JP2008271758A - Dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter which exhibits high conversion efficiency with respect to a wide range of load state. <P>SOLUTION: The DC-DC converter 10 comprises a switching element 5 which is supplied with a DC voltage to the input side; a circuit 9 for smoothing the voltage 11 on the output side of the switching element 5 and outputting the smoothed voltage as an output voltage; a circuit 1 generating a signal for controlling on/off of the switching element 5, depending on the difference between the output voltage 11 and a reference voltage; a gate driver 2 as a means for driving on/off of the switching element 5 by a signal from the control circuit 1; a temperature sensor 4 as a means for detecting the load state on the output side; and a variable voltage regulator 3 as a variable voltage control means for controlling the drive voltage of the gate driver 2, depending on the signal of the temperature sensor 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a DC-DC converter that converts an input DC voltage and outputs DC voltages of different voltages.

  A conventional DC-DC converter using a switching element detects the output voltage of the DC-DC converter, compares the detected output voltage with a reference voltage, and applies it to the switching element according to a voltage fluctuation difference from the reference voltage. The on-duty of a PWM (Pulse Width Modulation) signal is changed to control the voltage fluctuation difference to be zero.

  A DC-DC converter using such a switching element generates a ripple in the output voltage. In order to reduce this ripple, conventionally, the amount of ripple is detected by measuring the temperature near the switching element or the output current, and the frequency of the signal applied to the switching element is made variable according to the detected value. A technique has been proposed in which ripple is reduced by reducing the voltage or making the drive voltage applied to the switching element variable (see, for example, Patent Document 1).

  In addition, when the load current of the switching element of the DC-DC converter increases, the temperature of the switching element rises to increase the on-voltage (saturation voltage). A technique has also been proposed in which when an overcurrent flows through the switching element, the switching element is turned off to protect the switching element and a device serving as a load (see, for example, Patent Document 2).

Further, the temperature of the switching element is detected from the temperature dependence of the forward voltage of the diode arranged in the vicinity of the switching element of the DC-DC converter, and the switching element whose temperature rises due to the overcurrent flowing through the switching element is turned off. A technique for protecting a switching element and a load device has also been proposed (see, for example, Patent Document 3).
JP 2001-8441 A JP-A-5-344642 JP 2004-147391 A

  However, in the DC-DC converter that reduces the ripple as in Patent Document 1 described above, when the temperature of the switching element rises or the load current increases, such an increase in temperature or an increase in load current causes an increase in ripple. In this case, the resistance of the switching element is increased and the ripple is decreased by increasing the switching frequency of the switching element or decreasing the drive voltage for driving the switching element. For this reason, there existed a subject that the Joule loss of a switching element increased.

  Further, in the DC-DC converter having an overcurrent prevention function as in Patent Document 2, when the temperature of the switching element rises, the switching element is turned off, the switching element is brought into a high resistance state, and the operation of the DC-DC converter is performed. There was a problem of canceling.

  Further, in the DC-DC converter as in Patent Document 3, the resistance of the switching element is increased in response to an increase in load current or a temperature rise in the switching element, so that the Joule loss increases or the operation is stopped. -There was a problem of reducing the conversion efficiency of the DC converter.

  The present invention has been made to solve the above-described problem. By optimizing the driving voltage for driving the switching element in accordance with the load state, the DC- having high conversion efficiency in a wide range of load states. An object is to provide a DC converter.

  In order to achieve the above object, a DC-DC converter of the present invention includes a switching element to which a DC voltage is supplied to the input side, smoothing means for smoothing the voltage on the output side of the switching element and outputting the output voltage as an output voltage, DC-DC converter comprising: control means for generating a signal for controlling on / off of the switching element according to a voltage difference between the output voltage and the reference voltage; and driving means for driving on / off of the switching element by a signal from the control means In this configuration, detection means for detecting the load state on the output side and variable voltage control means for controlling the drive voltage of the drive means in accordance with a signal from the detection means are provided.

  By configuring the DC-DC converter in this way, when the signal from the detection means for detecting the load state indicates a light load, the output voltage of the variable voltage control means is controlled to be a low voltage, thereby The amplitude voltage of the output signal of the driving means for driving on / off of the switching element becomes low. Thus, when the load is light, the drive voltage of the drive means for driving the switching element is low, the drive loss due to the drive means is reduced, and the conversion efficiency of the DC-DC converter is increased.

  Further, when the signal from the detection means for detecting the load state indicates a heavy load, the output voltage of the drive means for driving on / off of the switching element is controlled by controlling the output voltage of the variable voltage control means to be a high voltage. The amplitude voltage is increased, thereby reducing the on-resistance of the switching element. Thus, when the load is heavy, the on-resistance of the switching element is reduced, the Joule loss of the switching element is reduced, and the conversion efficiency of the DC-DC converter is increased.

  As described above, by driving the switching element with the optimum driving voltage according to the load state, a DC-DC converter having high conversion efficiency can be realized in a wide range of load states.

  The DC-DC converter of the present invention has a configuration in which the switching element is a MOS FET.

  By configuring with MOS type FET, drive means and control means can be integrated on the same chip, power saving and area reduction are possible, realizing low cost and high conversion efficiency DC-DC converter can do.

  In the DC-DC converter of the present invention, the detection means is a temperature detection means for detecting a temperature disposed in the vicinity of the switching element.

  By using the temperature detection means as the detection means for detecting the load state, the output signal of the temperature detection means is an electric signal, and can be directly input to the variable voltage control means without the need for a device for conversion to an electric signal. The cost can be reduced, and the detection of the load state by the temperature detection means can detect the average fluctuation of the load state, realizing a high conversion efficiency DC-DC converter that operates stably can do.

  In the DC-DC converter of the present invention, the detection means is a current detection means for detecting an output current on the output side of the switching element.

  Since the means for detecting the load state is constituted by the current detecting means for detecting the output current on the output side of the switching element, the output signal of the current detecting means is an electric signal, and directly without requiring a device for converting to an electric signal. The low voltage is possible by being able to input to the variable voltage control means, and the detection of the load state by the current detection means can operate at a fast response speed with respect to the fluctuation of the load state, and the load fluctuation In contrast, a DC-DC converter having a high response speed and a high conversion efficiency can be realized.

  In the DC-DC converter according to the present invention, the detection means includes a temperature detection means for detecting a temperature disposed in the vicinity of the switching element and a current detection means for detecting an output current on the output side of the switching element. Yes.

  By configuring the load detecting means to be a temperature detecting means arranged in the vicinity of the switching element and a current detecting means for detecting the output current on the output side of the switching element, the output signals of the temperature detecting means and the current detecting means are It is an electric signal and can be directly input to the variable voltage control means without the need for a device that converts it into an electric signal, so that low cost is possible, and load detection combined with a temperature detection means and a current detection means By the means, it is possible to realize a high conversion efficiency DC-DC converter having a fast response speed and a stable operation with respect to fluctuations in the load state.

  The DC-DC converter of the present invention can vary the drive voltage for driving on / off of the switching element according to the load state, and lowers the drive voltage for driving on / off of the switching element in the light load state. The drive loss of the drive means can be reduced. In the heavy load state, the driving voltage for driving on / off of the switching element can be increased, the on-resistance of the switching element can be decreased, and the Joule loss can be reduced. Thereby, it is possible to provide a DC-DC converter with high conversion efficiency under a wide range of load conditions.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals may be omitted from the description. In addition, for easy understanding, the drawings mainly show each component mainly, and the shape and the like are not accurate.

(Embodiment 1)
FIG. 1 is a configuration diagram of a DC-DC converter according to Embodiment 1 of the present invention.

  The DC-DC converter 10 according to Embodiment 1 of the present invention smoothes the switching element 5 to which the DC voltage 13 is supplied to the input side, and the output side voltage of the switching element 5 to obtain a smoothed output voltage 11. A smoothing circuit 9 as a smoothing means for outputting, a control circuit 1 as a control means for generating a signal for controlling on / off of the switching element 5 in accordance with a voltage difference between the output voltage 11 and a reference voltage, Via a signal, a gate driver 2 which is a driving means for driving on / off of the switching element 5 by a signal, a temperature sensor 4 as a temperature detecting means which is a detecting means for detecting a load state on the output side, and a control circuit 1 for the temperature sensor 4 The variable voltage regulator 3 is a variable voltage control means for controlling the drive voltage of the gate driver 2 in accordance with the signal 23. That.

  The switching element 5 is composed of a MOS N-channel FET, and the drain side which is the input side of the switching element 5 is connected to a DC voltage 13 which is an input voltage of the DC-DC converter 10. The source side, which is the output side, is connected to the input side of the smoothing circuit 9 composed of a coil and a capacitor, and the anode side of the diode 8. The output side of the smoothing circuit 9 outputs an output voltage 11. The cathode side of the diode 8 is grounded. The gate side of the switching element 5 is connected to the output 25 of the gate driver 2.

  One power supply terminal side of the gate driver 2 is connected to the output 27 of the variable voltage regulator 3 via the diode 6. The other power supply terminal side of the gate driver 2 is connected to the source side of the switching element 5. A capacitor 7 is connected between both power supply terminals of the gate driver 2. The control circuit 1 receives the output voltage 11 and the output 24 of the control circuit 1 is connected to the input of the gate driver 2.

  The input 26 side of the variable voltage regulator 3 is connected to the signal 23 of the temperature sensor 4 via the control circuit 1, the power supply terminal side is connected to the DC power supply 12, and the output side is connected to the gate driver 2 via the diode 6. It is connected to the power terminal side.

  The DC-DC converter 10 of the first embodiment is configured as described above.

  Next, the operation of the DC-DC converter 10 shown in FIG. 1 will be described.

  In the control circuit 1, the output voltage 11 is compared with a reference voltage (not shown) in the control circuit 1, and the PWM signal is turned on according to a voltage fluctuation difference that is a voltage difference between the output voltage 11 and the reference voltage. The duty is controlled, and the PWM signal thus controlled is output from the output 24. For example, when the output voltage 11 is higher than the reference voltage, the output 24 of the control circuit 1 is a PWM signal having a small on-duty, that is, a narrow on-pulse period. As a result, the on-duty of the switching element 5 decreases and the control circuit 1 performs feedback control so that the switching circuit 5 operates in a direction to lower the output voltage 11 and the voltage fluctuation difference from the reference voltage becomes zero. When the output voltage 11 is lower than the reference voltage, the output 24 of the control circuit 1 is a PWM signal with a large on-duty. As a result, the on-duty of the switching element 5 increases, and the control circuit 1 operates so as to increase the output voltage 11 so that the voltage fluctuation difference from the reference voltage becomes zero. Here, the reference voltage is a voltage equal to a desired output voltage.

  The variable voltage regulator 3 inputs a signal 23 of the temperature sensor 4 that detects the temperature in the vicinity of the switching element 5 from the input 26 via the control circuit 1, and in response to the signal 23 of the temperature sensor 4, Controls the voltage supplied to the power supply terminal. The signal 23 is a signal indicating a voltage or the like according to the temperature in the vicinity of the switching element 5. That is, for example, when the load current is in a heavy load state, the signal 23 of the temperature sensor 4 indicates that the temperature is high. In response to this signal 23, the variable voltage regulator 3 outputs a high output voltage, and the gate driver 2 Supply to the power terminal. Further, when the load current is light and the load is light, the signal 23 of the temperature sensor 4 indicates that the temperature is low. In response to this signal 23, the variable voltage regulator 3 outputs a low output voltage, and the power supply of the gate driver 2 Supply to the terminal.

  As an example of the circuit of the variable voltage regulator 3, it is also possible to control the variable voltage by A / D converting the signal 23 of the temperature sensor 4 and selecting the division ratio of the division resistor by the digital signal. Further, the signal of the temperature sensor 4 is compared with the comparison signal. When the signal 23 of the temperature sensor 4 is larger than the comparison signal, a voltage higher than the standard output voltage is output. When the signal 23 of the temperature sensor 4 is smaller than the comparison signal, A voltage lower than the standard output voltage may be output.

  The temperature sensor 4 can also detect the temperature by using the temperature characteristic of the forward voltage of the diode disposed in the switching element 5. As the diode, a base-emitter voltage of the transistor or a forward voltage between the drain and the substrate of the FET can be used. A temperature sensitive element such as a thermistor arranged in the vicinity of the switching element 5 can also be used.

  The gate driver 2 connects the PWM signal from the control circuit 1 to the input terminal, connects the output voltage of the variable voltage regulator 3 to the power supply terminal, and connects the ground terminal to the source side of the switching element 5.

  FIG. 2 is a diagram schematically showing an input waveform and an output waveform of the gate driver 2 in the first embodiment of the present invention. FIG. 2A is a diagram illustrating an input waveform of the gate driver 2, and FIG. 2B is a diagram illustrating an output waveform of the gate driver 2.

  The operation of the gate driver 2 will be described with reference to FIG. FIG. 2A shows an input signal of the gate driver 2 and also an output signal of the control circuit 1. When the output voltage 11 is the same as the reference voltage, the input waveform is the input waveform 31 and the output voltage 11 is the reference voltage. The input waveform when the output voltage 11 is lower than the reference voltage is the input waveform 33 when the output voltage 11 is lower than the reference voltage.

  When the output voltage 11 becomes higher than the reference voltage, the input waveform 32 is obtained, and the on-duty is reduced from the input waveform 31. The same on-duty waveform as the input waveform is output from the gate driver 2, the switching element 5 is turned on during the on-duty, and current is supplied to the output side of the switching element 5. Therefore, when the on-duty is decreased, the output voltage 11 operates so as to decrease, and is controlled so as to obtain a desired output voltage. When the output voltage 11 is lower than the reference voltage, the input waveform 33 is obtained, and the on-duty is increased from the input waveform 31. The same on-duty waveform as the input waveform is output from the gate driver 2, the switching element 5 is turned on during the on-duty, and current is supplied to the output side of the switching element 5. Therefore, when the on-duty increases, the output voltage 11 operates in a direction that increases, and is controlled to a desired output voltage.

  The gate driver 2 receives the output signal of the control circuit 1 and uses the output voltage of the variable voltage regulator 3 as a power source. As a result, the output signal of the gate driver 2 varies in on-duty due to variation in the output voltage 11 and varies in amplitude depending on the temperature in the vicinity of the switching element 5. As described above, the DC-DC converter 10 is characterized in that the amplitude of the output signal of the gate driver 2 is also adaptively changed.

  FIG. 2B shows the output waveform of the gate driver 2, and the output waveform when the temperature near the switching element 5 is normal is the output waveform 34, and it is detected that the temperature near the switching element 5 is high. The output waveform immediately after is the output waveform 35. The on-duty D1 of the output waveform 35 is the same as that of the output waveform 34, but the amplitude is the amplitude V2, which is larger than the amplitude V1 of the output waveform 34.

  That is, when the load is a heavy load in which a large amount of current flows through the load of the output voltage 11, the current of the switching element 5 increases and the temperature in the vicinity increases. The temperature sensor 4 detects a temperature rise, and the detected signal 23 is input to the variable voltage regulator 3, the output voltage of the variable voltage regulator 3 rises, and the power supply voltage of the gate driver 2 rises. Therefore, the amplitude of the output signal of the gate driver 2 increases and the on-resistance of the switching element 5 decreases. Thereby, the Joule loss of the switching element 5 can be reduced, and the conversion efficiency of the DC-DC converter 10 can be increased.

  Further, when the on-resistance of the switching element 5 decreases, the output voltage 11 tends to increase because the current flowing through the load increases. The control circuit 1 detects the fluctuation of the output voltage 11, and performs control so as to decrease the on-duty as indicated by the output waveform 36 in FIG. Therefore, in a heavy load state, the joule loss of the switching element 5 decreases due to the decrease in the on-resistance and the decrease in the on-duty of the switching element 5, and the conversion efficiency of the DC-DC converter 10 can be increased.

  The output waveform when the temperature in the vicinity of the switching element 5 is low is an output waveform 37. The on-duty D1 of the output waveform 37 is the same as that of the output waveform 34, but the amplitude is the amplitude V3, which is lower than the amplitude V1 of the output waveform 34.

  When the load of the output voltage 11 is small and the load is light, the current of the switching element 5 is small and the temperature in the vicinity does not rise. The temperature sensor 4 detects a low temperature, and the variable voltage regulator 3 lowers the output voltage and supplies it to the power supply terminal of the gate driver 2. As a result, the amplitude of the output signal of the gate driver 2 is reduced, and the drive loss of the gate driver 2 is reduced. As a result, the drive loss of the gate driver 2 is reduced, and the conversion efficiency of the DC-DC converter 10 can be increased.

  Thus, according to the present embodiment, it is possible to realize the DC-DC converter 10 having high conversion efficiency with respect to a wide range of load states.

  Further, since the switching element 5 is composed of a MOS type N-channel FET, the area occupied on the chip can be made smaller than in the case of the P-channel, and the cost can be reduced.

  In addition, since the switching element 5 is composed of a MOS type FET, the drive means and the control means can be integrated on the same chip, power saving and area reduction are possible, and low cost and high conversion efficiency. A DC-DC converter can be realized.

(Embodiment 2)
FIG. 3 is a configuration diagram of the DC-DC converter according to Embodiment 2 of the present invention. The DC-DC converter 20 of the present embodiment differs from the DC-DC converter 10 of the first embodiment in that a resistor 41 is inserted on the output side of the smoothing circuit 9 instead of the temperature sensor of the DC-DC converter 10. The current flowing through the output voltage 11 is directly detected by the current detector 42 using the voltage across the resistor 41 and input to the variable voltage regulator 43.

  The difference between the DC-DC converter 10 and the DC-DC converter 20 of the first embodiment is the configuration of the variable voltage regulator 43. The control circuit 1, the gate driver 2, the switching element 5, and the smoothing circuit 9 are DC-DC. The same as the converter 10.

  As an example of the configuration of the variable voltage regulator 43, it is also possible to control the variable voltage by A / D converting the signal of the current detector 42 and selecting the division ratio of the dividing resistor by the digital signal. Further, the signal of the current detector 42 is compared with the comparison signal. When the signal of the current detector 42 is larger than the comparison signal, a voltage higher than the standard output voltage is output, and when the signal of the current detector 42 is smaller than the comparison signal. A voltage lower than the standard output voltage may be output.

  Although the operation of the DC-DC converter 20 is the same as that of the DC-DC converter 10, since the output current of the output voltage 11 is directly detected by the resistor 41, there is an advantage that the response speed with respect to the load state fluctuation is fast.

  Similarly to the DC-DC converter 10, the operation of the DC-DC converter 20 can realize the DC-DC converter 20 having high conversion efficiency for a wide range of load states.

  Further, like the DC-DC converter 30 shown in FIG. 4, the temperature sensor 4 and the current detector 42 can be combined as a detector for detecting a load state. As a result, the current detector 42 responds instantaneously to fluctuations in the load state, and the combination with the temperature sensor 4 that reacts to the average fluctuations in the load state increases the response speed to the fluctuations in the load state. In addition, it is possible to realize the DC-DC converter 30 having a high conversion efficiency with respect to a wide range of load states, which operates stably without malfunction.

  As described above, the DC-DC converter of the present invention includes a switching element to which a DC voltage is supplied to the input side, a smoothing unit that smoothes the voltage on the output side of the switching element and outputs the output voltage, and the output voltage. Means for generating a signal for controlling on / off of the switching element in accordance with a voltage difference between the switching element and the reference voltage, driving means for driving on / off of the switching element by a signal from the control means, and detecting a load state on the output side This is a configuration provided with detection means such as a temperature sensor or a current detector, and variable voltage control means for controlling the drive voltage of the drive means in accordance with a signal from the detection means. Since the DC-DC converter according to the present invention has such a configuration, when the load is light, the drive voltage of the drive means for driving the switching element is low, and the drive loss due to the drive means is reduced. While the conversion efficiency of the converter is increased, when the load is heavy, the on-resistance of the switching element is reduced, the Joule loss of the switching element is reduced, and the conversion efficiency of the DC-DC converter is increased.

  Therefore, according to the DC-DC converter of the present invention, it is possible to provide a DC-DC converter having high conversion efficiency in a wide range of load conditions.

  The present invention provides a DC-DC converter having high conversion efficiency for a wide range of load states, and is useful for reducing the size and power consumption of electronic devices such as portable information devices and information home appliances.

Configuration diagram of DC-DC converter according to Embodiment 1 of the present invention It is the figure which showed typically the input waveform and output waveform of the gate driver in Embodiment 1 of this invention, (a) shows the input waveform of a gate driver, (b) shows the output waveform of a gate driver Configuration diagram of DC-DC converter in Embodiment 2 of the present invention Configuration diagram of another DC-DC converter according to the second embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control circuit 2 Gate driver 3,43 Variable voltage regulator 4 Temperature sensor 5 Switching element 6,8 Diode 7 Capacitor 9 Smoothing circuit 10,20,30 DC-DC converter 11 Output voltage 12 DC power supply 13 DC voltage 23 Signal 24,25 27 output 26 input 31, 32, 33 input waveform 34, 35, 36, 37 output waveform 41 resistance 42 current detector

Claims (5)

A switching element to which a DC voltage is supplied to the input side, a smoothing means for smoothing a voltage on the output side of the switching element and outputting it as an output voltage, and the switching element according to a voltage difference between the output voltage and a reference voltage A DC-DC converter comprising: control means for generating a signal for controlling on / off of the driving circuit; and driving means for driving on / off of the switching element by a signal from the control means,
A DC-DC converter comprising: a detecting unit that detects a load state on the output side; and a variable voltage control unit that controls a driving voltage of the driving unit in accordance with a signal from the detecting unit. The DC-DC converter according to claim 1, wherein the switching element is a MOS FET. 3. The DC-DC converter according to claim 1, wherein the detection unit is a temperature detection unit that detects a temperature arranged in the vicinity of the switching element. 4. 3. The DC-DC converter according to claim 1, wherein the detection unit is a current detection unit that detects an output current on an output side of the switching element. 4. The said detection means is comprised from the temperature detection means which detects the temperature arrange | positioned in the vicinity of the said switching element, and the current detection means which detects the output current of the output side of the said switching element, It is characterized by the above-mentioned. The DC-DC converter according to claim 1 or 2.

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