RU2693925C1 - Overcurrent protection device - Google Patents

Abstract

FIELD: electronic equipment.

SUBSTANCE: present invention relates to electronic engineering and can be used in switched power supplies with overcurrent protection. To achieve the technical result, overcurrent protection device is proposed, which includes a resistive current sensor, buses of negative and positive potential of input and output voltages, control and commuting p-MOS transistors. Control of p-MOS transistors at limitation and/or interruption of current through the device is performed by change of output voltage at change of load, for example, at short circuit in it, and by change of voltage on resistive current sensor installed in series with output filter capacitor.

EFFECT: shorter time of operation of protection at overload by current, protection of load from output voltage at its values higher than permissible, simplification of device and increase in its efficiency.

1 cl, 4 dwg

Description

The present invention relates to hardware electronic equipment and can be used to transfer voltage from the power source to the load unit with protection from overcurrent, as well as to protect against overloading of both the power source and the voltage switch itself. In addition, the device provides the ability to protect the load from unacceptably low or high voltage by completely removing it from the load.

Known compensatory voltage stabilizer [Sources of power electronic equipment. Handbook edited by G.S. Neivelt. Moscow “Radio and Communication”, 1986, p. 189, fig. 5.19] with protection against overcurrent, containing an electronic switch, made on the transistor, the limiting resistor and the second transistor that controls the electronic switch.

The disadvantage of this device is the inability to completely disconnect the load from the voltage source with unauthorized lowering of the input voltage, which can lead to unacceptable modes of operation of the load. For example, if the load unit is an electronic device, then the elements of this device will be under reduced unacceptable voltage.

The number of known devices - voltage switches [Description of the invention to the patent of the Russian Federation No. 22210183 H03K 17/08, Description of the invention to the patent of the Russian Federation No. 2240647 H03K 17/08, Description of the invention to the patent of the Russian Federation No. 2208292 H03K 17/08, Description of the invention to the patent of the Russian Federation No. 23585843 H03K 17/08], built on the basis of series-connected electronic key and shunt; by increasing the voltage drop on which several times, using comparators and logic elements, the electronic key is controlled (turned off).

The disadvantage of such devices is insensitivity to occasional significant short-term decreases in input voltage, at which the voltage at the load is not removed, but reaches unacceptably low values.

As a prototype of the claimed device, by its construction and functionality, it is possible to point to “Overcurrent Protection Device” [Description of the invention to the patent of Russian Federation №2542950 H03K 17/08].

The prototype device contains series-connected positive potential input voltage busines, a resistive current sensor, an electronic key with its on / off control circuit associated with the electronic key output through an aperiodic link (timing circuit), a positive potential output voltage bus, and a negative input bus and output voltage. The busses of the positive and negative potentials of the input voltage are the input of the device, the buses of the positive and negative potentials of the output voltage are the output of the devices.

The disadvantages of the known device is the long response time of protection against overcurrent, leading to significant pulsed energy release on the electronic key, the lack of load protection from the pulse increase of the input voltage, as well as the complexity of constructing the device. In addition, the inclusion of a resistive current sensor in the switching current circuit leads to the release of additional power on it.

The technical result of the invention is the expansion of functionality by reducing the response time of protection when current overload, protect the load from the output voltage when its values are higher than acceptable, simplifying the device and increasing its efficiency.

The technical result is achieved in that an overcurrent protection device containing a resistive current sensor, a capacitor of the timing circuit, a busbar of negative and positive potential of the input and output voltages, the control and switching p-MOS transistors, the last output of which is connected to the first output of the resistor feedback and bus potential of the output voltage, while the bus potential of the negative input voltage is connected to the bus potential of the negative output voltage In addition, a filter is introduced in the form of a series-connected filter capacitor and a resistive current sensor connected between the output potential negative voltage bus and a low-potential output of a filter capacitor connected through the first resistor to the gate of the control p-MOS transistor connected to the second output of the feedback resistor and through the second resistor, - with its drain and the gate of the switching p-MOS transistor connected through the third resistor to the negative potential bus in Output voltage, while the source of the control p-MOS transistor is connected via the fourth resistor to the positive potential input voltage bus, the source of the switching p-MOS transistor and, via a capacitor of the timing circuit, with its gate, the high-potential output of the filter capacitor is connected to the drain of the switching p- MOS transistor.

The operation of the claimed device is illustrated in FIG. 1 ... 4.

FIG. 1 shows an overcurrent protection device.

FIG. 2 ... 4 shows the results of modeling (oscillograms) of processes.

FIG. 1 shown:

1 - bus positive potential input voltage (hereinafter, in the description - "bus 1"),

2 - bus potential negative input voltage (hereinafter, in the description - "bus 2"),

3 - switching MOSFET transistor (hereinafter, the transistor 3),

4 - control r-MOS transistor (hereinafter referred to as transistor 4),

5 - feedback resistor,

6 ... 9 - the first - the fourth resistors, respectively

10 - resistive current sensor,

11 - capacitor timing circuit (hereinafter, the capacitor 11),

12 - bus positive potential output voltage (hereinafter, in the description - "bus 12"),

13 - bus negative potential output voltage (hereinafter, in the description - "bus 13"),

14 - load with capacitive (capacitor 15) and active (16) components

17 - input voltage source with voltage switch (18), 19 - filter capacitor.

FIG. 2 shows the results of modeling (oscillograms) of processes, explaining the general principle of operation of the device.

FIG. 3 shows the simulation results (oscillograms) of the processes, explaining the principle of the device operation at the settings of protection against impulse drops ("dips") of the input voltage.

FIG. 4 shows the simulation results (oscillograms) of the processes, explaining the principle of the device operation at the settings of protection against impulse exceedances of the input voltage.

FIG. 2 ... 4 shows: + IN - an example of the voltage form entering the device input, I _ADD - an example of load change (additional current flowing through the device), I _H - load current flowing through bus 12, + OUT - device output voltage , E is the energy (mJ) dissipated by the transistor 3. E _prototype is the energy (mJ) dissipated by the switching transistor in the device-prototype.

The plots shown in FIG. 2 ... 4 are the result of mathematical modeling of the claimed device, in which explanatory inscriptions are entered.

The device shown in FIG. 1 performed as follows.

Bus 1 is connected to the source of the transistor 3 and the first terminals of the capacitor 11 of the timing circuit and resistor 9. The drain of the transistor 3 is connected to the bus 12, the high-potential output of the filter capacitor 19 and, through the feedback resistor 5, to the gate of the transistor 4. The source of the transistor 4 is connected to the second the output of the resistor 9. The drain of the transistor 4 is connected to the gate of the transistor 3, through the resistor 7, with its gate and, through the resistor 10 to the buses 2 and 13. The low-potential output of the filter capacitor 19 is connected through a resistive current sensor 10 to the buses 2 and 13 and cut resistor 6, with a gate of transistor 4. Load 14 is connected to buses 12 and 13. The timing circuit consists of a capacitor 11, resistors 5-8 and a resistive current sensor 10. The time constant of the timing circuit is determined by the capacitance of the capacitor 11 and the equivalent resistance of the resistors 5-8 and a resistive current sensor 10.

The basis of the operation of an overcurrent protection device is:

"smooth" turning on the transistor 3 to limit the current through it when turned on,

accelerated switching off of the transistor 3 with a sharp increase in the current through it, for example, during a short circuit in the load,

the absence of current interruption through the overcurrent protection device at permissible (set during the initial adjustment of the device) "surge" of the input voltage,

interruption of current through the overcurrent protection device with unacceptable (set during the initial adjustment of the device) "surges" of the input voltage.

The overcurrent protection device operates as follows.

At some time t ₁ (Fig. 2, a) at the input of the device (bus 1), at the source of the transistor 3, the first output of the capacitor 11 and the resistor 9. appears input voltage + IN (ends at time t ₂ ). At this point, the voltage on the capacitor 11 is zero, as a result of which the transistor 4 is closed. Transistor 3 is either open at the level of the passage of "small" currents, or closed - when the voltage on its gate is close to the opening of transistor 3. This is achieved by selecting the ratio of the values of R ₈ and R _{7 of} resistors 8 and 7. Relation (R ₈ / R ₇ ) must be in the range from 5 to 10 to ensure at the first moment (t ₁ ) the voltage between the gate and the source of transistor 3 is close to the level of its opening (depending on the type of transistor, this voltage can be from 2 to 4 V).

As the capacitor 11 charges, the voltage at the gate (relative to its source) of the transistor 3 increases, which leads to its opening (if it was closed at the initial moment), the current through it increases, and the voltage of the capacitors 19 and 15. The voltage at the gate of transistor 4 is formed of several components: a) an increase in the voltage on the capacitor 11 contributes to the opening of the transistor 4, b) the voltage that occurs on the resistive current sensor (from the passage of current through the filter capacitor 19) and coming through the resistor 6 on Thief transistor 4, facilitates its closure; the output voltage + OUT supplied to the gate of the transistor through the feedback resistor 5 also contributes to its closure.

The opening of the transistor 4 contributes to limiting the voltage between the gate and the source of the transistor 3 and, consequently, limiting the current through it. The closing of the transistor 4 provides full opening of the transistor 3.

If at time t ₃ (Fig. 2, b) an additional load I _DOP appears, causing a significant excess of the output current (for example, a short circuit appears in the load), then by reducing the output voltage + OUT (due to an increase in the voltage drop across transistor 3) , due to the discharge current of the filter capacitor 19, a negative voltage pulse (relative to bus 13) appears on the resistive current sensor 10, which (via resistor 6) hits the gate of transistor 4. Transistor 4 opens, closing transistor 3, resulting in Khodnev voltage + OUT continues to decrease. Further, the voltage on the gate of the transistor 4 connected through the feedback resistor 5 to the bus 12 tends to the potential of the bus 13 through the load 14, which leads to the closing of the transistor 3 and the current through it to stop. The process of stopping the current I _{H is} shown in FIG. 2, in and 2, w; in fig. 2, g shows the change in voltage on the load when turning off the transistor 3.

The effect achieved when using the invention is explained as follows.

By selecting resistive sensor ratings, a current of 10 (ranging from 1 to 8 Ω), a resistor 6 (ranging from 39 to 82 kΩ), a resistor 7 (ranging from 3 to 7.5 kΩ) can be used to tune the claimed device to: a) load shedding at a voltage below a given value (Fig. 3) and b) to disconnect the load at a voltage higher than a specified value (Fig. 4).

Tuning to option a) is based on the effect of lowering the resistance of the load, as described above, in part of the description of operation. The basis for tuning to option b) is an increase in the voltage drop across transistor 3 with an increase in the input voltage and, consequently, to a decrease in the output voltage. Further, the process of turning off the transistor is the same as described above in the description of the operation.

Simplification of the device is achieved by the fact that, at the same switched currents, a transistor 4 can be used as a transistor in a compact design due to the fact that the energy dissipated on it when it is turned off (current cutoff) is 20-50 times less than the energy dissipated on the transistor in the prototype . FIG. 2, d shows the value of E close to 0.02 J — in the inventive device. FIG. 2, e shows the value of E close to 0.8 J - in the device - prototype.

In practice, this leads to the fact that for the claimed device you can use transistors in the SMD-0.2 or SMD-0.5 package with an acceptable dissipation energy E <(0.05-0.08) J. For the prototype device, you need to use transistors in the SMD-2 package or case with large dimensions with permissible dissipation energy of E> 1.0 J.

The increase in efficiency is due to the fact that the resistive current sensor 10 is installed in the circuit of a capacitive load - the current through it flows during the transient time T, T <2 ms.

In the prototype device, a current sensor (shunt) is installed in the load current passage circuit. The output power on it, for example, when its resistance is 0.5 Ohms and a current of about 1.5 A, is more than 1 W.

The proposed set of features in the solutions considered by the author was not met to solve the task, and does not follow explicitly from the prior art, which allows to conclude that the technical solution meets the criteria of "novelty" and "inventive step".

Claims (1)

An overcurrent protection device containing a resistive current sensor, a capacitor of the time-drop circuit, a busbar of negative and positive potential of the input and output voltages, control and switching r-MOS transistors, the output of the latter of which is connected to the first output of the feedback resistor and the bus of the positive output potential the voltage of the negative potential of the input voltage is connected to the bus of the negative potential of the output voltage, characterized in that it A filter is introduced in the form of a series-connected filter capacitor and a resistive current sensor connected between an output voltage negative potential bus and a low-potential output of a filter capacitor connected through the first resistor to the gate of the control p-MOS transistor connected to the second output of the feedback resistor and through the second resistor - with its drain and the gate of the switching p-MOS transistor connected through a third resistor to the negative potential output voltage bus In this case, the source of the control p-MOS transistor is connected via the fourth resistor to the positive potential bus input voltage, the source of the switching p-MOS transistor and, via a capacitor of the timing circuit, to its gate, the high-potential output of the filter capacitor is connected to the drain of the switching p-MOS transistor.

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