JPH0789744B2 - Power supply - Google Patents

Description

TECHNICAL FIELD The present invention relates to a switching type power supply device (AC / DC converter) for producing a stable DC power supply from an AC power supply.

<< 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 composed of a diode bridge and input to a booster type chopper circuit 20 described in detail below. The chopper circuit 20 includes a switching element Q1 that is turned on / off by a PWM (pulse width control) circuit 31 at a frequency sufficiently higher than an AC power source, and an inductor L1 that is connected in series between the switching element Q1 and the output of the rectifier circuit 10.
And a diode D1 and a capacitor C1 connected in series at both ends of the switching element Q1 so that a current flows through the inductor L1 when the switching element Q1 is off. 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 an operational amplifier 33 via a VCA (voltage control type variable gain amplifier) 32. The current 11 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 operational 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. In addition, the reference voltage of the output voltage V2 of the chopper circuit 20
The error with respect to Vs is detected by the error amplifier 35, and this output is
It becomes the control voltage of VCA32.

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

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 off, a current due to the release of energy accumulated in the switching element Q1 is superimposed on the output of the rectifier circuit 10 and is supplied to the capacitor C1 side.

As a result, the pulse width control by comparing the input voltage waveform and the current waveform of the inductor L1 acts to shorten the ON time of the switching element Q1 as the input voltage V1 increases. By this control, the change of the current waveform becomes almost equal to the full-wave rectified waveform of the input voltage. That is, when viewed from the AC input side, the input voltage and the input current have substantially the same waveform and there is no phase difference, and the state is almost the same as when the load is a resistor. The above is the operation of the first control means.

Moreover, the second control means operates as follows. Output voltage
The gain of VCA32 decreases as V2 is higher than the reference voltage Vs, and the gain of VCA32 increases as V2 is lower than Vs. This VCA32 is a circuit through which the waveform signal of the input voltage in the first control means passes, and the gain thereof is a basic parameter of the first control means. That is, if the output voltage V2 is too high, the ON time of the switching element Q1 is shortened,
On the other hand, if it is too low, the on-time is extended and the output voltage V2 acts so as to approach the reference voltage Vs.

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 100V power supply to 200V AC power supply can be easily configured.

Further, in the conventional device shown in FIG. 2, in order to prevent an overcurrent from flowing through the transistor Q1, the inductor L1, the diode D1, etc., a zener diode 36 is connected to the output terminal of the VCA32 to set the output voltage of the VCA32. It does not exceed the value Vz.

The output of the VCA32 is the target signal of the current waveform, the PWM circuit 31 operates according to the deviation between this target signal and the actual current signal detected by the current transformer 34, and controls the drive pulse width of the switching element Q1. There is. Therefore, when the output of VCA32 (current target signal) increases, the current I1 flowing through inductor L1
The switching element Q1 is controlled so that is equal to the target value. By limiting the output of the VCA 32 to the constant value Vz by the Zener diode 36, the switching operation by the PWM circuit 31 is restricted, and the current I1 does not exceed the value corresponding to the set value Vz by the Zener diode 36.

<< Problems to be Solved by the Invention >> The above-described conventional power supply device has a problem that the overcurrent prevention function using the Zener diode 36 is not reliable. That is, the output waveform of the VCA 32 is a full-wave rectified waveform corresponding to the input voltage V1, and when its peak value exceeds the set value Vz set by the Zener diode 36, it is clipped at Vz. The differential amplifier 33 that amplifies the difference between the target signal and the detection signal of the current I1 has a very large gain in order to reduce the control error, and the frequency characteristic is lowered to some extent in order to stabilize the control. There is. Therefore, when the output of VCA32 (the target signal of current I1) is clipped by Zener diode 36, the control system cannot completely respond to the inflection of the target signal due to clipping, and the actual waveform of current I1 does not overshoot or Undershoot occurs. That is, the current
I1 could not be completely limited by the set value Vz by the Zener diode 36, and it was unavoidable that a current exceeding the target value would flow as an excessive response.

Further, this type of power factor correction type power supply device has a feature that it can be used for an AC power supply in a wide voltage range, but in the conventional device, a constant overcurrent protection circuit is provided regardless of the magnitude of the AC power supply voltage used. ing. Therefore, for example, if the maximum value of the current is set according to the input voltage of 100V, the overcurrent prevention function works with the same current even when the input voltage is 200V. If the power is not twice as high as the case, the protection will not work. Considering the protection of the element, it is necessary to prevent the power supplied to the element from exceeding a certain range, which is not the case in the conventional device.

The present invention has been made in view of the above problems, and an object thereof is to realize a reliable and reliable overcurrent protection function and to change the overcurrent protection characteristics according to the AC power supply voltage to be used. The purpose is to provide a power supply device.

<< Means for Solving the Problem >> Therefore, in the present invention, when the low frequency level of the current flowing through the rectifier circuit, the inductor, or the switching element exceeds the set level in the power supply device of the power factor correction system described above. And a third control means for decreasing the drive pulse width of the switching element as the level difference is larger, and a function generating means for decreasing the set level in the third control means as the amplitude of the AC power supply is larger. Added.

<< Operation >> The third control means operates in parallel with the first control means and the second control means described above, and when the low frequency level of the current exceeds the set level, the third control means responds to the level difference. It functions to reduce the drive pulse width of the switching element and suppresses the current. This current suppressing operation is not directly affected by the amplification gain or frequency characteristic of the feedback system of the first and second control means.

Further, when the voltage (amplitude) of the AC power supply to be used is largely changed, the function generating means sets the set level to be small, and the overcurrent prevention function works with a smaller current value.

<< Embodiment >> FIG. 1 shows the construction of an embodiment of the present invention. The Zener diode 36 in the conventional apparatus of FIG. 2 is eliminated and the following construction is provided as a third control means for preventing overcurrent. It is a thing. Since the configuration and operation of the power supply device itself have already been described in detail, a new part of the present invention will be extracted and described below.

Third control means for preventing overcurrent Another main body is a differential amplifier 37
Is. The current I1 flowing through the inductor L1 is detected by the current transformer 34, and a signal obtained by filtering the detection output (a low frequency level of the current I1) and an appropriately set reference voltage signal Vr are differential amplifier 37. Will be input. When the detection signal of the current I1 exceeds the reference voltage signal Vr, the differential amplification output is added to the output of the differential amplifier 33 via the diode 38 for backflow prevention, and the addition signal is input to the PWM circuit 31. Become. When the output of the differential amplifier 37 becomes negative, the output does not become the control input of the PWM circuit 31.

As described above, the differential amplifier 33 amplifies the difference between the target signal of the current I1 and the detection signal, and the greater the differential output, the higher the PW
The M circuit 31 operates so as to reduce the drive pulse width of the switching element Q1 and reduce the current I1. When the detection signal of the current I1 becomes larger than the reference voltage signal Vr, the difference between the two is added to the output of the differential amplifier 33 and input to the PWM circuit 31, so that only the differential output of the differential amplifier 37 corresponds to the switching element Q1. Drive pulse width becomes smaller. Thus, as the current I1 increases, the system of the differential amplifier 37, which is the third control means, works to reduce the pulse width of the switching element Q1 and prevent an 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 the overcurrent without being affected by the control system of the differential amplifier 33.

The reference voltage signal Vr input to the differential amplifier 37 is a function generator.
Given by 40. The function characteristic of this function generator 40 is
Shown in the figure. Output voltage V1 of rectifier circuit 10 Filter circuit 39
The smoothed output voltage Va is input to the function generator 40. This input voltage Va has a value proportional to the amplitude (voltage) of the AC power supply. As shown in FIG. 3, the function generator 40
Outputs a voltage Vr that is substantially inversely proportional to the voltage Va within a certain range of the input voltage Va. The larger the input voltage Va, the smaller the output voltage Vr.

Therefore, when the connection is changed from the 100V AC power supply to the 200V AC power supply, the reference voltage signal Vr input to the differential amplifier 37 is
It becomes about half that at 100V, and the overcurrent suppression function starts to work at the current value at 200V. As a result, the protection function works to prevent the power supplied to the device from becoming excessive.

In the embodiment shown in FIG. 1, the signal detected by the current transformer 34 is used as the input to both the differential amplifier 33 and the differential amplifier 37, but the respective current detecting means may be used separately. The position and configuration for detecting the current are not limited to those in the embodiment.

Further, although the chopper circuit 20 of the embodiment described above is a boost type, the present invention can be implemented by a chopper circuit of another type such as a polarity inversion type or a boost / step down type.

<< Effects of the Invention >> As described 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, the inductor or the switching element exceeds the set value,
A third control means for overcurrent prevention is provided which reduces the drive pulse width of the switching element as the level difference increases, and the third control means is operated in parallel with the first and second control means. So the first and second
The reliable overcurrent protection that reliably suppresses the input current to the set value or less can be realized without being affected by the amplification gain or frequency characteristic of the control means.

In addition, the current value of the overcurrent protection function changes according to the voltage of the AC power supply used, and the protection works with almost constant power regardless of the input voltage, so even in this aspect there is no adjustment for a wide input voltage range. Can be used in, and the fail-safe property in use is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a power supply device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional power supply device, and FIG. 3 is a characteristic diagram of a function generator in FIG. 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 40 ... Function generator

Claims (1)

[Claims] 1. A rectifying circuit for full-wave rectifying an AC power source to obtain a pulsating current output; a switching element which is on / off driven at a frequency sufficiently higher than the AC power source; and an output of the rectifying circuit together with this switching element. A chopper circuit having an inductor connected in series between the inductor and a capacitor for smoothing a current supplied through the inductor to obtain a stable DC output; and a low frequency component of a current flowing through the inductor or the switching element. First control means for controlling the drive pulse width of the switching element so that the waveform changes following the waveform of the output voltage of the rectifier circuit; reducing the error between the output voltage of the chopper circuit and the reference voltage. Second control means for controlling the drive pulse width of the switching element as described above; Third control means for reducing the drive pulse width of the switching element as the level difference increases when the low frequency level of the current flowing through the switching element exceeds a set level; and as the amplitude of the AC power source increases. A power generating unit for reducing the set level in the third control unit;