JPH11332220A - Dc power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a good constant voltage control operation by interrupting the switching operation of a switching means when the voltage level corresponding to an AC commercial power supply is higher than a predetermined threshold level. SOLUTION: A stop control circuit 2 comprises a comparator OP and a diode D5 to be connected with the output thereof. The comparator OP compares a divided value of an input voltage Vin with a reference voltage Vref. When the divided value of the input voltage Vin exceeds the reference voltage Vref, an H level signal is applied, as a detection signal Vop, to the terminal T3 of a switching control circuit 1 through the diode D5 in order to interrupt oscillation of a switching element Q1. Stabilization performance of the output voltage from a power factor improving circuit can thereby be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply circuit capable of obtaining a predetermined DC output voltage by boosting a commercial AC power supply and enabling a power factor improving operation, for example.

[0002]

2. Description of the Related Art In recent years, a booster power supply circuit has been known as a power supply circuit for rectifying a commercial power supply to obtain a desired DC voltage by developing a switching element capable of withstanding a relatively large current and voltage of a high frequency. Have been. Such a power supply circuit is used as a power supply for various electronic devices as a high-power DC-DC converter while increasing the switching frequency to reduce the size of a transformer and other devices.

In general, when a commercial power supply is rectified by a rectifying / smoothing circuit based on a so-called capacitor input method, a current flowing through the rectifying / smoothing circuit has a narrow conduction angle, so that there is a problem that a power factor indicating a power use efficiency is impaired. .

[0004] Therefore, there is known a method of providing a so-called active filter that provides a boost converter to make the power factor close to one.

FIG. 3 is a circuit diagram showing a configuration of a power factor improving circuit as such an active filter. In the configuration shown in this figure, an AC input voltage Vac supplied from a commercial AC power supply AC is rectified and smoothed by a rectifying and smoothing circuit including a bridge rectifier circuit D1 and a smoothing capacitor C1. The rectified and smoothed voltage obtained here is supplied to the subsequent active filter as the input voltage Vin.

The active filter is, as shown in the figure,
Inductor L1 (winding N1) and switching element Q1
As a boost converter.

The output of the active filter is rectified and smoothed by a rectifying and smoothing circuit including a rectifying diode D2 and a smoothing capacitor C2, and is supplied as a DC output voltage Vout to, for example, a load at a subsequent stage. In FIG. 3, the load resistance R is shown, but a DC-DC converter may be used instead.

The switching operation of the switching element Q1 is controlled by the switching control circuit 1. In the switching control circuit 1, a feedforward circuit for detecting a voltage contributing to boosting by inputting an output of the winding N2 of the inductor L1 to a terminal T1 is formed, and by inputting a DC output voltage Vout to a terminal T4. Form a feedback circuit. The terminal T
Reference numeral 3 denotes an overcurrent detection circuit for detecting an overcurrent by inputting a switching current component obtained at both ends of the resistor R1.

In the switching control circuit 1, based on the detection outputs obtained by the feedforward circuit and the feedback circuit, the rectified AC input current is adjusted so that the AC input voltage Vac approaches the same waveform as much as possible, that is, the power factor The switching operation of the switching element Q1 is controlled so that is improved. That is, the terminal T2
Variable control of the frequency (switching frequency) of the switching drive pulse to be output from the controller, or PWM (Pulse Width)
Modulation) control. Further, the switching control circuit 1 controls the switching operation based on the level of the DC output voltage Vout detected by the feedback circuit so that the DC output voltage Vout becomes constant within a predetermined level range. .

[0010]

By the way, a DC power supply circuit of a step-up type as shown in FIG.
For example, when the AC input voltage Vac is a high voltage, the potential difference between the input voltage Vin and the DC output voltage Vout may be small, or the input voltage Vin may be higher than the DC output voltage Vout. In such a case, the boosting operation is controlled, whereby the switching element Q1 may be intermittently oscillated to cause an unstable switching operation. In particular, when the DC output voltage Vout sharply rises due to light load conditions, the inductor L1 becomes excessively large due to a delay in the response of the switching operation control system (overcurrent detection circuit) in the switching control circuit 1. There is a possibility that a state in which excessive energy is accumulated and an overvoltage occurs may occur.
In other words, in a step-up DC power supply circuit, under conditions where the commercial AC power supply is at a high level and a light load, the increase in the output voltage may not be sufficiently suppressed by the control operation of the control circuit. (Constant voltage) may not be maintained.

In the case of a step-up type DC power supply circuit,
In consideration of the possibility that the regulation characteristics may become unstable as described above, the smoothing capacitor forming the rectifying and smoothing circuit at the subsequent stage of the active filter should have a rated voltage enough to cover the overvoltage state. Although it was necessary to select, the miniaturization of the circuit was hindered and the cost increased.

[0012]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in consideration of the above-described problems, and has been described in connection with a boost type DC power supply circuit under conditions where a commercial AC power supply has a high level and a light load. An object is to obtain a good constant voltage control operation.

Therefore, a rectifying means for rectifying and smoothing the commercial AC power supply, a step-up inductance element inserted into an output current path of the rectifying means, a switching means for interrupting a current flowing through the inductance, and DC voltage generating means for obtaining a DC output voltage by rectifying and smoothing the output of the switching means, and variably controlling the switching frequency of the switching means based on the excitation voltage of the inductance element and the output, so that at least the DC power supply In a DC power supply circuit having switching control means for stabilizing the output of the circuit, a voltage level corresponding to a commercial AC power supply is detected, and when the detected voltage level is higher than a predetermined threshold value, A switch configured to stop the switching operation of the switching means. Was the provision of the etching operation stopping means.

According to the above configuration, when the voltage level of the commercial AC power supply becomes equal to or higher than the predetermined level, the switching operation of the switching means in the active filter is stopped. Even under the condition that the voltage is light load, it is possible to avoid an excessive rise in the voltage of the inductance element.

[0015]

FIG. 1 is a circuit diagram schematically showing a configuration of a power factor improving circuit according to an embodiment of the present invention.
The basic configuration of the DC power supply circuit shown in this figure is to form a step-up chopper by switching the current flowing through the inductance, and to increase the conduction angle of the AC input current that flows from the commercial AC power supply by this switching operation. That is, a so-called active filter is formed.

In FIG. 1, first, a commercial AC power supply AC
Is input to a rectifying / smoothing circuit including a bridge rectifier circuit D1 and a smoothing capacitor C1. As a result, the AC input voltage Vac is subjected to full-wave rectification by the bridge rectifier circuit D1 to form a pulsating flow.
By being smoothed by the smoothing capacitor C1, the DC voltage (rectified smoothed voltage) is obtained. This DC voltage is used as an input voltage Vin, and is supplied to a step-up chopper (active filter) that operates as a power factor correction circuit in a subsequent stage.

That is, as a basic configuration, the winding N of the inductor L1 is connected between the positive output line of the rectifying and smoothing circuit (D1, C1) and the anode of the rectifying diode D2.
1 in series and the winding N1 of the inductor L1.
A switching control circuit 1 for controlling the switching operation of the switching element Q1 after inserting a switching element Q1 for interrupting the current flowing through the switching element Q1 is provided.

In this case, the inductor L1 (winding N1)
Is energy for accumulating electric energy during a period in which the switching element Q1 is on, and flowing the accumulated energy as a current to a load side (switching converter side) during a period when the switching element Q1 is off. Functions as storage means. And this

The inductor L1 shown in FIG. 1 is formed by winding a winding N2 in addition to the winding N1. One end of the winding N2 is grounded, and the other end is connected to the terminal T1 of the switching control circuit 1. A voltage excited by the switching current flowing through the winding N1 is generated in the winding N2. The voltage obtained through the winding N2 is supplied to the switching control circuit 1 as a detection voltage as described later. Is done.

In this case, for example, a MOS-FET transistor is used as the switching element Q1, the drain is connected to the connection point between the inductor L1 and the anode of the rectifier diode D2, and the source is connected via the resistor R1 to the primary side. It is provided so as to be grounded to ground. The switching element Q1 performs a switching operation when a switching drive signal output from a terminal T2 of a switching control circuit 1 described later is applied to the gate.

The output of the inductor L1 is rectified and smoothed by a rectifying and smoothing circuit including a rectifying diode D2 and a smoothing capacitor C2, and is supplied to the load resistor R as a DC output voltage Vout. As the load resistor R, for example, a switching power supply circuit as a DC-DC converter may be actually connected.

The switching control circuit 1 controls the switching operation of the switching element Q1 so that a proper power factor improving operation can be obtained, and the DC output voltage Vout is made constant. Stone IC
(Integrated Circuit).

The switching control circuit 1 has terminals T1 to T4 as shown in FIG. At terminal T1,
As described above, a voltage obtained by detecting the current flowing through the inductor L1 (winding N1) by the winding N2 is supplied. The voltage level supplied to the terminal T1 corresponds to a change in the switching current flowing through the winding N1, and the switching control circuit 1 forms a terminal T1 feedforward circuit that controls the switching operation by the detected voltage. Further, the DC output voltage Vout is supplied to the terminal T4, thereby forming a feedback circuit for controlling the DC output voltage Vout to be constant.

The terminal T3 is a terminal for detecting an overcurrent, and is connected to a connection point between the source of the switching element Q1 and the resistor R1 so that, for example, the switching control circuit 1
In this configuration, the switching current level can be detected based on the voltage across the resistor R1. In the present embodiment, a detection signal Vop output from the stop control circuit 2 described later is also input to the terminal T3. The terminal T2 outputs the switching drive signal generated by the switching control circuit 1 to the switching element Q1.
Is a drive terminal for applying a voltage to the gate.

The basic operation of the DC power supply circuit having the above configuration is as follows. For example, the switching control circuit 1 detects a voltage component level considered to contribute to boosting by a switching operation from a feedforward circuit, and inputs the voltage component level to an internal multiplier. On the other hand, a fluctuation difference of the rectified smoothed voltage (DC output voltage Vout) is detected based on the voltage value input from the feedback circuit. The switching control circuit 1 controls the average value of the DC output voltage Vout to be constant within a predetermined range based on the variation difference of the rectified smoothed voltage, and internally multiplies the variation difference of the DC output voltage Vout by an internal multiplication. Input to the container. Then, the multiplier multiplies the voltage component level contributing to the boosting by the variation difference between the DC output voltage Vout. The multiplication result generates, for example, a current command value having the same waveform as the AC input voltage Vac. And
The internal switching drive circuit compares the current command value with the actual AC input current level, generates a switching drive signal having a variable switching frequency according to the difference, and applies the switching drive signal to the switching element Q1. Note that instead of variably controlling the switching frequency, PWM control may be performed on a fixed frequency switching drive signal.

In this DC power supply circuit, the switching element Q1 performs a switching operation by the switching drive signal generated as described above. With this, the voltage generated at both ends of the inductor L1 is increased. And its inductance is controlled. As a result, the conduction angle of the input current flowing from the bridge rectifier circuit D1 is increased. Accordingly, the AC input current is controlled so as to approach the same waveform as the AC input voltage Vac, and as a result, the power factor is improved. Also, in this case, the current command value generated by the multiplier is controlled so that the amplitude changes according to the variation difference of the rectified smoothed voltage,
The fluctuation of the DC output voltage Vout is also suppressed.

In this embodiment, a stop control circuit 2 is provided for the above configuration. This stop control circuit 2
Detects the level of the AC input voltage Vac indirectly as described below, and if the detected level is equal to or higher than a predetermined level, controls to stop the switching operation of the switching element Q1.

This stop control circuit 2 adopts, for example, the configuration shown in the broken line in FIG.
It is formed with a diode D5 connected to P and its output. A voltage value obtained by dividing the input voltage Vin by the resistors R2 and R3 is input to the non-inverting input of the comparator OP, and the reference voltage Vre is input to the inverting input.
f is input. The diode D5 has an anode connected to the output of the comparator OP and a cathode connected to a terminal T3 (overcurrent detection) of the switching control circuit 1. In this case, the output of the diode D5 is the detection output of the stop control circuit 2, that is, the detection signal Vop.
It is said.

In this configuration, the comparator OP compares the divided value of the input voltage Vin with the reference voltage Vref,
It operates so as to output an H-level signal when the input voltage Vin divided value exceeds the reference voltage Vref. And
This H-level signal is applied to the terminal T3 of the switching control circuit 1 as the detection signal Vop via the diode D5. On the other hand, when the divided voltage of the input voltage Vin does not exceed the reference voltage Vref, an L level detection signal is output from the comparator OP, and the output is blocked by the diode D5. No detection signal is applied to the terminal T3. At this time, the detection signal Vop is GND.
Level.

Since the input voltage Vin is a pulsating current obtained by rectifying the AC input voltage Vac, the comparator OP compares the reference voltage Vref with the absolute value level of the AC input voltage Vac. You can see that there is. In this case, for example, a capacitor C3 for removing noise is inserted between the output of the comparator OP and the inverted input.

The operation of the stop control circuit 2 having the above configuration is described as follows.
This will be described with reference to the waveform diagram of FIG. Here, it is assumed that the input range of the AC input voltage Vac is AC85V to 276V, and the DC output voltage Vout is controlled to be substantially constant at 350V. Then, the reference voltage Vre
As f, the AC input voltage Vac is AC 245 V (35
0V × 0.7) or more, the comparator OP
It is assumed that the setting is made such that the H level is output from the.

For example, if an AC input voltage Vac is supplied as shown in FIG.
in is obtained as a waveform as shown in FIG.
Then, with respect to this input voltage Vin, the reference voltage Vref set as described above has a level including the ripple voltage indicated by the dashed line in FIG. 2B.

According to the relationship between the input voltage Vin and the reference voltage Vref shown in FIG. 2B, the detection signal V input from the comparator OP to the terminal T3 via the diode D5.
For op, a waveform shown in FIG. 2C is obtained.
That is, a predetermined H level is obtained during a period when the input voltage Vin exceeds the reference voltage Vref (a period when the AC input voltage Vac exceeds 245 V AC), and the input voltage Vin is obtained.
During the period when the voltage does not exceed the reference voltage Vref (the period when the AC input voltage Vac does not exceed 245 V AC).
This is a level signal.

When the detection signal Vop shown in FIG. 2C is input to the terminal T3, the switching control circuit 1 operates as follows. That is, as shown as the switching drive signal Vds in FIG.
During the period when p is at the H level, the switching control circuit 1 falsely detects the overcurrent state, and stops the output of the switching drive signal as a response operation. That is, the switching stop period T1 is provided. Then, during a period when the detection signal Vop is at the GND level, a switching drive signal according to a normal operation is output, and a switching period T2 is provided.

When the switching operation is controlled as described above, if the AC input voltage Vac is set to a high voltage exceeding 245 V AC, the switching operation is stopped and the boosting operation in the inductor L1 is also stopped. Will be. As a result, even at a light load,
Since the energy is prevented from being excessively accumulated in the inductor L1 by the action of the unstable switching operation such as the intermittent oscillation, the rapid rise of the DC output voltage Vout can be suppressed. That is,
This allows the regulation of the DC output voltage Vout to be ensured.

Here, for example, when the AC input voltage Vac is AC
When the voltage rises to 276 V, the actual input voltage Vi
Although n becomes approximately 390 V, in this case, according to the operation described with reference to FIG. 2, the switching operation of the switching element Q1 is stopped over the entire cycle. Therefore, the DC output voltage Vout can be suppressed to about 390 V, which is obtained by rectifying and smoothing the input voltage Vin even under a light load.

On the contrary, when the AC input voltage Vac is
When the voltage becomes 5 V or less, the detection signal Vop applied to the terminal T3 becomes the GND level, so that the switching control circuit 1 returns to the power factor improving operation as a normal active filter. Switching control will be performed.

In the present embodiment, the stabilization of the DC output voltage Vout is ensured as described above, so that, for example, the smoothing capacitor C2 for generating the DC output voltage Vout has a DC output voltage. Voltage Vou
Since it is no longer necessary to consider an excessive increase in t, it is possible to select one having a lower rated voltage than before.

The present invention is not limited to the configuration shown in FIG. 1, but the detailed configuration and the internal configuration of the stop control circuit 2 may be changed.

[0040]

As described above, according to the present invention, for example, in a DC power supply circuit provided with a so-called step-up type chopper to improve the power factor, the input voltage of the commercial AC power supply exceeds a predetermined level. In this state, the switching operation is stopped.However, even if the load is light, the switching element does not intermittently oscillate. Is accumulated to prevent an overvoltage condition from being caused. That is, in the present embodiment,
Even when a load change occurs at a high input voltage, the output voltage stabilization performance of the power factor correction circuit is improved.

Further, in the present invention, a phenomenon that the output voltage jumps excessively is also prevented. Therefore, as a component of the rectifying and smoothing circuit provided for the power supply circuit,
For example, a smoothing capacitor having a lower rated voltage than the conventional capacitor can be selected, and accordingly, cost reduction and circuit miniaturization can be achieved.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram showing an operation for stopping switching in the DC power supply circuit of the present embodiment.

FIG. 3 is a circuit diagram showing a configuration of a DC power supply circuit as a conventional example.

[Explanation of symbols]

1 switching control circuit, 2 stop control circuit, C1
Smoothing capacitor, C2 smoothing capacitor, C3 capacitor, D1 bridge rectifier circuit, D2 rectifier diode,
D5 diode, L1 inductor, N1 winding, N
2 winding, OP comparator, Q1 switching element, R1 resistance, R2 resistance, R load resistance, T1 to T
4 terminals

Claims (1)

[Claims] 1. A rectifier for rectifying and smoothing a commercial AC power supply, a step-up inductance element inserted into an output current path of the rectifier, a switching unit for interrupting a current flowing through the inductance, and the switching. DC voltage generating means for obtaining a DC output voltage by rectifying and smoothing the output of the means; and variably controlling the switching frequency of the switching means based on the excitation voltage of the inductance element and the output, so that at least the DC power supply. In a DC power supply circuit having switching control means for stabilizing the output of the circuit, a voltage level corresponding to the commercial AC power supply is detected, and when the detected voltage level is determined to be higher than a predetermined threshold value, Is configured to stop the switching operation of the switching means. DC power supply circuit, characterized in that a switching operation stopping means.