An automatic overcurrent protector circuit with temperature compensation function

Abstract

The present invention provides an overcurrent automatic protector circuit with a temperature compensation function, comprising: a Vin input terminal, a G input terminal, a RESET signal input terminal, an OFF signal input terminal, a Vout output terminal, a capacitor C1, a resistor R6, a voltage stabilizing diode D1, a MOS tube Q3, a resistor R7, a resistor R1, a resistor R2, a transistor Q1, a resistor R5, a resistor R4, a transistor Q2, a resistor R8, a resistor R9, and a resistor R3. When the RESET terminal signal is valid, the MOS tube Q3 is turned on to supply power to the load, when the OFF terminal signal is valid, the MOS tube Q3 is turned off, and the load is powered off, when the load is overcurrent, the MOS tube Q3 is automatically turned off and remains in a locked state until the RESET terminal signal is valid, and the MOS tube Q3 is turned on again. The present invention uses the voltage difference between the two ends of the MOS tube as the overcurrent protection threshold, without the need for a precision resistor, and automatically turns off and locks when the overcurrent value reaches the protection threshold, and turns on again through the RESET terminal, without the need for secondary power supply, and sets a temperature compensation circuit to compensate for the Rds positive temperature characteristic of the MOS tube, so that the overcurrent protection threshold remains constant.

Description

Technical Field

[0001] The present invention relates to the technical field of protectors, and in particular to an overcurrent automatic protector circuit with a temperature compensation function. Background Art

[0002] The primary power supply on the spacecraft is the electric power source of the spacecraft. Once there is a problem with the electric power source, the spacecraft will lose its electric power source and cause a success-or-failure failure. The short-circuit failure of the direct power load on the primary power supply bus will pose a threat to the failure of the spacecraft. Any components or equipment that may cause a short circuit in the power supply bus due to a single point failure, thereby causing the failure of the spacecraft, should adopt overcurrent protection measures.

[0003] Cutting off the electrical connection with the main bus to protect the primary power supply bus is a typical usage of input overcurrent protection on spacecraft. Commonly used methods include fuse protection, automatic overcurrent protection and remote control switching protection, and the three methods can be used in combination.

[0004] Most of the current equipment uses the protection form of fuse + MOS tube. The fuse is used for over-current shutdown, and the MOS tube is used for remote control switching and surge suppression. When the external command is in OC form and there is a state lock requirement, a small relay is used to control the P-MOS circuit. However, the number of relay switching times is limited, and the control current flowing through the contacts is generally mA level, which is not conducive to contact cleaning and is not suitable for use in working environments with frequent switching. In addition, the price of relays is relatively high, which is not conducive to the cost-effective design of the product.

[0005] Existing overcurrent automatic protection devices convert the current in the power circuit into voltage, compare it with the overcurrent threshold through an operational amplifier or comparator, and lock it when the overcurrent reaches the threshold. The disadvantage of this circuit method is that precision resistors are used to achieve IV conversion, and the converted voltage needs to be conditioned by an operational amplifier. There are many circuit components, which makes the protector larger in size and weight, and its application is limited. In addition, the protector requires a secondary power supply, which greatly limits its application flexibility. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides an overcurrent automatic protector circuit with a temperature compensation function, comprising: a Vin input terminal, a G input terminal, a RESET signal input terminal, an OFF signal input terminal, a Vout output terminal, a capacitor C1, a resistor R6, a voltage stabilizing diode D1, a MOS tube Q3, a resistor R7, a resistor R1, a resistor R2, a transistor Q1, a resistor R5, a resistor R4, a transistor Q2, a resistor R8, a resistor R9, and a resistor R3;

[0007] Among them, one end of the capacitor C1 is connected to the Vin terminal, one end of the resistor R6, the cathode of the voltage stabilizing diode D1 and the drain of the MOS tube Q3, the other end of the capacitor C1 is connected to the G terminal, the other end of the resistor R6, the anode of the voltage stabilizing diode D1, the gate of the MOS tube Q3 and one end of the resistor R7, the source of the MOS tube Q3 is connected to the Vout terminal, the other end of the resistor R7 is connected to the RESET terminal, one end of the resistor R1 is connected to the Vin terminal and the collector of the transistor Q1, and the other end of the resistor R1 is connected to the Connected to one end of resistor R2 and the base of transistor Q1, the emitter of transistor Q1 is connected to the emitter of transistor Q2, one end of resistor R5 is connected to the connection point of the emitter of transistor Q1 and the emitter of transistor Q2, the base of transistor Q2 is connected to the OFF end, one end of resistor R4 and one end of resistor R8, the other ends of resistors R2, R4 and R5 are grounded, resistor R9 is connected to resistor R8 in parallel, the other end of resistor R8 is connected to one end of resistor R3, and the other end of resistor R3 is connected to the Vout end.

[0008] Optionally, the resistor R8 is an NTC thermistor.

[0009] Optionally, the transistor Q1 and the transistor Q2 may be a transistor pair 2N2920.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] The voltage difference across the MOS tube is used as the overcurrent protection threshold. There is no need to use precision resistors. When the overcurrent value reaches the protection threshold, it is automatically shut down and locked. It can be turned on again through the RESET terminal without secondary power supply. By setting the temperature compensation circuit, the Rds positive temperature characteristic of the MOS tube can be compensated, and temperature compensation can be achieved in the full temperature range of -40℃ to +85℃, so that the overcurrent protection threshold remains constant. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0013] Figure 1 An overcurrent automatic protector circuit with a temperature compensation function provided in an embodiment of the present disclosure;

[0014] Figure 2 This is a temperature compensation effect diagram of the overcurrent automatic protector with temperature compensation function according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0016] The technical solution of the present invention is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0017] Figure 1 A schematic diagram of the circuit structure of an overcurrent automatic protector with a temperature compensation function provided by an embodiment of the present disclosure is shown in FIG. Figure 1 As shown, it includes: Vin input terminal, G input terminal, RESET signal input terminal, OFF signal input terminal, Vout output terminal, capacitor C1, resistor R6, voltage stabilizing diode D1, MOS tube Q3, resistor R7, resistor R1, resistor R2, transistor Q1, resistor R5, resistor R4, transistor Q2, resistor R8, resistor R9, resistor R3;

[0018] Vin is connected to a 42V voltage with a pull-off range of 36V to 47V. One end of capacitor C1 is connected to Vin, one end of resistor R6, the cathode of voltage zener diode D1 and the drain of MOS tube Q3. The other end of capacitor C1 is connected to G, the other end of resistor R6, the anode of voltage zener diode D1, the gate of MOS tube Q3 and one end of resistor R7. The source of MOS tube Q3 is connected to Vout. The other end of resistor R7 is connected to RESET. One end of resistor R1 is connected to Vin and the collector of transistor Q1. The other end of resistor R1 is connected to resistor R 2 is connected to the base of transistor Q1, the emitter of transistor Q1 is connected to the emitter of transistor Q2, one end of resistor R5 is connected to the connection point of the emitter of transistor Q1 and the emitter of transistor Q2, the base of transistor Q2 is connected to the OFF end, one end of resistor R4 and one end of resistor R8, the other ends of resistors R2, R4 and R5 are grounded, resistor R9 is connected in parallel with resistor R8, the other end of resistor R8 is connected to one end of resistor R3, the other end of resistor R3 is connected to Vout end, Vout end is connected to load R10, load R10 can be resistive, inductive or capacitive load;

[0019] The working principle of the overcurrent automatic protector circuit is as follows:

[0020] 1. Normal opening / closing

[0021] Transistors Q1 and Q2 use transistor pair 2N2920. The Vin voltage is divided by resistors R1 and R2. Transistor Q1 is turned on and transistor Q2 is not turned on. At this time, the gate voltage of MOS tube Q3 is 0 and the voltage of load R10 is 0.

[0022] When the collector open circuit instruction is applied to the RESET terminal, the gate voltage of MOS tube Q3 is 8.5V through the voltage division of R6 and R7, MOS tube Q3 is turned on, and the Vout voltage is about 42V. The Vout voltage is divided by resistors R3, R8, R9 and R4, and transistor Q2 is turned on. At this time, the Vin voltage is divided by resistor R6, transistor Q2 and resistor R5, and the voltage across resistor R6 is 5.0V. When the RESET terminal signal becomes high or open, MOS tube Q3 can also remain in the on state.

[0023] When the collector open circuit instruction is applied to the OFF end, the transistor Q2 is turned off, and the voltage across the resistor R6 becomes 0, that is, the gate-source voltage of the MOS tube is 0, and the voltage of the load R10 becomes 0.

[0024] 2. Overcurrent lock protection

[0025] When the load R10 is overcurrent, the current flowing through the MOS tube Q3 increases, and the voltage drop across the MOS tube Q3 increases, resulting in a decrease in the Vout voltage. The Vout voltage is divided by resistors R3, R8, R9 and R4, and the current flowing through the base of the transistor Q2 becomes smaller. The transistor Q2 is turned off, and the voltage across the resistor R6 becomes 0, that is, the gate-source voltage of the MOS tube Q3 is 0. The MOS tube Q3 is turned off and remains locked, which plays a role in protecting the circuit and the load.

[0026] 3. Capacitive load startup

[0027] In practical applications, capacitive loads are widely used, such as DC / DC, CPU circuit power supply, etc., which requires the protector to have a certain capacitive load capacity. When the load R10 is equivalent to a resistor and a capacitor in parallel, it is a capacitive load.

[0028] When the collector open circuit instruction is applied to the RESET terminal, the current flowing through the MOS tube Q3 increases instantly due to the capacitive load, and the load current is:

[0029]

[0030] The larger the capacitance, the greater the surge current. Vin forms a loop through capacitor C1 and resistors R6 and R7. The voltage across capacitor C1 is the gate-source voltage of MOS tube Q3. The voltage across capacitor C1 is charged in an exponential form with a time constant of τ. τ=C1×(R6 / / R7), so that the gate-source voltage of MOS tube Q3 increases slowly with a time constant of τ, which plays a role in surge suppression, thereby realizing the startup of capacitive load. Zener tube D1 is connected in parallel at both ends of the gate-source of MOS tube Q3, and the voltage regulation value is 10V, which protects the gate-source voltage of MOS tube Q3 from not exceeding 10V. Resistor R5 is a current limiting resistor to ensure that when transistors Q1 and Q2 are turned on, the collector current I c1 and I c2 Does not exceed the maximum collector current I cmax .

[0031] 4. Temperature compensation function

[0032] The on-resistance Rds of the MOS tube Q3 has a positive temperature coefficient. The on-resistance Rds at 125° C. is approximately 1.75 times that at room temperature (25° C.), and the on-resistance Rds at −55° C. is approximately 0.5 times that at room temperature (25° C.).

[0033] Resistors R8 and R9 form a temperature compensation circuit, which is used to compensate for the change of the on-resistance Rds of the MOS tube Q3 when the temperature changes, so as to ensure that the overcurrent protection point and protection time of the automatic protector are constant within the full temperature range. The principle is that, taking the load current of 5A as an example, at a normal temperature of 25°C, the on-resistance Rds of the MOS tube Q3 is 0.045Ω, at which time Vout is 42-0.045×5=41.775V; when the temperature is -40°C, the on-resistance Rds of the MOS tube Q3 is 0.045Ω×0.6=0.027Ω, at which time Vout is 42-0.045×5×0.6=41.865V; when the temperature is 55°C, the on-resistance Rds of the MOS tube Q3 is 0.045Ω×1.25=0.056Ω, at which time Vout is 42-0.045×5×1.25=41.72V. It can be seen that when the temperature is different, the voltage at the Vout terminal is different, and the base current of the transistor Q2 is different. Since the on-resistance Rds of the MOS tube Q3 has a positive temperature characteristic, the overcurrent protection point of the automatic protector changes with the temperature. When the temperature rises, the overcurrent protection point becomes smaller, and when the temperature rises, the overcurrent protection point becomes larger. Through the negative temperature characteristic of thermistor R8, the positive temperature characteristic of the on-resistance of the MOS tube Q3 is reversely compensated, thereby ensuring that the overcurrent protection point remains basically unchanged when the temperature changes.

[0034] Resistor R8 uses an NTC series thermistor for compensation. The model of resistor R8 is CMFA103J3600HANT. The resistance change in the full temperature range is shown in Table 1.

[0035] Table 1 Resistance of CMFA thermistor at different temperatures

[0036]

[0037]

[0038] The change is larger in the low temperature section and smaller in the high temperature section. The impact on the compensation circuit is that it is easier to compensate in the high temperature section. In the low temperature section, the impedance increases greatly, which will cause over-compensation, making it easy to trigger over-current lock in the low temperature section, or directly cause the switch to fail to open.

[0039] The following measures are taken to solve the problem: a resistor R9 is connected in parallel at both ends of the thermistor R8. In the low temperature range, R8 / / R9 mainly depends on the value of R9. In the high temperature range, R8 / / R9 will decrease accordingly, but the positive temperature coefficient characteristics of the MOS tube and the reduced resistance of R8 / / R9 will compensate. After calculation, R9=430Ω can achieve the best fitting and compensation effect.

[0040] It can be seen from Table 2 that after adding the temperature compensation circuit, the error is controlled within 0.18% in the full temperature range of -40℃ to 85℃, and within 0.1% in the range of -40℃ to 75℃, and the temperature compensation effect is obvious.

[0041] Table 2 Error before and after temperature compensation

[0042]

[0043]

[0044] like Figure 2 As shown, the data in Table 2 are plotted as a temperature compensation effect diagram, and a linear trend line is added. From the trend line, it can be seen that in the full temperature range, the error trend after temperature compensation is better than the uncompensated error.

Claims

1. An overcurrent automatic protector circuit with temperature compensation function, characterized in that: include: Vin input terminal, G input terminal, RESET signal input terminal, OFF signal input terminal, Vout output terminal, capacitor C1, resistor R6, voltage stabilizing diode D1, MOS tube Q3, resistor R7, resistor R1, resistor R2, transistor Q1, resistor R5, resistor R4, transistor Q2, resistor R8, resistor R9, resistor R3; Among them, one end of the capacitor C1 is connected to the Vin terminal, one end of the resistor R6, the cathode of the voltage stabilizing diode D1 and the drain of the MOS tube Q3, the other end of the capacitor C1 is connected to the G terminal, the other end of the resistor R6, the anode of the voltage stabilizing diode D1, the gate of the MOS tube Q3 and one end of the resistor R7, the source of the MOS tube Q3 is connected to the Vout terminal, the other end of the resistor R7 is connected to the RESET terminal, one end of the resistor R1 is connected to the Vin terminal and the collector of the transistor Q1, and the other end of the resistor R1 is connected to the Connected to one end of resistor R2 and the base of transistor Q1, the emitter of transistor Q1 is connected to the emitter of transistor Q2, one end of resistor R5 is connected to the connection point of the emitter of transistor Q1 and the emitter of transistor Q2, the base of transistor Q2 is connected to the OFF terminal, one end of resistor R4 and one end of resistor R8, the other ends of resistors R2, R4 and R5 are grounded, resistor R9 is connected in parallel with resistor R8, the other end of resistor R8 is connected to one end of resistor R3, and the other end of resistor R3 is connected to the Vout terminal; The resistor R8 is an NTC thermistor; The transistor Q1 and the transistor Q2 are transistor pairs 2N2920.

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