JP3215127B2 - Switching power supply control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention takes a sine wave AC power supply as an input, outputs a DC voltage, and reduces the harmonic component of the input current by making the input current waveform close to a sine wave. The present invention relates to an improvement in a control circuit of a high power factor switching power supply that sets a power factor to a value close to one, that is, an active filter.

[0002]

2. Description of the Related Art As an example of such a switching power supply, a circuit as shown in FIG. 1 has been conventionally proposed. FIG.
, A reactor 4 and a switch element 6 for performing on / off operations are connected in series to an output of a full-wave rectifier 3 connected to an AC power supply 1 via a high-frequency rejection filter 2, and a diode is connected to both ends of the switch element 6. The capacitor 7 and the capacitor 8 are connected in series, and an electric load 9 is connected to both ends of the capacitor 8 to supply a DC voltage. The error amplifier 11 amplifies the difference voltage between the DC voltage at both ends of the capacitor 8 as one input, a predetermined reference voltage source 12 as the other input, and the output thereof connected to the pulse generator 13. Have been. The error amplifier 11 and the reference voltage source 12
0. The zero current detector 5 connected to the pulse generator 13 outputs a signal when the current flowing through the reactor 4 becomes zero. The pulse generator 13 uses the output signal of the error amplifier 11 as a first input and the output signal of the zero current detector 5 as a second input, and turns the switch element 6 from off to on when the current flowing through the reactor 4 becomes zero. This is a circuit having a function of outputting a pulse such that the ON period is determined by the output signal of the error amplifier 11.

The operation of the conventional example having the above configuration will be briefly described with reference to the operation waveform diagram of FIG. In the description, the saturation voltage of the switch element, the forward voltage drop between the rectifier and the diode, the resistance component of the reactor, and the like are ignored. The positive half cycle of the AC voltage will be described, but the same applies to the negative half cycle, except that the polarity is inverted. In FIG. 2, the switching frequency is not shown to be much higher than the frequency of the AC power supply, but in practice, the switching frequency is sufficiently higher than the frequency of the AC power supply. Therefore, the input voltage Vi can be regarded as a substantially constant value in one switching cycle. Since the voltage applied to both ends of the reactor 4 during the on-period Ton of the switch element 6 is Vi, the peak value Ilpk of the current Il flowing through the reactor 4 at the end of Ton assumes that l is zero at the beginning of the on-period. , As shown in the following equation. Ilpk = (Vi / L) × Ton (Equation 1) Here, Vi: instantaneous value of AC input voltage L: inductance value of reactor 4 Ton: ON period of switch element 6 Here, in the cycle of frequency, switch element 6 Assuming that the on-period Ton is a constant value, Equation 1 shows that the peak value Ilpk of the current flowing through the reactor 4 is proportional to the output Vi of the full-wave rectifier 3. The current Il flowing through the reactor 4 during the off period of the switch element 6 is supplied to a capacitor 8 and a load 9 through a diode 7. The voltage applied to both ends of the reactor 4 during this period becomes a constant value of Vo-Vi when the DC output voltage is Vo, so that Il decreases linearly. When Il becomes zero, the pulse generator 13 turns the switch element 6 from off to on according to the output signal of the zero current detection circuit 5, and the next switching cycle starts.

Since the waveform Il of the current flowing through the reactor 4 in one cycle of the switching is a triangle as shown in FIG. 2, the average value of one cycle is 1/2 of the peak value Ilpk, as described above. Since the peak value Ilpk is proportional to Vi, the average value of Il is also proportional to Vi. By removing the high-frequency component by the high-frequency rejection filter, the current becomes an average of the input current Il.
Is a sine wave similar to the sine wave, the switching power supply that operates as described above can achieve a high power factor.

Next, stabilization of the DC output voltage will be described in connection with the operation of the error amplifier. First, when the DC output voltage is going to be high, the output of the error amplifier 11 (a in FIG. 1) is low.
The reference numeral 3 shortens the ON period of the switch element 6, and as a result, the input current is reduced to limit the rise of the DC output voltage.
Conversely, if the DC output voltage is about to decrease, the ON period is lengthened to limit the drop of the DC output voltage, so that the DC output voltage can be stabilized. As described above, the circuit example shown in FIG. 1 can achieve a high power factor and can supply a stabilized DC output voltage.

[0006]

However, in the conventional switching power supply of the configuration of this example, in order to obtain a high power factor by making the current waveform close to a sine wave, as described above. Since the on-period Ton of the switch element 6 must be substantially constant, the frequency of the AC power
In the case of z or 60 Hz, it is necessary to set the roll-off frequency of the error amplifier to several hertz. For this reason, the stable system cannot obtain a sufficient gain in a high frequency range, so that the response of the stabilization control is delayed when the input / output conditions change suddenly. As a result, the transient fluctuation of the output voltage increases. There were drawbacks.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an error amplifying circuit which can suppress a transient fluctuation of an output voltage even when an input / output condition changes suddenly.

[0008]

FIG. 3 shows an embodiment of the error amplifier circuit according to the present invention. The configuration of FIG. 3 will be described. In FIG. 3, the same components as those described in FIG. 1 are denoted by the same reference numerals. 14 is a second error amplifier, 15 is a third error amplifier, 16 is a second reference voltage source, 17 is a third reference voltage source, and the voltage V2 of the second reference voltage source is the first reference voltage source. The voltage V3 of the third reference voltage source, which is slightly lower than the voltage V1 of
Slightly higher than 1. A series circuit of a resistor and a capacitor connected to the output and the negative input of each error amplifier is for setting the frequency characteristics of each error amplifier.

[0009]

The operation of the present invention will be described with reference to FIG. In the switching power supply, when the input / output suddenly changes, for example, when the load current (I1 in FIG. 4) increases in a short time such as several milliseconds, the response of the first error amplifier 11 cannot catch up, and the error amplifier circuit 10 The output a gradually rises, and as a result, Ton (Ton in FIG. 4) gradually increases. However, the output voltage (Vo in FIG. 4) decreases because the rapid increase in the output current cannot be covered. When the second error amplifier 14 decreases to a point where the second error amplifier 14 operates (B of Vo in FIG. 4), the output a of the error amplifier circuit 10 rapidly increases due to the operation of the second error amplifier 14, and Ton also increases rapidly. Output voltage drop is limited. Similarly, when the load current suddenly decreases, the third error amplifier 15 operates to suppress an increase in the output voltage. In FIG. 4, Il represents a load current, Ton represents an on-period Vo, an output voltage, and t represents time. In FIG. 4, the portion represented by the dotted line in the Ton and Vo curves is a conventional example, and the solid line is an improved example according to the present invention.

The operation is as follows. Second error amplifier 14
When the output voltage drops below the set deviation, the output a of the error amplifier circuit 10 is increased to increase the output voltage. In other cases, the diode 18 does not contribute to the stabilizing operation. The third error amplifier 15 functions to lower the output a of the error amplifier circuit and lower the output voltage when the output voltage rises above the set deviation. In other cases, the diode 19 does not contribute to the stabilizing operation. The set deviation at which the second error amplifier 14 and the third error amplifier 15 operate is set by reference voltage source voltages V2 and V3, respectively.
Because of the resistance 20, the output of the second error amplifier 14 or the third error amplifier 15 has priority over the output of the first error amplifier 11.

The frequency of the AC power supply is 50 Hz or 60 Hz.
In the case of Hz, the roll-off frequency of the first error amplifier 11 is set to several hertz, and the roll-off frequencies of the second error amplifier 14 and the third error amplifier 15 are higher than this, for example, several hundred hertz. This is set as above.

[0012]

As described above, according to the present invention, it is possible to suppress the transient fluctuation of the output voltage due to the sudden change of the input power supply and the sudden change of the load, which has been considered as the weak point of the switching power supply. Further, the frequency characteristic of the error amplifier that is optimal for these sudden changes can be set by a series circuit of a resistor and a capacitor connected in parallel with the error amplifier. The control circuit of the high power factor type switching power supply according to the present invention is not limited to the circuit system shown in FIG. 1, but is another type of high power factor type in which the roll-off frequency of the error amplifier needs to be set to a low frequency. It is also applicable to a control circuit of a switching power supply.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of a conventional high power factor switching power supply.

FIG. 2 is an operation waveform diagram for explaining the operation of the conventional example.

FIG. 3 is a circuit connection diagram showing one embodiment of the present invention.

FIG. 4 is an operation waveform diagram for explaining the operation of the control method according to the present invention.

[Explanation of symbols]

 1 * ── * AC power supply 2 * ── * High-frequency rejection filter 3 * ── * Full-wave rectifier 4 * ── * Reactor 5 * ── * Zero current detection circuit 6 * ── * Switch element 7 * ── * Diode 8 * ── * Smoothing capacitor 9 * ── * Electrical load 10 * ─ * Error amplifier circuit 10 '** Error amplifier circuit 11 * ─ * First error amplifier 12 * ─ * First Reference voltage source 13 * ─ * pulse generator 14 * ─ * second error amplifier 15 * ─ * third error amplifier 16 * ─ * second reference voltage source 17 * ─ * third reference voltage source 18 * ─ * diode 19 * ─ * diode 20 * ─ * resistance

Claims (1)

(57) [Claims] A control circuit for a switching power supply that receives an AC power supply as an input, supplies a stabilized DC voltage to an output, and controls the input current to have a waveform close to a sine wave. A first differential amplifier that amplifies the deviation of the first differential amplifier, a pulse generator that controls the turning on and off of the switch element according to the output of the first differential amplifier, and the detection voltage exceeds the set value of the vertical deviation When the first and second differential amplifiers operate preferentially over the first differential amplifier to stabilize the output voltage, the second and third differential amplifiers have a DC reference voltage. And a response speed higher than that of the first differential amplifier.