JPH02280670A - Power source equipment - Google Patents

Abstract

PURPOSE:To improve the reliability by providing a third control means for preventing overcurrent and operating the third control means in parallel with first and second control means. CONSTITUTION:An AC/DC converter performs full-wave rectification of AC input through a rectifier 10 and provides the rectified output to a booster type chopper circuit 20. The chopper circuit 20 comprises a switching element Q1 to be turned ON/OFF through a PWM circuit 31, and the like, and further provided with first and second control means comprising a VCA 32, a differen tial amplifier 33, an error amplifier 35, and the like. A differential amplifier 37 and the like are also provided as a third control means for preventing overcurrent, and the output therefrom is added through a diode 30 to the output from the differential amplifier 33.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a switching power supply device (AC/DC converter) that generates stable DC power from AC power.

(Prior Art) Recently, a power factor correction type AC/DC converter as shown in FIG. 2 has been developed. In FIG. 2, a sine wave AC input is full-wave rectified by a rectifier circuit 10 consisting of a diode bridge, and is input to a step-up chopper circuit 20, which will be described in detail below. The chopper circuit 20 includes a switching element Q1 that is driven on/off by a PWM (pulse width control) circuit 31 at a frequency sufficiently higher than that of the AC power supply, and an inductor L1 that is connected in series between the output of the rectifier circuit 10 together with the switching element Q1. and a diode D connected in series across the switching element Q1 so that current flows through the inductor L1 when the switching element Q1 is off.
1 and a capacitor C1. The capacitor C1 has a considerably large capacity, and a DC output that has been smoothed and voltage stabilized (described later) is taken out from both ends of the capacitor C1. Note that the capacitor C2 is a small capacitor for absorbing high frequency ripples, and is not essential to this device.

The signal of the output voltage V1 of the full-wave rectification of the rectifier circuit 10 is VCA
The signal is input to a differential amplifier 33 via a (voltage controlled variable gain amplifier) 32. Inductor L1 of chopper circuit 20
Current 11 flowing through is detected by current transformer 34, and its low frequency component signal is input to differential amplifier 33. The PWM circuit 31 operates according to the differential output of the differential amplifier 33, and changes the drive pulse width (on time) of the switching element Q1 so that the differential output is minimized. Further, the error of the output voltage V2 of the chopper circuit 20 with respect to the reference voltage Vs is detected by the error amplifier 35, and this value becomes the control voltage of the VCA 32.

In the above configuration, the differential amplifier 33 compares the waveform of the input V1 of the chopper circuit 20 with the waveform of the current 11 flowing through the inductor L1, and operates the PWM circuit so that the current waveform changes to follow the voltage waveform. 31 changes the on-time of the switching element Q1.

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 this on-period is proportional to the input voltage V1 and proportional to the on-time. When the switching element Q1 is turned off, a current due to the release of the energy stored therein is superimposed on the output of the rectifier circuit 10 and is supplied to the capacitor C1 side.

Pulse width control based on the comparison between the input voltage waveform and the current waveform of the inductor L1 works to shorten the on-time of the switching element Q1 as the input voltage v1 increases. Through this control, the change in the current waveform becomes approximately equal to the full-wave rectified waveform of the input voltage. In other words, when viewed from the AC input side, the input voltage and input current have almost the same waveform and there is no phase difference, resulting in almost the same state as if the load were a resistor. The above is the operation of the first control means.

Further, the second control means operates as follows.

The larger the output voltage v2 is than the reference voltage Vs, the more vcA32
The smaller the gain is, and the smaller v2 is than Vs, the more VC
The gain of A32 increases. This VCA 32 is a circuit through which the waveform signal of the input voltage in the first control means passes, and its gain becomes a basic parameter of the first control means. That is, when the output voltage v2 is too high, the on time of the switching element Q1 is shortened, and on the other hand, when the output voltage v2 is too low, the on time is extended, which acts to bring the output voltage v2 closer to the reference voltage Vs.

As explained in detail above, in this type of power supply,
The input current changes almost following the AC input voltage, becoming almost a sine wave with no phase difference, and the relationship between voltage and current seen from the AC power supply side is almost the same as that of a resistive load (the power factor is improved). ). Therefore, unlike conventional capacitor input type rectifier circuits, large pulse currents do not flow intensively in a short period of time, and restrictions on the current withstand characteristics of circuit elements are relaxed, and various It is possible to reduce harmful noise.

Further, due to the boosting action of the chopper circuit and the feedback control action of the output voltage by the second control means,
Even if the AC input voltage fluctuates or the voltage rank changes, the output voltage can be kept constant.

As a result, a power supply device that does not require any switching and is compatible with, for example, an AC 100 V power source to an AC 20 OVi source can be easily constructed.

In addition, in the conventional device shown in Fig. 2, the transistor
, inductor L1, diode D1, etc., a Zener diode 36 is connected to the output terminal of the VCA 32 to prevent the output voltage of the VCA 32 from exceeding a set value Vz.

The output of the VCA 32 is a current waveform target signal, and the PWM circuit 31 operates according to the deviation between the actual current signal detected by the current transformer 34 and this target signal, and controls the drive pulse width of the switching element Q1. There is. Therefore, VCA3
When the output of 2 (current target signal) increases, the switching element Q1 is controlled so that the current 1 flowing through the inductor L1 becomes equal to the target value. By limiting the output of the VCA 32 to a constant value Vz by the Zener diode 36, the switching operation by the PWM circuit 31 is restricted, and the current 11 is reduced to the set value Vz by the Zener diode 36.
It is made not to exceed the value corresponding to z.

(Problem to be Solved by the Invention) In the conventional power supply device described above, the Zener diode 36
There was a problem that the overcurrent prevention function using the In other words, the output waveform of the VCA 32 is a full-wave rectified waveform corresponding to the input voltage v1, and when its peak value attempts to exceed the set value Vz by the Zener diode 36, V
Clipped at z. The differential amplifier 33 that amplifies the difference between the target signal and the detection signal of current 1 has a very large gain in order to reduce control errors, and has a frequency characteristic that is low to some extent in order to stabilize control. ing. Therefore, if the output of the VCA 32 (target signal of current 11) is clipped by the Zener diode 36, the control system will not be able to fully respond to the inflection of the target signal due to clipping, and the actual waveform of current 11 will have an overshoot or Undershoot occurs. In other words, the current 11 could not be completely limited by the set value Vz by the Zener diode 36, and it was not possible to avoid a current exceeding the target value flowing as a transient response. Furthermore, it has been impossible to continuously vary the current value setting.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a power supply device having an overcurrent prevention function that is more reliable than the conventional one.

(Means for Solving the Problems) Therefore, in the present invention, in the power factor correction type power supply device described above, when the low frequency level of the current flowing through the rectifier circuit, the inductor, or the switching element exceeds a set level, A third control means for overcurrent prevention is added, which reduces the driving pulse width of the switching element as the level difference becomes larger.

(Function) The third control means operates in parallel with the first control means and the second control means, and when the low frequency level of the current exceeds the set level, the third control means operates in parallel with the first control means and the second control means, and when the low frequency level of the current exceeds the set level, It functions to reduce the driving pulse width of the switching element and suppresses the current. This current suppression operation is not directly affected by the amplification gain or frequency characteristics of the feedback systems of the first and second control means.

(Embodiment) FIG. 1 shows the configuration of an embodiment of the present invention, in which the Zener diode 36 in the conventional device shown in FIG. 2 is eliminated, and
The following configuration is provided as the third control means for overcurrent prevention. Note that since the configuration and operation of the power supply device itself have already been described in detail, the novel parts according to the present invention will be extracted and explained below.

The main body of the third control means function for overcurrent prevention is the differential amplifier 3.
It is 7. The current 11 flowing through the inductor L1 is detected by the current transformer 34, and a signal (
The low frequency level of the current (1) and an appropriately set reference voltage signal Vr are input to the differential amplifier 37. When the detection signal of the current 11 exceeds the reference voltage signal Vr, its differential amplified output is added to the output of the differential amplifier 33 via the reverse current blocking diode 38, and the added signal is input to the PWM circuit 31. becomes. Note that when the output of the differential amplifier 37 becomes negative, the output does not become the control input of the PWM circuit 31.

As mentioned above, the difference between the target signal and the detection signal of the current 11 is amplified in the differential amplifier 33, and the larger the differential output is, the PWM circuit 31 decreases the drive pulse width of the switching element Q1 to increase the current 11. Works to make it smaller.

When the detection signal of the current 11 becomes larger than the reference voltage signal Vr, the difference between the two is added to the output of the differential amplifier 33 and P
Since it is input to the WM circuit 31, the driving pulse width of the switching element Q1 becomes smaller by the differential output of the differential amplifier 37. In this manner, as the current 11 increases, the system of the differential amplifier 37, which is the third control means, works to further reduce the pulse width of the switching element Q1, thereby preventing overcurrent from flowing through each element.

Here, the differential amplifier 37 does not need to have a low frequency response like the differential amplifier 33, and can suppress overcurrent without being affected by the control system of the differential amplifier 33.

In the embodiment shown in FIG. 1, the signal detected by the current transformer 34 is used as an input to both the differential amplifier 33 and the differential amplifier 37, but it is also possible to use separate current detection means for each. Furthermore, the position and configuration for current detection are not limited to the embodiments.

Further, although the chopper circuit 20 of the embodiment described above is of the step-up type, the present invention can be practiced with chopper circuits of other types such as the polarity inversion type and the step-up-step-down type.

(Effects of the Invention) As explained in detail above, in the power supply device of the present invention, when the low frequency level of the current flowing through the rectifier circuit, inductor, or switching element exceeds the set value,
A third control means for overcurrent prevention is provided, which reduces the driving pulse width of the switching element as the level difference is larger, and the third control means is operated in parallel with the first and second control means. So, the first and second
It is possible to realize highly reliable overcurrent protection that reliably suppresses the input current below the set value without being affected by the amplification gain or frequency characteristics of the control means.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a power supply device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional power supply device. 10... Rectifier circuit 20... Chopper circuit 31... PWM circuit 32... VCA 33... Differential amplifier 34... Current transformer 35... Differential amplifier 36... Zener diode (Conventional) 37...Differential amplifier Fig. 1

Claims (1)

[Scope of Claims] A rectifier circuit that full-wave rectifies an AC power source to obtain a pulsating output; a switching element that is driven on/off at a frequency sufficiently higher than that of the AC power source; A chopper circuit having an inductor connected in series between outputs, and a capacitor that smoothes the current supplied through the inductor to obtain a stable DC output; A low frequency component of the current flowing through the inductor or the switching element; a first control means for controlling the driving pulse width of the switching element so that the waveform of the switching element changes in accordance with the waveform of the output voltage of the rectifier circuit; a second control means for controlling the drive pulse width of the switching element so that; when the low frequency level of the current flowing through the rectifier circuit, the inductor, or the switching element exceeds a set level, the level difference is A power supply device comprising: third control means that reduces the driving pulse width of the switching element as the width of the driving pulse increases.