JPH0710177B2 - Switching regulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chopper-controlled switching regulator that produces a stable DC power supply from an AC power supply, and in particular,
The present invention relates to a power factor improving switching regulator that performs pulse width control so that an input voltage and an input current change with substantially the same waveform and substantially the same phase.

<< Prior Art >> For example, as disclosed in JP-A-2-7869,
2. Description of the Related Art A power factor improving switching regulator having a configuration as shown in FIG. 2 is known.

In FIG. 2, a sine wave AC input is full-wave rectified by a rectifier circuit 10 composed of a diode bridge and input to a booster type chopper circuit 20 described in detail below. Chopper circuit 20
Is a switching element Q1 that is turned on / off by a PWM (pulse width control) circuit 31 at a frequency sufficiently higher than that of an AC power source, an inductor L1 connected in series with the switching element Q1 to the output of the rectifier circuit 10, and a switching element.
A diode connected in series across switching element Q1 so that current flows through inductor L1 when Q1 is off.
It has D1 and a capacitor C1. The capacitor C1 has a considerably large capacity, and a smoothed and voltage-stabilized DC output (described later) is taken out from both ends thereof. The capacitor C2 is a small-capacity capacitor for absorbing high-frequency ripple, and is not essential to this device.

A signal of the full-wave rectified output voltage V1 of the rectifier circuit 10 is input to a differential amplifier 33 via a VCA (voltage control type variable gain amplifier) 32. The current I1 flowing through the inductor L1 of the chopper circuit 20 is detected by the current transformer 34, and the signal of the low frequency component is input to the differential amplifier 33. The PWM circuit 31 operates according to the differential output (difference signal between the input current waveform and the input voltage waveform) of the differential amplifier 33, and the drive pulse width (ON time) of the switching element Q1 so that the differential output is minimized. Change. That is, the difference signal from the differential amplifier 33 and the triangular wave signal from the oscillator 36 are compared to generate a control signal for the switching element Q1 as is well known. Also, the output voltage of the chopper circuit 20
The error of V2 with respect to the reference voltage V _S is detected by the error amplifier 35, and this output becomes the control voltage of VCA32.

In the above configuration, the differential amplifier 33 has a chopper circuit.
Input voltage V1 waveform of 20 and current I1 flowing through inductor L1
The waveform of the switching element Q1 is compared by the PWM circuit 31 so that the current waveform changes following the voltage waveform.
The on-time of can be changed.

When the switching element Q1 is on, current flows from the rectifier circuit 10 to the inductor L1 through the switching element Q1 and energy is stored in the inductor L1. The current increase value during the ON period is proportional to the input voltage V1 and also to the ON time. When the switching element Q1 is turned on, the current due to the release of the energy stored in the switching element Q1
Is extended to the capacitor C1 side by being superposed on the output of the capacitor C1 and acts so as to bring the output voltage V2 closer to the reference voltage V _S.

As described in detail above, in this type of power supply device,
The input current changes almost according to the AC input voltage, and becomes almost sinusoidal with no phase difference, and the relationship between the voltage and current seen from the AC power supply side is almost the same as in the case of a resistive load (the power factor is improved. Be done). Therefore, unlike the conventional capacitor-input type rectifier circuit, a large pulse current does not flow intensively in a short time, the restrictions on the withstand current characteristics of the circuit elements are relaxed, and various AC power lines are connected. It is possible to reduce noise that has an adverse effect.

Further, by the boosting action of the chopper circuit and the feedback control action of the output voltage by the second control means,
The output voltage can be kept constant even when the voltage of the AC input fluctuates or the voltage rank is changed.
As a result, no switching is required, for example alternating current
A power supply device compatible with 85V power supply to 264V AC power supply can be easily configured.

When the power of the device is turned on, the power-on detection circuit 37 responds, and the control signal a is set to L for a fixed time immediately after the power is turned on.
It keeps the level, and thereby prohibits the operation of the PWM circuit 31, and after a certain period of time, sets the control signal a to the H level
The circuit 31 is activated to start the switching operation. At the same time, the ramp voltage generating circuit 39 is activated when the control signal a becomes H level. The generating circuit 39 generates a ramp voltage b that gradually decreases after being activated as shown in FIG. 3, and the ramp voltage b is input to the PWM circuit 31.

Immediately after the switching operation of the chopper circuit 20 is started, the output voltage V2 is low. Therefore, according to the control based on the difference signal c between the input current waveform and the input voltage waveform from the differential amplifier 33, the switching element Q1 is driven. The pulse width becomes extremely large, and control is performed so that the capacitor C1 is quickly charged with a large current. Due to the control overshoot at this time, an overcurrent transiently flows and switching element Q1
Excessive stress is applied to each element of the input line. The above-mentioned lamp voltage generating circuit 39 is provided for performing the soft start control for preventing the overcurrent immediately after the power is turned on.

When the switching operation of the chopper circuit 20 is started, the difference signal c between the input current waveform and the input voltage waveform has the same pulsating flow waveform as that of the full-wave rectified AC input, as shown in FIG. On the other hand, the ramp voltage b generated from the circuit 39 changes from the high level to the low level over a period of several thousand times the pulsating current cycle of the difference signal c. As is well known, the PWM circuit 31 has a built-in comparator for comparing the difference signal c and the triangular wave signal and a comparator for comparing the ramp voltage b and the triangular wave signal, among the drive pulses obtained from both comparators. Switching element with narrow pulse signal
Q1 is designed to be driven on. That is, the difference signal c
When the ramp voltage b is at a higher level, the pulse voltage of the switching element Q1 is controlled by the ramp voltage b. In the steady state, the lamp voltage b is zero, which is meaningless. However, the lamp voltage b becomes a high level in the transient state immediately after the power is turned on, and the pulse width control is performed based on this signal b. When b gradually decreases and becomes smaller than the difference signal c, the meaning becomes meaningless.

The overvoltage detection circuit 38 sets the control signal a to the L level when the output voltage V2 becomes abnormally high, stops the operation of the PWM circuit 31, and returns the control signal a to the H level when the overvoltage state is resolved. At this time, the PWM circuit 31 restarts its operation and the lamp voltage generation 39 is started, and the soft start control by the lamp voltage is performed as described above.

<Problem to be Solved by the Invention> In the conventional soft start control described above, when the soft start control is performed by the lamp voltage b, the function of making the input current the same as the full-wave rectified waveform as the input voltage is almost the same. It is lost and a large current flows at the peak of the pulsating flow of the input voltage, and the operation becomes similar to that of the conventional capacitor input type rectifier circuit. Therefore, there is no power factor improving effect, and noise easily occurs. Further, the peak value of the input current is relatively large, but the average value is very small, and therefore it takes a long time for the output voltage to reach the reference value. In other words, the soft start period must be set very long. If this time is shortened, the purpose of soft start to suppress the overcurrent will not be achieved.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a switching regulator capable of performing a soft start control in a transient state while maintaining the operation of the power factor correction method. is there.

<< Means for Solving the Problem >> Therefore, in the present invention, a switching regulator of a chopper control system that obtains a stabilized DC output by switching a pulsating current input that is full-wave rectified from an AC power source at a high frequency, and an output voltage error In a power factor correction type switching regulator that controls the pulse width of switching operation based on the difference signal between an input voltage waveform signal with a gain proportional to the signal and an input current waveform signal, an output signal is issued in response to power-on A power-on detection circuit, a ramp voltage generation circuit that generates a ramp voltage that gradually changes from a predetermined value A to a predetermined value B in response to an output signal of the power-on detection circuit, and a ramp voltage from the ramp voltage generation circuit. In response to this, a circuit means for gradually changing the gain of the input voltage waveform signal generation system from a predetermined value to a predetermined value is provided. .

Here, the circuit means may be replaced with a circuit means that receives the ramp voltage from the ramp voltage generation circuit and gradually changes the gain of the difference signal generation system from a predetermined value to a predetermined value. The circuit means may be replaced with a circuit means for receiving the ramp voltage from the ramp voltage generating circuit and gradually changing the gain of the output voltage error signal generation system from a predetermined value to a predetermined value.

Furthermore, an overvoltage detection circuit that outputs an output signal when the output voltage of the switching regulator exceeds a predetermined value is provided, and the lamp voltage generation circuit is also triggered by the output signal of the overvoltage detection circuit, and the output voltage of the generation circuit Can first be set to a predetermined value A and then gradually changed to a predetermined value B.

<< Operation >> When the lamp voltage generating circuit is triggered and the lamp voltage is output, the gain is gradually changed from a predetermined value to a predetermined value by the circuit means, and this change is caused by an input current waveform signal. The PWM circuit that controls the pulse width of the switching operation on the basis of the difference signal is used to gradually increase the pulse width from a sufficiently small state.
That is, the pulse width control of the switching operation by the PWM circuit is performed in the direction in which the input current gradually increases from a sufficiently small state. As a result, in the transient state immediately after the power is turned on or immediately after the overvoltage state is eliminated, the input current is gradually increased from the suppressed state to the steady state while maintaining the operation of the power factor correction method.

<< Embodiment >> FIG. 1 shows a configuration of a switching regulator according to an embodiment of the present invention, and most of the configuration is the same as the conventional configuration shown in FIG. Will be explained.

In this embodiment, the VCA 32 for amplifying the input voltage waveform signal is provided with another control input terminal, to which the ramp voltage b from the ramp voltage generating circuit 39 is applied, and VCA3
The gain of 2 is also changed by the lamp voltage b.

The lamp voltage b in the steady state is zero, and then the lamp voltage b does not contribute to the gain of the VCA 32, and the gain of the VCA 32 is determined by the output of the differential amplifier 35.

Immediately after the switching regulator is powered on, the control signal a is output by the power-on detection circuit 37.
Rises from the L level to the H level, and the lamp voltage generating circuit 39 is triggered. Further, when the output voltage V2 becomes abnormally high in the steady operation state of the present switching regulator, the overvoltage detection circuit 38 operates to set the control signal a to the L level and stop the operation of the PWM circuit 31 as in the conventional case. After that, when the overvoltage state is eliminated, the control signal a is returned to the H level. The rising of the control signal a at this time also triggers the ramp voltage generating circuit 39. When the lamp voltage generation circuit 39 is triggered, the lamp voltage b increases from zero to a predetermined value, and then gradually returns to zero at a predetermined rate of change.

By controlling the ramp voltage b, the gain of the VCA 32 changes, and as a result, the generated gain of the difference signal c changes so as to reduce the input current from the steady state, and then gradually returns to the steady state gain.

Although the gain of the VCA 32 is changed by the ramp voltage b in the present embodiment, the present invention is not limited to this, and the gains of the differential amplifier 53 and the differential amplifier 33 may be changed by the ramp voltage b. It may be configured, or a VCA may be separately provided in the generation system of the difference signal c.

<< Effects of the Invention >> As described in detail above, in the switching regulator according to the present invention, power factor correction is performed in which the pulse width control is performed so that the input current waveform changes substantially in the same phase as the input voltage waveform. While maintaining the operation of the method,
Soft start control that gradually increases the input current in the transient state to the steady value can be performed, and the load current can be reliably suppressed even if the input current in the transient state is changed to the steady state in a very short time compared to the conventional method. The power factor improving effect and the noise generation preventing effect are maintained even in the transient state.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a switching regulator according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional switching regulator, and FIG. 3 is a waveform diagram for explaining problems in the conventional technique. 10 …… Rectifier circuit 20 …… Chopper circuit 31 …… PWM circuit 32 …… VCA 33,35 …… Differential amplifier a …… Control signal b …… Lamp voltage c …… Difference signal

Claims (4)

[Claims] 1. A switching regulator of a chopper control system for obtaining a stabilized DC output by switching a pulsating current input, which is a full-wave rectified AC power supply, at a high frequency, and an input voltage waveform having a gain proportional to an output voltage error signal. In a power factor correction type switching regulator that controls the pulse width of switching operation based on the difference signal between the signal and the input current waveform signal, a power-on detection circuit that issues an output signal in response to power-on, and this power-on A ramp voltage generating circuit that generates a ramp voltage that gradually changes from a predetermined value A to a predetermined value B in response to an output signal of the detection circuit, and a ramp voltage from the ramp voltage generating circuit that receives the input voltage waveform signal A switching regulator provided with a circuit means for gradually changing the gain of the generation system from a predetermined value to a predetermined value. Data. 2. The circuit means according to claim 1, wherein the gain of the difference signal generating system is gradually changed from a predetermined value to a predetermined value in response to a ramp voltage from the ramp voltage generating circuit. A switching regulator comprising circuit means for controlling the switching regulator. 3. Instead of the circuit means in claim 1, a ramp voltage from the ramp voltage generating circuit is received, and a gain of a system for generating the output voltage error signal is changed from a predetermined value to a predetermined value. A switching regulator comprising circuit means for gradually changing. 4. A switching regulator according to any one of claims 1, 2 and 3, wherein:
An overvoltage detection circuit that compares the output voltage of the switching regulator with a set voltage is provided, and the lamp voltage generation circuit responds also by the output signal of the overvoltage detection circuit when the overvoltage state is resolved, and the lamp voltage generation circuit A switching regulator in which an output voltage first reaches a predetermined value A and then gradually changes to a predetermined value B.