JPH07264867A - AC-DC converter - Google Patents

Abstract

(57) [Abstract] [Purpose] AC-DC in which the boost chopper circuit and the DC-DC converter circuit are driven by one PWM circuit.
In the converter, the input power factor of the AC-DC converter is improved while suppressing the maximum voltage value of the DC voltage increased by the boost chopper circuit. [Structure] Rectifier 3, step-up chopper circuit 4, DC-DC
An AC-DC converter composed of the converter circuit 5 is provided with a PWM circuit 6, a frequency dividing circuit 7, and a voltage detection circuit 8, and the first pulse signal S _Pa output from the PWM circuit 6 is output to D
It is input to the first switching transistor Q1 of the C-DC converter circuit 5 and the frequency dividing circuit 7. The frequency divider circuit 7 changes the amount of step-down of the pulse frequency of the first pulse signal S _Pa according to the signal output from the voltage detection circuit 8, and the second pulse signal S _Pb generated thereby is boosted by a boost chopper circuit. 4 to the second switching transistor Q2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving a power factor of an AC-DC converter.

[0002]

2. Description of the Related Art A conventional AC-DC converter with improved power factor is an AC-DC converter including a rectifier for rectifying an AC input voltage and a DC-DC converter circuit for obtaining a stabilized DC output. Some have an active filter added by a chopper circuit. When operating the AC-DC converter to which this active filter is added, the switching element of the step-up chopper circuit and D
Simultaneously driving the switching elements of the C-DC converter circuit is the simplest circuit, and in this case, a high power factor of about 0.98 is obtained. However, when two switching elements are simultaneously operated by one control circuit, the voltage value of the DC voltage increased by the boost chopper circuit changes according to the voltage value of the AC input voltage. C. If the voltage is 100 [V], the maximum value of the DC voltage increased by the boost chopper circuit is about 270.
[V] while the AC input voltage is A.V. C. 20
When it is 0 [V], the maximum value of the DC voltage exceeds 500 [V].

Therefore, the means of simultaneously operating the two switching elements with one control circuit cannot take a wide range of application of the AC input voltage in consideration of the breakdown voltage of the circuit elements. Therefore, the inventor of the present invention is
No. 254757 proposed that a signal from a control circuit applied to a switching element of a DC-DC converter circuit should be applied to a switching element of a boost chopper circuit after the on-duty is reduced by a frequency dividing circuit. The AC-DC converter provided with this frequency dividing circuit can suppress the voltage value of the DC voltage rising by the step-up chopper circuit to a low value, so that it is possible to obtain a wide range of application of the AC input voltage. .

[0004]

In an AC-DC converter to which a boost chopper circuit is added to obtain a high power factor, it has been found that the average current flowing into the boost chopper circuit is represented by the following formula. There is.

[0005]

[Equation 1]

In the equation (1), however, T ₀ is the switching period, d is the on-duty of the switching element of the boost chopper circuit, V _C is the voltage across the terminals of the capacitor on the output side of the boost chopper circuit, and V _s (t ) Indicates the rectified sine wave rectified output voltage of the rectifier. Here, if the on-duty of the switching element of the step-up chopper circuit is reduced in order to suppress the voltage value of the DC voltage increased by the step-up chopper circuit, d and V _C shown in the equation (1) will decrease. As can be seen from the right side of the equation (1), V
_{When C} is sufficiently large, the current [i (t)] _avr is proportional to the sinusoidal voltage V _S (t), but if V _C is reduced to suppress the voltage rise in the circuit, the current [i (t t))
The degree of proportionality between _avr and the sinusoidal waveform voltage V _S (t) deteriorates, and the power factor of the AC-DC converter deteriorates. Therefore, an object of the present invention is to improve the power factor of the AC-DC converter while suppressing the maximum voltage value of the DC voltage that rises by the boost chopper circuit.

[0007]

The present invention is directed to a rectifier for rectifying an AC input voltage from an AC power supply line, a boost chopper circuit for boosting a rectified output voltage from the rectifier, and a high output voltage of the boost chopper circuit. In the AC-DC converter including a DC-DC converter circuit that receives the stabilized DC voltage to the load,
A converter drive circuit that detects the output voltage of the converter and supplies a first pulse signal having a pulse width corresponding to the output voltage to the switching element of the DC-DC converter circuit, and an instantaneous value of the rectified output voltage of the rectifier A voltage detection circuit that detects and outputs a signal according to the instantaneous value of the rectified output voltage, and receives the first pulse signal output from the converter drive circuit and the signal from the voltage detection circuit, and responds to the signal. A frequency divider circuit for supplying the second pulse signal obtained by stepping down the pulse frequency of the first pulse signal to the switching element of the boost chopper circuit, and the instantaneous value of the rectified output voltage of the rectifier is high. Sometimes, the amount of step-down of the pulse frequency of the frequency divider circuit is increased, and when the instantaneous value is low, the amount of step-down of the pulse frequency of the frequency divider circuit is decreased.
A DC converter.

[0008]

FIG. 1 shows a circuit of an embodiment of an AC-DC converter according to the present invention in which the power factor is improved while suppressing the maximum value of the DC voltage rising by the boost chopper circuit.
In FIG. 1, the AC-DC converter according to the present invention is configured as follows. Input terminals 1A and 1B are connected to the AC power supply line, and are connected to the AC input terminals of the rectifier 3, respectively. The (+) side output terminal of the rectifier 3 is connected to the anode of the diode D1 via the choke coil L1. The cathode of the diode D1 is connected to one end of the primary winding N1 of the converter transformer T and is connected to the primary winding N1.
Is connected to the drain of the first switching transistor Q1.

The source of the first switching transistor Q1 is connected to the (-) side output terminal of the rectifier 3. The drain and source terminals of the second switching transistor Q2 are connected between the anode of the diode D1 and the (−) side output terminal of the rectifier 3, and between the cathode of the diode D1 and the (−) side output terminal of the rectifier 3. The output capacitor C1 is connected. One end of the secondary winding N2 of the converter transformer T is connected to the output terminal 2B, and the other end is connected to the anode of the diode D2. The cathode of the diode D2 is connected to the output terminal 2A via the choke coil L2. The cathode of the diode D2 is a flywheel diode D
Connect to the cathode of 3 and flywheel diode D3
Is connected to the output terminal 2B. Output terminal 2A,
A smoothing capacitor C2 is connected between 2B.

In the above circuit configuration, the choke coil L1, the diode D1, the second switching transistor Q2, and the output capacitor C1 form the boost chopper circuit 4, and the converter transformer T, the first switching transistor Q1, the diode D2, and the flywheel. The diode D3, the choke coil L2, and the smoothing capacitor C2 form the DC-DC converter circuit 5. Further, in FIG. 1, in order to drive the boost chopper circuit 4 and the DC-DC converter circuit 5, a PWM circuit 6, a frequency dividing circuit 7, and a voltage detecting circuit 8 are provided in the following configuration. The feedback input terminal of the PWM circuit 6 as the converter drive circuit is connected to the output terminal 2A, and the pulse output terminal is connected to the gate of the first switching transistor Q1 and the pulse input terminal of the frequency dividing circuit 7. The voltage input terminal of the voltage detection circuit 8 is connected to the (+) side output terminal of the rectifier 3, and the signal output terminal is connected to the control input terminal of the frequency divider circuit 7. The pulse output terminal of the frequency dividing circuit 7 is connected to the gate of the second switching transistor Q2.

A having the above-mentioned circuit configuration is shown in FIG.
The control operation of the C-DC converter will be described below with reference to the waveform diagram of each signal shown in FIG. AC shown in FIG.
-When the DC converter is in a stable steady-state operation,
The PWM circuit 6 supplies the first pulse signal S _{Pa in} which an on-pulse is generated periodically to the gate of the first switching transistor Q1 and the frequency dividing circuit 7 as shown in the third stage of FIG. Here, a sine-wave full-wave rectified voltage is supplied to the step-up chopper circuit by rectifying the AC voltage from the outside by the rectifier 3, and at the same time, the voltage detection circuit 8 receives the full-wave rectified voltage as shown in the uppermost stage of FIG. The voltage signal S _S based on the wave rectified voltage is input. In the voltage detection circuit 8, the input voltage signal S _S
The voltage value of _S is monitored, and when the voltage signal S _S exceeds the set value, the high level signal S _D is output.

The frequency dividing circuit 7 sets the step-down amount of the pulse frequency small when the signal S _D output from the voltage detecting circuit 8 is low level, that is, when the instantaneous value of the full-wave rectified voltage output from the rectifier 3 is low. However, when the signal S _D output from the voltage detection circuit 8 is at a high level, that is, when the instantaneous value of the full-wave rectified voltage output from the rectifier 3 is high, the step-down amount of the pulse frequency is set large. As a result, the frequency dividing circuit 7
The step-down amount of the pulse frequency is changed according to the voltage value of the rectified output voltage of the rectifier 3, and the second pulse signal S _{Pb in} which the long pulse period and the short pulse period are mixed is mixed as shown in the lowermost stage of FIG. Output. As in the above description of the operation, the step-down amount of the pulse frequency is changed according to the first pulse signal S _{Pa in} which the pulse width of the on-pulse changes according to the output voltage and the voltage value of the rectified output voltage of the rectifier 3. When an AC-DC converter driven by the second pulse signal S _Pb in which a portion having a long pulse period and a portion having a short pulse period are mixed is actually configured, the measured values of the respective characteristics are as follows. .

However, the input condition of the AC-DC converter is A. C. 170 [V], 50 [Hz], and output conditions are D.I. C. 5 [V] and 10 [A], and V _C is shown in FIG.
The voltage [V] between the terminals of the output capacitor C1 at, and θ indicate the input power factor of the AC-DC converter. When S _Pb is only 1/8 frequency division; V _C = 251 [V], θ
= 0.85 S _Pb is only 1/8 frequency division; V _C = 280 [V], θ
= 0.91 S _Pb mixed with ⅛ and ¼ frequency division; V _C = 256
[V], θ = 0.91 As can be seen from the actually measured value, according to the present invention in which the step down amount of the pulse frequency is changed according to the voltage value of the rectified output voltage, the DC voltage increased by the step-up chopper circuit. Although the maximum value of is suppressed low, the power factor becomes high.

In the above description of the embodiment of the present invention, the second pulse signal S _Pb output from the frequency dividing circuit 7 changes the step-down amount by only one step in response to the signal S _D from the voltage detecting circuit 8. Although not performed, the step-down amount may be changed in two or more steps. As means for changing the step-down amount in two or more steps, the voltage detection circuit 8 is provided with a plurality of voltage detection setting values having different levels, and a different signal S _D is output for each setting value. A method of changing the amount of step-down of the pulse frequency in the frequency dividing circuit 7 according to the signal S _D , and a plurality of detection circuits having different detection levels as the voltage detection circuit 8 are provided, and which detection circuit outputs the signal. It is considered that the frequency dividing circuit 7 is caused to change the step-down amount of the pulse frequency. Further, when the frequency dividing circuit 7 changes the amount of step-down of the pulse frequency according to the signal S _D from the voltage detection circuit 8, the frequency dividing circuit 7 has a function of gradually changing the amount of step-down with a certain time difference. Means can be considered.

[0015]

As described above, the AC-according to the present invention is
The DC converter drives the DC-DC converter circuit with the first pulse signal output from the PWM circuit, and the second pulse signal obtained by stepping down the pulse frequency of the first pulse signal with the frequency dividing circuit. AC- which drives the boost chopper circuit with
In the DC converter, the step down amount of the pulse frequency of the frequency dividing circuit is changed according to the voltage value of the instantaneous voltage of the rectified output voltage of the rectifier. As a result, the power factor of the AC-DC converter can be improved while suppressing the maximum voltage value of the DC voltage increased by the boost chopper circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an AC-DC converter of the present invention.

FIG. 2 is a waveform chart of each signal in the circuit shown in FIG.

[Explanation of symbols]

 1A, 1B input terminal 2A, 2B output terminal 3 rectifier 4 boost chopper circuit 5 DC-DC converter circuit 6 PWM circuit 7 frequency divider circuit 8 voltage detection circuit Q1 first switching transistor Q2 second switching transistor

Claims (5)

[Claims] 1. A rectifier for rectifying an AC input voltage from an AC power supply line, a boost chopper circuit for boosting a rectified output voltage from the rectifier, and a DC voltage stabilized by receiving a high output voltage of the boost chopper circuit. Supply DC to the load
In an AC-DC converter including a -DC converter circuit, an output voltage of the AC-DC converter is detected, and a first pulse signal having a pulse width corresponding to the output voltage is output to a switching element of the DC-DC converter circuit. To the converter drive circuit, a voltage detection circuit that detects an instantaneous value of the rectified output voltage of the rectifier, and outputs a signal in accordance with the instantaneous value of the rectified output voltage, and the first voltage output from the converter drive circuit. And a signal from the voltage detection circuit, and supplies a second pulse signal obtained by stepping down the pulse frequency of the first pulse signal according to the signal to the switching element of the boost chopper circuit. A frequency dividing circuit is provided to increase the step-down amount of the pulse frequency of the frequency dividing circuit when the instantaneous value of the rectified output voltage of the rectifier is high, and when the instantaneous value is low AC-DC converter, characterized in that to reduce the step-down amount of the circuit of the pulse frequency. 2. The AC-DC converter according to claim 1, wherein the voltage detection circuit outputs a signal when the instantaneous value of the rectified output voltage is higher than a predetermined value. 3. The voltage detection circuit has a plurality of set values of different levels to be compared with the instantaneous value of the rectified output voltage to output a signal, and a plurality of output signals different for each of the set values. The AC-D according to claim 1 or 2, wherein the frequency changing circuit changes the amount of step down of the pulse frequency according to the output signal from the voltage detecting circuit.
C converter. 4. The voltage detection circuit comprises a plurality of detection circuits, each of which has a set value to be compared with an instantaneous value of a rectified output voltage to output a signal and a signal output from the set value. The AC-DC converter described in item 3. 5. The frequency dividing circuit, when receiving a signal from the voltage detecting circuit to change the step-down amount of the pulse frequency, gradually changes the step-down amount with a certain time difference. AC range described in the first and second ranges of
DC converter.