JPH05219728A - Switching regulator - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a power factor improving switching regulator that controls the switching operation of a chopper circuit so that the input current waveform follows the input voltage waveform. Ensure stable operation even when the input voltage is high. [Structure] A Zener diode 20 is provided as a voltage limiting circuit in a circuit system in which an input voltage V1 is divided by resistors R3 and R4 and led to a multiplier 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chopper circuit type switching regulator which obtains a stabilized DC output by switching a pulsating current input which is a full-wave rectified AC power supply at a high frequency, and more particularly to an input voltage whose input current waveform is an input voltage. The present invention relates to improvement of a power factor improving switching regulator that controls the switching operation of a chopper circuit so as to follow a waveform.

[0002]

2. Description of the Related Art A typical conventional configuration of a power factor improving switching regulator is shown in FIG. this is,
The output of the rectifier circuit 10 for full-wave rectifying the AC power source is added to the boost chopper circuit to obtain a stable DC output.
The chopper circuit has a well-known configuration, and is connected in series between a switching element Q1 that is on / off driven at a frequency sufficiently higher than an AC input power source and the output of the rectifier circuit 10 together with the switching element Q1 as described below. The inductor L1 and the switching element Q1 are arranged so that a current flows through the inductor L1 when the switching element Q1 is off.
Diode D1 and capacitor C connected in series at both ends of
It consists of 1. The capacitor C1 has a considerably large capacity, and a smoothed and voltage-stabilized DC output is taken out from both ends thereof. The input-side capacitor 18 is a small-capacity capacitor for absorbing high-frequency ripple and is not essential to this device.

Reference voltage V of output voltage V2 of the chopper circuit
The error with respect to s is detected by the error amplifier 11, and the error signal ΔV becomes one input of the multiplier 12. Also, the multiplier 12
A voltage V11 obtained by dividing the input voltage V1 of the chopper circuit (full-wave rectified waveform of AC input) by the resistors R3 and R4 is input to the multiplier 12, and the full-wave rectification of the same phase as the input voltage V11 of the chopper circuit is input from the multiplier 12. Waveform and output voltage V of chopper circuit
A threshold value signal (current reference value) Va having an amplitude corresponding to the error ΔV of 2 is output.

The instantaneous value of the current flowing through the switching element Q1 of the chopper circuit is detected by the current detecting resistor R1. The terminal voltage of this resistor R1 is the resistor R2 and the capacitor C.
It is input to the current comparator 13 as the current detection signal Vb via the high cut filter circuit of 2. The comparator 13 compares the current detection signal Vb with the threshold signal Va from the multiplier 12.

The switching control circuit 14 for driving the switching element Q1 on / off turns on the switching element Q1 in response to a pulse signal having a frequency sufficiently higher than the AC input from the oscillator 15, and turns on the switching element Q1. The switching element Q1 is turned off in response to the output. When the switching element Q1 is turned on, the current flowing through the switching element Q1 through the inductor L1 gradually increases, but when the current detection signal Vb reaches the level of the threshold signal Va, the output of the current comparator 13 is inverted to the L level. By this signal, the flip-flop of the switching control circuit 14 is reset and the switching element Q1 is turned off. This operation is performed by the oscillator 15
Repeat in synchronization with the high frequency pulse from.

As a result, the switching element Q1 is turned on / off at a frequency sufficiently higher than that of the AC power source, and the envelope waveform of the current flowing through the inductor L1 is the threshold signal Va.
The control is performed so as to match (full-wave rectified waveform of AC input).

A resistor R inserted in the system for inputting the terminal voltage (current detection signal) of the resistor R1 to the current comparator 13.
The high cut filter circuit including 2 and the capacitor C2 is a circuit for preventing various noises from being input to the current comparator 13. If pulsed noise is superimposed on the input line of the current detection signal Vb, the current comparator 13 malfunctions due to the noise, and the switching element 1 is turned off earlier than the correct timing. In order to prevent this malfunction as much as possible, a high cut filter circuit including a resistor R2 and a capacitor C2 is inserted.

[0008]

The conventional switching regulator configured as shown in FIG. 2 has the following problems. Here, the operations when the voltage of the AC power supply is high and when the voltage of the AC power supply is low are compared in the state where the output powers are equal. Since the output power is constant, the input current becomes smaller when the input voltage is high than when it is low. That is, when the input voltage is high, the threshold signal (current reference value) Va from the multiplier 12
Becomes smaller. At this time, of the two inputs to the multiplier 12, the input voltage signal V11 increases in proportion to the input voltage V1, so the error signal ΔV from the error amplifier 11 becomes extremely small, and as a result, the multiplier 12 Output signal Va
Is getting smaller. As described above, the higher the voltage of the AC power supply is, the more the error signal ΔV of the error amplifier 11 is operating in a very small state (close to zero), and the operation state becomes extremely unstable, which is easily affected by noise. Since the operation becomes unstable in this way, the upper limit of the allowable voltage range of the AC power supply is restricted.

As a measure against the above-mentioned problem, it can be considered to increase the resistance division ratio R3 / R4 and decrease the level of the voltage signal V11. However, in this case, the voltage signal V11 operates in a very small state in a region where the input voltage is low, and an unstable state is likely in which noise is apt to be introduced into this signal system.

By using a resistor having a positive temperature coefficient as the voltage dividing resistor R3 or a resistor having a negative temperature coefficient as R4, the voltage dividing ratio R3 / R4 is automatically adjusted according to the power supply voltage. I can think of a way to change it. However, in this case, stable operation of the switching regulator cannot be expected until the temperatures of the voltage dividing resistors R3 and R4 are stabilized.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a switching regulator which is always operated stably even when a voltage with an AC power source is largely changed in a wide range. Especially.

[0012]

Therefore, in the present invention, a chopper circuit which obtains a smoothed DC output from both ends of an output capacitor by switching a pulsating current input obtained by full-wave rectifying an AC power source at a high frequency, and a chopper circuit of this chopper circuit. A resistance voltage dividing circuit for detecting an input voltage, a current detecting circuit for detecting a switching current of the chopper circuit, a voltage error detecting circuit for detecting an error component of an output voltage of the chopper circuit with respect to a reference value, and this voltage error detecting circuit. A multiplier for multiplying the error signal of the circuit and the input voltage signal by the resistance voltage divider circuit, and the voltage signal from this multiplier and the current signal from the current detection circuit are compared, and the input current waveform is the input voltage waveform. In a switching regulator including a circuit that controls the switching operation of the chopper circuit so as to follow the A circuit system for guiding force to the multiplier, excessive output of the resistor divider is provided with a voltage limiting circuit for preventing the input to the multiplier.

[0013]

Even if the voltage of the AC power supply becomes high, it is not directly input to the multiplier, and the voltage limiting circuit prevents an excessive voltage from being input to the multiplier. As a result, the switching operation of the chopper circuit is stably controlled without the output of the voltage error detection circuit becoming extremely small.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an improvement of the conventional switching regulator of FIG. The improvement according to the present invention is that the input voltage signal V11 is multiplied by the multiplier 12 from the midpoint of the voltage dividing resistors R3 and R4.
A Zener diode 20 as a voltage limiting circuit is connected in parallel with the resistor R4 in the circuit system leading to the. Further, in this embodiment, the noise absorbing capacitor 21 is connected in parallel with the Zener diode 20.

Therefore, even if the input voltage V1 increases, the voltage V11 input to the multiplier 12 is limited by the Zener voltage. As a result, even when the voltage of the AC power supply is extremely high, the error signal ΔV does not become extremely small unlike the conventional case,
The entire control system operates stably. When the voltage limiting function of the Zener diode 20 is working, the input voltage signal V11 is not a waveform obtained by full-wave rectifying a sine wave, but a waveform with the head clipped. As a result, the effect of increasing the power factor by making the input current waveform follow the input voltage waveform is reduced, but the advantage of stable operation at a high input voltage even if the power factor is slightly sacrificed. Much larger in reality. It should be noted that the noise absorbing capacitor 21 is not an essential element of the present invention, but it is desirable to add a capacitor 21 having a capacity that does not cause a phase shift due to the resistors R3 and R4 and the capacitor 21.

In the configuration shown in FIGS. 1 and 2, the oscillator 15
Although the switching element Q1 is turned on in response to the output of the switching regulator, various switching regulators that turn the switching element Q1 on by another method are known, and the present invention can be applied to switching regulators of other methods. Can be applied.

[0017]

As described above in detail, according to the present invention, even if the voltage of the AC power supply is very high, an excessive input voltage signal is not applied to the multiplier, and therefore, the output error is large. Does not cause instability where the signal operates at extremely low levels. That is, the upper limit of the allowable input voltage that operates stably can be expanded more than ever before.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a conventional switching regulator.

[Explanation of symbols]

 10 Rectifier circuit 11 Error amplifier 12 Multiplier 13 Current comparator Q1 Switching element R3, R4 Voltage dividing resistor 20 Zener diode (voltage limiting circuit)

Claims (1)

[Claims] 1. A chopper circuit that obtains a smoothed DC output from both ends of an output capacitor by switching a pulsating current input, which is a full-wave rectified AC power supply, at a high frequency, and a resistance voltage divider circuit that detects an input voltage of the chopper circuit. A current detection circuit that detects a switching current of the chopper circuit, a voltage error detection circuit that detects an error component of the output voltage of the chopper circuit with respect to a reference value, an error signal of the voltage error detection circuit, and the resistor voltage divider. A multiplier for multiplying the input voltage signal by the circuit, the voltage signal from this multiplier and the current signal from the current detection circuit are compared, and the input current waveform of the chopper circuit is made to follow the input voltage waveform. In a switching regulator including a circuit for controlling a switching operation, a circuit system that guides the output of the resistance voltage dividing circuit to the multiplier, A switching regulator provided with a voltage limiting circuit for preventing an excessive output of the resistance voltage dividing circuit from being input to the multiplier.