JPH0576169A - Switching power source circuit - Google Patents

Abstract

PURPOSE:To stabilize an output voltage by inputting a DC voltage and a control reference voltage to an error amplifier, supplying a triangular wave formed based on the output voltage and the output signal of a latch circuit to a PWM comparator, and resetting the latch circuit. CONSTITUTION:In order to set a DC voltage Vout to a desired stable voltage, the DC voltage and a reference voltage Vref corresponding to the voltage Vout to be set are input to an error amplifier EA. A switching transistor T1 is provided across a capacitor C1, controlled to be switched by an inverted output QB of a latch circuit FF to generate a triangular wave. Then, the output QB is altered from an H level to an L level to turn OFF the transistor T1. As a result, the capacitor C1 is started to be charged by a constant current Io to generate a triangular wave having a slope of excellent linearity. When the voltage value of the triangular wave overrides the output voltage of the amplifier EA, the circuit FF is reset.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit, and more particularly to a technique effective for use in a pulse width modulation system having a constant switching frequency.

[0002]

2. Description of the Related Art As a pulse width modulation (hereinafter simply referred to as PWM) control IC for a switching regulator, "M5197" announced by Mitsubishi Electric Corporation in 1988.
7, FP ”. This IC is, for example, Mitsubishi Electric Corp.
Published application technical data H01-006 (4300-63.
See 2).

[0003]

There is a V (voltage) mode system in which a switch element for driving an inductive load is controlled by a latch circuit set by a periodic pulse signal and the latch circuit is reset by the output of a comparator. There is something called. In this configuration, the latch circuit,
The gain of the control loop composed of a comparator or the like becomes very high. Therefore, the output voltage becomes unstable because it responds to a slight change in the output voltage. Therefore, as shown in FIG. 3, a voltage V generated by the oscillator circuit OSC is supplied to the comparator PWMCP.
There is a mode method. In this configuration, it is difficult to operate the switching frequency in synchronization with the external signal because the triangular wave is formed by the oscillator circuit OSC. On the other hand, there is a C (current) mode system as shown in FIG. This C
In the mode method, the fact that the main switch current becomes a triangular wave is utilized, and it is amplified via the amplifier circuit Amp and supplied to the comparator PWMCP. The inclination of the triangular wave lowers the gain in the control loop to stabilize the output. Can be planned. However, in this C-mode method, since the triangular wave of the main switch current is used, the current flowing through the main switch must be an inductance current, which can be used for the flyback transformer but cannot be used for the forward transformer. There is a problem that is limited. An object of the present invention is to provide a switching power supply circuit which has a simple structure and which has stabilized output voltage and has been made versatile. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0004]

The outline of the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, the switch element is controlled by the output signal of the latch circuit set by the periodic pulse signal to drive the inductance or the transformer,
The DC voltage formed based on this inductance or the output signal of the transformer, the control reference voltage, and the error amplifier circuit are input, and the triangular wave formed based on this output voltage and the output signal of the latch circuit is supplied to the PWM comparator. Then, the latch circuit is reset.

[0005]

According to the above-mentioned means, since the switching frequency is determined by the pulse signal, the external synchronization is simplified, and since the triangular wave is formed by the output signal of the latch circuit, it can be used for both the forward and flyback transformers and the PWM. The output voltage can be stabilized because the gain in the control loop can be optimally set by the slope of the triangular wave supplied to the comparator.

[0006]

1 is a circuit diagram of an embodiment of a switching power supply circuit according to the present invention. The main circuit elements in the figure are formed on one semiconductor substrate such as single crystal silicon by a known semiconductor manufacturing technique. In this embodiment, the oscillator circuit O is used to facilitate external synchronization.
SC forms a pulse with a constant period. Therefore, the oscillating circuit OSC is configured to form a constant pulse signal by a circuit which is itself configured by the outside and receives only the pulse signal or a synchronizing signal which is supplied from the outside.

The pulse signal having a constant cycle is supplied to the latch circuit FF as a set input signal. The output signal Q of the latch circuit FF is the power switch MOSF.
It is used as a switch control signal for a switch element such as ETQ1. The switch MOSFET Q1 has a source connected to the ground potential of the circuit and a drain provided with an inductance L as a load. Switch MOS above
When the FET Q1 is turned on, a current is passed through the inductance L to store energy. Switch MOSFET Q1
A large back electromotive force is generated in the inductance L due to the off state. This back electromotive force is smoothed by the smoothing circuit composed of the diode D and the capacitor C2, and the operating voltage V
A DC voltage Vout boosted with respect to B is formed.

In order to set the above DC voltage Vout to a desired stable voltage, this DC voltage and the DC voltage V to be set are set.
The reference voltage Vref corresponding to out is input to the error amplification circuit EA.

In this embodiment, the inverted output QB of the latch circuit FF is used to stabilize the control loop. That is, the constant current Io is supplied to the capacitor C1 to perform the charging operation, and the switch transistor T1 is provided at both ends of the capacitor C1. The switch transistor T1 is switch-controlled by the inverting output QB of the latch circuit FF to generate a triangular wave. In response to the set operation of the latch circuit FF as described above, the inverting output QB changes from the high level to the low level, turning off the transistor T1. As a result, the charging operation by the constant current Io is started in the capacitor C1, and a triangular wave having a linearly good slob is generated. This triangular wave VC is supplied to the comparator PWMCP together with the output signal of the error amplification circuit EA.
The comparator PWMCP generates a signal for resetting the latch circuit FF when the voltage value of the triangular wave formed by the charging operation of the constant current Io to the capacitor C1 exceeds the output voltage of the error amplification circuit EA, The switch MOSFET Q1 is turned off.

In this configuration, the slope of the triangular wave can be freely set by the capacitance value of the capacitor C1 or the current value of the constant current Io, so that the gain in the control loop of the switching controller can be optimally adjusted. Since the latch circuit FF is set by a pulse signal having a constant frequency, it has a feature that external synchronization is easy to take. Further, since the output DC voltage Vout and the reference voltage Vref are supplied to the error amplification circuit to control the output voltage,
Flyback transformers, howard transformers or inductance drives are also possible and the applications can be expanded.

FIG. 2 is a waveform diagram for explaining an example of the operation of the switching power supply circuit. Since the latch circuit FF is set by the pulse signal formed by the oscillator circuit OSC or the pulse signal supplied from the outside, the output signal Q changes from the low level to the high level in synchronization with the pulse signal.

In response to the change of the output signal Q from low level to high level, the inverted output QB changes from high level to low level. As a result, the transistor T1
Is changed from the on state to the off state, and the charging operation by the constant current Io is started in the capacitor C1. Capacitor C1
The holding voltage VC of is raised in a triangular wave shape by this charging operation.

When the voltage value of the triangular wave VC reaches the output voltage of the error amplification circuit shown by the broken line in the figure, the comparator PWMCP generates a reset signal for resetting the latch circuit FF. By this reset operation, the output signal Q of the latch circuit FF changes to low level, and the switch MO
Switch SFET Q1 to the off state. Further, the inverted output QB of the latch circuit FF changes to the high level, the transistor T1 is turned on, and the capacitor C1 is discharged. By such an operation, the period in which the latch circuit FF is set for the pulse signal of the above-mentioned constant cycle changes corresponding to the output voltage of the error amplification circuit, in other words, the pulse width modulation is performed. The output voltage is controlled.

The operational effects obtained from the above embodiment are as follows. That is, (1) a switch element is controlled by an output signal of a latch circuit set by a periodic pulse signal to drive an inductance or a transformer, and a DC voltage formed based on the output signal of the inductance or the transformer. Then, the control reference voltage and the error amplification circuit are input, and the triangular wave formed based on the output voltage and the output signal of the latch circuit is supplied to the PWM comparator to reset the latch circuit. With this configuration, since the switching frequency is determined by the pulse signal, external synchronization is simplified, and since the triangular wave is formed by the output signal of the latch circuit, it can be used for both the forward and flyback transformers, and the triangular wave supplied to the PWM comparator is used. Since the gain in the control loop can be optimally set by the slope of, the output voltage can be stabilized. First MO
Supply the ECL level input signal to the gate of SFET,
Supply the ground potential of the level-shifted circuit to the source,
The input signal is supplied to the source of the second MOSFET,
By supplying a predetermined reference voltage to the gate, the second MOSF
A load means is connected to the drain of ET to form an amplified output in phase with the input to drive a third MOSFET connected in series with the first MOSFET and having a conductivity type opposite to that of the first MOSFET. These first and third MOSFs
An internal signal converted to a level is formed from the connection point of ET. With this configuration, since the level conversion operation is performed substantially in a single-stage circuit, it is possible to obtain an input buffer having a low power consumption and a high-speed level conversion function with a small number of elements. (2) By using a capacitor, a constant current source for charging, and a switch element for discharging as the triangular wave generating circuit, it is possible to obtain a triangular wave with a simple configuration, with easy slope setting and good linearity. can get.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the control signal supplied to the base of the transistor T1 forming the triangular wave is not only the inverted signal of the latch circuit FF but also the oscillation circuit O.
Various embodiments can be adopted such as one formed from the clock pulse of SC or its inverted signal, one formed from the output Q of the latch circuit FF, and the like. This can be configured so that the phase in the control loop is a negative feedback, and therefore the discharge signal of the capacitor C1 can take various embodiments depending on how to assemble the logic. Similarly, even if the set input and the reset input of the latch circuit FF are exchanged, it suffices that the entire control loop be negative feedback.

[0028]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, the switch element is controlled by the output signal of the latch circuit set by the periodic pulse signal to drive the inductance or the transformer,
The DC voltage formed based on this inductance or the output signal of the transformer, the control reference voltage, and the error amplifier circuit are input, and the triangular wave formed based on this output voltage and the output signal of the latch circuit is supplied to the PWM comparator. Then, by resetting the latch circuit, the external synchronization becomes simple, and since the triangular wave is formed by the output signal of the latch circuit, it can be used for both the forward and flyback transformers, and the triangular wave is supplied to the PWM comparator. Is stabilized

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching power supply circuit according to the present invention.

FIG. 2 is a waveform diagram for explaining an example of the operation.

FIG. 3 is a circuit diagram for explaining an example of a conventional V-mode switching power supply circuit.

FIG. 4 is a circuit diagram for explaining an example of a conventional C-mode switching power supply circuit.

[Explanation of symbols]

OSC ... Oscillation circuit, FF ... Latch circuit, PWMCP ... Comparator, EA ... Error amplification circuit, Q1 ... MOSFE
T, T1 ... Transistor, C1 ... Capacitor, Io ... Constant current source, L ... Inductance, D ... Diode, C2 ... Smoothing capacitor.

Claims (2)

[Claims] 1. A latch circuit set by a periodic pulse signal, a switch element which is switch-controlled by an output signal of the latch circuit, an inductance or a transformer driven by the switch element, and the inductance or the transformer. A rectifier circuit that forms a DC voltage based on the output signal of, and an error amplification circuit that receives the output voltage and the control reference voltage formed by the rectifier circuit,
A triangular wave generating circuit that forms a triangular wave based on the output signal of the latch circuit; and a PWM comparator that receives the output signal of the error amplifier circuit and the triangular wave formed by the triangular wave generating circuit to form a reset signal of the latch circuit. A switch power supply circuit comprising: 2. The triangular wave generating circuit comprises a capacitor for performing a charging operation by a constant current, and a transistor provided at both ends of the capacitor to form a discharging path and receive an inverted output signal of the latch circuit. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is provided.