JP2019129588A - Switching power supply and USB power supply device - Google Patents

Abstract

A switching power supply having a temperature protection function realized by a simple circuit is provided. A switching power supply includes a rectifier circuit that rectifies input AC power and a DC / DC converter. The DC / DC converter 12 is switched according to the switching element 17, the current detection circuit 19, the non-inverting amplifier circuit 20 that amplifies the voltage output from the current detection circuit 19, and the voltage output from the non-inverting amplifier circuit 20. And a control circuit 18 that controls switching of the element 17. The non-inverting amplifier circuit 20 is connected between the non-inverting input terminal to which the voltage output from the current detection circuit 19 is input, the operational amplifier Amp having the inverting input terminal, and the inverting input terminal and the reference potential. A first resistance element R1, and a second resistance element R2 connected between the inverting input terminal and the output terminal of the operational amplifier Amp. At least one of the first resistance element R1 and the second resistance element R2 is a thermistor. [Selection] Figure 3

Description

  The present invention relates to a switching power supply and a USB power supply device provided with the switching power supply.

  Conventionally, various types of switching power supplies having a function of stabilizing an output voltage using a switching element have been proposed (see, for example, Patent Document 1).

  Patent Document 1 proposes a flyback switching power supply including a switching element and a control IC that controls the switching element.

International Publication No. 2009/069649

  By the way, in the switching power supply, if current supply to the load continues, heat may be generated at multiple points such as the switching element, flyback transformer, and rectifier diode on the output side. It is difficult to provide a heat dissipation structure. For example, in a USB power supply device such as a power adapter, it is necessary to provide a switching power supply in a limited space. Therefore, it is required to provide the switching power supply with a temperature protection function that suppresses output when the temperature of the switching power supply rises abnormally.

  Here, some control ICs for switching power supplies have a built-in temperature protection function. However, such a control IC has a problem that the threshold is too high at around 150 ° C. and the operation is stopped when the threshold is exceeded, so that it cannot withstand the actual application.

  Therefore, to add a temperature protection function to a small switching power supply incorporated in a product with limited heat dissipation, use a control IC with some high-level functions or a programmable control IC. And cost increases.

  Therefore, the present invention has been made to solve the above problems, and it is an object of the present invention to provide a switching power supply and a USB power supply device having a temperature protection function realized by a simple circuit.

  In order to achieve the above object, a switching power supply according to an aspect of the present invention converts a first DC voltage output from the rectifier circuit into a second DC voltage, and a rectifier circuit that rectifies input AC power. A DC / DC converter comprising: a switching element; a current detection circuit detecting a current flowing through the switching element; and outputting a voltage corresponding to the detected current; and an output from the current detection circuit And a control circuit for controlling switching of the switching element in accordance with the voltage output from the non-inversion amplifier circuit, the non-inversion amplifier circuit comprising: An operational amplifier having a non-inverting input terminal and an inverting input terminal to which the output voltage is input, and between the inverting input terminal and a reference potential And a second resistive element connected between the inverting input terminal and the output terminal of the operational amplifier, wherein at least one of the first resistive element and the second resistive element is connected. Is a thermistor.

  In order to achieve the above object, a USB power supply apparatus according to an aspect of the present invention includes a USB connector, a circuit board supporting the USB connector, and the switching power supply mounted on the circuit board, The DC / DC converter included in the switching power supply supplies the second DC voltage to the power supply terminal of the USB connector.

  According to the present invention, a switching power supply and a USB power supply device having a temperature protection function realized by a simple circuit are provided.

FIG. 1A is an external view showing a structure of a USB power supply device according to an embodiment. FIG. 1B is an external view of the back side of the circuit board shown in FIG. 1A. FIG. 2 is a circuit diagram of a switching power supply included in the USB power supply device shown in FIG. FIG. 3 is a circuit diagram showing a detailed configuration of the non-inverting amplifier circuit in FIG. FIG. 4 is a circuit diagram showing a non-inversion amplifying circuit according to a modification of the above embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of the constituent elements, operation procedures, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are described as optional constituent elements. Moreover, each figure is not necessarily illustrated exactly. In the drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted or simplified.

  FIG. 1A is an external view showing a structure of a USB power feeding device 6 according to the embodiment. The USB power supply device 6 is a power supply device used for a power adapter or an embedded wiring device that supplies power via a USB connector 8. As shown in the drawing, the USB power supply device 6 includes a USB connector 8, a circuit board 7 that supports the USB connector 8, and a switching power supply 10 mounted on the circuit board 7.

  The USB connector 8 is, for example, a USB Type-A receptacle (female).

  The circuit board 7 has a USB connector 8 mounted on the front surface (upper surface in the figure), and various electronic components constituting the switching power supply 10 mounted on the back surface.

  Switching power supply 10 receives an AC power (here, commercial AC power) and supplies a stabilized DC voltage (here, 5 V) to power supply terminal VBUS of USB connector 8. A flyback having a temperature protection function Power supply circuit.

  FIG. 1B is an external view of the back surface of the circuit board 7 shown in FIG. 1A. In the center of the circuit board 7, a terminal of the USB connector 8 attached to the opposite side (the surface of the circuit board 7) passes through and is fixed by soldering. Of the terminals of the USB connector 8, the terminal located at the left end in the figure is the power supply terminal VBUS, and the terminal located at the right end is the ground terminal GND.

  Further, on the upper left of the circuit board 7, a diode 15 which is an example of a semiconductor element that rectifies AC power on the secondary side of a flyback transformer described later and outputs DC power is mounted.

  The power supply terminal VBUS and the diode 15 of the USB connector 8 are electronic components with a high risk of heat generation. Therefore, in the present embodiment, between the power supply terminal VBUS and the diode 15 in plan view of the circuit board 7, the second resistance element R2 which is a thermistor for detecting the temperature of the power supply terminal VBUS and the diode 15 is mounted. ing. That is, the second resistance element R2 also serves as a sensor that detects the temperatures of both the power supply terminal VBUS and the diode 15.

  FIG. 2 is a circuit diagram of the switching power supply 10 provided in the USB power supply device 6 shown in FIG. Switching power supply 10 receives as input AC power from AC power supply 5 (in this case, commercial AC power) and supplies stabilized DC voltage (here, 5 V) to power supply terminal VBUS of USB connector 8. It is a flyback type power supply circuit having a function.

  As shown in the figure, the switching power supply 10 converts a first direct current voltage output from the rectification circuit 11 into a second direct current voltage and converts the first direct current voltage output from the rectifying circuit 11 into a second direct current voltage. And a DC / DC converter 12 for supplying the power supply terminal VBUS.

  The rectifier circuit 11 is a circuit that rectifies AC power (in this case, commercial AC power) from the AC power source 5 into DC power, and includes, for example, a diode bridge.

  The DC / DC converter 12 includes a snubber circuit 13, a flyback transformer 14, a diode 15, a capacitor 16, a switching element 17, a control circuit 18, a current detection circuit 19, and a non-inverting amplifier circuit 20.

  The snubber circuit 13 is a protection circuit which is connected to both ends of the primary winding of the flyback transformer 14 and absorbs a high voltage generated in the primary winding when the switching element 17 is off.

  The flyback transformer 14 is an isolation transformer having a primary winding and a secondary winding.

  The diode 15 is an example of a semiconductor element that rectifies AC power generated in the secondary winding of the flyback transformer 14. Note that such a semiconductor element for rectification is not limited to a diode, and may be a switching element for synchronous rectification (for example, an FET).

  The capacitor 16 is a smoothing capacitor that smoothes the waveform of the voltage and current rectified by the diode 15.

  The switching element 17 is an element that is connected in series to the primary winding of the flyback transformer 14 and that repeatedly switches on and off under the control of the control circuit 18, and is, for example, a MOS transistor.

  The current detection circuit 19 is a circuit that detects the current flowing through the switching element 17 and outputs a voltage corresponding to the detected current, and is, for example, a resistance element connected in series with the switching element 17.

  The non-inverting amplifier circuit 20 is a circuit that non-inverts the voltage output from the current detection circuit 19 and outputs the amplified voltage to the control circuit 18.

  The control circuit 18 is a circuit that controls the switching of the switching element 17 in accordance with the voltage output from the non-inverting amplifier circuit 20, and is, for example, an IC. Specifically, the control circuit 18 changes the ON time in switching of the switching element 17 so that the voltage input from the current detection circuit 19 via the non-inverting amplifier circuit 20 does not exceed a predetermined limit value. PWM (Pulse Width Modulation) control is performed.

  FIG. 3 is a circuit diagram showing a detailed configuration of non-inverting amplification circuit 20 in FIG. The non-inverted amplification circuit 20 outputs a voltage Vo obtained by amplifying the voltage Vi output from the current detection circuit 19 with an amplification factor depending on the temperature detected by the thermistor contained inside to the control circuit 18 Amplifier circuit. As shown in the figure, the non-inverting amplifier circuit 20 includes a low-pass filter 21, an operational amplifier Amp, a first resistance element R1, and a second resistance element R2.

  The low-pass filter 21 is a filter that generates a flat voltage waveform by smoothing the voltage Vi output from the current detection circuit 19, and includes a resistor R3 and a capacitor C1.

  The operational amplifier Amp is an operational amplifier having a non-inverting input terminal to which a voltage passing through the low-pass filter 21 is input from the current detection circuit 19 and an inverting input terminal. The operational amplifier Amp non-inverts and amplifies the input voltage at an amplification factor determined by the resistance value of the first resistance element R1 and the second resistance element R2, and outputs the voltage as the voltage Vo to the control circuit 18.

  The first resistance element R1 is a fixed resistance element connected between the inverting input terminal of the operational amplifier Amp and the reference potential (GND).

  The second resistance element R2 is a feedback resistance element connected between the inverting input terminal of the operational amplifier Amp and the output terminal of the operational amplifier Amp, and in the present embodiment, the positive characteristic that the resistance value increases as the temperature rises. It is a thermistor. When the temperature detected by the second resistance element R2 is a normal temperature (temperature range determined to be normal), the resistance value of the first resistance element R1 is set to be the resistance value of the second resistance element The resistance values of the first resistance element R1 and the second resistance element R2 are selected.

  Next, the operation of the USB power supply apparatus 6 according to the present embodiment configured as described above will be described.

  The AC power from the AC power supply 5 is rectified to DC power by the rectifier circuit 11, and the DC power after rectification is stabilized by the DC / DC converter 12 to become a DC voltage (here, 5 V). It is supplied to the power supply terminal VBUS of the connector 8.

  In the DC / DC converter 12, the DC power applied to the primary winding of the flyback transformer 14 is chopped by the switching element 17 under the control of the control circuit 18 to become AC power, and the two flyback transformers 14 AC power is generated in the winding. The AC power generated in the secondary winding of the flyback transformer 14 is rectified by the diode 15 and further smoothed by the capacitor 16 to become a DC voltage (here, 5 V).

  The control circuit 18 is a circuit that controls the on time in switching of the switching element 17 so that the voltage input from the current detection circuit 19 through the non-inverting amplification circuit 20 does not exceed a predetermined limit value. , Control IC. Specifically, when the voltage input from the current detection circuit 19 through the non-inverting amplification circuit 20 exceeds the limit value, the control circuit 18 limits the current flowing through the switching element 17. Reduce the on-time at switching. As a result, the output current from the power supply terminal VBUS of the USB connector 8 is limited so that the current detected by the current detection circuit 19 does not exceed a value corresponding to the limit value.

  Here, the operation of the non-inversion amplification in the non-inversion amplification circuit 20 is as follows.

  The amplification factor Vo / Vi of the non-inverted amplification circuit 20 is expressed as follows.

  Vo / Vi = 1 + R2 / R1 (Equation 1)

  “R1” is the resistance value of the first resistance element R1, and “R2” is the resistance value of the second resistance element R2.

  Under normal conditions, that is, when the temperature detected by the second resistive element R2 that is a positive temperature coefficient thermistor is normal temperature, R1 >> R2, and therefore Vo / Vi / 1.

  On the other hand, when abnormal, that is, when the temperature detected by the second resistive element R2 which is a positive temperature coefficient thermistor is abnormally high, R1 ≦ R2 because of the high resistance of the second resistive element R2, Vo / Vi It becomes ≧ 1. This corresponds to the appearance of the control circuit 18 receiving the output voltage from the non-inverting amplification circuit 20 apparently detecting that the current detected by the current detection circuit 19 is larger than it actually is. This corresponds to the reduction of the current limit value. As a result, the control circuit 18 limits the output current from the power supply terminal VBUS of the USB connector 8 more than usual. When a very high temperature is detected by the second resistor element R2, the resistance value of the second resistor element R2 exponentially increases, and the output current is suppressed to zero (A).

  Thus, the switching power supply 10 having the temperature protection function is realized only by adding the non-inversion amplification circuit 20 to the normal switching power supply having no temperature protection function without changing the control IC. Ru.

  As described above, the switching power supply 10 according to the present embodiment includes the rectifier circuit 11 that rectifies the input AC power, and the DC / DC that converts the first DC voltage output from the rectifier circuit 11 into the second DC voltage. And a DC converter 12. The DC / DC converter 12 detects the current flowing through the switching element 17 and the switching element 17, and amplifies a voltage output from the current detection circuit 19 that outputs a voltage corresponding to the detected current. A non-inverting amplifier circuit 20 and a control circuit 18 that controls switching of the switching element 17 in accordance with the voltage output from the non-inverting amplifier circuit 20 are provided. The non-inverted amplification circuit 20 is connected between the non-inversion input terminal to which the voltage output from the current detection circuit 19 is input and an operational amplifier Amp having an inversion input terminal, the inversion input terminal and the reference potential. A first resistance element R1, and a second resistance element R2 connected between the inverting input terminal and the output terminal of the operational amplifier Amp. At least one of the first resistance element R1 and the second resistance element R2 (in this embodiment, the second resistance element R2) is a thermistor.

  As a result, the voltage output from the current detection circuit 19 is input to the control circuit 18 after non-inverting amplification using the thermistor is performed in the non-inverting amplifier circuit 20. Therefore, the signal based on the temperature detection is superimposed on the signal based on the current detection and input to the control circuit 18, and the output suppression with respect to the temperature is also performed by the control of the output voltage stabilization of the control circuit 18. Become. That is, the switching power supply 10 with the temperature protection function is realized by adding the non-inverting amplifier circuit 20 to the normal switching power supply without the temperature protection function without changing the control IC. . Therefore, the switching power supply 10 having a temperature protection function realized by a simple circuit is realized.

  The first resistance element R1 is a fixed resistance element, and the second resistance element R2 is a positive temperature coefficient thermistor.

  Thus, a temperature protection function can be easily realized by using a positive temperature coefficient thermistor as a feedback resistance element of the operational amplifier Amp.

  The USB power supply device 6 according to the present embodiment includes a USB connector 8, a circuit board 7 that supports the USB connector 8, and the switching power supply 10 mounted on the circuit board 7. The DC / DC converter 12 included in the switching power supply 10 supplies the second DC voltage to the power supply terminal VBUS of the USB connector 8.

  As a result, since the USB power supply 6 is provided with the switching power supply 10 having a temperature protection function realized by a simple circuit, a small-sized, low-cost USB power supply is realized.

  Further, the DC / DC converter 12 includes a semiconductor element (in the embodiment, the diode 15) that rectifies AC power generated by switching by the switching element 17, and the thermistor (in the embodiment, the second resistance element R2). The temperature of at least one of the power supply terminal VBUS and the semiconductor element is detected.

  As a result, the temperature of at least one of the power supply terminal VBUS of the USB connector 8 and the semiconductor element for rectification that is highly likely to generate heat is detected.

  In the above embodiment, in the non-inverting amplifier circuit 20, the first resistance element R1 is a fixed resistance element and the second resistance element R2 is a positive temperature coefficient thermistor. However, the present invention is not limited to this. As shown in FIG. 4, the first resistance element R1 may be a negative characteristic thermistor, and the second resistance element R2 may be a fixed resistance element.

  FIG. 4 is a circuit diagram showing a non-inverting amplifier circuit 20a according to a modification of the non-inverting amplifier circuit 20 provided in the switching power supply 10 of the above embodiment. The non-inverting amplifier circuit 20a according to this modification includes a negative characteristic thermistor as the first resistance element R1, and a fixed resistance element as the second resistance element R2. When the temperature detected by the first resistance element R1 is a normal temperature (temperature range determined to be normal), the resistance value of the first resistance element R1 is set to be the resistance value of the second resistance element. The resistance values of the first resistance element R1 and the second resistance element R2 are selected.

  Even the non-inverting amplifier circuit 20a having such a configuration operates in the same manner as the non-inverting amplifier circuit 20 according to the above embodiment. That is, the amplification factor Vo / Vi of the non-inverted amplification circuit 20 a is expressed by the above equation 1. Then, in the normal state, that is, when the temperature detected by the first resistance element R1 which is the negative characteristic thermistor is a normal temperature, R1 >> R2 holds, and therefore Vo / ViVi1. On the other hand, when abnormal, that is, when the temperature detected by the first resistance element R1 which is a negative characteristic thermistor is abnormally high, R1 ≦ R2 because of the reduction of the resistance of the first resistance element R1, Vo / Vi It becomes ≧ 1. This corresponds to the appearance of the control circuit 18 receiving the output voltage from the non-inverting amplification circuit 20 apparently detecting that the current detected by the current detection circuit 19 is larger than it actually is. This corresponds to the reduction of the current limit value. As a result, the control circuit 18 limits the output current from the power supply terminal VBUS of the USB connector 8 more than usual. When a very high temperature is detected by the first resistor element R1, the resistance value of the first resistor element R1 exponentially decreases and the output current is suppressed to zero (A).

  As described above, according to the switching power supply including the non-inverting amplifier circuit 20a according to the present modification, the same effects as those of the above-described embodiment can be obtained. That is, a switching power supply having a temperature protection function is realized only by adding the non-inversion amplification circuit 20a to a normal switching power supply having no temperature protection function without changing the control IC.

  In the non-inverting amplifier circuit 20a according to the present modification, the first resistance element R1 is a negative characteristic thermistor, and the second resistance element R2 is a fixed resistance element.

  As a result, by using a negative characteristic thermistor as the first resistance element R1 connected between the inverting input terminal of the operational amplifier Amp and the reference potential, the temperature protection function is easily realized.

  As mentioned above, although the switching power supply and USB electric power feeder which concern on this invention were demonstrated based on embodiment and a modification, this invention is not limited to these embodiment and a modification. Unless it deviates from the main point of the present invention, what applied various modification which a person skilled in the art thinks to this embodiment or modification, and another form constructed combining some components in the embodiment and modification. Also included within the scope of the present invention.

  For example, in the above embodiment, the USB power feeding device 6 is provided with a USB Type-A receptacle (female) as the USB connector 8. However, the present invention is not limited thereto. The USB Type-B or USB Type-C It may be a connector.

  In the above embodiment, the USB power supply device 6 includes one USB connector 8, but may include a plurality of USB connectors. In that case, the non-inverted amplification circuit 20 preferably detects the temperatures of the plurality of USB connectors. For example, by using a negative characteristic thermistor as the first resistance element R1 and using a positive characteristic thermistor as the second resistance element R2, a switching power supply having a plurality of thermistors and having a temperature protection function for a plurality of distant places is realized. Ru.

  Further, in the above embodiment, the thermistor included in the non-inverted amplification circuit 20 detects the temperature of both the power supply terminal VBUS of the USB connector 8 and the diode 15. However, even if the temperature of only one of these is detected. Good.

  Also, in the switching power supply 10 according to the above embodiment, the output voltage on the secondary side is not fed back to the primary side, but the output voltage on the secondary side is fed back to the control circuit 18 using a photocoupler or the like. Control may be performed to output a constant voltage.

  Moreover, although the switching power supply 10 which concerns on the said embodiment was a switching power supply of a flyback system (that is, insulation type), it is not restricted to such a type, You may be non-insulation type. Further, the DC / DC converter may be any of a step-down type, a step-up type, and a step-up / down type. As long as the non-inverting amplifier circuit according to the present invention is a switching power supply including a current detection circuit and a control circuit, it can be applied to any kind of switching power supply by being added between these circuits.

5 AC power supply 6 USB power supply device 7 Circuit board 8 USB connector 10 Switching power supply 11 Rectifier circuit 12 DC / DC converter 15 Diode (an example of a semiconductor element)
17 switching element 18 control circuit 19 current detection circuit 20, 20a non-inverting amplifier circuit R1 first resistance element R2 second resistance element Amp operational amplifier

Claims (5)

A rectifier circuit that rectifies input AC power;
A DC / DC converter for converting a first DC voltage output from the rectifier circuit into a second DC voltage;
The DC / DC converter is
A switching element,
A current detection circuit that detects a current flowing through the switching element and outputs a voltage corresponding to the detected current;
A non-inverting amplifier circuit for amplifying a voltage output from the current detection circuit;
A control circuit that controls switching of the switching element in accordance with the voltage output from the non-inverted amplification circuit;
The non-inverting amplifier circuit
An operational amplifier having a non-inversion input terminal to which the voltage output from the current detection circuit is input, and an inversion input terminal;
A first resistance element connected between the inverting input terminal and a reference potential;
A second resistance element connected between the inverting input terminal and the output terminal of the operational amplifier;
At least one of the first resistance element and the second resistance element is a thermistor. The first resistance element is a fixed resistance element,
The switching power supply according to claim 1, wherein the second resistance element is a positive temperature coefficient thermistor. The first resistance element is a negative characteristic thermistor,
The switching power supply according to claim 1, wherein the second resistance element is a fixed resistance element. USB connector,
A circuit board supporting the USB connector;
The switching power supply according to any one of claims 1 to 3, mounted on the circuit board,
The DC / DC converter included in the switching power supply supplies the second DC voltage to a power supply terminal of the USB connector. The DC / DC converter includes a semiconductor element that rectifies AC power generated by switching by the switching element,
The USB power supply device according to claim 4, wherein the thermistor detects a temperature of at least one of the power supply terminal and the semiconductor element.

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