JP2774886B2 - Switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 2 shows a conventional typical configuration of a switching regulator of a power factor improving system. this is,
The output of the rectifier circuit 10 for full-wave rectifying the AC power is added to a 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 turned on and off at a frequency sufficiently higher than an AC input power supply and an output of the rectifier circuit 10 together with the switching element Q1 as described below. The switching element Q1 is connected to the inductor L1 such that a current flows through the inductor L1 when the switching element Q1 is turned 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 of the capacitor C1. The input-side capacitor 18 is a small-capacity capacitor for absorbing high-frequency ripple, and is not essential for the present apparatus.

The reference voltage V of the output voltage V2 of the chopper circuit
An error with respect to s is detected by the error amplifier 11, and the error signal ΔV becomes one input of the multiplier 12. The multiplier 12
The input voltage V1 (full-wave rectified waveform of AC input) of the chopper circuit is input to the input terminal. The multiplier 12 outputs a full-wave rectified waveform having the same phase as the input voltage V1 of the chopper circuit and the output voltage V2 of the chopper circuit. A threshold signal (current reference value) Va having an amplitude corresponding to the error ΔV is output.

The instantaneous value of the current flowing through the switching element Q1 of the chopper circuit is detected by a current detecting resistor R1, and the terminal voltage of the resistor R1 is changed to a resistor R2 and a capacitor C2.
The current detection signal Vb is input to the current comparator 13 via a high cut filter circuit composed of two. The comparator 13 compares the current detection signal Vb with the threshold signal Va from the multiplier 12.

A switching control circuit 14 for driving the switching element Q 1 on and off inverts the switching element Q 1 to on in response to a pulse signal having a frequency sufficiently higher than the AC input from the oscillator 15, and outputs a signal from the current comparator 13. The switching element Q1 is turned off in response to the output. When the switching element Q1 is turned on, the current flowing to the switching element Q1 through the inductor L1 gradually increases. However, 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 H level. The signal resets the flip-flop of the switching control circuit 14, and the switching element Q1 is turned off. This operation is repeated in synchronization with the high frequency pulse from the oscillator 15.

As a result, the switching element Q1 is turned on and off at a frequency sufficiently higher than the AC power supply, so that the envelope waveform of the current flowing through the inductor L1 matches the threshold signal Va (AC input full-wave rectified waveform). Control is exercised.

[0007]

In the circuit configuration shown in FIG. 2, a resistor R2 and a capacitor C are inserted in a system for inputting the terminal voltage (current detection signal) of the resistor R1 to the current comparator 13.
The high cut filter circuit composed of two current comparators 13
This is a circuit for preventing various types of noise from being input to the circuit. When pulse 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. Therefore, the terminal voltage waveform of the resistor R1 is filtered by the filter circuits R2 and C2,
As shown in (2), the current detection signal Vb has a waveform obtained by performing envelope detection on the terminal voltage waveform of the resistor R1.

The problem here is that if the current flowing through the switching element Q1 becomes zero, the terminal voltage of the resistor R1 also becomes zero, but the current detection signal Vb obtained through the filter circuits R2 and C2 becomes , As shown in FIG.
And it is not completely zero due to the time constant of R2 and R2. In order to minimize the power consumption of the control system of the switching regulator, the terminal voltage of the resistor R1 must be received by a high impedance circuit.
2, the residual voltage of the terminal voltage Vb (current detection voltage) of the capacitor C2 becomes relatively large even when the terminal voltage of the resistor R1 becomes zero.

When the current detection signal Vb input to the current comparator 13 has a waveform floating by the residual voltage without completely dropping to the zero volt line, the switching element is determined based on the erroneous current detection signal Vb. The switching operation of Q1 is controlled (switching element Q1 turns on in response to the output of oscillator 15 if Vb is completely zero, but switching element Q1 does not turn on if Vb is not zero). As shown in FIG. 4, the current waveform of the AC input (waveform excluding high-frequency ripple) does not become a complete sine wave as shown by the solid line, and a distortion occurs in which the current becomes too small before and after the zero-cross point. That is, the input current waveform does not correctly follow the input voltage waveform (sine wave), and the power factor improvement effect of this method cannot be realized as expected. If distortion occurs in which the current becomes too small in the vicinity of the zero crossing of the AC input, a relatively large neutral current flows, particularly when the present apparatus is applied to a three-phase four-wire power supply.

The present invention has been made in view of the above-described conventional problems, and has been improved in a portion for detecting a current flowing through a switching element of a chopper circuit and inputting the detected current to a control system.
An object of the present invention is to prevent the occurrence of distortion in which the current becomes too small near the zero cross of the AC input.

[0011]

Therefore, according to the present invention, a current detecting circuit system for supplying the input current waveform signal to a circuit system for controlling the switching operation is connected in series with a switching element of the chopper circuit. A current detection resistor, a high cut filter circuit that receives a terminal voltage of the resistor as an input, and a clamp circuit that applies a predetermined direct current to an output of the filter circuit are provided.

[0012]

Since the terminal voltage of the current detecting resistor is filtered by the high cut filter circuit, the output of the filter circuit does not become completely zero and a residual voltage is generated. Can be supplied to a circuit system that controls the switching operation by inputting an input current waveform signal that correctly becomes zero level at the zero-cross point of the AC input.

[0013]

FIG. 1 shows the conventional switching regulator of FIG. 2 which has already been described in detail and is improved by the present invention. An improvement according to the present invention is a configuration in which a clamp circuit including a series circuit of a resistor R3 and a constant voltage source E1 is connected in parallel with a capacitor C2 that supplies a current detection signal Vb to a current comparator 13. That is, a negative voltage appropriately set by the constant voltage source E1 is added to the output terminal of the high cut filter circuit including the resistor R2 and the capacitor C2 via the resistor R3, thereby reducing the residual voltage of the capacitor C2 shown in FIG. Correction is made so that the current detection signal Vb becomes zero volt at the zero cross point of the AC input.

1 and 2, the oscillator 15
The switching element Q1 is turned on in response to the output of the switching element Q. However, various types of switching regulators for inverting the switching element Q1 to be turned on by other methods are also known, and the present invention is applied to those other types of switching regulators. Can be applied.

[0015]

As described above in detail, according to the present invention, there is no residual voltage in the current detection system for providing the input current waveform signal to the circuit system for controlling the switching operation, and the zero-cross point of the AC input is eliminated. The switching operation of the chopper circuit is controlled with the input current waveform signal also being zero. As a result, the current waveform of the AC input follows the voltage waveform of the AC input with very high accuracy, and the switching regulator is highly accurate and has a large power factor improvement effect.

[Brief description of the 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.

FIG. 3 is a waveform diagram showing a problem of a conventional switching regulator.

FIG. 4 is a waveform diagram showing distortion of an input current waveform of a conventional switching regulator.

[Explanation of symbols]

 Reference Signs List 10 Rectifier circuit 11 Error amplifier 12 Multiplier 13 Current comparator Q1 Switching element R1 Current detection resistor R2, C2 High cut filter circuit R3, E1 Clamp circuit

Claims (1)

(57) [Claims] A chopper circuit type switching regulator for obtaining a stabilized DC output by switching a pulsating current input obtained by rectifying an alternating current in a full-wave manner at a high frequency, so that an input current waveform follows an input voltage waveform. In a switching regulator of a power factor improvement system for controlling a switching operation of a chopper circuit, as a current detection circuit system for providing the input current waveform signal to a circuit system for controlling the switching operation, a switching element of the chopper circuit is connected in series. A switching regulator comprising: a connected current detection resistor; a high-cut filter circuit that receives a terminal voltage of the resistor as an input; and a clamp circuit that applies a predetermined direct current to an output of the filter circuit.