JP2654732B2 - Active filter type switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter type switching power supply.
The present invention relates to a switching power supply that controls a DC converter as an active filter, thereby suppressing generation of harmonics and increasing a power factor.

[0002]

2. Description of the Related Art An active filter type switching power supply makes a line consumption current a sine wave in the same phase as an input voltage by appropriately controlling an on-off operation of a switching transistor of a DC-DC converter circuit, thereby greatly increasing a power factor. The power supply device has been improved. This method has the following advantages. Since the input current waveform is a sine waveform, the peak value of the input current is reduced, it can cope with a wide input voltage range, the load on the input line equipment of the device is reduced,
Improved waveform distortion, reduction of various harmonic disturbances, stable input voltage, miniaturization of converter circuit,

FIG. 2 shows an example of a typical active filter type switching power supply. This power supply mainly has a step-up DC-DC converter circuit 10 and an active filter control circuit 20. In this power supply, the switching transistor Q of the converter circuit is turned on and off to control the line current consumption to be a sine wave having the same phase as the input voltage of the commercial power supply, thereby improving the power factor and controlling the output at a constant voltage.

The converter circuit 10 comprises a switching transistor Q and a smoothing capacitor C arranged in parallel with the load 40, a choke coil L and a flywheel diode D arranged in series with the load 40, and the like. When the switching transistor Q is turned on, a current flows through the choke coil L to store energy, and when the switching transistor Q is turned off, the energy stored in the choke coil L is released and passes through the flywheel diode D to be smoothed by the smoothing capacitor C. And supplied to the load 40. The output voltage Vo is determined by the ON / OFF duty ratio of the switching transistor Q.

[0005] active filter control circuit 20, a voltage corresponding to the current i _L flowing through the choke coil L of the converter circuit 10, while comparing the target voltage proportional to the input voltage v _in, turn on the switching transistors Q - off Thus, the input current waveform is shaped into a sine wave having the same phase as the input voltage waveform. At this time, the output is stabilized by adding the detection signal of the output voltage Vo to the target voltage to be compared. This type of circuit is already commercially available in the form of an IC (for example, "TDA4814" manufactured by Siemens), and can be configured by adding a few external components.

This active filter control circuit 20
It comprises a control amplifier 22, a multiplier 24, a comparator 26, a status register 28 and the like. The voltage dividing resistor R ₁ of the output voltage V _O ,
The difference between the divided voltage Vf due to R ₂ and the reference voltage Vr is amplified by the control amplifier 22, and the product (target voltage) of the control voltage Vs and the instantaneous value of the input voltage is obtained by the multiplier 24. The comparator 26 compares the voltage drop (corresponding to the instantaneous value of the choke current) of the current sense resistor Rs of the switching transistor Q with the target voltage from the multiplier 24, and controls the state register 28. The comparator 26 resets the status register 28 when the voltage drop of the current sense resistor Rs reaches the target voltage, and sets the status register 28 when the choke coil L has finished discharging. By this operation, the switching transistor Q repeatedly turns on and off, and the choke current i _L becomes a triangular wave as shown in FIG. The peak value corresponds to the target voltage by the multiplier 24, and the average input current i _in is half of the choke current i _L, is shaped to a sine wave of the input voltage v _in phase with the result, at the same time the output voltage Vo Is stabilized.

[0007]

In order to improve the output voltage accuracy, the control amplifier 22 needs to have a high gain, and to improve the power factor, the gain at the commercial frequency needs to be zero. is there. Therefore, the resistor R ₅ is connected to the control amplifier 22.
And to have a frequency characteristic - desired gain is provided a negative feedback loop formed by a serial connection of the capacitor C ₁ and.

In this circuit, since the control amplifier needs to have a high gain as described above, overshoot (increase in output voltage) occurs when the input is turned on. In order to prevent overshoot, for example, an overvoltage protection circuit having an overvoltage protection set value slightly higher than the output voltage set value is provided so that the overvoltage protection set value is not exceeded (when the overvoltage protection set value is exceeded, Control (so that the switching transistor is turned off) can be considered. However, if the control amplifier 22 has the above-described negative feedback loop, the transient state (the operation state of the overvoltage protection circuit) continues for a long time, during which the input current is disturbed and a high power factor cannot be realized. The duration of the transient state becomes longer as the overvoltage protection set value is closer to the output voltage set value. In other words, the transient state continues for a long time to suppress the overshoot, and the overshoot increases when the transient state is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide an active filter type switching power supply which can solve the above technical problems and realize high output voltage accuracy in a steady state and reduced overshoot in a transient state and reduced duration of a transient state. It is to be.

[0010]

In a conventional circuit, as a result of investigating the cause of a long-lasting transient state when an input is turned on, a control amplifier having a negative feedback loop consisting only of a series connection of a resistor and a capacitor has a high gain. It was also found that the response was slow. At the time of input, while the output voltage Vo does not yet reach the predetermined voltage, the divided voltage Vf becomes lower than the reference voltage Vr.
Becomes a value higher than the reference voltage Vr, that is, "H" level.
During this time, the capacitor C ₁ is charged. Next, the output voltage V
When o reaches a predetermined voltage and the divided voltage Vf becomes equal to or higher than the reference voltage Vr, the control amplifier 22 inverts and the control voltage Vs attempts to become a value lower than the reference voltage Vr, that is, the “L” level. However, since the gain at a commercial frequency to zero, because it is necessary to high resistance capacitors C ₁ was dividing resistors R ₁ and large capacity, R _2, the charge stored in the capacitor C ₁ easily discharge Therefore, the control voltage Vs decreases only gradually. That is, it takes time to reach the “L” level. For this reason, the continuation time of the transient state at the time of input input was long.

According to the present invention, there is provided a DC-DC converter circuit having a switching transistor, and a difference between a voltage proportional to an output voltage of the converter circuit and a fixed reference voltage is amplified by a control amplifier, and a line consumption current of the converter circuit is sinusoidally calculated. An active filter type switching power supply comprising: an active filter control circuit that controls the switching transistor at a constant voltage so as to generate a wave. In order to solve the above problem, in the present invention, a negative feedback in which a series connection of a resistor and a capacitor and a series connection of a resistor and a diode are combined in parallel between the output terminal and the negative-phase input terminal of the control amplifier. The loop is arranged such that the cathode end of the diode faces the negative-phase input end. In particular, the present invention is characterized in that a series connection of a resistor and a diode is added.

The switching power supply of the present invention usually includes an overvoltage protection circuit that turns off the switching transistor when the output voltage of the converter circuit exceeds a set value.

[0013]

When the output voltage is low, such as when the power is turned on, the negative-phase input voltage of the control amplifier (divided power supply output voltage) is lower than the common-mode input voltage (constant reference voltage). The voltage (control voltage) is at the “H” level higher than the fixed reference voltage. At this time, the capacitor is charged. Next, when the power supply output voltage reaches a predetermined voltage and the negative-phase input voltage becomes equal to or higher than the in-phase input voltage (constant reference voltage), the control amplifier inverts and the control voltage is lower than the constant reference voltage. At the same time, the capacitor of the negative feedback loop begins to discharge as the voltage of the negative feedback loop starts to decrease. At this time, since the control voltage is still at the “H” level, the charge of the capacitor is discharged through the series connection of the resistor and the diode. In this way, the control voltage quickly reaches the "L" level, and during that time, since the gain is low while the diode is in the on state, overshoot is unlikely to occur, and the duration of the transient state is also reduced. In the steady state (constant voltage operation), the diode keeps the off state due to the reverse bias, so that the resistor connected in series with the diode comes out of the negative feedback loop, and a highly accurate power supply output can be obtained.

[0014]

FIG. 1 is a circuit diagram showing one embodiment of an active filter type switching power supply according to the present invention. DC
Since the basic circuit configurations of the DC converter circuit 10 and the active filter control circuit 20 are substantially the same as those shown in FIG. 2, the corresponding portions are denoted by the same reference numerals, and description thereof will be omitted. The present invention, in series connection between the output terminal and the inverting input terminal of the control amplifier 22 of the active filter control circuit 20, a series connection of a resistor R ₅ and capacitor C _1, a resistor R ₆ and the diode D ₁ Are arranged in parallel such that the cathode end of the diode faces the negative-phase input end.

Further, in this embodiment, an overvoltage protection circuit 30 is incorporated. The overvoltage protection circuit 30, dividing the output voltage Vo by the resistors R _3, R _4, and compares the divided voltage by the comparator 32 with the overvoltage setting value Vp, the switching transistor Q when exceeding the over-voltage set value Vp Generates an overvoltage protection signal that turns off. Therefore, this overvoltage protection signal and the operating state signal of the choke coil (diode D
The AND circuit 34 calculates the logical product of the current flowing through the circuit and the zero-crossing control signal, and controls the switching transistor Q to stop while the output voltage Vo is in an overvoltage state.

When the output voltage Vo is low, such as when the power is turned on, the control voltage Vs is at the "H" level higher than the reference voltage Vr. In this case the capacitor C ₁ is charged. If the output voltage Vo reaches the predetermined voltage, the control amplifier 22 with inverting and control voltage Vs begins as low as would reference voltage lower than Vr "L" level, the capacitor C ₁ is also beginning the discharge. Control voltage Vs at this time is, because of the still "H" level, the charge of the capacitor C ₁ will be discharged through the series connection of a resistor R ₆ and the diode D _1. Thus, the control voltage Vs is changed to the capacitor C ₁
Promptly without being obstructed by the discharge reaches the "L" level, the and between the diode D ₁ the gain is lowered in the on state, the overshoot is less likely to occur, to reduce at the same time the duration of the transient Become.

[0017] it is necessary to provide always diode D ₁ in a negative feedback loop in a predetermined orientation. If this diode D ₁
Without this, the divided voltage Vf is simply the resistance R ₃ , of the output voltage Vo.
Not the partial pressure by R _4, the control voltage Vs, is governed by the current flowing from the resistor R _6, so that the resulting output voltage Vo is varied. However, since the negative feedback loop has diodes D _1, the control when the voltage Vs is below the reference voltage Vr, by performing the circuit designed to output voltage Vo is stabilized at a set value, the steady state (constant voltage operation) sometimes, diode D ₁ is to keep the off state, the power output of the high accuracy can be obtained.

FIG. 4 shows the results of actual measurement of the duration of the transient state when the power is turned on. This shows an output voltage waveform when the conditions are set to: input voltage: 135 V (AC), output voltage set value: 385 V, and overvoltage protection set value: 400 V. A indicates the case where the resistor R ₆ and the diode D ₁ are not provided ( B) When B is added with a resistor R ₆ and a diode D ₁ (the present invention)
It is. Overvoltage protection operation area (transient state continuation time) ta up to constant voltage operation area (steady state continuation state) tb
In the switching power supply according to the present invention, as shown in FIG. 4A, which took about 1.2 seconds in the conventional switching power supply, as shown in FIG. 2
It could be shortened to about a second.

The present invention is not limited to only such a configuration. The DC-DC converter circuit is applicable not only to the above-described step-up type, but also to a step-up / step-down type and a flyback converter.

[0020]

The present invention provides a control amplifier of an active filter control circuit provided with a negative feedback loop in which a series connection of a resistor and a capacitor and a series connection of a resistor and a diode are combined in parallel. When the control voltage (output voltage) is going to become lower than the reference voltage (input voltage), the charge of the capacitor is discharged through the series connection of the resistor and the diode. And during that time the diode is on and the gain is low. For this reason, overshoot hardly occurs, and at the same time, the duration of the transient state is reduced. Also, in a steady state (constant voltage operation), the diode is kept off by a reverse bias, so that the resistor connected in series with the diode comes out of the negative feedback loop, and a highly accurate power supply output can be obtained. As described above, according to the present invention, it is possible to quickly stabilize and stabilize a transient state while maintaining the characteristics of the active filter type.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a switching power supply according to the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional switching power supply.

FIG. 3 is an operation waveform diagram of the active filter type switching power supply.

FIG. 4 is an output voltage measurement waveform diagram when power is turned on.

[Explanation of symbols]

10 DC-DC converter circuit 20 an active filter control circuit 22 controls the amplifier 30 over-voltage protection circuit D ₁ diode R ₆ resistance

Claims (2)

(57) [Claims] 1. A DC having a switching transistor.
A DC converter circuit, and a control amplifier that amplifies a difference between a voltage proportional to an output voltage of the converter circuit and a fixed reference voltage, and controls the switching transistor at a constant voltage so that a line consumption current of the converter circuit is converted into a sine wave. In an active filter type switching power supply comprising an active filter control circuit, a series connection of a resistor and a capacitor and a series connection of a resistor and a diode are connected in parallel between an output terminal and a negative-phase input terminal of the control amplifier. An active filter type switching power supply characterized in that a combined negative feedback loop is arranged such that a cathode end of the diode faces an opposite phase input end. 2. The switching power supply according to claim 1, further comprising an overvoltage protection circuit that turns off the switching transistor when an output voltage of the converter circuit exceeds a set value.