JP4051899B2 - Power supply circuit and control method of power supply circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit that can suppress generation of harmonics and is less affected by load fluctuations, and a method for controlling the power supply circuit.
[0002]
[Prior art]
Many AC-input switching power supplies include a capacitor input type rectifier circuit. As shown in FIG. 5A, in the power supply circuit 7, an input capacitor 72 (C _IN ) is provided on the output side of the rectifier circuit 71 having the AC input terminals a ₁ and a ₂ . At the subsequent stage of the input capacitor 72, a switching circuit including a transistor switch 73, a flyhole diode 74, and a coil 75 is provided, and an output capacitor 76 is provided between the output terminals b ₁ and b ₂ .
[0003]
The AC input voltage v _IN is full-wave rectified by the rectifier circuit 71, and then charges are stored in the capacitor 72. When the switching circuit operates, the energy stored in the capacitor 72 is given as a DC output voltage E _OUT between b ₁ and b ₂ . FIG. 5B shows a relationship among the input voltage v _IN , the input current i _IN, and the terminal voltage E _CIN of the input capacitor 72. In FIG. 5B, the input voltage v _IN and the input current i _IN are shown as absolute values.
[0004]
In the power supply circuit 7 described above, there is a period in which the input voltage v _IN is lower than the terminal voltage E _CIN of the input capacitor 72, and harmonics are generated. In order to eliminate this inconvenience, a choke input type power supply circuit or a power supply circuit using an active filter is used.
[0005]
In the choke input type power supply circuit 8 shown in FIG. 6, a low frequency coil (choke) 82 is provided on the output side of a rectifier circuit 81 formed of a diode bridge. A switching circuit comprising a transistor switch 84, a flyhole diode 85 and a coil 86 is provided downstream of the low frequency coil 82 and downstream of the input capacitor 83. An output capacitor 87 is provided between the output terminals b ₁ and b _2. Is provided. In the power supply circuit 8, the input voltage v _IN is full-wave rectified by the rectifier circuit 81 and then smoothed by the low-frequency coil 82, and the DC voltage E _OUT is applied between the output terminals b ₁ and b ₂ .
[0006]
An active filter type power supply circuit 9 shown in FIG. 7A is also used for the purpose of widening the conduction angle and preventing the generation of harmonics. The power supply circuit 9 includes a rectifier circuit 91 and a boost chopper 92. The step-up chopper 92 includes a T-shaped circuit composed of a transistor switch 923 connected in a T-shape to a series connection circuit of a choke coil 921 and a diode 922, and an output capacitor 924 provided in a subsequent stage of the T-shaped circuit. The control circuit (not shown) makes the input current waveform similar to the input voltage waveform, and controls each element of the bridge so that the current phase matches the voltage. Boosting. As a result, the DC voltage E _OUT is applied between the output terminals b ₁ and b ₂ . FIG. 7B shows a relationship among the input voltage v _IN , the input current i _IN, and the DC output voltage E _OUT (the terminal voltage of the output capacitor 924). In FIG. 7B, the input voltage v _IN and the input current i _IN are shown as absolute values.
[0007]
[Problems to be solved by the invention]
In the circuit shown in FIG. 5A, as shown in FIG. 5B, when | v _IN |> E _CIN , the rectifier circuit 71 is turned on and the capacitor 72 is charged. _{When IN} | ≦ _EOUT , the rectifier circuit 71 is turned off and the capacitor 72 is not charged. For this reason, the input voltage range is narrowed, that is, the period (conduction angle) during which the rectifier circuit 71 is in the on state is shortened. As a result, harmonics are generated as described above, and the output voltage E due to load fluctuations. _OUT becomes unstable.
[0008]
In the circuit shown in FIG. 6, the conduction angle of the rectifier circuit 71 can be made slightly larger than that of the circuit shown in FIG. 5A, but there is a problem that the weight is increased by the low-frequency coil 82.
[0009]
Furthermore, in the circuit of FIG. 7 (A), as previously described, the waveform of the input current i _IN waveform input voltage v _IN and similar, and combined the phase of the input current i _IN to the input voltage v _IN phase There must be. For this reason, a special control element (control element for waveform adjustment) and a rectifying element are required, and the choke coil 921 corresponding to the current to be controlled is required, resulting in an increase in product cost.
[0010]
An object of the present invention is to provide a power supply circuit that can reduce the influence of load fluctuation by increasing the conduction angle of the rectifier circuit and can suppress the generation of higher harmonics, and a control method for the power supply circuit. There is.
[0011]
[Means for Solving the Problems]
In the power supply circuit (AC / DC converter) of the present invention, a switch element is T-connected to a series connection of (1) a rectifier circuit, (2) a coil provided on the output side of the rectifier circuit and a discharge prevention diode, A step-up chopper having an output capacitor, (3) a unidirectional conducting element connected in series between the input side and the output side of the step-up chopper, and (4) an output current (current flowing through the coil) of the step-up chopper is predetermined. And a control circuit including a controller for controlling the switch element so as not to exceed the current limit value.
[0012]
The power supply circuit of the present invention is controlled as follows.
[0013]
That is, when the power supplied to the load is small, the control circuit prevents the output voltage from exceeding a predetermined voltage limit value (that is, the output voltage stabilizes at the predetermined voltage limit value) and the boost chopper. The controller of the control circuit controls the switch element of the step-up chopper so that the output current does not exceed a predetermined current limit value. Thereby, electric power is supplied to the output side via the step-up chopper. At this time, since the output voltage of the step-up chopper is higher than the input voltage, power is not supplied via the unidirectional conducting element connected between the input / output terminals of the step-up chopper, and the power is 100%. It is supplied to the load via the boost chopper. In this case, when viewed from the rectifier circuit input side (AC input terminal side), since the current flows over the entire period, the conduction angle is widened.
[0014]
When the power supplied to the load is large, the controller of the control circuit controls the switch element of the chopper circuit so that power is not supplied from the chopper circuit. As a result, the output voltage of the chopper circuit decreases, and power is supplied to the output side via the unidirectional conducting element. Also in this case, when viewed from the input side of the rectifier circuit, since the current flows over the entire period, the conduction angle is widened.
[0015]
Thus, a waveform similar to, and will not need to use the phase for special control elements of the input voltage v _IN the phase of the input current i _IN (waveform adjustment control element). In the active filter type power supply circuit 9 shown in FIG. 7A, the input current i _IN flows through the chopper circuit as it is, and therefore a coil 921 having a current rating (2 ^1/2 × i _IN ) suitable for control is required. It becomes. On the other hand, in the power supply circuit of the present invention, when the input current increases (when the output power increases), the current flows through the unidirectional conducting element, so that the coil current rating is low (low cost). ) Can be used.
[0016]
The rectifier circuit is typically a full-wave rectifier circuit configured by a diode bridge. Further, the unidirectional conducting element connected between the input side and the output side of the boost chopper is typically a diode.
[0017]
In the power supply circuit of the present invention, in order to detect the output current of the chopper, an output current detection resistor can be provided in the path of the output current. In this case, the control circuit can detect whether or not the output current has reached the current limit value by comparing the voltage drop of the output current detection resistor with a predetermined reference voltage.
[0018]
Further, in the power supply circuit of the present invention, the voltage generated in the voltage detection resistor circuit of the series connection circuit of the voltage detection resistor circuit provided on the output side and the current detection resistor is applied to the voltage on the output side of the boost chopper. A descent can be detected.
[0019]
The power supply circuit control method according to the present invention includes a boost chopper provided on the output side of a rectifier circuit, in which a switch element is T-connected to a series connection of a coil and a discharge blocking diode, and an output capacitor is provided in a subsequent stage. It has a unidirectional conducting element connected in series between the input side and the output side,
When the power supplied to the load is small, the switch element is controlled so that the output voltage does not exceed the predetermined voltage limit value and the output current of the chopper does not exceed the predetermined current limit value. Supply power to the output side,
When the power supplied to the load is large, the switch element is controlled so that the output current of the chopper does not exceed a predetermined current limit value, and power is supplied to the output side through the unidirectional conducting element. And In this case, for example, one cycle of the rectified wave is defined as a front region, a middle region, and a rear region.
(1) In the previous region where the output voltage is higher than the rectified voltage, the control circuit controls the switch element so that the output current of the chopper does not exceed the predetermined current limit value, and passes through the boost chopper. Supply power to the output side,
(2) In the middle region where the output voltage is lower than the rectified voltage, the unidirectional conducting element is turned on and power is supplied to the output side via the unidirectional conducting element.
(3) In a post-region where the output voltage becomes higher than the rectified voltage again, the switch element is controlled so that the output current of the chopper does not exceed the predetermined current limit value, and the output current is output via the boost chopper. Electric power can be supplied. The boost chopper is operated in the first region and the third region, and the power supply of the boost chopper is limited by keeping the current limit value low. Thereby, the waveform of the input current of the power supply circuit can be substantially similar to the waveform of the input voltage, and the phases of both waveforms can be matched.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory diagram showing an embodiment of the present invention. In FIG. 1, a power supply circuit 1 includes a rectifier circuit 11, an input capacitor 12 (C _IN ) provided on the output side of the rectifier circuit 11, a boost chopper 13 provided at a subsequent stage of the input capacitor 12, and an input of the boost chopper 13. The circuit includes a bypass diode 14 (D ₂ ) connected between the terminal and the output terminal, a current detection resistor 15 (R ₁ ), a voltage limiting resistor circuit 16, and a control circuit 17 that controls the boost chopper 13. . In FIG. 1, a load 20 is connected between the output terminals b1 and b2.
[0021]
The rectifier circuit 11 is composed of a diode bridge, and an AC voltage _vIN is applied between the input terminals a1 and a2.
[0022]
The input capacitor 12 is connected between the two output terminals ((+), (GND)) of the rectifier circuit 11.
[0023]
The step-up chopper 13 includes a coil 131, a discharge blocking diode 132 (D ₁ ), an N-channel FET transistor 133 (Q ₁ ), and an output capacitor 134 (C _OUT ). The coil 131 and the discharge blocking diode 132 are connected in series, and the FET transistor 133 is T-shaped connected to these connection points. The discharge prevention diode 132 is connected in the direction in which the coil 131 side becomes the anode A, and the FET transistor 133 is connected in the direction in which the connection point between the coil 131 and the discharge prevention diode 132 becomes the drain D.
[0024]
The output capacitor 134 is provided at the subsequent stage of the discharge prevention diode 132, and output terminals b1 (+) and b2 (−) are drawn from both terminals.
[0025]
The bypass diode 14 has an anode A connected to the input side of the boost chopper 13, that is, the (+) terminal side of the input capacitor 12, and a cathode K connected to the output side of the boost chopper 13, that is, the (+) terminal side of the output capacitor 134 ( b1 terminal side).
[0026]
The current detection resistor 15 is for detecting a current flowing through the output capacitor 114 and the load 20 and is provided between the source terminal S of the FET transistor 133 and the ground (GND).
[0027]
The voltage detection resistor circuit 16 includes resistors 161 (R ₂ ) and 162 (R ₃ ). A series circuit of the voltage detection resistor circuit 16 and the current detection resistor 15 (R ₄ ) is connected between the output terminals b 1 and b 2, and the voltage between the output terminals b 1 and b 2 is equal to that of the voltage detection resistor circuit 16. It is detected as a voltage drop (as a voltage at a connection point between the resistor 161 and the resistor 162).
[0028]
The control circuit 17 includes a current comparator 171, a voltage comparator 172, a controller 173, and a resistor 174.
[0029]
The current comparator 171 compares the voltage drop of the current detection resistor 15 with the reference voltage V _ref1, and when the voltage drop of the current detection resistor 15 reaches the reference voltage V _ref1 , that is, the coil 131 and the FET transistor 133. When the current flowing through the path reaches a predetermined value (current limit value I _LMT ), an H level output V _COMP1 is output to the controller 173.
[0030]
The voltage comparator 172 outputs an H-level output V _COMP2 to the controller 173 when the voltage at the connection point between the resistor 161 and the resistor 162 reaches the reference voltage _Vref2 . The reference voltage V _ref2 corresponds to a voltage limit value E _LIM between the output terminals (b1, b2).
[0031]
The controller 173 outputs the control signal V _{Q1_DRV} to the control terminal of the FET transistor 133 via the resistor 174 (R ₄ ).
[0032]
When the output V _COMP1 of the current comparator 171 becomes H level, the controller 173 sends a control signal V _{Q1_DRV} for a predetermined on time so that the current flowing through the coil 131 does not exceed the current limit value I _LMT .
[0033]
Further, the controller 173 determines that when the output V _COMP2 of the voltage comparator 172 becomes H level (when the voltage at the connection point between the resistor 161 and the resistor 162 is larger than the reference voltage _Vref2 ), the boost chopper 133 Stop driving.
[0034]
Hereinafter, the operation of the power supply circuit 1 will be described with reference to the waveform diagrams of FIGS. 2 (A), 2 (B), FIG. 3 and FIG.
[0035]
2 (A) is, when the power supplied to the load 20 is relatively small, the input voltage _{| v IN} | a, (the terminal voltage of the output capacitor 134) and the current _{I L} flowing through the coil 131, the output voltage _{E OUT} Shows the relationship. FIG. 2B shows the relationship between the input voltage | v _IN |, the input current | I _IN |, and the terminal voltage V _CIN of the input capacitor 12.
[0036]
When the power supplied to the load 20 is relatively small, the current I _L flowing through the coil 131 does not reach the current limit value I _LIM , and the controller 173 makes the output voltage E _OUT equal to the voltage limit value E _LIM. As described above (so as not to exceed the voltage limit value E _LIM ), the control signal V _{Q1_DRV} is output to the control terminal of the FET transistor 133. In addition, the current I _D2 flowing through the bypass diode 14 at the time is zero.
[0037]
3, when power is high, which is supplied to the load 20, the input voltage _{| v IN} | a, and the current _{I L} flowing through the coil 131, and the terminal voltage _{V COUT} output capacitor 134, a current flows through the bypass diode 14 I The relationship with _D2 is shown. FIG. 4 shows the relationship between the input voltage _vIN and the input current _IIN .
[0038]
In the region I, the voltage of the AC input v _IN rises from zero, but the controller 173 operates the FET transistor 133 with the maximum on-time T _MAX . The current I _L flowing through the coil 131 rises while being limited by the input voltage | v _IN |, the maximum on-time T _MAX , and the inductance L of the coil 131. In region I, since a large amount of power is supplied to the load 200, the voltage V _COUT of the output capacitor 134 gradually decreases.
[0039]
In region II, the current _{I L} flowing through the coil 131, after reaching the current limit value _{I LMT,} constant (i.e., the current limit value _{I LMT)} is maintained. As described above, when the current limit value I _LMT is reached, the current comparator 171 sends the V _{COMP1 of the} H level output to the controller 173, and the controller 173 shortens the ON time of the FET transistor 133. The control signal V _{Q1_DRV} is output to the control terminal of the FET transistor 133.
[0040]
In the region I and the region II, the voltage of the output capacitor 134 is larger than the voltage of the input capacitor 12 (that is, the input voltage | v _IN | of the power supply circuit 1), so that no current flows through the bypass diode 14.
[0041]
In the region III, the voltage of the output capacitor 134 (the output voltage E _OUT of the power supply circuit 1) becomes lower than the input voltage | v _IN |, and current flows from the input capacitor 12 side via the bypass diode 14 to the output capacitor 134 side. Flows out. At this time, current _{I L} flowing through the coil 131 is reduced.
[0042]
In the region IV, the voltage of the output capacitor 134 (output voltage E _OUT ) is lower than the input voltage | v _IN |, so that the bypass diode 14 is completely turned on. At this time, a drive signal is supplied to the drive terminal of the FET transistor 133, but no current flows from the input capacitor 134 to the boost chopper 13 side. That is, since the impedance on the boost chopper 13 side is higher than the impedance of the bypass diode 14, the current flowing through the path of the coil 131 and the FET transistor 133 becomes zero.
[0043]
In the region V, the input voltage | v _IN | decreases, and the voltage of the output capacitor 134 (output voltage E _OUT ) becomes higher than the input voltage | v _IN |. Accordingly, the current _{I D2} starts to decrease flowing through the bypass diode 14, the path the current _{I L} of the coil 131, FET transistor 133 begins to flow. Then, the current _ID2 flowing through the bypass diode 14 becomes zero, and all the current from the input capacitor 134 side to the output terminals b1 and b2 side (output capacitor 134 side) flows through the boost chopper 13.
[0044]
In the region VI, the current _{I L} which flows in the path of the coil 131, FET transistor 133 reaches the current limit value _{I LMT,} this after current _{I L} is maintained at the current limit value _{I LMT.}
[0045]
In the region VII, the voltage of the input capacitor 12 (i.e., the input voltage of the power supply circuit 1 _{| v IN |)} because decreases, the coil 131, current _{I L} flows through the path of the FET transistor 133 is reduced.
[0046]
In the present embodiment, as shown in FIG. 4, the waveform of the input current I _IN is substantially similar to the waveform of the input voltage v _IN , and the phases of I _IN and v _IN are the same. Therefore, the generation of harmonics can be suppressed, and stable power can be supplied even when the load fluctuation is large.
[0047]
【The invention's effect】
(1) Generation of harmonics can be suppressed.
(2) In a general active filter, the current flows to the coil up to the peak value of the input current. However, in the power supply circuit of the present invention, when the input current value increases (that is, when the supplied power increases), The input current flows through the unidirectional conducting element. Accordingly, a small-capacity coil (that is, a small coil) can be used for the boost chopper coil, and the size of the power supply circuit itself can be reduced.
(3) Since the chopper circuit is stopped when the input voltage of the chopper circuit exceeds the output voltage, the burden on the chopper circuit can be reduced even if the supplied power is increased. That is, unlike a conventional active filter, a switch element, a rectifier element, and a coil having a large current rating are unnecessary, and it is not necessary to use a special control element. Therefore, it is not necessary to use expensive parts, and the manufacturing cost of the power supply circuit can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of a power supply circuit according to the present invention.
2A is a diagram showing a relationship among an input voltage, an output current of a chopper circuit, and an output voltage when the power supplied to the load is relatively small in the power supply circuit of FIG. B) is a diagram illustrating a relationship among an input voltage, an input current, and a terminal voltage of the input capacitor.
3 is a diagram showing the relationship between the input voltage, the current flowing through the coil, the terminal voltage of the output capacitor, and the current flowing through the bypass diode when the power supplied to the load is large in the power supply circuit of FIG. It is.
4 shows a relationship between input voltage and input current of the power supply circuit of FIG.
5A and 5B are explanatory diagrams of a conventional power supply circuit, in which FIG. 5A shows a power supply circuit using a capacitor input type rectifier circuit, and FIG. 5B shows a relationship among an input voltage, an input current, and a DC output voltage. ing.
FIG. 6 is an explanatory diagram of a conventional power supply circuit, and shows a power supply circuit using a choke input type rectifier circuit.
7A and 7B are explanatory diagrams of a conventional power supply circuit, where FIG. 7A shows an active filter type power supply circuit, and FIG. 7B shows an input voltage and an input current in absolute values.
[Explanation of symbols]
1 Power supply circuit 11 Rectifier circuit 12 Input capacitor (C _IN )
13 Boost chopper 14 Bypass diode (D ₂ )
15 Resistance for current detection (R ₁ )
16 Voltage limiting resistor circuit 17 Control circuit 20 Load 131 Coil 132 Discharge blocking diode (D ₁ )
133 FET transistor (Q ₁ )
134 Output capacitor (C _OUT )
161, 162 resistance (R ₂ , R ₃ )
171 Current comparator 172 Voltage comparator 173 Controller 174 Resistance

Claims (2)

A rectifier circuit;
A step-up chopper provided on the output side of the rectifier circuit, in which a switch element is T-connected to a series connection of a coil and a discharge blocking diode, and an output capacitor is provided at a subsequent stage;
A unidirectional conducting element connected in series between the input side and the output side of the boost chopper;
A control circuit including a controller for controlling the switch element so that the output current of the boost chopper does not exceed a predetermined current limit value;
Have
When the power supplied to the load is small, the controller controls the control circuit so that the output voltage does not exceed a predetermined voltage limit value and the output current of the chopper does not exceed a predetermined current limit value. Control the switch element to supply power to the output side via the boost chopper,
When the power supplied to the load is large, one cycle of the rectified wave is defined as a front region, a middle region, and a rear region.
In the previous region where the output voltage is higher than the rectified voltage, the control circuit controls the switch element so that the current flowing through the coil does not exceed the predetermined current limit value, and outputs it to the output side via the boost chopper. To supply power,
In the middle region where the output voltage is lower than the rectified voltage, the unidirectional conducting element is turned on and power is supplied to the output side through the unidirectional conducting element.
In the rear region where the output voltage becomes higher than the rectified voltage again, the control circuit controls the switch element so that the current flowing through the coil does not exceed the predetermined current limit value, and outputs the voltage via the boost chopper. you like to supply electric power to the side,
A power supply circuit characterized by that. A rectifier circuit;
A step-up chopper provided on the output side of the rectifier circuit, in which a switch element is T-connected to a series connection of a coil and a discharge blocking diode, and an output capacitor is provided at a subsequent stage;
A unidirectional conducting element connected in series between the input side and the output side of the boost chopper;
In the control method of the power supply circuit having
When the power supplied to the load is small, the control circuit controls the switch element so that the output voltage does not exceed a predetermined voltage limit value and the output current of the chopper does not exceed a predetermined current limit value. Then, power is supplied to the output side through the boost chopper,
When the power supplied to the load is large, one cycle of the rectified wave is defined as a front region, a middle region, and a rear region.
In the previous region where the output voltage is higher than the rectified voltage, the control circuit controls the switch element so that the current flowing through the coil does not exceed the predetermined current limit value, and outputs it to the output side via the boost chopper. Supply power,
In the middle region where the output voltage is lower than the rectified voltage, the unidirectional conducting element is turned on and power is supplied to the output side through the unidirectional conducting element.
In the rear region where the output voltage becomes higher than the rectified voltage again, the control circuit controls the switch element so that the current flowing through the coil does not exceed the predetermined current limit value, and outputs it via the boost chopper. Supply power to the side,
A method for controlling a power supply circuit.

Images