SU849175A1 - Device for voltage stabilizer protection from current overload - Google Patents

Description

(54) DEVICE FOR 13 SAFETY VOLTAGE STABILIZER FROM OVERLOAD ON CURRENT

one

The invention relates to electrical engineering and can be used in voltage stabilizers to protect them from overload until short-circuiting.

A device for protection against overcurrent is known, which contains a current sensor, a comparison node and a transistor actuator fl

The disadvantages of such a device are the large power dissipated by the actuator transistor, the absence of an automatic return after elimination of the overload, is triggered by protection upon switching on the capacitive load.,

It is also known to protect a voltage stabilizer against a current overload, containing in series a connected transistor switch and a resistor current sensor connected between a power source and a voltage regulator, as well as a threshold element whose input is connected to a resistor current sensor

The disadvantages of the known device are the high power dissipated by the transistor switch and the unstable operation under capacitive load.

The purpose of the invention is to reduce the power dissipation of the transistor switch.

The goal is achieved by the addition of a second transistor switch, a limiting resistor, a charging pulse shaper, an AND circuit, a circuit

10 delay, shutdown pulse shaper and narrow pulse shaper, while the second transistor switch is connected through a limiting resistor in parallel to the main transistor switch, the control input of which is connected to the output of the OR circuit, one of the inputs of which is connected to the output of the threshold element and the delay circuit and for 20 inputs the world leader of the charge pulse, and the other with the output of the shut-off pulse shaper, whose input is connected to the output of the AND circuit, one of the inputs of which is connected to the output of the junction circuit and the other with the output of a narrow pulse driver, the input of which is connected to the output of a charge pulse driver and the control input of the second transistor

30 keys. The drawing shows the functional protection scheme of the device. In the proposed device, the main transistor switch 1 is connected to the output of the power supply and is a powerful transistor. In parallel, a chain and a series-connected limiting resistor 2 and an additional transistor switch 3 are connected. The resistance of resistor 2 is such that it provides the maximum allowable current through the load and the minimum allowable load resistance. Resistor sensor 4 current is connected at one end to the common connection point of the main transistor the key 1 and the additional transistor switch 3 (to the emitters of the transistors of these keys), the second end to the protected stabilizer 5 is voltage and and to the input of the threshold element 6, for example, the Schmitt trigger can be used as the threshold element. The output of the threshold element 6 is connected simultaneously with three functional elements: with one of the inputs of the OR circuit 7, through the delay circuit 8 with one of the inputs of the circuit AND 9, with the input of the charging pulse generator 10, the simplest implementation of which is the waiting multiplier. The output of the charge pulse shaper 10 is connected to the control input of the additional transistor switch 3 and the narrow pulse shaper 11, the output of which is connected to another input of the circuit AND-9. Pulse generator 12 is disconnected (which can also be used as a waiting multiplier with a short recovery time) with its input connected to the output of the AND 9 circuit, and output to the second input of the OR 7 circuit. The output of the OR 7 is connected to the control input of the main transistor key 1. The device operates as follows. If the current in the load (through the voltage regulator 5) does not exceed the maximum allowable value, the voltage on the resistor sensor 4 current is less than the threshold voltage of the threshold element 6. The output voltage of the threshold element b, passing through the circuit OR 7, goes to control the input of the transistor switch 1, and, filling the transistor, Z11makayut him. The current from the rectifier to the load flows through the saturated transistor of transistor switch 1 and the resistor sensor 4. In this state, the circuit will remain until those nopj until the load current exceeds the maximum allowable value. In the case of an increase in the current through the protected voltage regulator to a value greater than the allowable (or in the case of a short circuit of the load of the stabilizer 5), the voltage on the resistor sensor 4 exceeds the threshold value of the voltage of the threshold element 6 ,. The threshold element b is triggered, its output voltage abruptly changes its value, which causes an abrupt / change in voltage at the output of the circuit OR 7 and, ultimately, leads to a fast opening of the transistor switch 1. The voltage drop across the transistor the output of the threshold device b when it is triggered, starts the shaper 10 charge pulse. The charging pulse simultaneously closes the transistor switch 3 and opens the switch 1 only for the duration of its action. In this case, the current in the load flows only through the limiting resistor 2, the transistor switch 3 and the resistor sensor 4 current. During a short circuit, the rectified voltage almost drops on the limiting resistor 2. If the short circuit (or overload) is not eliminated for a long time, then after the end of the charging pulse the transistor switch 3 is open, the current through the limiting resistor 2 and transistor switch 3 stops . At the same time, a pulse is generated from the rear edge of the charge pulse of the pulse former 11 from one of the two inputs of the circuit 9. This pulse passes through the circuit 9 only in the presence of a short circuit or overload. This means that the voltage at the second input of the AND 9 circuit, which allows the passage of pulSa, must come from the triggered threshold element b. Since after the end of the charge pulse, the current through the current sensor 4 is stopped, the threshold element b returns to its original position. Therefore, the signal of the threshold element b to the circuit 9 is fed through the delay circuit 8, which ensures a reliable passage of the pulse. The output pulse of the circuit AND 9 starts the shutdown pulse shaper 12. The trip pulse, pass through the circuit OR 7, arrives at the main transistor switch 1 and continues to hold it in the open, off state. During the time corresponding to the duration of the shutdown pulse, both transistor switches 1 and 3 are open, the current does not flow through the load circuit. Upon termination of the turn-off pulse, transistor switch 1 opens, and the process repeats.

Claims (1)

Formula of the invention on a transistor key, a second transistor switch, a limiting resistor, impulse, delay, pulse closure, a charge driver And, an OR circuit, a pulse generator and a narrow driver while the second transistor switch is connected in parallel with the main a transistor switch, the control input of which is connected to the output of the OR circuit, one of the inputs of which is connected to the output of the threshold element and the inputs of the delay circuit and a charge pulse shaper, and the other with the output of the shutdown pulse shaper 25, the input of which is connected to the output of the And circuit, one of the inputs of which is connected to the output of the delay circuit, and the other with the output of the narrow pulse shaper, the input of which is connected to the output of the charge pulse shaper and the control input of the second transistor switch.