JPH0739162A - Power supply circuit - Google Patents

Abstract

PURPOSE:To provide a power supply circuit wherein the current capacity of a switching element which connects and disconnects a DC power supply given via a choke coil is limited to a definite value or lower, the radiation of energy to the outside due to a switching operation is suppressed and an output voltage is adjusted. CONSTITUTION:In a power supply circuit, a commercial AC power supply 1 is rectified by a rectifier circuit 2, a DC power supply given via a choke coil 3 is short-circuited and opened by a switching element 6, energy stored in the choke coil 3 is stored again in a capacitor 8 via a diode 5, and electric power is supplied to a load 9. In the power supply circuit, a control circuit 9 controls the make-and-break of the switching element 6 according to the voltage of the load 9, and it controls the break of the switching element according to the voltage of a detection resistance 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to a power supply circuit using a switching regulator.

[0002]

2. Description of the Related Art FIG. 12 is a circuit diagram of a conventional step-up switching regulator. The input current input from the commercial alternating current 1 is full-wave rectified by the rectifier circuit 2 to become a direct current including a pulsating current, and the choke coil 3 and the diode 5 are connected in series from the positive side of the rectifier circuit 2. Is charged, power is further supplied to the load 9, and the load 9 is returned to the negative side of the rectifier circuit 2.

A switching element 6 is interposed between the connection point of the coil 3 and the diode 5 and the negative side of the rectifier circuit 2.
The control circuit 7 detects the voltage across the load 9 (hereinafter referred to as the load voltage), and the switching element 6 is detected according to the detection result.
It controls the opening and closing of. The control circuit 7 has a built-in pulse generator whose output pulse width is variable in output frequency, and is set with a reference voltage for keeping the load voltage constant. When the load voltage is lower (higher) than the reference voltage, the control circuit 7 raises (lowers) the output frequency, controls the switching element 6 to be closed during the period when the output pulse appears, and adjusts the load voltage.

The direct current output from the rectifier circuit 2 flows through the choke coil 3 to supply energy to the choke coil 3 when the switching element 6 is closed.
Stores its energy. Next, when the switching element 6 is open, the energy stored in the choke coil 3 generates an electromotive force, and charges are stored in the capacitor 8 through the diode 5. By repeating this, the potential of the capacitor 8 gradually rises. This capacitor 8
The electric charge stored in is discharged to the load 9. When the energy supplied from the choke coil 3 becomes equal to the energy consumed by the load 9, the voltage of the capacitor 8 or the load 9 is balanced. Therefore, the load voltage is adjusted by controlling the opening / closing of the switching element 6. When the load voltage becomes low (high), the control circuit 7 makes the duty ratio of the output pulse large (small), so that the load voltage becomes high (low) and stable.

FIG. 13 is a waveform diagram of the input current shown in FIG. 12, and schematically shows a half cycle of the commercial AC power supply 1. When the switching element is closed, the current flowing through the choke coil 3 and the switching element 6 rapidly increases, and electric energy is stored in the choke coil 3. This current is indicated by the white right triangle. When the switching element 6 is opened, the electric energy stored in the choke coil 3 becomes a current, charges the capacitor 8 through the diode 5, and further supplies the electric power to the load 9 to decrease sharply. This current is indicated by a hatched right triangle.
Then, the input current forms a peak value at the moment when the switching element switches from the closed circuit to the open circuit. The triangle in the center corresponds to the maximum value of the commercial AC input voltage, and the peak value of the input current is also the maximum. When the direct current is interrupted rapidly, energy is radiated from the whole circuit to the outside.

[0006]

Since the conventional step-up switching regulator is constructed as described above,
Since the peak value of the input current in one switching cycle of the switching element is larger than the average value thereof, it is necessary to increase the current capacity of the switching element in comparison with the load current. In order to suppress the current capacity of the switching element, the peak value of the input current must be suppressed eventually. In order to suppress the peak value of the input current, for example, in Japanese Utility Model Laid-Open No. 3-3183, a chopper that chops the output of the rectifier circuit according to the current detected by the current detection circuit provided between the rectifier circuit and the switching circuit. A high voltage power supply device with a circuit is proposed.

However, this proposal is to make the peak value of the input current for rapidly charging the large-capacity capacitor on the load side uniform, and not to limit the current of the choke coil of the switching regulator, but the current of the switching element. Is not limited, nor is the load voltage adjusted. Further, according to the embodiment, the resistor for detecting the input current is not connected in series with the coil or the switching element through which the input current flows. When the switching regulator configured as described above is used as a power supply circuit of a video device, the difference component between the high frequency signal component of the horizontal synchronizing signal of the video signal and the switching frequency of the energy radiated outside the switching regulator becomes a beat, There was a problem that it might appear as thin horizontal stripes on the CRT screen.

This is true even if the input power source is not a commercial AC source but a DC power source. When rectifying the commercial AC, it is necessary to suppress the current of the switching element especially at the maximum value and the portion close to the maximum value.
The present invention has been made in view of such circumstances,
Detect the current of choke coil or switching element,
Then, by detecting the input voltage of the commercial AC and controlling the switching element according to the detection result, the current capacity of the switching element is kept below a certain value to suppress the radiation of energy to the outside due to switching, and output An object is to provide a power supply circuit that adjusts a voltage.

[0009]

A first invention (or a fifth invention) is a detection circuit for detecting the current of a choke coil (or a switching element), and the current of the switching element is below a certain value based on the detection result. And a control circuit for controlling the current of the choke coil to be a predetermined value or less. In the second invention or the sixth invention, a plurality of predetermined values are set in the control circuit.

According to a third invention (or a seventh invention), the first detection circuit for detecting the current of the choke coil (or the switching element) and the current of the switching element is limited to a certain value or less based on the detection result, A first control circuit that controls the current of the choke coil to be a predetermined value or less, a second detection circuit that detects the voltage of the AC input, and a second control that controls the cycle of opening and closing the switching element based on the detection result. And a circuit. The fourth invention or the eighth invention is the first invention.
A plurality of predetermined values are set in the control circuit.

[0011]

In the first invention (or the fifth invention), the detection circuit detects the current of the choke coil (or the switching element), and the control circuit makes the current of the choke coil less than a predetermined value based on the detection result. By controlling the open circuit of the switching element, the current of the switching element is kept below a certain value. In the second invention or the sixth invention, the control circuit adjusts the load voltage by selecting an appropriate predetermined value from a plurality of predetermined values and making the current of the choke coil correspond to the current of the load.

In the third invention (or the seventh invention), the first invention
The detection circuit detects the current of the choke coil (or switching element), and the first control circuit controls the open circuit of the switching element so that the current of the choke coil becomes a predetermined value or less based on the detection result. Of the current is less than a certain value, the second detection circuit detects the voltage of the AC input, and the second control circuit detects that the switching element operates in accordance with the load voltage during the period when the AC input exhibits a high value based on the detection result. The load voltage is adjusted by controlling the open / close cycle so that the choke coil current corresponds to the load current. In the fourth invention or the eighth invention, the first control circuit adjusts the load voltage by selecting an appropriate predetermined value from a plurality of predetermined values and making the current of the choke coil correspond to the current of the load.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. First Embodiment FIG. 1 is a circuit diagram of a first embodiment of a power supply circuit according to the present invention. The input current input from the commercial AC power supply 1 is full-wave rectified by the rectifier circuit 2. The + side of the rectifier circuit 2 is connected to the − side of the rectifier circuit 2 via the choke coil 3, the detection resistor 4, the diode 5 and the capacitor 8, and the capacitor 8
A load 9 is connected to both ends of the. Two detection lines each for detecting the voltage across the load 9 and the voltage across the detection resistor 4 are connected to the control circuit 7, and between the connection point of the detection resistor 4 and the diode 5 and the-side of the rectification circuit 2. The switching element 6 is interposed between the switching element 6 and the control circuit 7.
And are connected by a control line.

The control circuit 7 has a built-in pulse generator having a constant output pulse width and a variable output frequency, and the first reference voltage for maintaining the load voltage constant and the current of the switching element 6 below a certain value. The second reference voltage (E) for limiting the voltage is set in the control circuit 7. Load voltage is first
When the voltage is lower (higher) than the reference voltage, the control circuit 7 raises (lowers) the output frequency and controls the switching element 6 to be closed during the period when the output pulse appears. When the voltage of the detection resistor 4 is higher than the second reference voltage (E), the control circuit 7 controls the switching element 6 to open.

Next, the operation will be described. The direct current output from the rectifier circuit 2 flows through the choke coil 3 and the detection resistor 4 when the switching element 6 is closed.
To the choke coil 3, and the choke coil 3 stores the energy. Next, when the switching element 6 is open, the energy stored in the choke coil 3 generates an electromotive force, and the charge is stored in the capacitor 8 through the diode 5. By repeating this, the potential of the capacitor 8 gradually rises. The charges accumulated in the capacitor 8 are discharged to the load 9. When the energy supplied from the choke coil 3 becomes equal to the energy consumed by the load 9, the voltage of the capacitor 8 or the load 9 is balanced.

Therefore, the load voltage is adjusted by controlling the opening / closing of the switching element 6. When the load voltage becomes low (high), the control circuit 7 detects it and changes the output frequency of the output pulse according to the load voltage to make the duty of the output pulse large (small). It becomes high (low) and the output voltage becomes equal to the first reference voltage and becomes stable. When the switching element 6 is closed and the voltage across the detection resistor 4 becomes higher than the second reference voltage (E) while energy is being stored in the choke coil 3, the switching element 6 is opened and the current of the switching element 6 is increased. Is cut off, and the energy of the choke coil 3 is released. The period in which the switching element that is opened next is closed is a period in which an output pulse having a duty ratio corresponding to the load voltage appears.

2, FIG. 3, FIG. 4 and FIG. 5 are waveform diagrams of the input current in FIG. 1, and schematically show a half cycle of the commercial AC power supply 1. In FIG. 2, E'is the amplitude of the input current limited by the second reference voltage (E). The control circuit 7 outputs an output pulse having an output frequency corresponding to the load voltage, so that the switching element 6 opens and closes, and the input current is intermittent. As a result, the load voltage becomes equal to the first reference voltage and is kept constant. In this case, the value of the input current is small, the voltage of the detection resistor 4 is smaller than E, and the control by the second reference voltage (E) is not performed.

FIG. 3 shows the case where the load current increases and the resulting amplitude of the input current is equal to E '. In this case, the open circuit of the switching element based on the control of the output pulse of the control circuit 7 and the voltage of the detection resistor 4 are detected, and the second
It is synchronized with the open circuit of the switching element based on the control by the reference voltage (E). In the figure, the amplitudes of the input currents at the left end and the right end are small because the input voltage value of the commercial AC is small.

In FIG. 4, since the load current further increases and the amplitude of the input current is limited by the second reference voltage (E), the load voltage decreases, and the control circuit 7 which detects it decreases the frequency of the output pulse. It shows a situation in which the load current is increased by increasing. As a result, the load voltage is maintained constant and the duty ratio of the output pulse increases.

In FIG. 5, the load current further increases, and the control circuit 7 limits the amplitude of the input current by the second reference voltage (E) and further increases the duty ratio of the output pulse to increase the load current. It shows the situation. As a result, the load voltage is maintained constant and the duty ratio is 50%. If the duty ratio is further increased, the load current does not increase but decreases.

As described above, the control circuit 7 which adjusts the voltage by opening / closing the switching element 6 according to the load voltage further detects the current of the choke coil by the voltage across the detection resistor 4, and the detection result is Second reference voltage (E)
If the value exceeds, the current of the switching element is kept small by opening the switching element 6. Then, the load voltage when it exceeds the second reference voltage (E) is adjusted by the control circuit 7 changing the duty ratio of the output pulse to increase or decrease the load current, and is maintained constant.

Second Embodiment The circuit diagram of the second embodiment is similar to that of FIG. 1, and a plurality of second reference voltages for limiting the current of the switching element 6 to a certain value or less are set in the control circuit 7. Since the load current flowing through the detection resistor 4 is limited, if the limit value of the peak value is set small, the current capacity of the switching element 6 becomes small, but the current of the load 9 also becomes small, and the load due to fluctuations in the load current The voltage adjustment range is narrowed. Further, when the limit value of the peak value is set large, the adjustment range of the load voltage becomes wide, but the current capacity of the switching element becomes large. Therefore, by setting multiple peak value limit values and selecting the limit value according to the load voltage, the load voltage can be adjusted in a wide range and the current of the switching element can be increased. It can be limited to a certain value or less.

The control circuit 7 of the second embodiment is configured to operate in this way. The values of the voltage of the detection resistor 4 due to the currents having the plurality of limit values of the peak value of the load current are the plurality of second reference voltages, the low voltage value is E, and the high voltage value is F. The rest of the configuration is similar to that of the first embodiment, so the explanation is omitted.

Next, the operation will be described. When the control circuit 7 adjusts the voltage based on the second reference voltage (E) and the duty ratio of 50% and the load voltage is balanced (see Fig. 5)
At, when the load current increases and the load voltage decreases, the control circuit 7 selects the second reference voltage (F) and lowers the frequency of the output pulse. As a result, the input current increases, the duty ratio decreases, and the load voltage is maintained constant.

FIG. 6 is a waveform diagram of the input current in this case, and schematically shows a half cycle of the commercial AC power supply 1. In the figure, F'is the amplitude of the input current limited by the second reference voltage (F). The amplitude of the input current at the left end and the right end is small because the input voltage value of the commercial AC is small. When the load current further increases, the amplitude of the input current is limited by the second reference voltage (F), so that the load voltage decreases. The control circuit 7 which has detected it increases the load current by increasing the frequency of the output pulse. As a result, the load voltage is maintained constant and the duty ratio of the output pulse increases. FIG. 7 is a waveform diagram of the input current in this case, and shows that the duty ratio is 50%.

In the above description, the control circuit 7 adjusts the fluctuation of the load voltage when the load current increases, but the control circuit 7 changes the load voltage when the load current decreases. It goes without saying that the operation of adjusting is the opposite. In addition, the second reference voltage
When the output frequency of the output pulse becomes the lower limit value or the voltage of the detection resistor 4 becomes a small value during the voltage adjustment by (F), the voltage is selected by selecting the second reference voltage (E). Make adjustments. Second like this
By setting a plurality of reference voltages and selecting the second reference voltage according to the load voltage, the current of the switching element 6 is limited to a certain value or less and the adjustment range of the load voltage is widened.

Third Embodiment FIG. 8 is a circuit diagram of a third embodiment of the power supply circuit according to the present invention. Detecting resistors 10 and 11 are provided between two connection points of the commercial AC power source 1 and the rectifying circuit 2 and the ground.
Then, a third reference voltage is set in the control circuit 7 in order to identify whether or not the input voltage of the commercial AC power supply 1 is equal to or higher than a predetermined voltage value. The control circuit 7 detects the input voltage and changes the pulse frequency of the built-in pulse generator according to the load voltage when the input voltage is higher than the third reference voltage in case the input current needs to be increased or decreased. Let In this case, the pulse width is not constant. This is because the input current is increased or decreased while the duty ratio is 50% and the peak value of the load current is maintained. More specifically, when the load voltage is higher (lower) than the first reference voltage, the pulse frequency is lowered (higher) after the switching element is opened. This is for opening and closing the switching element while maintaining the peak value. Figure 1 for other configurations
Since it is similar to the above, the same reference numerals are given to the corresponding portions and the description thereof will be omitted.

Next, the operation will be described. When the control circuit 7 adjusts the voltage with the second reference voltage (F) and the duty ratio of 50% and the load voltage is balanced, if the load current increases and the load voltage decreases, the control circuit 7 In the period higher than the third reference voltage, the pulse frequency is increased without making the pulse width constant. FIG. 9 is a waveform diagram of the input current in this case.
Is schematically shown for a half cycle. In the figure, T / 2
Is a period of a half cycle of the commercial AC input voltage, T'is a period in which the input voltage is higher than the third reference voltage, and F'is a second period.
It is the amplitude of the input current limited by the reference voltage (F).

In the period T ', the control circuit 7 first opens the switching element and then opens and closes the switching element in a short cycle according to the load voltage. As a result, the input current increases and the load voltage remains constant. In the above description, the operation in which the control circuit 7 adjusts the change in the load voltage when the load current increases has been described. However, the operation in which the control circuit 7 adjusts the change in the load voltage when the load current decreases is described. It goes without saying that the opposite is true. As described above, by detecting the input voltage of the commercial AC power supply 1 and opening / closing the switching element 6 in a short cycle in the maximum value of the input voltage and the period around the maximum value, the switching element 6 is opened / closed in a shorter cycle than in the case where the switching element 6 is not opened / closed. The input current is increased to further widen the load voltage adjustment range, and the current of the switching element 6 is limited to a certain value or less.

Fourth Embodiment FIG. 10 is a circuit diagram of a fourth embodiment of the power supply circuit according to the present invention. A switching element 6 and a detection resistor 4 are provided in series between the connection point of the choke coil 3 and the diode 5 and the-side of the rectifier circuit 2. Since other configurations are the same as those in FIG. 1, corresponding parts are designated by the same reference numerals and the description thereof will be omitted. The detection resistor 4 is a switching element 6
Since the current is detected, the second reference voltage can be set so that the switching element 6 is not destroyed, and the current of the switching element 6 can be limited. The other operations are the same as those in the first embodiment, and the description thereof will be omitted.

In this way, the control circuit 7 for adjusting the voltage by opening and closing the switching element 6 according to the load voltage.
However, when the current of the switching element 6 is further detected by the voltage across the detection resistor 4 and the detection result exceeds the second reference voltage, the current capacity of the switching element 6 is reduced by opening the switching element 6. Keep it small,
Then, the load voltage is adjusted and kept constant. By providing a plurality of the second reference voltages, the voltage adjustment range can be expanded and the current capacity of the switching element 6 can be suppressed small.

Fifth Embodiment FIG. 11 is a circuit diagram of a fifth embodiment of the power supply circuit according to the present invention. Detecting resistors 10 and 11 are provided between two connection points of the commercial AC power source 1 and the rectifying circuit 2 and the ground.
Then, a third reference voltage is set in the control circuit 7 in order to discriminate whether or not the input voltage of the commercial AC power supply 1 is equal to or higher than a predetermined voltage value. The control circuit 7 detects the input voltage and changes the pulse frequency according to the load voltage without making the pulse width of the built-in pulse generator constant when the input voltage is higher than the third reference voltage. is there. More specifically, when the load voltage is higher (lower) than the first reference voltage, the pulse frequency is lower (higher). Further, a switching element 6 and a detection resistor 4 are provided in series between the connection point of the choke coil 3 and the diode 5 and the-side of the rectifier circuit 2. Since other configurations are the same as those in FIG. 1, corresponding parts are designated by the same reference numerals and description thereof is omitted.

Next, the operation will be described. Control circuit 7
Regulates the load voltage by keeping the pulse width of the pulse generator constant under the second reference voltage (F) and changing the pulse frequency in accordance with the load voltage, thereby maintaining the current of the switching element. It is limited to a certain value or less. When the load current increases and the load voltage decreases, the control circuit 7 increases the input current by increasing the pulse frequency of the pulse generator and maintains the load voltage constant. When such a state continues, the pulse duty ratio reaches 50%. When the load voltage further decreases, the control circuit 7 raises the pulse frequency without making the pulse width constant during the period when the input voltage is higher than the third reference voltage. As a result, the input current increases and the load voltage remains constant.

In the above description, the operation in which the control circuit 7 adjusts the fluctuation of the load voltage when the load current increases has been described. However, the control circuit 7 changes the load voltage when the load current decreases. It goes without saying that the operation of adjusting is the opposite. In this way, the voltage across the load 9 and the detection resistor 4 and the input voltage are detected, and the switching element 6 is opened / closed according to the detection result, thereby suppressing the current capacity of the switching element 6 to be small and adjusting the load voltage. And keep it constant.

In the above five embodiments, the current limitation of the switching element 6 in the step-up chopper type power supply circuit is described, but the same applies to the step-down chopper type power supply circuit or the buck-boost chopper type power supply circuit. Needless to say.

[0036]

According to the first invention (or the fifth invention) and the third invention (or the seventh invention), the current of the choke coil (or the switching element) is detected, and the input voltage of the commercial AC is detected. Based on the detection result, the current of the choke coil is set to a predetermined value or less so that the current of the switching element is set to a predetermined value or less and the voltage is adjusted.

According to the second invention (or sixth invention) and the fourth invention (or eighth invention), an appropriate predetermined value is selected from a plurality of predetermined values, and the current of the choke coil is set as the load current. As a result, the current of the switching element is kept below a certain value and the voltage is adjusted widely. As a result, the current capacity of the switching element can be reduced, and the excellent effect of suppressing the energy radiation to the outside due to the switching and eliminating the beat interference on the CRT screen is achieved. When the present invention is applied to a large-sized power supply circuit, its effect becomes larger.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment and a second embodiment of a power supply circuit according to the present invention.

FIG. 2 is a waveform diagram of an input current in FIG.

FIG. 3 is a waveform diagram of an input current in FIG.

FIG. 4 is a waveform diagram of an input current in FIG.

5 is a waveform diagram of the input current in FIG.

FIG. 6 is a waveform diagram of an input current in FIG.

FIG. 7 is a waveform diagram of the input current in FIG.

FIG. 8 is a circuit diagram of a power supply circuit according to a third embodiment of the present invention.

9 is a waveform diagram of the input current in FIG.

FIG. 10 is a circuit diagram of a fourth embodiment of the power supply circuit according to the present invention.

FIG. 11 is a circuit diagram of a fifth embodiment of the power supply circuit according to the present invention.

FIG. 12 is a circuit diagram of a conventional power supply circuit.

FIG. 13 is a waveform diagram of the input current in FIG.

[Explanation of symbols]

 1 Commercial AC power supply 2 Rectifier circuit 3 Choke coil 4 Detection resistor 5 Diode 6 Switching element 7 Control circuit 8 Capacitor 9 Load 10,11 Detection resistor

Claims (8)

[Claims] 1. A detection circuit for detecting a current of a choke coil in a power supply circuit for adjusting a voltage of a load by opening and closing a direct current power supply supplied through a choke coil with a switching element, and a detection result of the detection circuit. And a control circuit for controlling the current of the switching element so as not to exceed a predetermined value and the current of the choke coil to fall below a predetermined value. 2. The power supply circuit according to claim 1, further comprising a control circuit that sets a plurality of predetermined values, and selects the predetermined value according to the voltage of the load to control the current of the choke coil. 3. A first detection circuit for detecting a current of a choke coil in a power supply circuit for adjusting a load voltage by opening and closing a direct current power supply for rectifying an AC input through a choke coil by a switching element. A first control circuit for controlling the current of the switching element to be a constant value or less and a current of the choke coil to be a predetermined value or less based on the detection result of the first detection circuit; and a second control circuit for detecting an AC input voltage. A power supply circuit comprising: a detection circuit; and a second control circuit that controls a cycle of opening and closing a switching element based on a detection result of the second detection circuit. 4. A power supply circuit according to claim 3, further comprising a first control circuit for controlling the current of the choke coil by setting a plurality of predetermined values and selecting the predetermined value according to the voltage of the load. . 5. A detection circuit for detecting a current of a switching element, and a detection result of the detection circuit, in a power supply circuit for adjusting a voltage of a load by opening and closing a direct current power supply supplied through a choke coil with a switching element. And a control circuit for controlling the current of the switching element so as not to exceed a predetermined value and the current of the choke coil to fall below a predetermined value. 6. The power supply circuit according to claim 5, further comprising a control circuit that sets a plurality of predetermined values and selects the predetermined value according to the voltage of the load to control the current of the choke coil. 7. A first detection circuit for detecting a current of a switching element in a power supply circuit for adjusting a voltage of a load by opening and closing a DC power supply which rectifies an AC input and is supplied through a choke coil by a switching element. A first control circuit for controlling the current of the switching element at a constant value position so that the current of the choke coil is set to a predetermined value or less based on the detection result of the first detection circuit; and a second control circuit for detecting the voltage of the AC input. A detection circuit, and a second circuit for controlling a cycle of opening and closing the switching element based on a detection result of the second detection circuit.
A power supply circuit comprising a control circuit. 8. The power supply circuit according to claim 7, further comprising a first control circuit for controlling the current of the choke coil by setting a plurality of predetermined values and selecting the predetermined value according to the voltage of the load. .