CN1026642C - Device for overload and short circuit protection of output exciter - Google Patents

Abstract

A method and apparatus for overload and short circuit protection of output drivers using a circuit operating at control voltage levels in which at least one output driver (Q31, Q41) is Under normal circumstances, it is controlled by the reference value (+Vd) which is set to be irrelevant to the external control (11-17), but in the case of short circuit or overload, the exciter only receives the control voltage for a short time, and when the output exciter When the load current exceeds a given limit value, the reference value starts to drop rapidly.

Description

The invention relates to a method and device for overload and short circuit protection of an output exciter.

Output drivers (transistors, field effect transistors, etc.) used to control the output of the control output to control the power applied to the load will break down when overloaded or shorted. For example, US patent application 4695915 proposes an overload and short circuit protection device. The device does not use any reference value, which means that the overload current limit value cannot be adjusted to the desired value. Additionally, the current limit value varies with changes in the voltages supplied to the load because changes in these voltages cause changes in the base current. In addition, the output transistor also needs to have a large control current, so that the heat loss becomes larger. It is therefore practically impossible to integrate several outputs on a single integrated circuit. Moreover this device is not connected at once when adding control signal, but needs to have a separate external pulse.

The object of the present invention is to eliminate the above-mentioned disadvantages and to realize a protection system which does not require resistors connected in series with the load which both consume electricity and generate heat. The heat loss caused by these resistors makes it impossible to integrate several protection devices in the same housing. The overload and short-circuit protection method of the output driver of the present invention has such characteristics, that is, at least one output driver is controlled by a reference voltage that can be adjusted independently of external control under normal conditions, and in overload or In the case of a short circuit, when the control signal is only applied for a short time and the load current of the output driver exceeds a certain limit value, the reference value starts to drop rapidly.

The remaining embodiments of the method of the invention and the device designed for its application have the following characteristics:

When the input voltage is turned on, the control circuit provides a detection pulse to the exciter to detect whether there is an overload or short circuit condition at the output and prevent the exciter from receiving control in this case signal, and the duration of the overload or short-circuit condition is monitored by means of detection pulses provided periodically to the exciter via the control circuit, once the overload or short-circuit condition disappears, the exciter can continue to work according to the input;

The reference value fed to the output driver is reduced by limiting the control current flowing into the base of the output driver in the event of a short circuit or overload by arranging that the control current is provided with an additional path in addition to the path through the output driver. one path diverting at least part of said current into said other path in the event of an overload or short circuit;

The current in the other path flows through a switch controlled by the collector or emitter voltage of the output driver;

The device has a control circuit, an overload and short-circuit monitoring circuit and an oscillator, all for the exciters, the control circuit being used to control by means of a reference value set independently of the external control and obtained from a reference voltage unit The exciter, overload and short circuit monitoring circuit prevents control current from flowing to the exciter in an overload or short circuit condition, and the oscillator monitors the duration of the short circuit or overload condition by means of a detection pulse supplied to the exciter via the control circuit.

When the input voltage is turned on, the control circuit sends out a detection pulse to detect whether there is an overload or short circuit;

The device is provided with controllable solid-state switches, a resistor and an oscillator. In a normal state, the first switch among the controllable solid-state switches prevents the The conduction of the second switch is turned on, the first switch is turned on, so that the fourth switch starts to conduct, and the output driver is turned on. The resistor and the second switch together form an overload and short circuit monitoring circuit. In this circuit , when the output voltage drops under overload or short-circuit conditions, the second switch starts to conduct, thereby diverting the control current from the base of the output driver. The oscillator is common to all drivers and sends out periodically detecting a pulse which turns on the first switch, the effect of which is to stop the conduction of the second switch and cause the output driver to receive its control current through the fourth switch;

The device has a number of controllable solid-state switches in which, when in normal conditions When the input voltage is turned on, the first switch is turned on, thus preventing conduction due to the second switch, so that the control current can flow into the base of the output driver, while the collector voltage of the output driver or equivalent drops to A certain level and the excitation is still in the conduction state, and in the case of overload or short circuit, the second switch is turned on, the effect is to make the control current flow into the ground through the second switch, so that the output driver does not receive control The current is thus kept disconnected, and the overload and short-circuit monitoring circuit of the device includes a resistor and a second switch, and the common oscillator periodically feeds pulses to each exciter to detect whether the short-circuit or overload condition has disappeared, so that when e.g. When the short circuit condition disappears, the oscillator pulse causes the collector voltage or equivalent of the exciter to drop, in which case the second switch receives no control current and opens, allowing the control current to flow into the base of the exciter , thereby keeping it turned on.

An important advantage of the invention is that the output driver is completely disconnected even in the event of a brief overload, which means that the generation of heat is immediately prevented. In addition, the present invention takes measures to monitor whether there is an overload or a short circuit by applying a very short pulse at a certain time interval, and in order to make the exciter turn on again, the load current must be lower than the current at the time of overload. This arrangement ensures that overheating never occurs. This makes it possible to integrate several (eg 7) outputs in a single circuit. In addition, the circuit can be directly controlled by a microprocessor, and the control circuit can be implemented as a sink circuit or as a source circuit.

This circuit protects the output driver from any form of short circuit or overload conditions. This makes it virtually impossible for the actuator to overheat, increasing its reliability and life. This circuit does not use any power resistors, nor does it use components that generate heat. This makes it possible to manufacture an integrated circuit containing, for example, eight control outputs without having to solve complex housing problems. In addition, it is possible to manufacture circuits whose pins can be used with existing common circuits, so that short-circuit protection can be achieved simply by replacing the old circuit with a new circuit.

The content of the present invention is illustrated below by means of some examples with reference to the accompanying drawings. In the attached picture:

Figure 1a is a block diagram of the principle of short-circuit and overload protection when the source controls the output;

Figure 1b is a block diagram of the principle of short circuit and overload protection when the leakage control output terminal is used;

Figure 2 shows a source overload and short circuit protector;

Figure 3 shows a drain type overload and short circuit protector;

Figure 4 is the duty cycle of the overload and short circuit protection circuit under normal conditions;

Figure 5 is the duty cycle of the overload and short circuit protection circuit during an overload or short circuit condition;

Let's start by looking at source-controlled output drivers (transistors, FETs, etc.) that break down when overloaded or shorted. The block diagram in Figure 1 illustrates the operation of the exciter's short-circuit and overload protection circuits. When an input signal is connected, the control circuit 1' sends a short detection pulse to the exciter, and at the same time monitors whether there is a short circuit or an overload at the output terminal. If the short circuit or overload does not occur frequently, the control circuit 1' applies a control signal determined by the control reference value 2' to the exciter 3', whereupon the exciter is switched on. However, if short-circuits or overloads occur frequently, the overload and short-circuit monitoring circuit 4' interrupts the control signal from the circuit board to the actuator. After the overload or short circuit condition has disappeared, the exciter is switched on again by a pulse from the oscillator 5'. The oscillator monitors the duration of the short circuit or overload condition by periodically providing short detection pulses to the exciter via the control circuit, and once no overload/short condition is detected, allows the exciter to continue operating according to the input.

Fig. 2 is a control unit of a source exciter with seven inputs I1...I7, the figure shows the control unit of inputs I1 and I7. All these control units have the same structure and work, so only the unit at input I1 is described here. In the figure, the last number of each component number of the input terminal I1 is 1, and that of each component of the input terminal I7 is 7.

The output driver comprises two transistors Q31 and Q41 connected as a Darlington pair. The emitter of the Darlington pair is connected to the supply voltage +Vcc, and the collector is connected to the output terminal O1. In the circuit controlling the output driver, the emitter of the first transistor Q1 is connected to the collector of the auxiliary transistor Q21, the collector is connected to the base of the second transistor Q11, and the base is connected to the first resistor R71 and A point between the second resistor R61, the other end of the first resistor R71 is connected to the supply voltage +Vcc, and the other end of the second resistor R61 is connected to the oscillator collector of oscillator transistor Q50. The emitter of the auxiliary transistor Q21 is connected to the supply voltage +Vcc. The emitter and base of Q21 are connected by a third resistor R1. The input signal I1 is applied to the base of the third transistor Q51 through the fourth resistor R21, the emitter of the third transistor Q51 is grounded, and the collector is connected to the base of the first transistor Q1 through the capacitor C1. The collector of Q51 is also connected to the base of the auxiliary transistor Q21 via the fifth resistor R41, and is connected to the base of the fourth transistor Q61 via the sixth resistor R31. The emitter of the second transistor Q11 is connected to the collector of the auxiliary transistor Q21, the base is connected to the output terminal O1 via the seventh resistor R11, and the collector is connected to the base of the output driver and connected via the eighth resistor R51 Connected to the emitter of the fourth transistor Q61. In each cell, the collector of the fourth transistor Q61 is connected to a point between the Zener diode D8 and the ninth resistor R10 from which the reference voltage Vd is obtained, and the other end of the Zener diode is connected to the supply voltage +Vcc, the other end of resistor R10 is grounded.

The circuit includes an oscillator common to each control unit, a capacitor C2 and two Schmitt trigger ICs (Integrated Circuits). A resistor R9 and a series circuit composed of a diode D9 and a resistor R8 are connected across the Schmitt trigger. The output of the amplifier is connected via a resistor R50 to the base of a transistor Q50, the emitter of which is connected to ground.

When the voltage on input I1 increases above the threshold, the third transistor Q51 becomes conductive, thereby also turning on the auxiliary transistor Q21. The signal obtained at this time via capacitor C1 turns on the first transistor Q1. The second transistor Q11 then receives a base signal which prevents it from conducting. As a result of these actions the fourth transistor Q61 becomes conductive, thereby applying the control voltage to the base of the output driver. Diode D8 forms a bias regulator, ensuring that small variations in supply voltage do not affect control of the output stage. The overload and short circuit monitoring circuit includes a second transistor Q11 and a seventh resistor R11. A drop in the voltage of the output signal O1 causes the second transistor Q11 to start conducting, thereby causing the base voltage of the output driver to change, causing the output driver to start turning off. This again makes the output voltage O1 further rapid decline. The output driver is thus switched off extremely quickly. Leakage current is prevented by means of the auxiliary transistor Q21, the third resistor R1 and the fifth resistor R41.

The oscillator circuit periodically outputs a short pulse to monitor for, for example, a short circuit condition. The oscillator pulse turns on the first transistor Q1, preventing conduction by the second transistor Q11. The output driver is now controlled by the fourth transistor Q61. When the short circuit condition has disappeared, the output voltage at O1 does not drop, so the output driver remains on. When the input terminal I1 is driven to a low state, the third transistor Q51 stops conducting, thereby turning off the fourth transistor Q61. The output driver is then disabled by losing its control signal.

Next let's look at sink-controlled output drivers (transistors, FETs, etc.) that break down when overloaded or shorted. In this case, the overload/short circuit protection is based on the principle shown in Fig. 1b, which is completely equivalent to that in Fig. 1a. The only difference is that in this case the load is connected to the supply voltage, whereas in the case of source protection circuits the load is grounded.

FIG. 3 shows the control unit of the individual sink drivers for the seven inputs I1'...I7'. The construction and operation of the control units are identical and they have the same components. The elements in each unit are numbered, with the last digit of each number corresponding to the number of the input concerned. Let us now consider the control unit of the input I1' as an example.

In this case the output driver also comprises two transistors Q31' and Q41' connected as a Darlington pair. In the circuit controlling the output driver, the collector of the first transistor Q1' is connected to the resistor R11' and to the base and emitter of the second transistor Q11' to the On the emitter, the base is connected to the input terminal I1' via the capacitor C1', and the other end of the resistor R11' is connected to the input terminal O1'. The base of the output driver and the collector of the second transistor Q11' are connected via the second resistor R31' to a point between the third resistor R100' and the grounded Zener diode D8', the reference voltage Vd' being obtained from this point. The third resistor R100' is common to all exciters and is connected to the power supply voltage Vcc'. A second diode D1' is connected between the input terminal I1' and the second resistor R31'. The base of the auxiliary transistor Q21' is connected to the input via a fourth resistor R'1 and the collector is connected to the emitter of the second transistor Q11' which is grounded together with the emitter of the output driver. The base of the first transistor Q1' is connected to an oscillator via a fifth resistor R21'.

The oscillator is common to all control units and consists of two Schmitt trigger IC' (Integrated Circuit) connected to a capacitor C8'. Connected across the Schmitt trigger is a resistor R9' and a series circuit consisting of a diode D9' and a resistor R8'.

When the level of the driving input I1' becomes high, the voltage applied to the base of the first transistor Q1' through the capacitor C1' will make the first transistor Q1' conduct, thereby preventing the second transistor Q11' from conduction. The current flowing through the second resistor R31' now flows through the base of the output driver. If the collector of the output driver is properly loaded, the collector voltage drops below a value such that the second transistor Q11' receives no base voltage and the output driver remains on. When the input is low, leakage current cannot flow from the collector of the output driver to ground through the first resistor R11' and the base of the second transistor Q11' because the auxiliary transistor Q21' is non-conductive.

If the collector of the output driver is shorted to the supply voltage, then after a short pulse from capacitor C1 to the base of the first transistor, the second transistor receives the base voltage from the collector of the output driver. And turn on. The current flowing through the second resistor R31' then flows to ground via the second transistor so that the output driver receives no control current and thus remains off.

Capacitor C1' directly forces the output into the state corresponding to the input without waiting for a pulse from the oscillator.

For example, in the event of a short circuit, periodic pulses from the oscillator monitor the occurrence of a short circuit. If the collector of the output driver is still shorted to the supply voltage, the control voltage applied to its base will not cause the collector voltage to drop sufficiently, so the output driver remains due.

When the short circuit condition disappears, the pulse supplied by the oscillator causes the collector voltage of the output driver to drop, so that the second transistor Q11' does not receive the control voltage and is therefore turned off. The current from the second resistor R31' then flows into the base of the output driver, thus keeping the output driver in the conducting state.

If necessary, the output driver can be switched off by driving input I1 low, in which case the current from the second resistor R31' will not flow to the base of the output driver, thus stopping the output driver conduction. A pulse from the oscillator does not turn on the output exciter either.

The Zener diode D8' keeps the base voltage constant even when the supply voltage Vcc' varies.

Figure 4 is the duty cycle under normal conditions and Figure 5 is the duty cycle under overload or short circuit conditions, showing the action of the circuit (see Figure 1b) at the following points: 1 input, 2 exciter input, 3 Exciter output, 4 oscillators. Each arrow indicates the sequence of each process. Under normal conditions, the input to the control unit controls the input to the actuator, which in turn controls the output from the actuator. In Figure 5, the short circuit or overload condition occurs at time 1" and disappears at time 2". During this process, the oscillator sends a pulse which appears at the input of the exciter and thus also at its output. The pulses provided by the oscillator have the effect of restoring normal operation when the abnormal condition has disappeared.

It will be readily understood by those skilled in the art that various embodiments of the present invention are not limited to the examples described above, but that they may be modified without departing from the scope of the following claims.

Claims (1)

1. A device for controlling an output actuator, said device comprising: A control circuit (1') via a reference value (+Vd; +Vd') obtained from a reference value unit (2') set independently of external control (I1-I7; I1'-I7') , to control each exciter (3'); An overload and short-circuit monitoring circuit (4') for detecting and eliminating overload or short-circuit conditions, in which circuit, by means of semiconductor switches (Q11, Q11'), another current path through said switches is configured such that The control current of the output driver is limited during an overload or short circuit condition, at which time at least a portion of the control current flows in a current path, and the circuit does not require the use of a resistor in series with said driver to control the driver current, and an oscillator (5') generating a detection signal by means of which the control circuit independently monitors the duration of an overload or short circuit, It is characterized in that the control circuit has a first semiconductor switch (Q1, Q1') The overload and short circuit circuit consists of a second semiconductor switch (Q11, Q11') and a resistor (R11, R11) connected to the control electrode of the second switch and to the actuator output (01-07; 01'-07') '), The first switch is connected to the control electrode of the second switch in such a way that in the normal state the first switch conducts to control the output actuator while preventing the second switch from conducting and in the overload or short circuit state, By means of a control signal from the output of the actuator via a resistor, the second switch is turned on, The oscillator continuously gives the detection signal, the control signal has constant voltage elements (D8, D8') for maintaining the reference value of the actuator at a constant value, and The control circuit has a capacitor (C1, C1') connected to the gate of the first switch, enabling the control of the actuator to be equivalent without external control from the oscillator control.

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