Intrinsic safety protection circuit for explosion-proof system

Abstract

The utility model belongs to the field of circuit protection, particularly relates to an intrinsic safety protection circuit for an explosion-proof system, and aims to solve the problems that unnecessary shutdown is caused by a fixed fault protection mechanism, the capability of flexibly adjusting a protection strategy according to actual conditions is lacked, and the adaptability to different application scenes is poor. The circuit comprises a real-time current signal sampling circuit, an amplification comparison circuit and a two-stage conditioning circuit. When overcurrent is detected, the first stage outputs a high-level protection signal, and a load switch is controlled by adjusting the pulse width; and meanwhile, the protection signal energy storage circuit of the second-stage circuit starts to charge, and cuts off the power supply and discharges after reaching a set level so as to protect the equipment. According to the multifunctional integrated protection circuit design, the reliability, the stability and the safety of the system can be remarkably improved, the maintenance cost is reduced, and the service life of equipment is prolonged.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of circuit protection, specifically relates to a kind of intrinsic safety protection circuit for explosion-proof system. BACKGROUND

[0002] With the continuous improvement of industrial automation level, various electrical equipment is increasingly widely applied, especially in flammable and explosive environment such as chemical industry, petroleum, natural gas, the safety requirement of electrical equipment is extremely strict. As an effective explosion-proof measure, intrinsic safety (IS) technology ensures that even in the most adverse conditions, such as short circuit or component failure, no spark or heat effect sufficient to cause explosion is generated, so as to protect the safety of equipment and personnel.

[0003] The existing intrinsic safety protection circuit usually includes current limiting and voltage limiting components, for limiting the energy transmission from non-intrinsic safety area to intrinsic safety area, to prevent potential explosion risk. However, these traditional protection measures have some shortcomings:

[0004] Fixed fault protection mechanism: most of the existing intrinsic safety protection circuit adopts fixed fault protection mechanism, that is, once fault is detected, power supply will be immediately cut off, such design can effectively prevent further spread of fault, but at the same time, it may also cause unnecessary downtime, affecting production efficiency.

[0005] Lack of flexibility: since traditional protection circuit cannot flexibly adjust protection strategy according to actual fault condition, for example, in some cases, short power interruption may be enough to avoid fault aggravation, while long time downtime will cause economic loss; while in other cases, longer time may be needed to completely solve the problem to prevent fault from occurring again.

[0006] Inadequate recovery mechanism: existing intrinsic safety protection circuit often needs to be manually reset to restore normal working state after fault removal, which not only increases the workload of operating personnel, but also may delay the recovery production time in emergency.

[0007] Poor adaptability: fault characteristics and safety requirements are different in different application scenarios, but traditional intrinsic safety protection circuit is often difficult to adapt to these changes, resulting in its applicability being limited in specific environment.

[0008] Based on this, the utility model provides a kind of intrinsic safety protection circuit for explosion-proof system. UTILITY MODEL CONTENT

[0009] In order to solve the above problems in the prior art, that is, the fixed fault protection mechanism leads to unnecessary downtime, the lack of ability to flexibly adjust the protection strategy according to the actual situation, the imperfect recovery mechanism needs manual reset, and the poor adaptability to different application scenarios, the utility model provides a kind of intrinsic safety protection circuit for explosion-proof system.

[0010] The utility model provides a kind of intrinsic safety protection circuit for explosion-proof system, including current real-time signal sampling circuit, current signal amplification comparison circuit, first regulating circuit, second regulating circuit and protection control circuit;

[0011] The input of the current real-time signal sampling circuit is connected with the input of the power supply and the protected device, the output of the current real-time signal sampling circuit is connected with the input of the current signal amplification comparison circuit, the output of the current signal amplification comparison circuit is connected with the input of the first regulating circuit, the output of the first regulating circuit is connected with the input of the second regulating circuit, the output of the second regulating circuit is connected with the input of the protection control circuit, and the output of the protection control circuit is connected with the protected device.

[0012] Further, the input of the current signal amplification comparison circuit is also connected with the current protection threshold signal adjustment circuit, and the current protection threshold signal adjustment circuit is used for outputting threshold signals.

[0013] Further, the second regulating circuit is built-in with a protection signal energy storage circuit.

[0014] Further, the input of the second regulating circuit is also connected with an overvoltage protection detection circuit, when the overvoltage protection circuit detects an overvoltage signal, the discharge speed of the protection signal energy storage circuit is controlled by regulating the pulse width of the overvoltage signal.

[0015] Further, a temperature sensor is mounted on the surface of the protection control circuit, the temperature sensor is used for acquiring real-time temperature, the maximum dissipation power is calculated based on the real-time temperature, when the maximum dissipation power is greater than the heat power of the protection control circuit, the input of the power supply is cut off through the temperature monitoring circuit connected with the protection control circuit.

[0016] Further, the current protection threshold signal adjustment circuit includes a resistor R30, a resistor R29 and a capacitor C16.

[0017] One end of the resistor R30 is connected with the voltage network after voltage stabilization of the voltage stabilization circuit, the other end of the resistor R30 is connected with the resistor R29, and the other end of the resistor R29 is connected with the current signal amplification comparison circuit.

[0018] Both ends of the capacitor C16 are connected with both ends of the resistor R29.

[0019] According to the required threshold signal, the proportion of the resistance R30 and the resistance R29 is adjusted, so that the current passes through the resistance R30 and the resistance R29, and the threshold signal is output.

[0020] Further, the first conditioning circuit comprises a capacitor C9, a resistance R20 and a diode D4;

[0021] Both ends of the capacitor C9 are connected with the output of the current signal amplification comparison circuit, one end of the capacitor C9 is connected with one end of the resistance R20, the other end of the resistance R20 is connected with the negative electrode of the diode D4, the first positive electrode of the diode D4 is connected between one end of the capacitor C9 and one end of the resistance R20, and the second positive electrode of the diode D4 is grounded.

[0022] Further, the second conditioning circuit comprises a diode D3, a resistance R18 and a capacitor C8;

[0023] The positive electrode of the diode D3 is connected with the output of the current signal amplification comparison circuit, the negative electrode of the diode D3 is connected with one end of the resistance R18 and a first node P1, the first node P1 is respectively connected with one end of the capacitor C8 and the gate of the load switch in the protection control circuit, the other end of the resistance R18 is connected with the other end of the capacitor C8, and the other end of the capacitor C8 is connected with the power supply ground of the first set threshold value.

[0024] Further, the overvoltage protection detection circuit comprises a triode Q2, a voltage stabilizing tube Z2, a resistance R16 and a resistance R17;

[0025] The first pin of the triode Q2 is connected with the negative electrode of the diode D3, the second pin of the triode Q2 is connected with the power supply ground of the second set threshold value, the third pin of the triode Q2 is connected with one end of the resistance R16, and the other end of the resistance R16 is connected with the power supply ground of the second set threshold value;

[0026] One end of the voltage stabilizing tube Z2 is connected between the third pin of the triode Q2 and one end of the resistance R16, the other end of the voltage stabilizing tube Z2 is connected with one end of the resistance R17, and the other end of the resistance R17 is grounded.

[0027] Further, the protection control circuit comprises a voltage stabilizing tube Z4, a load switch Q4 and a feedback resistance FB2;

[0028] One end of the voltage stabilizing tube Z4 is connected with the gate of the load switch Q4, the other end of the voltage stabilizing tube Z4 is connected with a second node P2, and the second node P2 is respectively connected with the resistance R31 and the resistance R32;

[0029] The drain of the load switch Q4 is connected with one end of the feedback resistor FB2 and the output voltage of 12V, the source of the load switch Q4 is connected with the third node P3, and the third node P3 is connected with the other end of the feedback resistor FB2 and the second node P2.

[0030] The utility model discloses the beneficial effect:

[0031] High-precision protection: the protection circuit design current of the utility model is accurate, and is set to 1.35A, which ensures that the protection mechanism will not be triggered by mistake within the normal working current range, and improves the reliability and stability of the system. At the same time, the fault response time is fast, and the time from the occurrence of the fault current to the cutting off of the output is not more than 0.5 milliseconds, which can quickly cut off the fault current and effectively prevent potential safety hazards.

[0032] The utility model discloses the beneficial effect:

[0033] Low voltage drop loss: through current signal sampling, current signal amplification, accurate calculation and design of the current signal comparison circuit, the utility model realizes that the voltage drop loss between input and output is minimized, and is not more than 0.1% (0.12V) at most. This feature ensures that even in the protection state, the protected device can also provide stable high driving ability, and the impact on load power supply can be almost ignored.

[0034] Protection signal width modulation function: under the overcurrent condition, the duration of cutting off the power output is controlled by adjusting the charging and discharging time of the capacitor. This dynamic adjustment method can not only ensure the effectiveness of the protection function, but also can flexibly respond to actual fault conditions, reduce unnecessary downtime, and improve the overall efficiency of the system.

[0035] Overvoltage protection function: the utility model designs the protection circuit with a rated working voltage of 12.0V, and when the input voltage is higher than the set protection threshold of 13.0-13.5V, the device will automatically cut off the power output to prevent damage to the equipment or other safety hazards caused by overvoltage, further enhancing the safety of the system.

[0036] Self-recovery output power supply: the utility model adopts a fault signal real-time monitoring circuit design, which can continuously monitor the overcurrent overload and input overvoltage fault of the load. Once the fault disappears, the circuit will automatically restore the power output without manual reset, greatly reducing the workload of the operator, and at the same time, it can quickly restore production in emergency, improving the emergency response capability of the system.

[0037] Optimize equipment heat dissipation: by flexibly adjusting the protection strategy, the utility model can ensure safety at the same time, give the protected equipment sufficient time for natural heat dissipation, avoid the problem of too high temperature caused by long time high load operation, help to prevent further development of failure, protect the equipment from damage. BRIEF DESCRIPTION OF DRAWINGS

[0038] Other features, objects and advantages of the application will become more apparent with the reading of the following detailed description of non-restrictive embodiments made with reference to the attached drawings:

[0039] Figure 1 It is a kind of schematic diagram of connection between each circuit in intrinsic protection circuit for explosion-proof system of the utility model;

[0040] Figure 2 It is the working flow schematic diagram of intrinsic protection circuit for explosion-proof system of the utility model;

[0041] Figure 3 It is the overall structure schematic diagram of intrinsic protection circuit for explosion-proof system of the utility model;

[0042] Figure 4 It is the structure schematic diagram of current stabilizing circuit in intrinsic protection circuit for explosion-proof system of the utility model;

[0043] Figure 5 It is the structure schematic diagram of current real-time signal sampling circuit and protection control circuit in intrinsic protection circuit for explosion-proof system of the utility model;

[0044] Figure 6 It is the structure schematic diagram of current protection threshold signal adjusting circuit and signal amplification comparison circuit in intrinsic protection circuit for explosion-proof system of the utility model;

[0045] Figure 7 It is the structure schematic diagram of primary conditioning circuit in intrinsic protection circuit for explosion-proof system of the utility model;

[0046] Figure 8 It is the schematic diagram of overvoltage protection detection circuit and secondary conditioning circuit in intrinsic protection circuit for explosion-proof system of the utility model.

[0047] Figure 9 It is the connection relationship schematic diagram of primary conditioning circuit and secondary conditioning circuit in intrinsic protection circuit for explosion-proof system of the utility model. DETAILED DESCRIPTION

[0048] The application will be described in further detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related utility model, and not limit the utility model. In addition, it should be noted that, for the convenience of description, only the parts related to the utility model are shown in the drawings.

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0050] As Figures 1-9 shown, referring to Figure 1 , the utility model discloses a kind of intrinsic safety protection circuit for explosion-proof system, including current real-time signal sampling circuit, current signal amplification comparison circuit, primary conditioning circuit, secondary conditioning circuit and protection control circuit;

[0051] The input end of the current real-time signal sampling circuit is connected with the input of power supply and protected device, the output end of the current real-time signal sampling circuit is connected with the input end of current signal amplification comparison circuit, the output end of the current signal amplification comparison circuit is connected with the input end of primary conditioning circuit, the output end of the primary conditioning circuit is connected with the input end of secondary conditioning circuit, the output end of the secondary conditioning circuit is connected with the input end of protection control circuit, and the output end of the protection control circuit is connected with protected device.

[0052] In the utility model, the current real-time signal sampling circuit is connected with the input of power supply, and is used to collect the real-time current signal of protected device, the current signal amplification comparison circuit is used to obtain real-time current signal to carry out signal amplification processing, and the current signal after amplification processing is compared with threshold signal, whether it needs to trigger overcurrent protection signal is judged, if yes, overcurrent protection signal is sent to primary conditioning circuit output high level protection signal, and the time of protection control circuit shutdown is controlled by adjusting the pulse width of high level protection signal.

[0053] The high level protection signal is also used to excite the protection signal energy storage circuit built-in secondary conditioning circuit to charge until reaching the level value required by protection signal, and the output of power supply to protected device is cut off by protection control circuit, protected device is powered off, and protected device is discharged by protection signal energy storage circuit, and the secondary conditioning circuit is used to control the discharging speed of the protection signal energy storage circuit.

[0054] As Figure 3As shown, the current real-time signal sampling circuit in the utility model, utilize the voltage difference signal of both ends of the current flowing through the resistance to amplify, compare.If exceed the set current threshold value, then change the level value of output signal (from high to low, or low to high), close the load switch, cut off the fault current, in particular:

[0055] The current real-time signal sampling circuit in the utility model is two parallel sampling resistors, which are connected in series at the input port of the circuit after being connected in parallel, and the sampling resistor is resistance R31 and resistance R32 in the embodiment;

[0056] The sampling resistor selection in the design adopts a device with high power (to ensure that the normal load current can pass through without heating), high precision (to make the sampled current more accurate and the action threshold more accurate), and low temperature drift (to make the current sampling of the circuit least affected by temperature in various temperature ranges).

[0057] Resistance value:

[0058] According to the maximum action current value of the overcurrent design target 1.35A and the maximum voltage drop 0.12V of the sampling resistor on the output voltage, the resistance value is calculated and selected, that is:

[0059] Sampling resistor size: R=U / I

[0060] Substitute the current and voltage parameters to calculate: R=0.12 / 1.35

[0061] The calculation shows that the maximum sampling resistor cannot exceed 0.8889 ohms

[0062] Considering the parameters that affect the current signal accuracy, such as the current amplification circuit accuracy of the whole system, the input real-time voltage (Vos) of the signal comparator, etc., the sampling resistor value is finally selected as 0.075 ohms, and the accuracy is not less than 1%, which can realize that the input and output loss voltage difference is within 0.1%

[0063] The sampling signal of the protection action current when the 0.075 ohm resistor is selected in the design is:

[0064] Vsample=1.35*0.075=0.1013 (volt)

[0065] Resistance power: after determining the resistance value of 0.75 ohms, the power consumed by the resistance under the condition of the maximum rated working current 1.35A is: W=I2*R, calculation: W=1.35*1.35*0.075=0.137W.

[0066] That is, the resistance power cannot be less than 0.137W, considering the working environment temperature, thermal resistance and other factors, the sampling resistance uses two 0.15 ohm resistors with a power of 1W in parallel to obtain a resistance of 0.075 ohm, the main advantage of this design is to improve the power of the sampling resistance by parallel connection, improve the heat dissipation and reduce the precision drift caused by temperature rise, and improve the circuit stability.

[0067] Resistance accuracy: the design uses a sampling resistance with an accuracy of not less than 1%, which ensures the sampling accuracy of the current signal.

[0068] Resistance temperature drift: the design uses a low-temperature drift alloy sampling resistance of 50ppm / ℃, and the maximum resistance change in the working temperature range is not more than 0.3%;

[0069] In this embodiment, the threshold signal is obtained by:

[0070] The current signal amplification and comparison circuit is connected with the current protection threshold signal adjustment circuit, and the current protection threshold signal adjustment circuit is used for outputting the threshold signal.

[0071] Specifically, as shown in Figure 6 The current protection threshold signal adjustment circuit includes resistors R30, R29 and capacitor C16;

[0072] One end of the resistor R30 is connected with the voltage network after the voltage stabilization of the voltage stabilization circuit, the other end of the resistor R30 is connected with the resistor R29, and the other end of the resistor R29 is connected with the current signal amplification and comparison circuit;

[0073] Both ends of the capacitor C16 are connected with both ends of the resistor R29;

[0074] According to the required threshold signal, the proportion of the resistance values of the resistor R30 and the resistor R29 is adjusted, so that the current passes through the resistor R30 and the resistor R29, and the threshold signal is output.

[0075] The circuit uses the resistance voltage division principle, and the voltage signal REF2 on R29 in the ground series circuit of R29 and R30 is used as the comparison threshold of the current overcurrent protection signal, so that the size of the fault current protection value can be adjusted:

[0076] The overcurrent protection signal size calculated in the above subsection is 2.03V, it can be known that adjusting the resistance value in the proportional-integral circuit composed of R29 and R30 (the capacitor C16 increases the delay, stabilizes the output signal, and reduces the disturbance caused by input fluctuation) can obtain the required comparator reference voltage input signal value size on the REF2 signal network, and the calculation formula is as follows:

[0077] Vvref2=((Vin-Vgnd) / (R29+R30))×R29;

[0078] Wherein, Vin = 12 (volts), Vgnd = 7 (volts);

[0079] Vvref2 cannot be greater than the protection current signal value 2.03V;

[0080] In the case of selecting R30 as 20k 1% resistance, R29 = 13.7k is calculated from the above formula.

[0081] That is, the reference voltage of the comparator when the overcurrent protection is less than 2.03V can reliably act, and the maximum sampling resistance R29 cannot exceed 13.7K.

[0082] Wherein, the current protection threshold signal adjusting circuit further comprises a capacitor C17, two ends of the capacitor C17 are arranged between IN2+ and IN2-, and specifically connected between the IN+ pin and the IN- pin of U2.

[0083] In the embodiment, as shown in Figure 4 The voltage stabilizing circuit comprises a voltage stabilizer U6, a capacitor C18, a voltage stabilizing tube Z9 and a voltage stabilizing tube Z10.

[0084] The first end of the voltage stabilizer U6 is grounded, the second end of the voltage stabilizer U6 is connected to a 12V input voltage, and the third end of the voltage stabilizer U6 is provided with a fourth node P4 and a fifth node P5.

[0085] The fourth node P4 is connected with one end of the capacitor C18 and the fifth node P5, the fifth node P5 is connected with one end of the voltage stabilizing tube Z9 and one end of the voltage stabilizing tube Z10, the other end of the voltage stabilizing tube Z9 and the other end of the voltage stabilizing tube Z10 are connected and then connected with the other end of the capacitor C18, and the other end of the capacitor C18 is connected to the 12V input voltage.

[0086] Wherein, the capacitor C18, the voltage stabilizing tube Z9 and the voltage stabilizing tube Z10 are connected in parallel with each other and then connected in series on the third end of the voltage stabilizer U6.

[0087] As shown in Figure 8 And Figure 9 In the embodiment, the secondary conditioning circuit is further connected with an overvoltage protection detection circuit, when the overvoltage protection circuit detects an overvoltage signal, the discharge speed of the protection signal energy storage circuit is controlled by regulating the pulse width of the overvoltage signal.

[0088] The overvoltage protection detection circuit comprises a triode Q2, a voltage stabilizing tube Z2, a resistor R16 and a resistor R17.

[0089] The first pin of the triode Q2 is connected with the negative pole of the diode D3, the second pin of the triode Q2 is connected with the power supply ground of the second set threshold, the third pin of the triode Q2 is connected with one end of the resistor R16, and the other end of the resistor R16 is connected with the power supply ground of the second set threshold.

[0090] One end of the voltage stabilizing tube Z2 is connected between the third pin of the triode Q2 and one end of the resistor R16, the other end of the voltage stabilizing tube Z2 is connected with one end of the resistor R17, and the other end of the resistor R17 is grounded.

[0091] The second set threshold is 12V.

[0092] In the utility model, the overvoltage protection detection circuit can cut off the output when the input voltage exceeds the allowed or set threshold, in the utility model, the overvoltage protection detection circuit does not adopt the scheme of directly comparing voltage signals, but adopts a simpler and lower cost scheme, utilizes the avalanche voltage stabilizing principle characteristics of the voltage stabilizing diode, and monitors the power supply voltage through the Z2 voltage stabilizing tube with a stabilizing value of 12V, when the power supply voltage is greater than the Z2 stabilizing value, the voltage on the negative pole of Z2 is clamped and stabilized at about 12V (R16 and R17 are current limiting resistors, and the working current of Z2 is ensured to be within the rated range), and the switching characteristic of the PNP triode Q2 is utilized, when the emitter voltage (power supply voltage) is greater than the base voltage (Z2 stabilizing), the triode is turned on, that is, the high and low level signals are output from the collector (equivalent to turning on the power supply voltage to the collector).

[0093] As shown in Figure 6 and Figure 7 In the embodiment, the overcurrent protection signal amplification comparison circuit: the device U2 with a built-in operational amplifier and a voltage comparator is used to complete the amplification and comparison of the load current signal (the actual collected is the voltage difference signal between the resistors), and the signal comparison is completed in about 400ns, and the control signal U5_2B is output, and the flip-flop U5 is triggered:

[0094] The INA381A1 high-speed current sensing amplifier is selected in the circuit, and the amplification multiple is 20 times, so that the signal during overcurrent protection is:

[0095] Vcompare=0.101×20=2.02 (volt);

[0096] Advantages: the signal amplification comparison speed is fast, but there are interference signals in the circuit running process, the RC filter circuit composed of R14 and C19 can filter out the high-frequency interference burr, and ensures that the circuit does not malfunction.

[0097] As shown in Figure 6As shown, the ALERT pin of the device U2 of the voltage comparator is connected with the sixth node P6, the sixth node P6 is connected with one end of the resistor R2 and one end of the resistor R14, the other end of the resistor R2 is connected with the 12V input voltage, the other end of the resistor R14 is connected with one end of the capacitor C19 and U5, the other end of the capacitor C19 is connected with the voltage stabilizing circuit.

[0098] In the embodiment, the protection control circuit comprises the voltage stabilizing tube Z4, the load switch Q4 and the feedback resistor FB2.

[0099] One end of the voltage stabilizing tube Z4 is connected with the gate of the load switch Q4, the other end of the voltage stabilizing tube Z4 is connected with the second node P2, the second node P2 is connected with the resistor R31 and the resistor R32 respectively.

[0100] The drain of the load switch Q4 is connected with one end of the feedback resistor FB2 and the 12V output voltage, the source of the load switch Q4 is connected with the third node P3, the third node P3 is connected with the other end of the feedback resistor FB2 and the second node P2.

[0101] As shown, Figures 7-9 In the embodiment, the primary conditioning circuit comprises the capacitor C9, the resistor R20 and the diode D4.

[0102] Both ends of the capacitor C9 are connected with the output of the current signal amplification and comparison circuit, one end of the capacitor C9 is connected with one end of the resistor R20, the other end of the resistor R20 is connected with the negative electrode of the diode D4, the first positive electrode of the diode D4 is connected between one end of the capacitor C9 and one end of the resistor R20, and the second positive electrode of the diode D4 is grounded.

[0103] The secondary conditioning circuit comprises the diode D3, the resistor R18 and the capacitor C8.

[0104] The positive electrode of the diode D3 is connected with the output of the current signal amplification and comparison circuit, the negative electrode of the diode D3 is connected with one end of the resistor R18 and the first node P1, the first node P1 is connected with one end of the capacitor C8 and the gate of the load switch respectively, the other end of the resistor R18 is connected with the other end of the capacitor C8, and the other end of the capacitor C8 is connected with the power supply ground of the first set threshold.

[0105] The diode D3 and the diode D4 are connected in parallel after the negative electrodes of the two diodes are connected.

[0106] The first set threshold value is 7V, which is a "power ground" after the input power supply is stepped down and stabilized, but not 0V, 7V is used as the ground, compared with the input 12V, it is equivalent to 5V after stepped down and stabilized, the input power supply voltage change is realized, but the threshold voltage of the threshold circuit (using the resistance voltage division principle) does not change.

[0107] Specifically, the first level regulating circuit and the second level regulating circuit constitute a belching protection circuit, when overcurrent and overvoltage faults occur, the corresponding monitoring circuit outputs a high level protection signal to control the gate (G) of the field effect switch tube to close the output.

[0108] For current protection, as described above, the current sampling resistor continuously monitors the current, and at the moment when the fault current occurs, the level signal is changed from high to low through the signal amplification comparator U2, thereby generating a high level pulse signal at the trigger device U5 (flip-flop), which enters the charging and discharging circuit composed of C8 and R18 after passing through the diode D3, and C8 is fully charged, and the high level pulse will give the load switch Q4 gate a signal of shutting down the output, and finally realize the design goal of protection.

[0109] For voltage protection, as described above, when overvoltage occurs, the triode Q2 is turned on. The protection signal also enters the charging and discharging circuit composed of C8 and R18, so that Q4_G becomes high level, and then the load switch Q4 is closed, until the voltage returns to normal, and because of the reverse blocking of the diode D3, this signal will not enter the current protection signal circuit, improving the reliability and stability of the circuit.

[0110] The duration of the belching protection is adjusted by the charging and discharging time of the capacitor. For overcurrent protection, it is divided into two levels. The first level is to control the charging time of the capacitor C9 through the trigger U5 after the trigger signal arrives to control the width of the protection pulse, which not only charges C8, but also directly affects the duration of the protection signal Q4_G, so that the protection duration is longer.

[0111] The second level adjustment is the charging and discharging circuit composed of C8 and R18. The size of the capacitor C8 can be adjusted to adjust the energy storage size. The larger the capacitor, the more energy is stored, and the longer the discharging time is. By adjusting the size of R18, the discharging speed (time) can be adjusted. The smaller the resistance, the faster the discharge. Based on the above design idea, the high level pulse signal output by U5 charges the larger capacitor, and the larger discharge resistance can increase the duration of the load switch shutdown, and vice versa. The advantage of this adjustment is that the protected device has sufficient time to dissipate heat and will not expand the fault.

[0112] Because U5 is only triggered when the trigger signal jumps (from high to low, or from low to high), only the protection signal level energy released by the protection can re-close the load switch from the off state in the event of a fault.

[0113] Therefore, if the fault disappears at this moment, the closing of the switch will not cause the signal of the signal amplification comparator U2 to jump (because the signal of the sampling resistor is within the normal range), thereby achieving the automatic recovery function after protection.

[0114] If the fault persists, the switch is closed, and because the fault still exists, the current signal collected by the sampling resistor is still abnormal, and the output signal of the signal amplification comparator U2 jumps again, the flip-flop U5 is triggered again and outputs a current fault protection pulse signal, and the load switch is closed again for a period of time (the duration is determined by the parameters of the two-stage protection signal setting circuit), and finally the repeated hiccup protection is realized.

[0115] In the normal working state, the load current is less than the designed 1.35A, at this time the two input signals of the comparator (real-time sampling signal and reference voltage signal) are the comparator reference voltage signal (comparison threshold) higher than the current real-time sampling signal, and the high level protection signal of the comparator output.

[0116] When a short circuit fault occurs in the protected device, the real-time sampling signal is higher than the comparator reference voltage signal, and the comparator jumps from a high level protection signal to a low level signal, generating a falling edge trigger signal.

[0117] The falling edge signal of the comparator due to overcurrent triggers the Schmidt trigger U5 (U5 is configured as a falling edge trigger), and the signal output by U5 is charged to C9 through R20, and the charging time is the high level pulse width that needs to be controlled. The duration of the high level width (duration) realizes the first stage control of the protection signal duration. The calculation is as follows:

[0118] t w =R X C X ;

[0119] Where t w is the first stage protection pulse width, which determines the size of the second stage protection pulse energy storage;

[0120] Rx, Cx are R20 (100k) and C9 (10uF) in this circuit, respectively;

[0121] The calculation can obtain the first stage pulse width of about 1000ms.

[0122] The first stage high level protection pulse after the flip-flop adjustment through the reverse diode D3 to charge C8, the charging time constant of C8 (i.e. the time required for the voltage at the terminals of capacitor C8 to reach the level required for the output control circuit to turn off Q4) can be calculated as follows:

[0123] t c = RC x ln[(V1-V0) / (V1-Vt)]; t

[0124] Where R C is the internal resistance of diode D3 after conduction, generally tens of ohms to hundreds of ohms, here taken as 100 Ω, V1 is the final voltage value that capacitor C8 can reach, V0 is the initial voltage value of capacitor C8, and V t is the voltage value when the load switch enters the conduction state.

[0125] C is 4.7 uF;

[0126] V1 = 4.7 V; (voltage value that the capacitor can reach, i.e. the signal level of the flip-flop output)

[0127] V0 = 0 V; (initial voltage value of capacitor C8)

[0128] Vt = 2.5 V; (voltage value at which the field effect transistor Q4 turns off, as can be known from the chip data)

[0129] The calculation gives: t c = 356 us (this time is also the main component of the overcurrent protection response time, other factors can be ignored)

[0130] Discharge time constant: (i.e. the time required for capacitor C8 to discharge through R18 until the voltage is lower than the level required for the field effect transistor Q4 to close, i.e. to discharge to the 1.6 V voltage value at which Q4 opens)

[0131] which can be calculated as follows:

[0132] tc = RC x Ln[(V1-V0) / (V1-Vt)];

[0133] Where: R is the R18 resistance of 51 k;

[0134] C is 4.7 uF;

[0135] V1 = 0 V; (voltage value that the capacitor can reach)

[0136] V0 = 4.7 V; (initial voltage value of capacitor C8)

[0137] Vt = 1.6 V; (voltage value at which the field effect transistor Q4 enters the conduction state, as can be known from the data) ​

[0138] The calculation is: tc=258ms (This time is also the duration of the field effect tube output closed when the overcurrent / overvoltage protection.)

[0139] Wherein, the VCC pin of the U5 is connected with one end of the capacitor C10 and a 12V current input, and the other end of the capacitor C10 is connected with a voltage stabilizing circuit.

[0140] In the embodiment, a temperature sensor is surface-mounted on the protection control circuit, the temperature sensor is used to acquire real-time temperature, the maximum dissipation power is calculated based on the real-time temperature, and when the maximum dissipation power is greater than the heat generation power of the protection control circuit, the input of the power supply is cut off through the temperature monitoring circuit connected with the protection control circuit.

[0141] Specifically:

[0142] The maximum junction temperature function P is constructed DMAX , and the maximum junction temperature function is the maximum allowable dissipation power of the semiconductor device at any ambient temperature:

[0143] P DMAX =(T JMAX -T A ) / θ JA .

[0144] Wherein: T JMAX =125℃ to 150℃.

[0145] The junction environmental thermal resistance θ JA is directly related to the packaging of the device, and the junction environmental thermal resistance of devices with different packaging is different under the same power, and the circuit design in the embodiment reduces the junction environmental thermal resistance through reasonable thermal design;

[0146] The ambient temperature (T A ) is the working environment temperature of the device.

[0147] If the maximum dissipation power is exceeded, the junction temperature of the device will exceed the maximum allowable range, and the device will not work normally or even be damaged.

[0148] In the design, the power load switch device is selected as AOD4185, and the packaging is TO252 (DPARK packaging). The working parameters are queried as follows:

[0149] T JMAX =150℃;

[0150] T A =25℃;

[0151] θ JA =50℃ / W (maximum 50);

[0152] Substitute the above formula PDMAX = (150-25) / 50 = 2.5 (W) ;

[0153] It can be obtained that the maximum dissipation power of the device is 2.5 W when the device works at the highest junction temperature and the ambient temperature is 25℃.

[0154] When the protection circuit is in the maximum working current condition, the heat power of the power load switch is:

[0155] w = I 2 × R;

[0156] Wherein I = 1.35A;

[0157] R = 0.02Ω;

[0158] It can be calculated that W = 0.036 (W), indicating that the heat power is far less than the maximum dissipation power in the normal working condition. Considering the fault condition and the environmental temperature factor, an NTC temperature sensor is arranged on the surface of the load switch in the actual design, the temperature value is converted into a voltage signal for comparison, and the output is cut off when the working temperature exceeds the set value, so that the overheat protection is realized.

[0159] As Figure 2 shown, the utility model discloses a second embodiment, a kind of intrinsic safety protection method for explosion-proof system, based on the intrinsic safety protection circuit for explosion-proof system of first embodiment, the method comprises the following steps:

[0160] Step S1, the real-time current signal of protected device is collected and amplified processing;

[0161] Step S2, the amplified current signal is compared with threshold signal, whether the amplified current signal exceeds threshold signal is judged, if yes, then trigger overcurrent protection signal, and adjust the pulse width of overcurrent protection signal, if no, then jump to step S1;

[0162] Step S3, protection signal energy storage circuit is charged and until reach the level value required by protection signal;

[0163] Step S4, protection control circuit cuts off power output, and protection signal energy storage circuit discharges to protected device;

[0164] Step S5, whether protection signal energy storage circuit is discharged is judged, if yes, then protection control circuit is closed, and power input is restored, if no, then jump to step S4.

[0165] Although the above-mentioned embodiments are described in the above-mentioned order, it can be understood by those skilled in the art that, in order to achieve the effect of the embodiments, the different steps do not have to be executed in such an order, and can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are within the protection scope of the present application.

[0166] In the description of the present application, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other terms indicating the direction or positional relationship are based on the direction or positional relationship shown in the drawings, which is merely for the convenience of description, and does not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0167] In addition, it also needs to be explained that, in the description of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. Those skilled in the art can understand the specific meaning of the above-mentioned terms in the present application according to the specific circumstances.

[0168] The term "comprising" or any other similar word is intended to cover non-exclusive inclusion, so that the process, method, article or equipment / device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes the elements inherent to the process, method, article or equipment / device.

[0169] So far, the technical scheme of the present application has been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without deviating from the principles of the present application, and the technical scheme after the changes or replacements will fall within the protection scope of the present application.

Claims

1. An intrinsically safe protection circuit for an explosion-proof system, characterized by, The current real-time signal sampling circuit, the current signal amplification comparison circuit, the first-stage regulating circuit, the second-stage regulating circuit and the protection control circuit are connected in series. The input end of the current real-time signal sampling circuit is connected with the input of the power supply and the protected device, the output end of the current real-time signal sampling circuit is connected with the input end of the current signal amplification comparison circuit, the output end of the current signal amplification comparison circuit is connected with the input end of the first-stage regulating circuit, the output end of the first-stage regulating circuit is connected with the input end of the second-stage regulating circuit, the output end of the second-stage regulating circuit is connected with the input end of the protection control circuit, and the output end of the protection control circuit is connected with the protected device.

2. An intrinsically safe protection circuit for an explosion-proof system according to claim 1, characterized in that, The input end of the current signal amplification comparison circuit is also connected with the current protection threshold signal adjustment circuit, and the current protection threshold signal adjustment circuit is used for outputting a threshold signal.

3. An intrinsically safe protection circuit for an explosion-proof system according to claim 1, characterized in that, The second-stage regulating circuit is internally provided with a protection signal energy storage circuit.

4. An intrinsically safe protection circuit for an explosion-proof system according to claim 3, characterized in that, The input end of the second-stage regulating circuit is also connected with an overvoltage protection detection circuit, when the overvoltage protection detection circuit detects an overvoltage signal, the discharge speed of the protection signal energy storage circuit is controlled by regulating the pulse width of the overvoltage signal.

5. An intrinsically safe protection circuit for an explosion-proof system according to claim 1, characterized in that, A temperature sensor is mounted on the surface of the protection control circuit, the temperature sensor is used for acquiring a real-time temperature, the maximum dissipation power is calculated based on the real-time temperature, when the maximum dissipation power is greater than the heat power of the protection control circuit, the input of the power supply is cut off through a temperature monitoring circuit connected with the protection control circuit.

6. An intrinsically safe protection circuit for an explosion-proof system according to claim 2, characterized in that, The current protection threshold signal adjustment circuit comprises a resistor R30, a resistor R29 and a capacitor C16. One end of the resistor R30 is connected with a voltage network after voltage stabilization of a voltage stabilization circuit, the other end of the resistor R30 is connected with the resistor R29, and the other end of the resistor R29 is connected with the current signal amplification comparison circuit. The capacitor C16 is connected with the resistor R29 at both ends. According to the required threshold signal, the proportion of the resistance values of the resistor R30 and the resistor R29 is adjusted, so that the threshold signal is output after the current passes through the resistor R30 and the resistor R29.

7. An intrinsically safe protection circuit for an explosion-proof system according to claim 1, characterized in that, The first-stage regulating circuit comprises a capacitor C9, a resistor R20 and a diode D4. Both ends of the capacitor C9 are connected with the output of the current signal amplification comparison circuit, one end of the capacitor C9 is connected with one end of the resistor R20, the other end of the resistor R20 is connected with the negative electrode end of the diode D4, the first positive electrode end of the diode D4 is connected between one end of the capacitor C9 and one end of the resistor R20, and the second positive electrode end of the diode D4 is grounded.

8. An intrinsically safe protection circuit for an explosion-proof system according to claim 4, characterized in that, The second-stage regulating circuit comprises a diode D3, a resistor R18 and a capacitor C8. The positive electrode end of the diode D3 is connected with the output of the current signal amplification comparison circuit, the negative electrode end of the diode D3 is connected with one end of the resistor R18 and a first node P1, the first node P1 is connected with one end of the capacitor C8 and the gate of a load switch in the protection control circuit respectively, the other end of the resistor R18 is connected with the other end of the capacitor C8, and the other end of the capacitor C8 is connected with a power supply ground of the first set threshold.

9. An intrinsically safe protection circuit for an explosion-proof system according to claim 8, characterized in that, The overvoltage protection detection circuit comprises a transistor Q2, a voltage stabilizing tube Z2, a resistor R16 and a resistor R17; The first pin of the transistor Q2 is connected with the negative electrode of a diode D3, the second pin of the transistor Q2 is connected with the power supply ground of the second set threshold, the third pin of the transistor Q2 is connected with one end of the resistor R16, and the other end of the resistor R16 is connected with the power supply ground of the second set threshold; One end of the voltage stabilizing tube Z2 is connected between the third pin of the transistor Q2 and one end of the resistor R16, the other end of the voltage stabilizing tube Z2 is connected with one end of the resistor R17, and the other end of the resistor R17 is grounded.

10. The intrinsic safety protection circuit for an explosion-proof system according to claim 1, wherein The protection control circuit comprises a voltage stabilizing tube Z4, a load switch Q4 and a feedback resistor FB2; One end of the voltage stabilizing tube Z4 is connected with the gate of the load switch Q4, the other end of the voltage stabilizing tube Z4 is connected with a second node P2, and the second node P2 is connected with the resistor R31 and the resistor R32 respectively; The drain of the load switch Q4 is connected with one end of the feedback resistor FB2 and the output voltage of 12V, the source of the load switch Q4 is connected with a third node P3, and the third node P3 is connected with the other end of the feedback resistor FB2 and the second node P2.

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