A circuit for increasing the capability of intrinsically safe power supplies

Abstract

This invention belongs to the field of integrated circuit design technology, specifically relating to a circuit that can improve the capability of intrinsically safe power supplies. This circuit connects a common-mode power inductor in series in the positive and negative paths of the intrinsically safe power supply. Through wiring, the currents in the positive and negative paths flow in the same direction through the two windings of the common-mode power inductor, forming a common-mode current relative to the inductor. This invention utilizes the mutual inductance flux superposition effect of the common-mode power inductor on the common-mode current, significantly improving the equivalent inductive reactance, effectively suppressing the current rise rate during output short circuits, and absorbing short-circuit energy through eddy current losses and hysteresis losses, providing sufficient time margin for the switching transistor to turn off. Without significantly increasing circuit size and cost, it improves the rated output current and output power of the intrinsically safe power supply, while enhancing its operational reliability and reducing the unit power cost, thus facilitating the widespread application of intrinsically safe power supplies in high-power explosion-proof scenarios.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit design technology, and specifically relates to a circuit that can improve the intrinsically safe power supply capability. Background Technology

[0002] Intrinsically safe power supplies (hereinafter referred to as "intrinsically safe power supplies") are power supply equipment specifically designed for flammable and explosive hazardous environments such as coal mines, chemical plants, and gas stations. Their core safety feature lies in the fact that even under fault conditions such as output short circuits or poor contact, the energy of the generated spark is lower than the critical value for igniting surrounding hazardous gases, thus preventing explosions. Therefore, intrinsically safe power supplies do not require additional explosion-proof treatment at the output end and can be directly applied to hazardous areas, offering significant safety and cost advantages and a wide range of applications.

[0003] According to the standard GB / T 3836-2021 Explosive Atmospheres, intrinsically safe power supplies must employ a dual design for their protection circuits. For example, both overvoltage and overcurrent protection must have two independent protection stages to ensure that safety protection functions are maintained even in the event of a single-point fault. The ultimate safety of intrinsically safe power supplies is verified through a spark test. This involves connecting the output to a spark test device under maximum output voltage and current conditions and conducting a specified number of short-circuit spark tests in an explosive gas atmosphere. If the gas is not ignited, the power supply is considered intrinsically safe.

[0004] In practical circuits, when a short circuit occurs at the output, the current rises rapidly. The protection circuit detects the abnormal current through a sampling circuit and drives the switching transistor to turn off the output. However, the turn-off speed of the switching transistor and its driving circuit is limited by the inherent physical characteristics of the devices and is difficult to significantly improve. Meanwhile, the rise rate of the short-circuit current is extremely fast, often reaching dangerous levels before the switching transistor has fully turned off. Therefore, existing intrinsically safe power supplies are often forced to set their normal operating current and voltage at lower levels to ensure that the peak current does not exceed the limit during a fault. This is the fundamental reason limiting the improvement of the output power of intrinsically safe power supplies.

[0005] Currently, in existing technologies, such as Figure 1 As shown, this is the basic structure of an intrinsically safe power supply. AC / DC or DC / DC converters transform external AC / DC power into DC power. Voltage and current control circuits control the voltage and current within a suitable range according to actual needs. Figure 2 It is an intrinsically safe power supply powered by a battery. The intrinsically safe protection circuit is the key core part of the intrinsically safe output. The sampling circuit, control circuit, and switch of this part of the circuit are all dual circuits to ensure the reliability of the circuit.

[0006] Figure 3This is one of the basic types of intrinsically safe protection circuits. The voltage and current sampling control and drive circuits, as well as the switches, are all doubled in configuration. The diodes in the diagram isolate faults in case of circuit malfunctions. The switches are generally transistors, including thyristors, triodes, and field-effect transistors. Under normal conditions, the voltage and current do not exceed the specified values, and the switches on both sides are in a conducting state. If the voltage or current exceeds the specified values, any one of the four sampling control circuits detects the abnormality and drives the switch to disconnect the output, preventing danger.

[0007] Figure 4 Another method utilizing series inductors is shown in the diagram, employing two inductors. In practice, a single inductor can also be used, typically at positions L1 and L2. Inductors provide inductive reactance to changing currents but have no effect on constant current. During a short circuit, the current rise rate is somewhat suppressed, thus improving the power supply's output reliability. However, due to limitations in practical applications, increasing the output current requires inductors with very low DC resistance and sufficiently large inductance for a significant improvement. Furthermore, these inductors are expensive and bulky, making them impractical. In practice, using a smaller inductance in series only improves reliability without substantially improving output capability.

[0008] Figure 5 This is another type of intrinsically safe power supply, and also the simplest with relatively lower output power. It is often used in instruments, indicators, and low-power audible warnings. Its maximum current is obtained from Ohm's law I=U / R, which is the intrinsically safe current (the maximum value, which should not be exceeded in practice). Once tested and confirmed to be safe, it can be used normally. The power supply on its input side is often a battery or a DC regulated power supply. The overvoltage protection circuit still has a dual protection circuit, and the fuse is generally a one-time fuse. It will blow when the output short circuit cannot be quickly restored, thus ensuring that the output will not accumulate energy due to prolonged short circuit and reach a dangerous temperature.

[0009] In summary, existing intrinsically safe power supplies have limited output power per unit. High-power applications require multiple independent intrinsically safe power supplies connected in parallel, which results in high cost and large space requirements, severely limiting the widespread application of intrinsically safe power supplies. Therefore, there is an urgent need for a circuit that can improve the intrinsic safety capabilities of power supplies. Summary of the Invention

[0010] In view of the above situation, the purpose of this invention is to form a common-mode signal by changing the current direction of one of the positive and negative paths. When the common-mode signal enters the common-mode power inductor, the inductive reactance it receives increases exponentially, and its energy is absorbed and converted into heat energy through eddy current and hysteresis losses. As a result, the current rise rate is significantly lower than that of the method of connecting in series with an ordinary inductor, thereby increasing the current value during normal operation, increasing the output power of the intrinsically safe power supply, and enhancing the reliability of the intrinsically safe power supply.

[0011] Therefore, the present invention adopts the following technical solution: A circuit that can improve the intrinsically safe power supply capability includes a power input port, a dual voltage sampling control and drive circuit, a dual current sampling control and drive circuit, a positive switch transistor, a negative switch transistor, and a current sampling resistor. The power input port is connected to the intrinsically safe output port via a positive path and a negative path. The dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit respectively acquire the voltage and current signals of the positive path and the negative path and control the switching on and off of the positive and negative switch transistors. A common-mode power inductor is connected in series in the positive path and the negative path. The common-mode power inductor includes two windings. The current in the positive path and the current in the negative path flow in the same direction through the two windings of the common-mode power inductor, so that the current in the positive path and the negative path form a common-mode current relative to the common-mode power inductor.

[0012] Preferably, the common-mode power inductor is connected in series between the positive switch, the negative switch, and the power input port.

[0013] Preferably, the common-mode power inductor is connected in series between the positive switch, the negative switch, and the intrinsically safe output port.

[0014] Preferably, both the positive and negative switching transistors are transistors, including field-effect transistors, triodes, or thyristors.

[0015] Preferably, the dual voltage sampling control and drive circuit includes two independent voltage sampling control and drive circuits, and the dual current sampling control and drive circuit includes two independent current sampling control and drive circuits. The dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit together constitute a dual overvoltage and overcurrent protection structure for intrinsically safe power supplies.

[0016] Preferably, the current sampling resistor is connected in series in the negative path, and the dual current sampling control and drive circuit acquires the voltage signal across the current sampling resistor to achieve current detection.

[0017] Preferably, the equivalent inductance of the common-mode power inductor to the common-mode current is significantly greater than its nominal differential-mode inductance, and its core material is ferrite or amorphous nanocrystalline material.

[0018] Preferably, the intrinsically safe power supply is a DC output intrinsically safe power supply, and its front-end power input is an AC / DC conversion circuit, a DC / DC conversion circuit, or a battery-powered circuit.

[0019] This invention also includes other components that enable the circuit to function properly, thereby improving the intrinsic safety of the power supply; all of these are conventional techniques in the art. Furthermore, any devices or components not specified in this invention employ conventional techniques in the art.

[0020] The working principle of this invention is: Under normal output conditions, the positive output current and the negative output current are equal in magnitude and opposite in direction. However, since the two currents are connected to the same common-mode power inductor in a specific way in this invention, the magnetic flux generated in the core is in the same direction, forming a common-mode signal. At this time, the inductor has no obstruction effect on the stable DC current and does not affect the normal output.

[0021] When a short-circuit fault occurs in the output circuit, the current rises sharply, and this changing current forms a changing common-mode current in the common-mode power inductor. Based on the mutual inductance effect and the principle of magnetic flux superposition, the common-mode power inductor exhibits an equivalent inductive reactance to this changing common-mode current that is much greater than its nominal inductance. At the same time, the sudden energy is absorbed and converted into heat energy through the eddy current loss and hysteresis loss of the magnetic core, thereby significantly suppressing the current rise rate.

[0022] Therefore, after a fault occurs, the two switching transistors have ample turn-off time, allowing them to complete the turn-off action before the current rises to the dangerous threshold, ensuring safety. Simultaneously, because the current rise rate is effectively suppressed, the intrinsically safe power supply can be set to a higher normal operating current value without reducing the safety margin, thereby increasing the output power.

[0023] The beneficial effects of this invention are: (1) Significantly improve output power capability: By effectively suppressing the rise rate of short-circuit current through the common-mode power inductor, the intrinsically safe power supply can improve the normal operating current setting value while maintaining the safety margin, thereby significantly improving the output power of a single intrinsically safe power supply.

[0024] (2) Enhanced system reliability: The common-mode power inductor’s suppression of sudden current provides sufficient time margin for the switching transistor to turn off, reducing the risk of spark energy exceeding limits due to turn-off delay, and improving the overall safety and stability of the power supply.

[0025] (3) Reduce device selection and manufacturing costs: Since the current rise rate is effectively controlled, the switching speed requirement of the switching transistor is reduced, and conventional devices can be used to replace high-speed and high-cost devices, thereby reducing manufacturing costs.

[0026] (4) Reduce size and improve integration: Compared with the scheme of multiple intrinsically safe power supplies in parallel, the present invention only needs to add a common mode power inductor to improve the output capability, occupy less space, and is conducive to the miniaturization of equipment.

[0027] (5) Wide range of applications: This invention can be widely applied to various intrinsically safe power supplies with DC or AC input, and is especially suitable for explosion-proof electrical equipment with large power requirements and limited space, such as intrinsically safe lighting fixtures, instruments and meters, etc., which have good social and economic benefits. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 This is a basic block diagram of an existing intrinsically safe power supply.

[0030] Figure 2 A basic block diagram of an intrinsically safe power supply powered by existing batteries.

[0031] Figure 3 This is the circuit diagram of a basic intrinsically safe protection circuit.

[0032] Figure 4 This is the circuit diagram of an existing series inductor-type intrinsically safe protection circuit.

[0033] Figure 5 The circuit diagram is for the existing simplified power supply in this case.

[0034] Figure 6 This is a circuit schematic diagram of an embodiment 1 of the present invention that can improve the intrinsically safe power supply capability.

[0035] Figure 7 This is a circuit schematic diagram of an embodiment 2 of the present invention that can improve the intrinsically safe power supply capability. Detailed Implementation

[0036] The present invention will now be clearly described with reference to specific embodiments. These descriptions are merely illustrative and are not intended to limit the scope of the invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art based on the embodiments of the present invention without inventive effort to obtain all other embodiments should be included within the scope of protection of the present invention.

[0037] Example 1 like Figure 6As shown, this embodiment of the invention provides a circuit that can improve the intrinsically safe power supply capability, including a power input port, a dual voltage sampling control and drive circuit, a dual current sampling control and drive circuit, a positive switch, a negative switch, and a current sampling resistor. The power input port is connected to the intrinsically safe output port via a positive path and a negative path. The dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit respectively collect the voltage and current signals of the positive and negative paths and control the switching on and off of the positive and negative switches. A common-mode power inductor is connected in series in the positive and negative paths. The common-mode power inductor includes two windings. The current in the positive path and the current in the negative path flow in the same direction through the two windings of the common-mode power inductor, so that the current in the positive and negative paths forms a common-mode current relative to the common-mode power inductor. Both the positive and negative switches are transistors. The current sampling resistor is connected in series in the negative path. The dual current sampling control and drive circuit collects the voltage signal across the current sampling resistor to realize current detection.

[0038] It should be further explained that the dual voltage sampling control and drive circuit includes two independent voltage sampling control and drive circuits, and the dual current sampling control and drive circuit includes two independent current sampling control and drive circuits. Together, the dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit constitute the dual overvoltage and overcurrent protection structure of the intrinsically safe power supply. The common-mode power inductor is connected in series between the positive and negative switching transistors and the power input port, and simultaneously connected in series between the positive and negative switching transistors and the intrinsically safe output port. The equivalent inductance of the common-mode power inductor to the common-mode current is significantly greater than its nominal differential-mode inductance, and its core material is ferrite.

[0039] In addition, intrinsically safe power supplies are DC output intrinsically safe power supplies, and their front-end power input is an AC / DC conversion circuit.

[0040] The working principle of this invention is: Under normal output conditions, the positive output current and the negative output current are equal in magnitude and opposite in direction. However, since the two currents are connected to the same common-mode power inductor in a specific way in this invention, the magnetic flux generated in the core is in the same direction, forming a common-mode signal. At this time, the inductor has no obstruction effect on the stable DC current and does not affect the normal output.

[0041] When a short-circuit fault occurs in the output circuit, the current rises sharply, and this changing current forms a changing common-mode current in the common-mode power inductor. Based on the mutual inductance effect and the principle of magnetic flux superposition, the common-mode power inductor exhibits an equivalent inductive reactance to this changing common-mode current that is much greater than its nominal inductance. At the same time, the sudden energy is absorbed and converted into heat energy through the eddy current loss and hysteresis loss of the magnetic core, thereby significantly suppressing the current rise rate.

[0042] Therefore, after a fault occurs, the two switching transistors have ample turn-off time, allowing them to complete the turn-off action before the current rises to the dangerous threshold, ensuring safety. Simultaneously, because the current rise rate is effectively suppressed, the intrinsically safe power supply can be set to a higher normal operating current value without reducing the safety margin, thereby increasing the output power.

[0043] Example 2 like Figure 7 The diagram shows an example of a 15V intrinsically safe power supply. The 15V input voltage is supplied by a regulated power supply, and voltage sampling is achieved by Z1, Z2, R1, and R2. The negative terminals of the two Zener diodes Z1 and Z2 are connected to the 15V positive terminal through resistors R1 and R2. The values ​​of these two resistors need to be adjusted online until the required voltage triggers Z1 and Z2 to break down. After breakdown, diode D8 and resistor R5, and diode D5 and resistor R26 respectively drive transistors Q7 and Q6 to conduct. The collectors of Q6 and Q7 are connected to pins 2 and 4 of chips U1 and U2, respectively. As the two transistors (Q6 and Q7) conduct, the level at pins 2 and 4 changes from high to low, triggering the output pin 3 of the flip-flop to flip from low to high and delay for a certain time. This high level is connected to diodes D1 and D2 through diodes D3 and D4. The negative terminal of D1 is connected to the base of transistor Q2 and directly drives Q2 to conduct. After conduction, the collector voltage of transistor Q1 becomes 0V. Its collector is connected to the 15V power supply through resistors R6 and R5, forming a voltage divider circuit. The base of transistor Q3 is connected to this voltage divider circuit, and the voltage changes from 15V to 7.5V (R5 and R6 have equal values, and each resistor receives half of the voltage, i.e., 7.5V). At this time, the base voltage of transistor Q3 is lower than the emitter voltage, so it conducts. Its collector is connected to the gate of MOS switch Q5. Because the collector and emitter of Q3 are conducting, the 15V power supply is directly connected to the gate of Q5, causing Q5 to turn off, thus disconnecting the positive output of 15V. The cathode of diode D2 is connected to the base of transistor Q1. When D2 sends a high level to Q1, Q1 conducts, and its collector is connected to the gate of MOS switch Q4. After Q1 conducts, the gate voltage of Q4 is directly converted to 0V, causing Q4 to turn off. At this time, the negative output of the power supply is also disconnected, thus achieving overvoltage protection.

[0044] When a short circuit occurs and the current exceeds the required level, the current outputs -Vout from the negative terminal, passes through MOS switch Q4 and resistor Rs, and returns to the negative terminal of the 15V output side. However, a voltage exceeding the set value is generated on Rs. Rs is connected to resistors R28 and R29, which in turn are connected to the bases of transistors Q6 and Q7. This voltage exceeding the set value drives Q6 and R7 to conduct and enters the same process as when the voltage exceeds the set value. Finally, the two MOS switches Q5 and Q4 on the positive and negative terminals are turned off, stopping the external discharge and ensuring safety. After the delay time of the two delay circuits expires, the voltage levels at the above points are flipped, and MOS switches Q4 and Q5 are turned on. If normal output is achieved, the process is successful. If a voltage or current exceeding the set value occurs, the above process is repeated. When the current changes and the voltage drop across resistor Rs is sufficient to turn on transistors Q1 and Q2, Q1 turns on and turns off Q4. When Q2 turns on, it pulls down the base level of Q3, causing Q3 to turn on and turn off Q5, thus achieving the purpose of disconnection. This process occurs earlier than when Q4 and Q5 are turned off by the two delay circuits, and the delay circuits further ensure that Q4 and Q5 are completely turned off.

[0045] L1 is a common-mode power inductor, and the direction of the output current is as follows: Figure 7 The connection shown makes the current through L1 a common-mode current or a common-mode signal when the output passes through L1. This makes L1 more effective at suppressing changes in the current passing through it. When serious faults such as short circuits occur, the rise rate of the current is significantly suppressed and the energy is absorbed. The protection circuit has a very sufficient time margin to perform the shutdown action. This provides room for increasing the normal operating current and also plays a very important role in improving reliability.

[0046] The embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A circuit that can improve the intrinsically safe power supply capability, comprising a power input port, a dual voltage sampling control and drive circuit, a dual current sampling control and drive circuit, a positive switching transistor, a negative switching transistor, and a current sampling resistor, characterized in that: The power input port is connected to the intrinsically safe output port via a positive path and a negative path. The dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit respectively collect the voltage and current signals of the positive path and the negative path and control the on and off of the positive and negative switching transistors. A common-mode power inductor is connected in series in the positive path and the negative path. The common-mode power inductor includes two windings. The current in the positive path and the current in the negative path flow in the same direction through the two windings of the common-mode power inductor, so that the current in the positive path and the negative path form a common-mode current relative to the common-mode power inductor.

2. The circuit according to claim 1 that can improve the intrinsic safety power supply capability, characterized in that: The common-mode power inductor is connected in series between the positive switch, the negative switch, and the power input port.

3. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: The common-mode power inductor is connected in series between the positive switch, the negative switch, and the intrinsically safe output port.

4. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: Both the positive and negative switching transistors are transistors, including field-effect transistors, triodes, or thyristors.

5. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: The dual voltage sampling control and drive circuit includes two independent voltage sampling control and drive circuits, and the dual current sampling control and drive circuit includes two independent current sampling control and drive circuits. The dual voltage sampling control and drive circuit and the dual current sampling control and drive circuit together constitute a dual overvoltage and overcurrent protection structure for intrinsically safe power supplies.

6. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: The current sampling resistor is connected in series in the negative terminal path, and the dual current sampling control and drive circuit collects the voltage signal across the current sampling resistor to achieve current detection.

7. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: The equivalent inductance of the common-mode power inductor to the common-mode current is significantly greater than its nominal differential-mode inductance, and its core material is ferrite or amorphous nanocrystalline material.

8. The circuit according to claim 1 that can improve the intrinsically safe power supply capability, characterized in that: The intrinsically safe power supply is a DC output type intrinsically safe power supply, and its front-end power input is an AC / DC conversion circuit, a DC / DC conversion circuit, or a battery-powered circuit.

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