JP2008086165A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress output ripples at a low temperature in a power supply unit. <P>SOLUTION: The power supply unit 40 is provided with a switching regulator 1 and a series regulator 2. The switching regulator 1 is provided with a differential amplifier 11, reference voltage generating circuit 12, switching controller 13, Pch MOS transistor PT1, resistor R1, resistor R2, diode D1, diode D2, inductor L1, and capacitor C1. The series regulator 2 is provided with a differential amplifier circuit 21, a reference voltage generating circuit 22, a resistor R21, a resistor R22, and a Pch MOS transistor PT21. A reference voltage Vref1a to be outputted from the circuit 12 of the switching regulator 1 and inputted into one side of the circuit 11 via the diode D1 has the temperature characteristic same as that of the capacitor C1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply device.

  The stabilized power supply devices that are generally used at present are highly efficient, but the output ripple of the output voltage and the switching regulator with large noise at the time of differential and the output ripple of the output voltage are small but the efficiency is low. Series regulators with low noise during operation are used. A stabilized power supply device composed of a switching regulator and a series regulator taking advantage of the advantages of the switching regulator and the series regulator is widely used. In this stabilized power supply device, first, an input voltage from a power supply is input to a switching regulator, and the switching regulator generates a necessary voltage. A necessary voltage generated from the switching regulator is input to the series regulator, and the series regulator supplies a predetermined voltage with less noise and output ripple to the load (for example, see Patent Document 1).

In the power supply device described in Patent Literature 1 and the like, a capacitor for smoothing an output voltage having a relatively large capacity is provided on the output side of the switching regulator. If this smoothing capacitor has a relatively large equivalent series resistance (ESR) temperature characteristic, such as an aluminum electrolytic capacitor or a tantalum electrolytic capacitor, the ripple of the output voltage of the switching regulator increases at low temperatures. There is a problem that output ripple occurs in the output voltage output from the series regulator.
JP 2003-235250 A

  An object of the present invention is to provide a power supply device capable of suppressing output ripple at a low temperature.

  In the power supply device of one embodiment of the present invention, a smoothing capacitor provided on the output side, a reference voltage having the same temperature characteristics as the smoothing capacitor are input to the − side, and a feedback voltage divided by resistance is supplied to the + side. A comparator that inputs and outputs a comparatively amplified signal, inputs a first input voltage, outputs a first output voltage, and inputs the first output voltage as an input voltage; And a series regulator that outputs two output voltages.

  A power supply device according to another aspect of the present invention includes a smoothing capacitor, an inductor, a first diode provided on the output side, and a band gap reference circuit, and generates a first reference voltage. A reference voltage generation circuit; a second diode that inputs the first reference voltage to the cathode and outputs a second reference voltage from the anode; and the second reference voltage that is input to the negative side and a positive side that is the positive side. A first regulator that inputs a first feedback voltage divided by resistance and outputs a comparatively amplified signal; a switching regulator that inputs the first input voltage and outputs the first output voltage; A second reference voltage generating circuit configured by a bandgap reference circuit and generating a third reference voltage; and a second feedback voltage obtained by inputting the third reference voltage on the negative side and resistance-dividing on the positive side The And a second comparator that outputs a signal that has been compared and amplified, and has a series regulator that receives the first output voltage as an input voltage and outputs the second output voltage. To do.

  ADVANTAGE OF THE INVENTION According to this invention, the power supply device which can suppress the output ripple at the time of low temperature can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a power supply device according to Embodiment 1 of the present invention will be described with reference to the drawings. 1 is a circuit diagram showing a configuration of a power supply device, FIG. 2 is a diagram showing an equivalent circuit of a smoothing capacitor used in a switching regulator, FIG. 3 is a diagram showing ESR characteristics of the smoothing capacitor, and FIG. 4 is a differential amplifier circuit It is a figure which shows the threshold voltage characteristic. In this embodiment, a step-down switching regulator and a step-down series regulator are used for the power supply device.

  As shown in FIG. 1, the power supply device 40 is provided with a switching regulator 1 and a series regulator 2. The power supply device 40 is used for in-vehicle use, and receives an input power supply (input voltage) Vin supplied from a battery, for example, a relatively high voltage of 18V, and reduces the input voltage, for example, a relatively low voltage of 5V. This is a stabilized power supply device that stably outputs the output voltage Vout.

  The switching regulator 1 is an asynchronous rectification type and a step-down switching regulator. The switching regulator 1 is provided with a differential amplifier 11, a reference voltage generation circuit 12, a switching controller 13, a Pch MOS transistor PT1, a resistor R1, a resistor R2, a diode D1, a diode D2, an inductor L1, and a capacitor C1. The MOS transistor is also referred to as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

  The Pch MOS transistor PT1 has a source connected to the input power supply (input voltage) Vin, a drain connected to the node N4, a gate connected to the node N3, and is output from the node N3 on the output side of the switching control unit 13. This is a power MOS transistor that operates “ON” and “OFF” in response to a control signal. An output signal of Pch MOS transistor PT1 is output from node N4.

  The resistor R1 has one end connected to the node N4 and the other end connected to the node N1. The resistor R2 has one end connected to the node N1 and the other end connected to a low potential power source Vss that is a ground potential. From the node N1, the feedback voltage Vk1 divided by the resistors R1 and R2 is fed back to the positive side of the differential amplifier circuit 11.

  The reference voltage generation circuit 12 is provided between the diode D1 and the low-potential-side power supply Vss, and is composed of a BGR (Band Gap Reference bandgap reference) circuit, and generates a reference voltage Vref1 having a constant voltage with almost no temperature dependence. To do. For example, with respect to the value of the reference voltage Vref1 to be used, the fluctuation range is 0.1% or less when the operating temperature is in the range of −40 ° C. to 150 ° C.

  The diode D1 is provided between the differential amplifier circuit 11 and the reference voltage generation circuit 12. The reference voltage Vref1 output from the reference voltage generation circuit 12 is input to the cathode side, and Vf (diode forward voltage from the anode side) is input. ) Is added to the negative side of the differential amplifier circuit 11.

  The differential amplifier circuit 11 is provided between the node N1 and the diode D1 and the switching control unit 13, and is a non-inverting comparison type comparator. The reference voltage Vref1a is input to the negative side, and the feedback voltage Vk1 is input to the positive side to perform comparative amplification. The output signal is output from the node N2 on the output side.

  Here, when the feedback voltage Vk1 is higher than the reference voltage Vref1a, the differential amplifier circuit 11 outputs an output signal of “High” level, and when the feedback voltage Vk1 is lower than the reference voltage Vref1a, the differential amplifier circuit 11 is “Low” level. Output the output signal.

  The switching control unit 13 is provided between the Pch MOS transistor PT1 and the differential amplifier circuit 11, and receives a signal (from the output side node N2) output from the differential amplifier circuit 11 and the control signal CLK, and receives the Pch MOS. A control signal for controlling the operation of the transistor PT1 is output from the output-side node N3 to the gate of the Pch MOS transistor PT1.

  The diode D2 has a cathode connected to the node N4 and an anode connected to the low potential power source Vss. The inductor L1 has one end connected to the node N4 and the other end connected to the output voltage Vouta side.

  The capacitor C1 is an output smoothing capacitor having one end connected to the output voltage Vouta side and the other end connected to the low potential side power source Vss. Here, as the capacitor C1, for example, an aluminum electrolytic capacitor that can have a maximum capacity with a minimum area, can handle a large capacity, can handle a relatively large voltage at a relatively low cost, for example, is used. A tantalum electrolytic capacitor or the like may be used instead of the aluminum electrolytic capacitor.

  The series regulator 2 is a step-down type series regulator. The series regulator 2 is provided with a differential amplifier circuit 21, a reference voltage generation circuit 22, a resistor R21, a resistor R22, and a Pch MOS transistor PT21.

  The Pch MOS transistor PT21 has a source connected to the output side of the switching regulator 1 (output voltage Vouta is input), a drain connected to the node N13, a gate connected to the node N12, and an output side of the differential amplifier circuit 21. This switching element operates “ON” and “OFF” in response to a control signal output from the node N12. An output signal Vout of the power supply device 40 is output from the node N13, and stable power having a constant voltage is supplied to the load 3.

  The resistor R21 has one end connected to the node N13 and the other end connected to the node N11. The resistor R22 has one end connected to the node N11 and the other end connected to the low potential side power source Vss. From the node N11, the feedback voltage Vk2 divided by the resistors R21 and R22 is fed back to the + side of the differential amplifier circuit 21.

  The reference voltage generation circuit 22 is provided between the differential amplifier circuit 21 and the low-potential-side power supply Vss, is configured by a BGR (Band Gap Reference) circuit, and generates a reference voltage Vref2 having almost no temperature dependence.

  The differential amplifier circuit 21 is provided between the node N11 and the reference voltage generation circuit 22 and the Pch MOS transistor PT21, and is a non-inverting comparison type comparator. The differential amplifier circuit 21 inputs the reference voltage Vref2 to the negative side and the feedback voltage Vk2 to the positive side. The comparatively amplified output signal is output from the node N12 on the output side.

  Here, the differential amplifier circuit 21 outputs an “High” level output signal when the feedback voltage Vk2 is higher than the reference voltage Vref2, and the “Low” level output signal when the feedback voltage Vk2 is lower than the reference voltage Vref2. Output the output signal.

  As shown in FIG. 2, an equivalent circuit of a smoothing capacitor used in a switching regulator is a capacitance Ca, equivalent series inductance (ESL) La, equivalent series resistance (ESR) between terminals Pad1 and Pad2. It can be expressed as comprising Ra and equivalent parallel resistance Rb.

  Here, the capacitor Ca and the equivalent parallel resistance Rb are arranged in parallel between the terminal Pad1 and one end of the equivalent series resistance (ESR) Ra. One end of the equivalent series inductance (ESL) La is connected to the other end of the equivalent series resistance (ESR) Ra, and the other end is connected to the terminal Pad2.

  As shown in FIG. 3, the ESR characteristic of the capacitor C1 used as the smoothing capacitor of the switching regulator 1 has temperature dependency and frequency dependency. In the temperature dependence, it has a large ESR value at a low temperature and a small ESR value at a high temperature, and the relationship between the actual operating temperature Ta of the capacitor C1 and the ESR value is substantially inversely proportional. In frequency dependence, the ESR value decreases at higher frequencies.

  Since the diode D1 is provided between the differential amplifier circuit 11 and the reference voltage generation circuit 12, as shown in FIG. 4, the threshold voltage characteristic of the differential amplifier circuit 11 is not constant with respect to temperature. It has a large threshold voltage at low temperatures and a small threshold voltage at high temperatures, and the relationship between the actual operating temperature Ta of the capacitor C1 and the threshold voltage is approximately inversely proportional.

Here, the threshold voltage corresponds to the reference voltage Vref1a. The reference voltage Vref1a input to the negative side of the differential amplifier circuit 11 is
Vref1a = Vref1 + Vf ..... Equation (1)
It is represented by The reference voltage Vref1 is a constant voltage having almost no temperature dependence. Vf is a forward voltage of the diode D1, has temperature dependency, and has a large value at a low temperature and a small value at a high temperature.

  Here, the shape and profile of the diode D1 are such that the ESR temperature characteristic of the capacitor C1 (FIG. 3) at the operating frequency (f) of the switching regulator 1 and the threshold voltage temperature characteristic of the differential amplifier circuit 11 are the same temperature characteristic. Is optimized. For example, the shape and profile of the diode D1 are optimized so as to correspond to the temperature characteristics of an aluminum electrolytic capacitor or a tantalum electrolytic capacitor used for the capacitor C1.

  Next, characteristics of the power supply device will be described with reference to FIGS. 5 is a diagram showing the output characteristics of the power supply device, FIG. 6 is a diagram showing the output characteristics of the switching regulator during the low temperature operation of the conventional power supply device, and FIG. 7 is a diagram showing the output characteristics during the low temperature operation of the conventional power supply device. It is. Here, in the conventional power supply device, no diode is provided between the reference voltage generation circuit of the switching regulator and the differential amplifier circuit.

  As shown in FIG. 5, when the power supply device 40 operates at a high temperature, for example, when the actual operating temperature Ta of the capacitor C1 is 150 ° C., the output voltage Vouta1 output from the switching regulator 1 has a relatively small output ripple.

  On the other hand, when the power supply device 40 is operated at a low temperature, for example, when the actual operating temperature Ta of the capacitor C1 is −40 ° C., the output voltage Vouta2 output from the switching regulator 1 is larger than that when the output ripple is high. However, the minimum value of the output voltage Vouta2 (at low temperature) output from the switching regulator 1 is larger than the minimum value of the output voltage Vouta1 (at high temperature) output from the switching regulator 1. Moreover, both are set higher than the output voltage Vout of the power supply device 40.

  Therefore, the output ripple of the output voltage Vouta2 (at low temperature) output from the switching regulator 1 does not affect the operation of the series regulator 2, and the output of the output voltage Vouta1 (at high temperature) output from the switching regulator 1 Ripple does not affect the operation of the series regulator 2. Therefore, the output voltage Vout output from the power supply device has greatly reduced output ripple and does not have temperature dependence.

  However, as shown in FIG. 6, when the conventional power supply device is operated at a low temperature, for example, when the actual operating temperature Ta of the capacitor is −40 ° C., the output voltage (at low temperature) output from the switching regulator is compared with the output ripple. Moreover, the minimum value of the output voltage (at low temperature) output from the switching regulator is smaller than the target output voltage value of the series regulator.

  Therefore, as shown in FIG. 7, the output ripple of the output voltage (at low temperature) output from the switching regulator affects the operation of the series regulator, and is output from the switching regulator as the output voltage output from the power supply device. A large output ripple occurs in the output voltage (at low temperature).

  As described above, in the power supply device of this embodiment, the switching regulator 1 and the series regulator 2 are provided. The switching regulator 1 includes a differential amplifier 11, a reference voltage generation circuit 12, a switching control unit 13, a Pch MOS transistor PT1, a resistor R1, a resistor R2, a diode D1, a diode D2, an inductor L1, and a capacitor C1, and is a series regulator. 2, a differential amplifier circuit 21, a reference voltage generation circuit 22, a resistor R21, a resistor R22, and a Pch MOS transistor PT21 are provided. The reference voltage Vref1a output from the reference voltage generation circuit of the switching regulator 1 and input to the negative side of the differential amplifier circuit 11 via the diode D1 has the same temperature characteristics as the capacitor C1. The threshold voltage is set so as to be large during low temperature operation and small during high temperature operation.

  For this reason, the minimum value of the output voltage Vouta2 (at the time of low temperature) output from the switching regulator 1 is larger than the minimum value of the output voltage Vouta1 (at the time of high temperature) output from the switching regulator 1. Moreover, both are set higher than the output voltage Vout of the power supply device 40.

  Accordingly, even when a capacitor having a large ESR temperature characteristic is used as the smoothing capacitor C1, the output ripple of the output voltage Vouta2 (at low temperature) output from the switching regulator 1 affects the operation of the series regulator 2. Thus, the output ripple of the output voltage Vouta1 (at high temperature) output from the switching regulator 1 does not affect the operation of the series regulator 2. Therefore, the output voltage Vout output from the power supply device 40 is greatly reduced in output ripple as compared with the conventional case.

  In this embodiment, the present invention is applied to a power supply device composed of a step-down switching regulator and a step-down series regulator. However, a step-up switching regulator, an inverting switching regulator, or a buck-boost switching regulator is used for the power supply device. Also good. In that case, it is preferable to change the configuration of the series regulator to be compatible with the switching regulator. Further, a MISFET (Metal Insulator Semiconductor Field Effect Transistor) having a gate insulating film may be used instead of the MOS transistor.

  Next, a power supply device according to Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 8 is a circuit diagram showing the configuration of the power supply apparatus. In this embodiment, the output characteristics of the reference voltage generation circuit of the switching regulator are changed.

  As shown in FIG. 8, the power supply device 40a is provided with a switching regulator 1a and a series regulator 2. The power supply device 40a is used for in-vehicle use, and receives an input power supply (input voltage) Vin supplied from a battery, for example, a relatively high voltage of 18V, and reduces the input voltage, for example, a relatively low voltage of 5V. This is a stabilized power supply device that stably outputs the output voltage Vout.

  The switching regulator 1a is an asynchronous rectification method and is a step-down switching regulator. The switching regulator 1a is provided with a differential amplifier 11, a reference voltage generation circuit 12a, a switching control unit 13, a Pch MOS transistor PT1, a resistor R1, a resistor R2, a diode D2, an inductor L1, and a capacitor C1.

  The reference voltage generation circuit 12a is provided between the differential amplifier 11 and the low potential side power source Vss, and generates a reference voltage Vref1b having the same temperature characteristics as the capacitor C1. In order to generate the reference voltage Vref1b having the same temperature characteristics as the capacitor C1, for example, two cascaded resistors (preferably formed on the field insulating film) using a polycrystalline silicon film having different temperature characteristics are used as the reference voltage. There is a method of providing a reference voltage Vref1b using a resistance-divided voltage provided on the output side of the generation circuit.

  The differential amplifier circuit 11 is provided between the node N1 and the reference voltage generation circuit 12a and the switching control unit 13, and is a non-inverting comparison type comparator. The differential amplifier circuit 11 inputs the reference voltage Vref1b to the negative side and the feedback voltage Vk1 to the positive side. The comparatively amplified output signal is output from the output side node N2.

  Here, when the feedback voltage Vk1 is higher than the reference voltage Vref1b, the differential amplifier circuit 11 outputs an output signal of “High” level, and when the feedback voltage Vk1 is lower than the reference voltage Vref1b, the differential amplifier circuit 11 outputs “Low” level. Output the output signal.

  As described above, in the power supply device of this embodiment, the switching regulator 1a and the series regulator 2 are provided. The switching regulator 1a is provided with a differential amplifier 11, a reference voltage generation circuit 12a, a switching control unit 13, a Pch MOS transistor PT1, a resistor R1, a resistor R2, a diode D2, an inductor L1, and a capacitor C1, and the series regulator 2 A differential amplifier circuit 21, a reference voltage generation circuit 22, a resistor R21, a resistor R22, and a Pch MOS transistor PT21 are provided. The reference voltage Vref1b output from the reference voltage generation circuit of the switching regulator 1a and input to the negative side of the differential amplifier circuit 11 has the same temperature characteristics as the capacitor C1, and the threshold voltage of the differential amplifier circuit 11 operates at a low temperature. It is set so that it is large in time and small in high temperature operation.

  For this reason, the minimum value of the output voltage Vouta2 (at the time of low temperature) output from the switching regulator 1a is larger than the minimum value of the output voltage Vouta1 (at the time of high temperature) output from the switching regulator 1a. Moreover, both are set higher than the output voltage Vout of the power supply device 40a.

  Accordingly, even when a capacitor having a large ESR temperature characteristic is used as the smoothing capacitor C1, the output ripple of the output voltage Vouta2 (at low temperature) output from the switching regulator 1a affects the operation of the series regulator 2. Thus, the output ripple of the output voltage Vouta1 (at high temperature) output from the switching regulator 1a does not affect the operation of the series regulator 2. Therefore, the output voltage Vout output from the power supply device 40a is greatly reduced in output ripple as compared with the conventional case.

  The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the invention.

  For example, in the embodiment, the present invention is applied to an asynchronous rectification switching regulator, but can be applied to a synchronous rectification switching regulator having a high side switching element and a low side switching element. Moreover, although it applied to the vehicle-mounted power supply device, it can apply to the general power supply device with a strong output ripple reduction request | requirement.

The present invention can be configured as described in the following supplementary notes.
(Supplementary Note 1) A smoothing capacitor, an inductor, and a first diode provided on the output side, and a first reference voltage generation circuit that generates a first reference voltage having the same temperature characteristics as the smoothing capacitor; A first comparator that inputs the first reference voltage on the-side and inputs a first feedback voltage resistance-divided on the + side and outputs a comparatively amplified signal; And a second reference voltage generation circuit for generating a second reference voltage, and a second reference voltage on the negative side. And a second comparator for inputting a second feedback voltage resistance-divided on the + side and outputting a comparatively amplified signal, the first output voltage being input as an input voltage, 2 output voltage A power supply device comprising a series regulator for output.
(Supplementary note 2) The power supply device according to supplementary note 1, wherein the switching regulator is a step-down type, a step-up type, a step-up / step-down type, or an inversion type.

1 is a circuit diagram showing a configuration of a power supply device according to Embodiment 1 of the present invention. The figure which shows the equivalent circuit of the smoothing capacitor used for the switching regulator which concerns on Example 1 of this invention. The figure which shows the ESR characteristic of the smoothing capacitor which concerns on Example 1 of this invention. FIG. 3 is a diagram illustrating threshold voltage characteristics of the differential amplifier circuit according to the first embodiment of the invention. The figure which shows the output characteristic of the power supply device which concerns on Example 1 of this invention. The figure which shows the switching regulator output characteristic at the time of low temperature operation | movement of the conventional power supply device which concerns on Example 1 of this invention. The figure which shows the output characteristic at the time of low temperature operation | movement of the conventional power supply device which concerns on Example 1 of this invention. The circuit diagram which shows the structure of the power supply device which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Switching regulator 2 Series regulator 3 Load 11, 21 Differential amplifier circuit 12, 22 Reference voltage generation circuit 13 Switching control part 40, 40a Power supply device C1 Capacitor Ca Capacity CLK Control signal D1, D2 Diode L1 Inductor La Equivalent series inductance N1-4, N11-13 Node Pad1, Pad2 Terminal PT1, PT21 Pch MOS transistors R1, R2, R21, R22 Resistor Ra Equivalent Series Resistance (ESR)
Rb Equivalent parallel resistance Vin Input power supply (input voltage)
Vk1, Vk2 Feedback voltage Vout, Vouta Output voltage Vref1, Vref1a, Vref1b, Vref2 Reference voltage Vss Low potential side power supply

Claims (5)

A smoothing capacitor provided on the output side and a reference voltage having the same temperature characteristics as the smoothing capacitor are input to the-side, a feedback voltage divided by resistance is input to the + side, and a comparatively amplified signal is output. A switching regulator that includes a comparator, inputs a first input voltage, and outputs a first output voltage;
A series regulator that inputs the first output voltage as an input voltage and outputs a second output voltage;
A power supply device comprising:   The reference voltage is provided on the output side of the reference voltage generation circuit to a voltage output from a reference voltage generation circuit configured by a band gap reference circuit, and is added by a forward voltage of the diode by the diode. The power supply device according to claim 1, wherein the power supply device is a device.   The power supply apparatus according to claim 1, wherein the switching regulator and the series regulator are of a step-down type.   4. The power supply device according to claim 1, wherein the smoothing capacitor is an aluminum electrolytic capacitor or a tantalum electrolytic capacitor. 5. A smoothing capacitor, an inductor, a first diode provided on the output side, a band gap reference circuit, a first reference voltage generation circuit that generates a first reference voltage, and the first reference voltage Is input to the cathode, the second diode that outputs the second reference voltage from the anode, the second reference voltage is input to the negative side, and the first feedback voltage that is resistance-divided is input to the positive side. A first comparator that outputs a signal that has been compared and amplified in this manner, a switching regulator that receives the first input voltage and outputs the first output voltage;
A second reference voltage generating circuit configured by a bandgap reference circuit and generating a third reference voltage; and a second feedback voltage obtained by inputting the third reference voltage on the negative side and resistance-dividing on the positive side And a second comparator that outputs a comparatively amplified signal, inputs the first output voltage as an input voltage, and outputs a second output voltage;
A power supply device comprising:

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