JPH0421359A - Switching regulator - Google Patents

Abstract

PURPOSE:To simplify the circuitry and to miniaturize a switching regulator by setting the load current of a first rectifying/smoothing circuit above a critical value and subjecting the variation of output voltage from a second rectifying/ smoothing circuit to frequency modulation and comparison. CONSTITUTION:A switching transistor Qs controls current flowing through the primary winding L1 of a high frequency transformer T. A DC voltage V1 produced in a first secondary winding L2 is fed to a load RL1, whereas a DC voltage V3 produced in a second secondary winding L3 is fed to a load RL2. The voltage V1 is detected through a differential amplifier 12 and fed to a differential amplifier 18. A voltage V2 is detected through a differential amplifier 14 and converted through an oscillation circuit 16 into a triangular wave signal Sa which is then fed to the differential amplifier 18. The differential amplifier 18 compares a differential signal 1 with the voltage of the triangular wave signal Sa and controls the switching transistor Qs to stabilize the voltage V2. The voltage V1 is stabilized by the differential amplifier 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-output switching regulator that generates a plurality of DC voltages.

[Prior art] Conventionally, as a multi-output switching regulator, the sixth
There was something shown in the figure.

This converts the rectified voltage VIN obtained by rectifying the AC voltage from the AC power supply 2 using the rectifier 4 and smoothing it using the smoothing capacitor 6 into the switching transistor Q.
s is converted into a pulsed alternating voltage by the on/off operation of is induced as a pulse voltage V l + V 2 proportional to the turns ratio, and each pulse voltage V I + V 2 is rectified and smoothed by two circuits to generate DC voltages V1 and v2, and these voltages ■, and ■2 load RL, and RL
2.

That is, the first circuit includes a saturable reactor S in the secondary winding L2.
L connects and diodes D1. .

D12, choke coil CH1, smoothing capacitor C01
A rectifying and smoothing circuit consisting of is connected, and a voltage detection circuit 8 detects the voltage obtained by dividing the voltage V across the smoothing capacitor C8 by the resistors R1 and R2,
By controlling the energization of the feedback transistor Q1, feedback control is performed to suppress fluctuations in the voltage 1.

In the second circuit, a rectifying and smoothing circuit consisting of a diode D21゜D2゜, a choke coil CH2 and a smoothing capacitor CO2 is connected to the secondary winding 3, and further a smoothing capacitor C
The pulse width control circuit 10 controls the fluctuation of the voltage ■2 generated at the
is detected, and the energization period control (PWM) of the switching transistor Qs is performed to suppress the fluctuation.

[Problems to be Solved by the Invention] In such conventional multi-output switching regulators, each output circuit is provided with an independent feedback circuit for suppressing fluctuations in output voltage. As many power control elements and control circuits as the number of circuits are required, there is a problem in that the overall size of the device increases and the price increases.

The present invention has been made in view of these conventional problems, and an object of the present invention is to provide a multi-output switching regulator that has a simpler circuit configuration and can be downsized.

[Means for Solving the Problem] In order to achieve such an object, the present invention converts an input voltage into an alternating voltage by the on/off operation of a power switching element such as a switching transistor, and converts the input voltage into an alternating voltage through a high frequency transformer. Targeted is a multi-output switching regulator that induces the AC voltage on the secondary side and forms two types of DC voltages using two rectifier and smoothing circuits from the AC voltage induced on the secondary side. shall be.

Then, the inductance of the first rectifying and smoothing circuit is set to a value at which the load current does not fall below a critical value, and the inductance of the second rectifying and smoothing circuit is set to a value at which the load current does not exceed the critical value. A drive formed by pulse width modulating the drive of the current switching element according to a change in the output voltage of the first rectifying and smoothing circuit and frequency modulating a change in the output voltage of the second rectifying and smoothing circuit. The energization period of the power switching element is controlled by using a signal.

[Function] According to the switching regulator of the present invention having such a configuration, two output circuits can be independently controlled with one power switching element.Therefore, the number of parts can be reduced, resulting in miniaturization and low cost. can be realized.

[Embodiment] A first embodiment of the present invention will be described with reference to the drawings. First, the circuit configuration will be explained with reference to FIG.
is converted into a rectangular wave voltage by the on/off operation of the switching transistor Qs, and is supplied to the primary winding L1 of the high frequency transformer T. Then, the first of the high frequency transformer T
Two types of DC voltages 1 and V2 are generated by two rectifying and smoothing circuits that rectify and smooth the voltages induced in the secondary winding L2 and the second secondary winding L3, respectively.

That is, the first rectifying and smoothing circuit connected to the first secondary winding L2 is a forward type circuit consisting of diodes Dll and D12, a choke coil CHI, and a smoothing capacitor C81, and converts the direct current generated in the smoothing capacitor Co1. Supply voltage 1 to load RL. In addition, load current 11
The inductance is set such that the value does not fall below a critical value.

Further, the second rectifying and smoothing circuit connected to the second secondary winding L3 includes a diode D2. ．． D2□ and choke coil C
It consists of a forward type circuit including H2 and a smoothing capacitor C62, and is configured to supply the DC voltage v3 generated in the smoothing capacitor CO2 to the load RL2. In addition, so that the load current I2 does not exceed the critical value,
The inductance is set.

Further, by detecting fluctuations in each of the DC voltages V, V2 and automatically controlling the energization period of the switching transistor Qs, the DC voltages V1, . A pulse width control circuit is provided to stabilize V2. That is, the pulse width control circuit outputs a difference signal Δ1 corresponding to the difference between the voltage V of the smoothing capacitor Co1 and the reference voltage V0F, and the voltage v2 of the smoothing capacitor C62 and the reference voltage V□. A differential amplifier 14 outputs a difference signal Δ2 corresponding to the difference, an oscillation circuit 16 generates a triangular wave signal SR whose frequency is changed by an amount corresponding to the voltage change of the difference signal Δ2, and a It is comprised of a differential amplifier 18 that generates a rectangular wave drive signal sb by comparing voltages, and is configured to control the energization period of the switching transistor Qs using the drive signal sb.

Next, the operation of the first embodiment will be explained.

First, when the voltage (1) of the rectifying and smoothing circuit fluctuates, the differential amplifier 12 detects this fluctuation as a difference signal Δ1, and the differential amplifier 18 compares the triangular wave signal Sa and the difference signal Δ1 to drive the signal. The on period T of the signal sb is adjusted according to the variation. Therefore, when the voltage V1 rises above the predetermined voltage, the on period T. Off period T for N
. When the FF ratio increases and the voltage (2) drops below the predetermined voltage, the on-period T is reached. Off period T for N. ,
The voltage v1 is stabilized by reducing the ratio of F.

Moreover, when the voltage v2 of the second rectifying and smoothing circuit fluctuates,
The differential amplifier 14 detects this variation as a difference signal Δ2,
The oscillation circuit 16 changes the frequency of the triangular wave signal Sa by the voltage of the difference signal Δ2. Then, the differential amplifier 18 compares the triangular wave signal Sa and the difference signal Δ1, whereby the frequency of the drive signal sb is adjusted according to the variation. Therefore, when the voltage v2 rises above a predetermined voltage, the energizing frequency of the switching transistor Qs increases, and conversely, when the voltage 2 falls below the predetermined voltage, the energizing frequency of the switching transistor Q+ decreases. in,
Stabilize voltage V2.

Here, in order to stabilize the fluctuation of the voltage (2), the energization period T of the drive signal sb is set. Feedback control of N causes some fluctuation in voltage V2 at the initial point of control, but this fluctuation in voltage v2 is stabilized by frequency adjustment by differential amplifier 14 and oscillation circuit 16. Furthermore, when the frequency of the drive signal sb is feedback-controlled in order to stabilize fluctuations in the voltage (2), a slight fluctuation occurs in the voltage V1 at the initial point of control, but this fluctuation in the voltage V is due to the differential Amplifier 14
The energization period T. It is stabilized by adjusting N. In this way, the energization period T of the drive signal sb. The voltages 2 and V3 are stabilized through the interaction of N and frequency control.

FIG. 2 shows the energization period T of the switching transistor Qs.
. N and the blocking period T. Source-drain voltage V in FF. , the corresponding current I flowing through the choke coil CHI of the first rectifying and smoothing circuit, and the current I flowing through the choke coil CH2 of the second rectifying and smoothing circuit.
2 and the average current I. 1 and ■. This shows the relationship between the two.

Next, a second embodiment will be explained with reference to FIG.

This is a configuration in which the first rectifying and smoothing circuit is configured using a flyback method, and the second rectifying and smoothing circuit is configured using a forward method. The voltages V, V2 are stabilized by pulse modulating them according to the fluctuations in the voltage v2 generated in the second rectifying and smoothing circuit and frequency modulating them according to the fluctuations in the voltage v2 generated in the second rectifying and smoothing circuit. let

Next, a third embodiment will be described with reference to FIG.

This converts the AC voltage converted by the on/off operation of the switching transistor Qs into two high frequency transformers Tl and T2.
are induced in the secondary windings L1□, L2° of each rectifying and smoothing circuit through the respective negative windings LIL+L21 of the flyback system, respectively. The second rectifying and smoothing circuit generates two types of DC voltages V1. The drive signal Sa for driving the switching transistor Qs is pulse-modulated according to fluctuations in the voltage V1 generated by the first rectifying and smoothing circuit, and is pulse-modulated by the second rectifying and smoothing circuit. The respective voltages V, V2 are stabilized by frequency modulating according to fluctuations in the generated voltage (2).

Next, a fourth embodiment will be described with reference to FIG.

This causes the alternating current voltage converted by the on/off operation of the switching transistor Qs to be induced in the secondary winding L32 of the rectifying and smoothing circuit through the primary winding L31 of the high frequency transformer T3, and Two types of DC voltages V, V2 are formed by two commonly connected rectifying and smoothing circuits.

That is, the first rectifying and smoothing circuit includes a diode D C++
A DC voltage V1 is generated by smoothing the voltage generated at one end of the rectifying bridge circuit consisting of D C21D dl and D a2 with a smoothing circuit consisting of a choke coil CHI and a smoothing capacitor C61, and a second rectifying and smoothing circuit is generated. generates a DC voltage v2 by smoothing the voltage generated at the other end of the rectifying bridge circuit with a smoothing circuit consisting of a choke coil CH2 and a smoothing capacitor C62. Then, the drive signal Sa for driving the switching transistor Qs is pulse-modulated according to the fluctuation of the voltage V1 generated in the first rectification and smoothing circuit, and the fluctuation of the voltage V2 generated in the second rectification and smoothing circuit. The respective voltages 1 and 2 are stabilized by frequency modulation according to the voltage.

"Effects of the Invention" As explained above, according to the switching regulator of the present invention, two output circuits can be independently controlled with one power switching element, so the number of parts can be reduced, resulting in miniaturization and low cost. can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the circuit of the first embodiment of the present invention;
The figure is a waveform diagram showing the main part operation of the first embodiment;
A circuit diagram showing the circuit of the embodiment; Fig. 4 is a circuit diagram showing the circuit of the third embodiment; Fig. 5 is a circuit diagram showing the circuit of the fourth embodiment; Fig. 6 is a circuit diagram showing the circuit of the conventional example. It is a diagram. Symbols in the figure; 2: AC power supply: Rectifier 6: Smoothing capacitor 12, 14.18: Differential amplifier 16: Oscillator circuit T, Tl, T2. T3: High frequency transformer D++, D+
□, D2+, D22. D. Db, DCI! DC21Dal, Da2:
Dio-CH1, CH2: York coil COI+ C02' Smoothing capacitor RLl/RL2: Load VREF: Reference power source

Claims (1)

[Claims] (1) Convert the input voltage into an alternating voltage by the on/off operation of the power switching element, induce the alternating voltage to the secondary side via a high frequency transformer, and convert the induced alternating voltage to the secondary side. , in a multi-output switching regulator in which two types of DC voltages are formed by two rectifying and smoothing circuits, the inductance of the first rectifying and smoothing circuit is set to a value that does not cause the load current to fall below a critical value. At the same time, the inductance of the second rectifying and smoothing circuit is set to a value at which the load current does not exceed a critical value, and the drive of the power switching element is pulsed according to the change in the output voltage of the first rectifying and smoothing circuit. width modulation and the second
1. A switching regulator comprising means for controlling the energization period of the power switching element by frequency modulating a change in the output voltage of the rectifying and smoothing circuit using a drive signal formed.