JP2004201478A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a switching power supply which outputs negative DC voltage without needing a dedicated negative power supply for driving an operational amplifier constituting a series regulator circuit. <P>SOLUTION: This power supply is provided with: a switching circuit 20 for generating a primary AC voltage by making DC voltage from a DC power supply 10 intermittent; a second rectification smoothing circuit 40 which rectifies and smooths a secondary AC voltage induced with the primary AC voltage generated with the switching circuit 20 and outputs DC voltage; and a series regulator circuit 50 which stabilizes the DC voltage output from the second rectification smoothing circuit 40 by controlling impedance of a MOSFET 51 connected with an output terminal of the second rectification smoothing circuit 40 by using an operational amplifier 52 and outputs the DC voltage as negative DC voltage. As a negative power supply of the operational amplifier 52, the negative DC voltage output from the series regulator circuit 50 is used. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply used as a DC power supply for various electronic devices.
[0002]
[Prior art]
In a conventional switching power supply device, in order to increase the voltage accuracy of the output DC voltage and obtain excellent EMC (ElectroMagnetic Compatibility) characteristics, for example, a rectified and smoothed DC voltage is converted to another dedicated power supply. Using a driven series regulator circuit, the DC voltage is further converted to a stabilized DC voltage and output.
[0003]
This series regulator circuit can be configured using a three-terminal regulator, but in recent years, in order to reduce loss in the series regulator circuit, for example, a field effect transistor is used as a variable impedance element, and this field effect transistor is controlled by an operational amplifier. A device that outputs a desired DC voltage has been developed (see Patent Document 1).
[0004]
However, when a series regulator circuit controlled by an operational amplifier is used as a switching power supply circuit that outputs a negative DC voltage, a positive power supply and a negative power supply are required to drive the operational amplifier. As a positive power supply, a power supply supplied to a control circuit for pulse width modulation can be used together, but a negative power supply is required separately. Therefore, the conventional switching power supply circuit includes a unit for outputting a dedicated negative DC voltage for driving the operational amplifier.
[0005]
By adopting the above configuration, even in a conventional switching power supply circuit that outputs a negative DC voltage, it is possible to improve the voltage accuracy of the negative DC voltage output from the switching power supply circuit and achieve excellent EMC characteristics. Can be realized.
[0006]
[Patent Document 1]
JP-A-9-233810 (FIG. 1)
[Patent Document 2]
JP 2001-078445 A [Patent Document 3]
JP-A-9-065653
[Problems to be solved by the invention]
However, in the above-described conventional switching power supply device, means for outputting a negative DC voltage for driving the operational amplifier included in the series regulator circuit is required, so that the manufacturing cost increases, the power consumption increases, and the circuit scale increases. In addition, there is a problem that the power conversion efficiency is reduced.
[0008]
The present invention has been made in order to solve the above-described problem, and has a switching function capable of outputting a negative DC voltage without requiring a dedicated negative power supply for driving an operational amplifier constituting a series regulator circuit. The purpose is to obtain a power supply.
[0009]
[Means for Solving the Problems]
A switching power supply according to the present invention includes a switching circuit that generates a first AC voltage by interrupting a DC voltage from a DC power supply, and a second AC voltage that is induced by the first AC voltage generated by the switching circuit. A rectifying and smoothing circuit for rectifying and smoothing the rectifying and smoothing circuit, and stabilizing a DC voltage output from the rectifying and smoothing circuit by controlling an impedance of an element connected to an output terminal of the rectifying and smoothing circuit with an operational amplifier. And a series regulator circuit that outputs the negative DC voltage as a negative DC voltage, wherein a negative DC voltage output from the series regulator circuit is used as a negative power supply of the operational amplifier.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 1 of the present invention. This switching power supply device includes a DC power supply 10, a switching circuit 20, a first rectifying and smoothing circuit 30, a second rectifying and smoothing circuit 40, a series regulator circuit 50, a pulse width modulation control circuit 60, and a gate drive circuit 70.
[0011]
DC power supply 10 generates DC voltage V and applies it to switching circuit 20.
The switching circuit 20 includes a transformer 21 and a field effect transistor (TR) 23 as a variable impedance element inserted in series with a primary winding 22 of the transformer 21. A DC voltage V is applied from the DC power supply 10 to both ends of the primary winding 22 of the transformer 21.
[0012]
The transformer 21 has two secondary windings such as a first winding 24 and a second winding 25. The first winding 24 is connected to a first rectifying / smoothing circuit 30, and the second winding 25 is connected to a second rectifying / smoothing circuit 40.
[0013]
The field effect transistor 23 is turned on / off according to a drive signal from the gate drive circuit 70. By repeatedly turning on / off the field effect transistor 23, the DC voltage V from the DC power supply 10 is intermittently applied and applied to the primary winding 22 of the transformer 21 as the first AC voltage.
[0014]
The first rectifying / smoothing circuit 30 rectifies and smoothes the AC voltage induced in the first winding 24 of the transformer 21 to generate a DC voltage. The output terminal T12 on the low voltage side of the first rectifying / smoothing circuit 30 is grounded. Accordingly, a positive DC voltage is output from the output terminal T11 on the high voltage side of the first rectifying / smoothing circuit 30 and supplied to the series regulator circuit 50 and the pulse width modulation control circuit 60. Although not described in detail, the first rectifying / smoothing circuit 30 is composed of a known circuit including diodes 31 and 32, an inductor 33, and a capacitor.
[0015]
The second rectifying / smoothing circuit 40 rectifies and smoothes the AC voltage induced in the second winding 25 of the transformer 21 to generate a DC voltage. The output terminal T21 on the high voltage side of the second rectifying / smoothing circuit 40 is grounded via the field effect transistor 51 in the series regulator circuit 50. Accordingly, a negative DC voltage is output from the output terminal T22 on the low voltage side of the second rectifying / smoothing circuit 40 and supplied to the series regulator circuit 50. Although not described in detail, the second rectifying / smoothing circuit 40 is constituted by a known circuit including diodes 41 and 42, an inductor 43, and a capacitor 44.
[0016]
The series regulator circuit 50 includes a field effect transistor 51, an operational amplifier 52, a resistor 53, a resistor 54, a resistor 55, and a zener diode 56. The resistor 53, the resistor 54, and the resistor 55 are connected in series, and are inserted between the output terminal T11 of the first rectifying / smoothing circuit 30 and the output terminal T22 of the second rectifying / smoothing circuit 40. Further, the Zener diode 56 is connected between a connection point between the resistors 53 and 54 and the output terminal T22 of the second rectifying / smoothing circuit 40.
[0017]
The drain of the field effect transistor 51 is connected to the output terminal T21 of the second rectifying / smoothing circuit 40, and the source is grounded. The gate of the field effect transistor 51 is connected to the output terminal of the operational amplifier 52.
[0018]
The positive power supply terminal of the operational amplifier 52 is connected to the output terminal T11 of the first rectifying / smoothing circuit 30. The positive power supply terminal is supplied with a positive DC voltage from the first rectifying and smoothing circuit 30. The negative power supply terminal of the operational amplifier 52 is connected to the output terminal T22 of the second rectifying / smoothing circuit 40. A negative DC voltage is supplied from the second rectifying / smoothing circuit 40 to the negative power supply terminal. The operational amplifier 52 requires a negative power supply to control the voltage applied to the inverting input terminal (+) so as to be equal to the voltage applied to the non-inverting input terminal (-).
[0019]
The inverting input terminal of the operational amplifier 52 is grounded, and a ground potential is applied to the inverting input terminal. The non-inverting input terminal of the operational amplifier 52 is connected to a connection point between the resistors 54 and 55. A potential obtained by dividing a positive DC voltage and a negative DC voltage by a resistor 53 and a resistor 54 connected in series with a resistor 55 is applied to the non-inverting input terminal.
[0020]
The series regulator circuit 50 controls the impedance between the drain and the source of the field effect transistor 23 so that the DC voltage generated by the second rectifying and smoothing circuit 40 is reduced to generate a negative DC voltage. A negative DC voltage is applied to the load 80 and supplied to the operational amplifier 52 as a negative power supply.
[0021]
The load 80 is connected between the source (ground potential) of the field effect transistor 51 and the output terminal T22 of the second rectifying / smoothing circuit 40, and receives a negative DC voltage.
[0022]
The pulse width modulation control circuit 60 generates a pulse signal having a pulse width corresponding to the positive DC voltage applied from the first rectifying and smoothing circuit 30 and sends the pulse signal to the gate drive circuit 70.
[0023]
The gate drive circuit 70 amplifies the pulse signal from the pulse width modulation control circuit 60 and sends it to the gate of the field effect transistor 23 as a drive signal. The field effect transistor 23 is turned on or off according to the drive signal.
[0024]
Next, the operation of the switching power supply according to Embodiment 1 of the present invention will be described.
The pulse width modulation control circuit 60 is started by receiving a start command from a start circuit (not shown) and starts generating a pulse signal. That is, the pulse width modulation control circuit 60 generates a pulse signal that repeats on and off with a pulse width corresponding to the positive DC voltage from the first rectifying / smoothing circuit 30 and sends the signal to the gate drive circuit 70.
[0025]
The gate drive circuit 70 amplifies the pulse signal from the pulse width modulation control circuit 60 to generate a drive signal, and supplies the drive signal to the gate of the field effect transistor 23. Thus, the field-effect transistor 23 repeats on / off in accordance with the pulse signal. As a result, the DC voltage V from the DC power supply 10 is interrupted and applied to the primary winding 22 of the transformer 21 as the first AC voltage.
[0026]
When the first AC voltage is applied to the primary winding 22 of the transformer 21, a third AC voltage and a second AC voltage are induced in the first winding 24 and the second winding 25, respectively, and a first rectifying and smoothing circuit is provided. 30 and the second rectifying / smoothing circuit 40. The AC voltage induced in the secondary windings 24 and 25 is determined by the turns ratio between the primary winding 22 and the secondary windings 24 and 25, respectively.
[0027]
The first rectifying / smoothing circuit 30 applies a positive DC voltage obtained by rectifying and smoothing the third AC voltage induced in the first winding 24 to the pulse width modulation control circuit 60 and the series regulator circuit 50. . In parallel with the operation of the first rectifying / smoothing circuit 30, the second rectifying / smoothing circuit 40 rectifies and smoothes the second AC voltage induced in the second winding 25 to generate a DC voltage. Send to 50.
[0028]
As a result, the pulse width modulation control circuit 60 generates a pulse signal having a pulse width corresponding to the positive DC voltage from the first rectifying / smoothing circuit 30 and sends it to the gate drive circuit 70. Thereafter, as described above, the pulse width of the pulse signal is constant due to the flow of the signal in a closed path such as the pulse width modulation control circuit 60, the gate drive circuit 70, the field effect transistor 23, the transformer 21, and the first rectifying and smoothing circuit 30. , And the switching power supply enters a balanced state.
[0029]
On the other hand, the series regulator circuit 50 is configured such that the positive DC voltage from the first rectifying / smoothing circuit 30 and the DC voltage from the second rectifying / smoothing circuit 40 are applied to the positive power supply terminal and the negative power supply terminal of the operational amplifier 52. The operation of the operational amplifier 52 is started. Thus, DC voltage stabilization control by the series regulator circuit 50 is started.
[0030]
That is, when the negative DC voltage decreases, the potential applied to the inverting input terminal of the operational amplifier 52 becomes higher than the positive potential applied to the non-inverting input terminal. Therefore, the output of the operational amplifier 52 decreases, and the voltage applied between the gate and the source of the field effect transistor 51 decreases. As a result, the voltage drop between the drain and the source of the field-effect transistor 51 increases, so that the operation is performed to increase the negative output voltage.
[0031]
On the other hand, when the negative DC voltage increases, the potential applied to the inverting input terminal of the operational amplifier 52 becomes lower than the potential applied to the non-inverting input terminal, so that the output of the operational amplifier 52 increases and the The voltage applied between the gate and the source increases. As a result, the voltage drop between the drain and the source of the field effect transistor 51 is reduced, so that the operation is performed to reduce the negative DC voltage. By the above operation, when the input voltage to the series regulator circuit 50 changes, the output voltage is continuously increased and decreased by the series regulator circuit itself, and control is performed so that a constant DC voltage is output.
[0032]
As described above, according to the switching power supply according to Embodiment 1 of the present invention, a negative DC voltage is generated via series regulator circuit 50, and the negative DC voltage is used in series regulator circuit 50. Since it is configured to be used also as a negative power supply of the operational amplifier 52, there is no need to provide a dedicated negative power supply for driving the operational amplifier. As a result, it is possible to improve the voltage accuracy of the output negative DC voltage and achieve excellent EMC characteristics without causing an increase in manufacturing cost, an increase in power consumption, an increase in circuit scale, and a decrease in power conversion efficiency. Can be realized.
[0033]
【The invention's effect】
As described above, according to the present invention, a switching power supply circuit includes a switching circuit that generates a first AC voltage by interrupting a DC voltage from a DC power supply, and a first AC voltage generated by the switching circuit. A rectifying / smoothing circuit for rectifying and smoothing the induced second AC voltage to output a DC voltage, and an output from the rectifying / smoothing circuit by controlling an impedance of an element connected to an output terminal of the rectifying / smoothing circuit with an operational amplifier; A series regulator circuit that stabilizes the DC voltage to be output as a negative DC voltage, and a negative DC voltage output from the series regulator circuit is used as a negative power supply of the operational amplifier. Requires a dedicated negative power supply to drive the operational amplifiers that constitute the series regulator circuit. There is an effect that it is possible to obtain the switching power supply unit capable of outputting a negative DC voltage without.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a switching power supply device according to Embodiment 1 of the present invention.
[Explanation of symbols]
Reference Signs List 10 DC power supply, 20 switching circuit, 21 transformer, 22 primary winding, 23 field effect transistor, 24 first winding, 25 second winding, 30 first rectifying / smoothing circuit, 40 second rectifying / smoothing circuit (rectifying / smoothing circuit) ), 50 series regulator circuit, 51 field-effect transistor (element), 52 operational amplifier, 53 to 55 resistor, 56 Zener diode, 60 pulse width modulation control circuit, 70
Gate drive circuit, 80 loads.

Claims (1)

A switching circuit that generates a first AC voltage by interrupting a DC voltage from a DC power supply;
A rectifying and smoothing circuit that rectifies and smoothes a second AC voltage induced by the first AC voltage generated by the switching circuit and outputs a DC voltage;
A series regulator circuit that stabilizes the DC voltage output from the rectifying / smoothing circuit by controlling the impedance of the element connected to the output terminal of the rectifying / smoothing circuit with an operational amplifier and outputs the DC voltage as a negative DC voltage;
A switching power supply device, wherein a negative DC voltage output from the series regulator circuit is used as a negative power supply of the operational amplifier.

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