrical appliance limiters limit the power consumption of users within a certain power range. Insert the electrical limiter into the user's power supply, and adjust the power consumption according to the power consumption indicators. If the user's electricity consumption exceeds the specified power, the electrical limiter immediately cuts off the power supply of the household and issues an alarm of over-power (load) to remind the user to reduce the over-current load; at the same time, the circuit itself will detect the power load at regular intervals until the user's power load is lower than the specified power, and normal power supply can be restored automatically.1． How the circuit worksThe circuit of the electrical limiter is shown in Figure 44-1. It is composed of an overload detection circuit, a delay detection circuit, an alarm sound circuit and a bridge rectifier and voltage stabilizing circuit. Figure 44-1In the figure, the reactance converter LH, bridge rectifier diodes D5~D8, capacitor C3, resistor R2 and potentiometer W form an overload detection circuit. When the user uses electricity under normal load, the current passing through the load passes through the primary of the reactance converter LH, and a certain value of voltage will be induced on the secondary of LH. This voltage is rectified by D5~D8 and then added to the resistors R1 and R3, thus generating an upper negative and lower positive voltage drop UCA on R3. This voltage will lower the potential of the base of transistor BG1 (i.e. point B), causing BG1 to bear a reverse bias. At the same time, the power supply is stepped down by capacitor C1, bridge rectified by D1~D4, and stabilized and filtered by C2 and DW. The output 12V DC current passes through resistor R2, adding a forward bias to the base of the BG1 tube. It can be seen that whether BG1 is turned on or not is determined by the combined action of the positive and reverse bias voltages. Under normal circumstances, due to the small negative bias value, the forward bias formed by the 12V power supply is mainly responsible. BG1 is always in the on state under the forward bias, while BG2 is in the cut-off state. Relay J1 does not act, and its normally open contact J1-1 disconnects the power supply of the delay detection circuit and alarm circuit, and the rear circuit does not work.When the user's power consumption is overloaded, the current flowing through the primary of reactance converter LH increases, and the secondary voltage of LH increases accordingly. After rectification, the voltage drop UCA across R3 increases, causing the base potential of BG1 to decrease, that is, the reverse bias takes effect, causing BG 1 changes from conduction to cut-off, the base potential of BG2 increases, changes from cut-off to conduction, J1 is electrically activated, and the normally open contact J1-1 on it is closed, so that the 12V DC power supply is added to the delay detection and alarm circuit, and an alarm sound is sounded to warn the user to reduce the electrical load. At this time, the 12V power supply charges the capacitor C5 through the resistor R6 and the potentiometer W2. Since the voltage at both ends of C2 cannot mutate, the emitter potential of BG3 is lower than the base potential at the beginning, and both BG3 and BG4 are cut off. The 12V power supply is added to the relay J2 coil through the resistor R9, J2 pulls in, and its normally open contact J2-1 closes to form a self-protection, while the normally closed contact J2-2 opens, cutting off the power supply and stopping supplying power to the user.When the charging voltage on C5 rises to the point where the emitter potential of BG3 is higher than the base potential, BG3 and BG4 are immediately turned on, bypassing the current flowing through J2, J2 is released, J2-2 is closed, and the power grid supplies power to the user; J2-1 disconnects the rear circuit power supply, and the delay detection and alarm stop working. When J2-2 is closed, if the user's power is still in an overload state, the above process will occur repeatedly, thus achieving detection at a certain interval until the overload is reduced to the specified load, and the power grid can provide normal power supply.The alarm sounding circuit emits a music alarm sound with the help of a music integrated block. The function of diodes D9~D11 is to generate barrier voltage and provide a voltage of about 3V to the music integrated circuit to make the music integrated block work. Capacitor C7 is used to improve the sound quality of pronunciation.2. Component selection and debuggingLH is a reactance converter, which is a key component of the current limiter. The size of its magnetic ring should be selected according to the limited power. The magnetic ring can be of MXO?000 type. The primary is wound with φ0.8mm enameled wire for 15 turns, and the secondary is wound with φ0.17mm enameled wire for 200 turns. If there is no magnetic ring, the LH can be controlled by the GEI (19) type iron core or the iron core of the 5W electric bell transformer. Wind the secondary winding first, cover it with 3 to 5 layers of insulating paper, and then wind the primary winding. The primary winding is wound with Φ1.4~1.6mm high-strength enameled wire for 6~8 turns; the secondary winding is wound with Φ0.16~0.18mm high-strength enameled wire for 1000~1200 turns.The working voltage of relays J1 and J2 is 12V, among which J2 should use the one with larger contact capacity.Dw is the voltage regulator tube, and the voltage regulator value is 12V.D1~D11 are diodes, which can be 2CZ type or 1N4001.For music integrated circuits, choose Cw9300 or KD?53.BG1, BG2 and BG4 are NPN transistors, choose 3DG6 or 9014, β>80.BG3 is a PNP transistor, choose 3AX31 or 9015. …

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