CN110460013A - An intrinsically safe power supply overcurrent and short circuit protection circuit - Google Patents

Abstract

An over-current and short-circuit protection circuit for an intrinsically safe power supply, including: a main current switch circuit, a current mirror secondary circuit, a secondary circuit current sampling resistor, a sampling voltage shift circuit, a short-circuit detection feedback circuit, a hysteresis comparator circuit, and a micro-current switch Circuit composition. The main circuit current is copied by the current mirror secondary circuit in a certain proportion, and the main circuit current is obtained by detecting the current of the current mirror circuit; the sampling voltage of the mirror circuit is shifted, and the short circuit detection feedback is respectively connected to the hysteresis comparator When an overcurrent or short circuit occurs, the output signal of the hysteresis comparator turns off the main current switch to cut off the main current of the load to realize overcurrent or short circuit protection, and at the same time activates the micro current switch so that the circuit can automatically return to normal after the fault is eliminated.

Description

An intrinsically safe power supply overcurrent and short circuit protection circuit

technical field

The patent of the invention relates to the design of an intrinsically safe power supply protection circuit, and is especially applied to the power supply protection of intrinsically safe portable measuring instruments in coal mines.

Background technique

Intrinsically safe circuit refers to a circuit in which any spark or any thermal effect produced under standard specified conditions (including normal operation and specified fault conditions) cannot ignite an explosive gas atmosphere. The power supply of various communication, monitoring, measuring instruments, meters and automation system equipment in coal, oil, natural gas mining and other industries with flammable and explosive gas hazards must meet the explosion-proof requirements, because intrinsically safe power supplies are the best for explosion-proof The best form, so its performance requirements are higher.

In the design of intrinsically safe power supply, the output voltage, current and power of the power circuit are fully considered to prevent sparks generated by overvoltage or overcurrent from igniting underground combustible gases, causing damage and casualties to equipment and personnel. According to the requirements of the national standard GB3836.4-2000, the various indicators of the intrinsically safe circuit mainly include: the output voltage or current cannot ignite the surrounding flammable gas; there must be reliable electrical isolation between the intrinsically safe circuit and the non-intrinsically safe circuit, Even some places require double or triple overvoltage and overcurrent protection circuits to improve the safety factor of circuit work. In addition, some working electrical appliances are required to have a self-recovery function, that is, they can automatically return to normal working conditions after troubleshooting.

Currently commonly used intrinsically safe power supply protection circuit forms include current-limiting protection, current-reducing protection, and cut-off protection. The cut-off overcurrent protection circuit can quickly and completely cut off the source of spark energy when there is an overcurrent or short circuit fault, and has a good energy limiting effect.

Contents of the invention

The purpose of the present invention is to provide a simple, safe and reliable protection circuit for quickly cutting off the main current of spark energy, and at the same time provide micro current to make the circuit automatically resume work after the fault is eliminated.

In order to achieve the above object, the technical solution adopted in the present invention includes: a main current switch circuit, a current mirror secondary circuit, a secondary circuit current sampling resistor, a sampling voltage shift circuit, a short circuit detection feedback circuit, a hysteresis comparator circuit, and a micro current switch circuit composition. The main circuit current is copied by the current mirror secondary circuit in a certain proportion, and the main circuit current is obtained by detecting the current of the current mirror circuit; the sampling voltage of the mirror circuit is shifted, and the short circuit detection feedback is respectively connected to the hysteresis comparator When an overcurrent or short circuit occurs, the output signal of the hysteresis comparator turns off the main current switch to cut off the main current of the load to realize overcurrent or short circuit protection, and at the same time activates the micro current switch so that the circuit can automatically return to normal after the fault is eliminated.

The main current switch circuit is controlled by a high-power PMOS FET to switch the load working current, the source S is connected to the power supply, and the drain D is connected to the load.

The current mirror secondary circuit is realized by a low-power PMOS field effect transistor connected in series with a detection resistor, wherein the low-power PMOS field effect transistor grid G is connected to the high-power PMOS field effect transistor grid G of the main road, and the source S is connected to the power supply. The drain D of the low-power PMOS field effect transistor is connected to the detection resistor, and then connected to the load, so as to obtain a micro-current source that is many times smaller than the operating current of the load.

The current sampling circuit is a detection resistor connected in series with the above-mentioned low-power PMOS field effect transistor, and the purpose of calculating the magnitude of the main current is realized by detecting the voltage drop of the resistor.

The level shifting function is completed by the combined transistor network, so that the voltage of the detection resistor of the mirror current source is shifted to about 1/2, which is lower than the feedback potential of the short circuit detection circuit when the load is working normally. At the same time, the potential latch function is adopted in the voltage shift circuit to ensure that the detection resistor locks the potential in the no-current state during the short circuit, so that the hysteresis comparison can work stably.

The output terminals of the level shift and short-circuit detection circuit are respectively connected to the "+" pole and "-" pole of the hysteresis comparator. When the circuit works normally, the potential of the output terminal of the short-circuit detection circuit is greater than the voltage shift of the detection resistor, and the comparator outputs a low level; flat.

Similarly, if the main current increases, the current mirror current increases in the same proportion, and the detection voltage of the sampling resistor increases accordingly. If it exceeds the "-" input terminal of the hysteresis comparator circuit, the hysteresis comparator outputs a low level, reaching the short-circuit detection circuit. The potential of the output terminal is greater than the voltage shift of the detection resistor, and the comparator outputs a low level.

The above-mentioned hysteresis comparator outputs a high-level signal to turn off the high-power PMOS FET in the main circuit to realize the function of cut-off current for short-circuit faults, and at the same time turn on the micro-current switch and connect a fixed current-limiting diode in series to connect to the load protection short-circuit detection circuit Normal operation, after the fault is eliminated, the potential of the load output terminal is greater than the voltage shift of the detection resistor, and the voltage comparator re-outputs a low level to turn on the high-power PMOS field effect transistor of the main circuit, and the circuit returns to normal state after the short-circuit fault is eliminated, while ensuring High reliability of turning off P power tube during short circuit fault.

The comparator adopts a hysteresis comparator, and the use of a hysteresis comparator can ensure the stability of the overcurrent and short circuit protection circuit, that is, there is a certain voltage threshold between shutdown protection and normal operation, ensuring overcurrent and short circuit protection circuit stability.

The beneficial effects of the technology of the present invention are: compared with the prior art, first, on the basis of limiting the current of the intrinsically safe power supply, it is ensured that the load can turn off the power MOS tube under a short-circuit fault, reducing the power loss of the system when the short-circuit occurs; The second is to use a small proportion of the current mirror circuit to copy the main circuit current controlled by the main power tube, and obtain the main circuit current through the detection resistor. Since the current mirror circuit current is small, the heat source in the circuit is reduced; the third is that the circuit has short-circuit detection and Over-current detection has dual functions, and the over-current threshold can be adjusted by adjusting the resistance of the current mirror; the fourth is that the circuit has fast action response and automatic recovery, and can effectively realize intrinsically safe output protection even if there is a lot of noise, and can ensure accurate power supply. The advantages of reliable operation; Fifth, through the common short-circuit detection circuit or hysteresis comparator circuit and the main current switch in series, or through the over-current and short-circuit protection circuit of the intrinsically safe power supply in series, the purpose of double or triple over-current and short-circuit protection is realized.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic block diagram of the circuit of the present invention.

Fig. 2 is a circuit diagram of a specific implementation of the present invention.

Fig. 3 is an integrated circuit diagram of a specific implementation of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, an over-current and short-circuit protection circuit for an intrinsically safe power supply includes: a main current switch circuit, a current mirror secondary circuit, a current sampling circuit, a sampling voltage shift circuit, a short-circuit detection feedback circuit, and a hysteresis comparator circuit , Composed of a micro-current switch circuit, the over-current and short-circuit protection signals are obtained from the positive pole of the power supply, that is, the input current and the output current have a common negative pole.

As shown in Figure 2, an intrinsically safe power supply overcurrent and short-circuit protection circuit, in which the main current switch circuit is a high-power P-channel MOS transistor Q2, and the current mirror secondary circuit is a low-power P-channel MOS transistor Q5, and the Q5 transistor is A certain ratio copies the current of the high-rate tube Q2, and converts it into a detection voltage through the current sampling resistor POT; the level shift function and the latch function are completed by the transistors Q6, Q8, Q9, Q10, Q11, Q12 and Q13, and then connected to the hysteresis Return to the "+" pole input terminal of the comparison circuit; R1, R2 and R6 are the short-circuit detection feedback circuit, and then connected to the "-" pole input terminal of the hysteresis comparison circuit; Q6 and Q7 form a diode-connected common-source amplifier circuit , to control the micro-current switch circuit Q1, wherein the diode of the micro-current switch circuit limits the current size, and then the Q3 inverting circuit controls the main current switch and its current mirror switch.

As shown in Figure 2, during normal operation, the gate potentials of MOS transistors Q2 and Q5 are at a high level. In normal operation of the circuit system, since the sampling resistor POT is connected to the secondary current, the current flowing through is small, and the circuit is reduced. The purpose of the heat source in.

As shown in Figure 2, once a short circuit occurs, the short circuit detection circuit will feed back a low level, and the "-" input terminal potential of the hysteresis comparator is 0 V. Because the "+" input terminal potential of the comparator is greater than 0 V, the final comparison The output of the device is at a high level, and then turn off the MOS transistors Q2 and Q5, and at the same time turn on the micro-current switch Q1, so that the entire load is limited to a micro-current, and the short-circuit protection of the intrinsically safe power supply is realized.

As shown in Figure 2, after the short circuit protection is realized, Q2 and Q5 tubes will be turned off; Q8, Q9, Q10, Q11, Q12 and Q13 of the voltage shift circuit form a potential latch function to ensure that the circuit is closed during the short circuit period. In the off state, the voltage of the "+" input terminal of the hysteresis comparison is always higher than the voltage of the "-" input terminal of the comparator, even if there is circuit noise, the output voltage of the comparator is always at a low level, ensuring that the circuit can always operate during the short circuit. Turn off the P power tube to realize the reliability of the protection circuit.

As shown in Figure 2, when a short circuit occurs, the micro-current switch circuit is turned on, so that a certain current flows to the load, and the short-circuit detection circuit is guaranteed to be fed back to a low level.

As shown in Figure 2, once an overcurrent phenomenon occurs, the mirror current will also amplify the current in the same proportion, and the sampling resistor POT will be converted into a corresponding increase in the detection voltage. After the voltage shifts, the "+" input terminal of the hysteresis comparison circuit exceeds the hysteresis comparison circuit. The "-" input terminal of the hysteresis comparator also makes the output of the hysteresis comparator low, and then turns off the MOS tubes Q2 and Q5, and at the same time turns on the micro-current switch Q1, so that the entire load is limited to the micro-current, and the over-current of the intrinsically safe power supply is realized. stream protection.

As shown in Figure 2, the overcurrent threshold is controlled by adjusting the size of the sampling resistor POT.

As shown in Figure 2, once the short-circuit or over-current fault is eliminated, that is, the load resistance is normal, the micro-current switch circuit will charge the load, the short-circuit detection circuit will increase the feedback voltage, the hysteresis comparator outputs a high level, and the MOS is turned on. Tube Q2 and Q5, and close the micro-current switch Q1 at the same time, the circuit automatically returns to normal state.

Similarly, when the overcurrent state returns to below the current threshold, the "+" input terminal of the hysteresis comparison circuit after the voltage shift is smaller than the "-" input terminal of the hysteresis comparison circuit, which also makes the hysteresis comparator output a high level. Turn on the MOS tubes Q2 and Q5, and turn off the micro-current switch Q1 at the same time, and the circuit automatically returns to normal state.

Figure 3 is an integrated circuit of an intrinsically safe overcurrent and short-circuit protection circuit. Only current sampling resistors and short-circuit detection resistors are used as peripheral circuits, which facilitates the integration of intrinsically safe power supply overcurrent and short-circuit protection circuits into a single-chip structure.

For special occasions that require intrinsically safe power supplies to have double or triple over-current short-circuit protection, by connecting the main current switch circuit of the present invention in series, sharing the short-circuit feedback circuit, parallel connection of current mirror secondary circuits, series connection of current sampling circuits or hysteresis comparison circuits, etc. To achieve double or triple over-current and short-circuit protection purposes. Similarly, direct series connection of the over-current and short-circuit protection circuit of the present invention can also achieve double or triple over-current and short-circuit protection.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (5)

1. a kind of intrinsic safety electric source overcurrent and short-circuit protection circuit, comprising: principal current switching circuit, current mirror pair circuit, electric current Sample circuit, sampled voltage shift circuit, short-circuit detecting feed circuit, hysteresis loop comparator circuit, micro-current switching circuit composition, It is characterized by: main road electric current is replicated by current mirror pair circuit in certain proportion, it is big by the electric current for detecting current mirroring circuit Small acquisition main road size of current；Hysteresis is respectively connected to by the sampled voltage displacement to mirror image circuit, and with short-circuit detecting feedback Comparator, if overcurrent or short trouble, shutdown principal current switch realizes the protection of power supply road, while starting set current limiting micro-current Switch, enables circuit after Failure elimination to restore normal automatically.

2. a kind of intrinsic safety electric source overcurrent according to claim 1 and short-circuit protection circuit, it is characterised in that: main power tube control The main road electric current of system is that loaded work piece current switch is controlled by high-power PMOS field-effect tube, and source S connects power supply, and drain D connects Load, current mirror pair circuit is by the concatenation detection resistance realization of small-power PMOS field-effect tube, middle low power PMOS field-effect Tube grid G docks the high-power PMOS fet gate G of main road, and source S connects power supply, the leakage of small-power PMOS field-effect tube Pole D connects detection resistance, then access load, to obtain one more small than loaded work piece electric current times of micro-current source.

3. a kind of intrinsic safety electric source overcurrent according to claim 1 and short-circuit protection circuit, it is characterised in that: current sample electricity Road is realized by being connected on the detection resistance of current mirror pair circuit, calculates principal current size by detection resistance voltage drop, and By completing level shift to detection resistance voltage 1/2 or so, when which is less than load normal work by transistor combination network Short-circuit detecting feedback level.

4. a kind of intrinsic safety electric source overcurrent according to claim 1 and short-circuit protection circuit, it is characterised in that: the level Displacement is respectively connected to the "+" pole and "-" pole of hysteresis loop comparator with short-circuit detecting circuit output end, when circuit works normally, short circuit Detection circuit exports the voltage shift that terminal potential is greater than detection resistance, and comparator exports low level；If short circuit, short-circuit detecting occurs Circuit output terminal potential is less than the voltage shift of detection resistance, and voltage comparator exports high level, equally, if principal current increases, Current mirror electric current increases in proportion, and the detection voltage of sampling resistor is increase accordingly, if be more than hysteresis comparison circuit "-" it is defeated Enter end, so that hysteresis loop comparator exports low level, reaches the voltage shift that short-circuit detecting circuit output terminal potential is greater than detection resistance Position, comparator export low level.

5. a kind of intrinsic safety electric source overcurrent according to claim 1 and short-circuit protection circuit, it is characterised in that: comparator is defeated High level signal shutdown principal current switch out, realizes the effect of short trouble cut-off current, while opening micro-current switch and ensureing Short-circuit detecting circuit works normally, and circuit restores normal condition after realizing short trouble elimination, can ensure that using hysteresis loop comparator Overcurrent and short-circuit protection circuit job stability.