A method and circuit for over-temperature protection of a power switch

Abstract

The present invention discloses an over-temperature protection method and circuit for a power switch, which are applied to a power switch including a power tube, a controller and a power tube temperature monitor. When the temperature of the power tube is greater than a first temperature threshold and a comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode; wherein the comparison voltage is generated after the controller receives a monitoring current output from the power tube temperature monitor, and the monitoring current represents the temperature of the power tube, thereby further improving the accuracy of the over-temperature protection of the power switch.

Description

Technical Field

[0001] The present application relates to the technical field of switching power supplies, and more specifically, to an over-temperature protection method and circuit for a power switch. Background Art

[0002] A power switch refers to a transistor that can withstand large currents, has small leakage currents, and has good saturation conduction and cutoff characteristics under certain conditions. It generally includes a power tube and a controller part. In the application field of weapons and equipment represented by aviation, it is a key component for controlling circuits such as motors, relays, and lighting. It plays a vital role in the reliability of different subsystems such as flight control systems, power systems, and lighting systems of aviation equipment.

[0003] Traditionally, in order to ensure the stability of the power switch under high current conditions, the temperature change of the power tube is sensed through the negative temperature characteristics of the transistor BE junction. This method does not directly monitor the current of the power tube in the power switch, so it cannot accurately monitor the temperature change of the power switch, which challenges the stability of the power switch. Summary of the invention

[0004] The present invention provides an over-temperature protection method for a power switch, which is used to solve the technical problem that the temperature change of the power switch cannot be accurately monitored in the prior art. The method is applied to a power switch including a power tube, a controller and a power tube temperature monitor.

[0005] When the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode;

[0006] The comparison voltage is generated after the controller receives a monitoring current output from the power tube temperature monitor, and the monitoring current represents the temperature of the power tube.

[0007] Preferably,

[0008] When the temperature of the power tube is greater than the first temperature threshold, generating the monitoring current;

[0009] generating the comparison voltage according to the monitoring current;

[0010] When the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode.

[0011] Preferably,

[0012] When the controller temperature is greater than a second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the controller, so that the power switch enters a temperature protection mode.

[0013] Preferably, the comparison voltage is obtained, and the specific process includes:

[0014] When the temperature of the power tube is greater than the first temperature threshold, outputting the monitoring current;

[0015] generating a mirror current according to the monitoring current;

[0016] The comparison voltage is obtained according to the mirror current.

[0017] Preferably, the mirror current is generated, and the specific process includes:

[0018] Generate a first mirror current based on a result of mirror amplifying the monitoring current;

[0019] Obtaining a second mirror current according to the first mirror current;

[0020] The second mirror current is determined as the mirror current.

[0021] Accordingly, the present invention also proposes an over-temperature protection circuit for a power switch, comprising a power tube, a controller and a resistor, and further comprising:

[0022] A first monitor, configured to output a monitoring current representing the temperature of the power tube to the controller according to a temperature change of the power tube; and

[0023] The voltage sensing node is connected to the second monitor and is used for generating a comparison voltage by sensing by the second monitor when the monitoring current amplified by the received mirror image passes through the resistor.

[0024] Preferably,

[0025] The first monitor includes an input terminal and an output terminal;

[0026] Wherein, the input end is connected to the source of the power tube, and the output end is connected to the controller.

[0027] Preferably,

[0028] The second monitor is used to output a high-level logic signal when the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than a threshold voltage, so that the power tube obtains a cut-off logic signal.

[0029] Preferably,

[0030] When the controller temperature is greater than the second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to enable the controller to obtain a cut-off logic signal.

[0031] Preferably, it also includes a first current mirror and a second current mirror,

[0032] The first current mirror is used to mirror-amplify the received monitoring current and output a first mirror current; and

[0033] The second current mirror is used to output a second mirror current according to the received first mirror current.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention discloses an over-temperature protection method and circuit for a power switch, which are applied to a power switch including a power tube, a controller and a power tube temperature monitor. When the temperature of the power tube is greater than a first temperature threshold and a comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode; wherein the comparison voltage is generated after the controller receives a monitoring current output from the power tube temperature monitor, and the monitoring current represents the temperature of the power tube, thereby further improving the accuracy of the over-temperature protection of the power switch and improving the stability of the power switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 A schematic flow chart of an over-temperature protection method for a power switch proposed in an embodiment of the present invention is shown;

[0038] Figure 2 A schematic diagram showing the principle of an over-temperature protection method for a power switch proposed in an embodiment of the present invention;

[0039] Figure 3 A schematic diagram showing the connection position of the first monitor is shown;

[0040] Figure 4 A schematic structural diagram of an over-temperature protection circuit of a power switch provided by an embodiment of the present invention is shown;

[0041] Figure 5 A schematic diagram showing the position of the temperature sampling diode in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] As described in the background art, in the prior art, the temperature change of the power tube is sensed through the negative temperature characteristic of the transistor BE junction. This method does not directly monitor the current of the power tube in the power switch, and therefore cannot accurately monitor the temperature change of the power switch.

[0044] To solve the above problems, the present application provides an over-temperature protection method for a power switch, which is applied to a power switch including a power tube, a controller and a power tube temperature monitor. Figure 1 The figure is a flow chart of an over-temperature protection method for a power switch proposed in an embodiment of the present application, comprising the following steps:

[0045] Step S101: when the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal for turning off the power tube is output, so that the power switch enters a temperature protection mode;

[0046] The comparison voltage is generated after the controller receives a monitoring current output from the power tube temperature monitor, and the monitoring current represents the temperature of the power tube.

[0047] Specifically, when the working current of the power tube is too large, overheating is likely to occur and the impact on the power tube is great. If the temperature change caused by the increase in current cannot be monitored in a timely and accurate manner, the stability and reliability of the power switch will be affected. Therefore, in the power switch, a power tube monitor connected to the power tube is used to monitor the current change of the power tube. When the temperature of the power tube is greater than the first temperature threshold, a monitoring current representing the temperature change of the power tube is output, and the monitoring current is converted into a comparison voltage for comparison with the threshold voltage. When the comparison voltage is greater than the threshold voltage, a high-level logic signal that cuts off the power tube is output, so that the power switch enters the temperature protection mode to avoid damage to the power tube due to inaccurate temperature monitoring or temperature monitoring delay, thereby affecting the stability of the entire system.

[0048] In order to improve the stability and reliability of the power switch, in a preferred embodiment of the present application, when the temperature of the power tube is greater than the first temperature threshold, the monitoring current is generated;

[0049] generating the comparison voltage according to the monitoring current;

[0050] When the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode.

[0051] Specifically, for power switches that bear large currents, it is very easy to overheat due to the increase in current, which can damage the power tube and seriously affect the normal use of the power switch. Therefore, it is necessary to accurately monitor the temperature of the power tube, that is, to convert the monitoring current that represents the temperature of the power tube into a comparison voltage. When the comparison voltage is greater than the threshold voltage, a high-level logic signal that turns off the power tube is output, so that the power switch enters the temperature protection mode.

[0052] It should be noted that the scheme of the above preferred embodiment is only a specific implementation scheme proposed in the present application. Those skilled in the art can flexibly select different methods of monitoring the temperature of the power tube according to actual conditions. For example, the temperature can be detected by using a polycrystalline silicon diode according to the principle that the forward voltage drop of a polycrystalline diode changes with temperature. The temperature can also be detected by using the principle that the reverse leakage current of a diode (or a transistor with the emitter and the base short-circuited) increases significantly with increasing temperature. The voltage that characterizes the temperature of the power tube can also be monitored, and a comparison voltage can be obtained by monitoring the voltage.

[0053] In order to further improve the stability and reliability of the power switch, in a preferred embodiment of the present application, when the controller temperature is greater than a second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the controller so that the power switch enters a temperature protection mode.

[0054] Specifically, the power switch includes two major parts: a power tube and a controller. When the temperature of the controller is too high, it will also affect the stability and reliability of the power switch. Therefore, when the temperature of the controller rises, its internal threshold voltage decreases with the increase in temperature. When the threshold voltage drops below the comparison voltage, that is, the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the controller, so that the power switch enters the temperature protection mode.

[0055] In order to obtain an accurate comparison voltage, in a preferred embodiment of the present application, the comparison voltage is obtained, and the specific process includes:

[0056] When the temperature of the power tube is greater than the first temperature threshold, outputting the monitoring current;

[0057] generating a mirror current according to the monitoring current;

[0058] The comparison voltage is obtained according to the mirror current.

[0059] Specifically, since the generated monitoring current is relatively small, if the monitoring current is not amplified, the generated comparison voltage will be small, and it is difficult to meet the situation where the comparison voltage is greater than the threshold voltage, that is, when the power tube temperature is greater than the first temperature threshold, its comparison voltage is still less than the threshold voltage. In order to make the generated comparison voltage meet the requirements of over-temperature protection under the monitoring current of nA level, an amplified mirror current is generated according to the monitoring current, and the comparison voltage is obtained according to the generated mirror current.

[0060] It should be noted that the scheme of the above preferred embodiment is only a specific implementation scheme proposed in this application. Those skilled in the art can flexibly choose different mirror current generation methods. The method of amplifying the monitoring current and generating a comparison voltage through the resistor in the controller and the method of using an external circuit to generate a comparison voltage according to the mirror current all fall within the protection scope of this application.

[0061] In order to generate an accurate mirror current, in a preferred embodiment of the present application, the mirror current is generated, and the specific process includes:

[0062] Generate a first mirror current based on a result of mirror amplifying the monitoring current;

[0063] Obtaining a second mirror current according to the first mirror current;

[0064] The second mirror current is determined as the mirror current.

[0065] Specifically, before generating the comparison voltage, it is necessary to obtain an amplified mirror current. Based on the received monitoring current, a first mirror current is generated to amplify the monitoring current. However, the output direction of the first mirror current after one mirroring cannot meet the needs of subsequent circuits. Therefore, a second mirror current with the correct output direction is obtained based on the generated first mirror current.

[0066] It should be noted that the above preferred embodiment is only a specific implementation scheme proposed in this application. Those skilled in the art can flexibly select different current amplification ratios to generate mirror current, which does not affect the protection scope of this application.

[0067] By applying the above technical solution, when the power tube temperature is greater than the first temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters the temperature protection mode; wherein the comparison voltage is generated after the controller receives the monitoring current output from the power tube temperature monitor, and the monitoring current represents the power tube temperature, thereby monitoring the power switch temperature by directly sensing the change of the power tube current, thereby improving the accuracy of controlling the temperature change of the power switch, and at the same time combining the power switch temperature monitoring with the controller temperature monitoring, further improving the stability and reliability of the power switch.

[0068] In order to further explain the technical idea of ​​the present invention, the technical solution of the present invention is now described in combination with specific application scenarios.

[0069] The prior art senses the temperature change of the power tube through the negative temperature characteristic of the BE junction of the transistor, that is, the current of the power tube in the power switch is not directly monitored.

[0070] The circuit of the embodiment of the present application is designed with a power tube temperature monitor connected to the power tube, i.e., a first monitor, and generates a monitoring current representing the temperature change of the power tube according to the temperature change of the power tube, i.e., directly monitoring the current change of the power tube in the power switch, thereby achieving the purpose of accurate monitoring and further improving the stability of the power switch and the accuracy of temperature monitoring.

[0071] The embodiment of the present invention provides a method for over-temperature protection of a power switch, such as Figure 2 The schematic diagram of the over-temperature protection method of the power switch is shown, which includes the following steps:

[0072] Step 1: when the temperature of the power tube is greater than a first temperature threshold, outputting a monitoring current;

[0073] Step 2, amplifying the monitoring current to obtain a first mirror current;

[0074] Step three, obtaining a second mirror current according to the first mirror current;

[0075] Step 4, obtaining a comparison voltage according to the mirror current;

[0076] Step 5: when the comparison voltage is greater than the threshold voltage, output a high-level logic signal to turn off the power tube; or when the controller temperature is greater than the second temperature threshold and the comparison voltage is greater than the threshold voltage, output a high-level logic signal to turn off the controller;

[0077] Step six, the power switch enters the temperature protection mode.

[0078] like Figure 4As shown, the first monitor outputs a monitoring current representing the temperature of the power tube; the controller generates a comparison voltage by receiving the monitoring current; the second monitor in the controller compares the comparison voltage with its threshold voltage, so that the power switch outputs a logic signal to control the power tube or controller to be cut off, so that the power switch enters the over-temperature protection mode, thereby improving the stability and reliability of the power switch.

[0079] The temperature sensor is used to detect the working temperature of the power tube. When the temperature of the power tube exceeds the set temperature, the temperature protection action is taken. There are two common types of products in this category:

[0080] (1) Using the principle that the forward voltage drop of a polycrystalline diode changes with temperature, a polysilicon diode is used to detect temperature. Although it can detect temperature more accurately, it occupies a large chip area, requires an additional photomask, and has a more complicated process, so the cost is relatively high.

[0081] (2) The temperature is detected by using the principle that the reverse leakage current of a diode (or a transistor with the emitter and base short-circuited) increases significantly with increasing temperature.

[0082] The embodiment of the present application adopts the second method, in which a diode (or a transistor with the emitter and base short-circuited) is formed outside the active area of ​​the power tube. The diode is formed simultaneously with the power tube in terms of process, and no additional photolithography is required, which has cost advantages. At the same time, multiple diodes of this type can be prepared at different positions of the chip to detect the temperature at different chip positions, which can ensure the extensiveness and accuracy of the power tube temperature collection.

[0083] refer to Figure 3 The first monitor can be a diode D. The drain of the power tube M1 is connected to the cathode of the diode D and then to the power supply VBB. When the power tube M1 is turned on, its diode D will generate a leakage current with a positive temperature coefficient. The leakage current is used as the monitoring current of the power tube. The change of the monitoring current represents the current change of the power tube M1, which can accurately and timely reflect the temperature of the power tube M1. In addition, M1 is the main power tube and M2 is the sampling tube. Since the diode D is a parasitic diode in the power tube, it can be formed at the same time as the main power tube in the process, and no additional photolithography is required, such as Figure 5 The figure shows the position of the temperature sampling diode. There is a certain current ratio between M2 and M1. By sampling the current on M2, we can know the current on the main power tube M1. There is a certain leakage current on the diode D, which is positively correlated with the temperature of the power tube.

[0084] In order to realize the control of the power tube M1, that is, when the temperature of the power tube M1 is greater than the first temperature threshold, the power tube M1 can be cut off to prevent the occurrence of over-temperature, then the monitoring current outputted by it needs to be connected to the logic circuit receiving high and low levels. That is to say, the first monitor generating the monitoring current representing the temperature change of the power tube M1 needs to be connected to the controller to generate a logic level.

[0085] The purpose of the first monitor designed in the present disclosure is to detect the current size of the power tube M1 when it is working, and take protective action when the current exceeds the design value, turning off the power tube M1, thereby achieving the effect of protecting the power switch. However, in order to improve the efficiency of the power switch, the monitoring current generated is relatively small, reaching the nA level, but the comparison voltage directly generated by such a small current is also relatively small. When the comparison voltage is too small, that is, when the temperature of the power tube has reached the upper limit it can withstand, and the comparison voltage is still less than the threshold voltage, then no high-level logic signal is generated, and the power tube M1 cannot be turned off, so the over-temperature protection function cannot be achieved.

[0086] In order to solve the above problem, the output end of the first monitor, that is, the anode of the diode D, is connected to the input end of the current mirror group in the monitor, and the output end of the current mirror group is connected to the resistor R1 and the second monitor, such as Figure 4 As shown in the figure, the monitoring current output by the first monitor is amplified by the first current mirror composed of M3 and M4 to generate a first mirror current that is twice the original monitoring current. Since the output direction of the first mirror current cannot meet the needs of the subsequent circuit, the first mirror current is input into the second current mirror composed of M5 and M6 to generate a second mirror current, and then the second mirror current with the correct output direction is input into the resistor R1 and the second monitor in the controller, thereby generating a larger comparison voltage.

[0087] During normal operation, the current mirror and the power tube are connected in parallel. According to the circuit parallel principle, the current flowing through the current mirror and the power tube is inversely proportional to their resistance values, that is, the on-resistance of the current mirror is large, but the current flowing through it is small, while the resistance of the power tube is small and the current flowing through it is large. In this way, by detecting the small current of the current mirror, the large current of the power tube can be sensed. The ratio of the current flowing through the power tube to the current flowing through the current mirror is a relatively important quantity. A good design requires that this current ratio changes less with temperature, gate voltage and drain current.

[0088] like Figure 4As shown in the figure, when the temperature of the power switch rises, the parasitic diode leakage current temp in the power tube increases. The diode leakage current temp flows from M7 to resistors R1 and R2 through the current mirror image relationship, the base voltage of transistor Q1 increases, and the VBE junction of transistor Q1 has a negative temperature coefficient. When the temperature rises to a certain value, transistor Q1 is turned on, and the output signal otp (OverTenperature Protection) becomes a high level.

[0089] M8 introduces positive feedback. When overtemperature does not occur, otp is low, M8 is turned on and resistor R2 is short-circuited. When overtemperature protection occurs, otp is high, M8 is turned off, and resistor R2 is connected to the circuit to further increase the voltage at point A. Positive feedback will introduce a certain amount of hysteresis to avoid thermal oscillation near the overtemperature point.

[0090] Therefore, through the above process, temperature detection is completed by relying on two temperature variables with opposite temperature coefficients (monitoring current and VBE junction voltage), ensuring more accurate temperature sampling.

[0091] In order to achieve the above technical objectives, the embodiment of the present application also proposes an over-temperature protection circuit of a power switch, including a power tube, a controller and a resistor, and also includes:

[0092] A first monitor, configured to output a monitoring current representing the temperature of the power tube to the controller according to a temperature change of the power tube; and

[0093] The voltage sensing node is connected to the second monitor and is used for generating a comparison voltage by sensing by the second monitor when the monitoring current amplified by the received mirror image passes through the resistor.

[0094] In specific application scenarios,

[0095] The first monitor includes an input terminal and an output terminal;

[0096] Wherein, the input end is connected to the drain of the power tube, and the output end is connected to the controller.

[0097] In specific application scenarios,

[0098] The second monitor is used to output a high-level logic signal when the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than a threshold voltage, so that the power tube obtains a cut-off logic signal.

[0099] In specific application scenarios,

[0100] When the controller temperature is greater than the second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to enable the controller to obtain a cut-off logic signal.

[0101] In a specific application scenario, it also includes a first current mirror and a second current mirror.

[0102] a first current mirror, configured to mirror-amplify the received monitoring current and output a first mirror current; and

[0103] The second current mirror is used to output a second mirror current according to the received first mirror current.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for over-temperature protection of a power switch, applied to a power switch including a power tube, a controller and a power tube temperature monitor, characterized in that: When the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode; Wherein, the comparison voltage is generated after the controller receives the monitoring current output from the power tube temperature monitor, and the monitoring current represents the temperature of the power tube; When the controller temperature is greater than a second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the controller, so that the power switch enters a temperature protection mode.

2. The method according to claim 1, characterized in that When the temperature of the power tube is greater than the first temperature threshold, generating the monitoring current; generating the comparison voltage according to the monitoring current; When the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to cut off the power tube, so that the power switch enters a temperature protection mode.

3. The method according to claim 1, characterized in that: The comparison voltage is obtained, and the specific process includes: when the temperature of the power tube is greater than the first temperature threshold, outputting the monitoring current; generating a mirror current according to the monitoring current; The comparison voltage is obtained according to the mirror current.

4. The method according to claim 3, characterized in that The mirror current is generated, and the specific process includes: generating a first mirror current based on the result of mirror amplification of the monitoring current; A second mirror current is obtained according to the first mirror current; and the second mirror current is determined as the mirror current.

5. An over-temperature protection circuit for a power switch, comprising a power tube, a controller and a resistor, characterized in that: The over-temperature protection circuit uses the over-temperature protection method of the power switch according to any one of claims 1 to 4, and the over-temperature protection circuit further includes a first monitor, which is used to output a monitoring current representing the temperature of the power tube to the controller according to the temperature change of the power tube; as well as A voltage sensing node connected to a second monitor, and configured to generate a comparison voltage by sensing the second monitor when the monitoring current amplified by the received mirror image passes through the resistor; Wherein, the second monitor is used to output a high-level logic signal when the temperature of the power tube is greater than a first temperature threshold and the comparison voltage is greater than a threshold voltage, so that the power tube obtains a cut-off logic signal.

6. The over-temperature protection circuit of a power switch according to claim 5, characterized in that: The first monitor includes an input terminal and an output terminal; Wherein, the input end is connected to the source of the power tube, and the output end is connected to the controller.

7. The over-temperature protection circuit of a power switch according to claim 5, characterized in that: When the controller temperature is greater than the second temperature threshold and the comparison voltage is greater than the threshold voltage, a high-level logic signal is output to enable the controller to obtain a cut-off logic signal.

8. The over-temperature protection circuit of a power switch according to claim 5, characterized in that: Also includes a first current mirror and a second current mirror, The first current mirror is used to mirror-amplify the received monitoring current and output a first mirror current; and The second current mirror is used to output a second mirror current according to the received first mirror current.

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