JP2542953B2 - Active filter device - Google Patents

Description

The present invention relates to an active filter device, and more particularly to an active filter device including a reactor current detection circuit.

(B) Conventional technology In recent years, active filters have been attracting attention from the viewpoint of noise countermeasures for rectified power supplies. A general active filter will be described with reference to FIG.

This active filter includes a bridge rectifier circuit composed of diodes D _{1 to} D ₄ , a reactor L whose one end is connected to the positive DC output end of the bridge rectifier circuit, and a collector and an emitter between the other end of the reactor L and the ground. A control pulse is connected to the connected transistor Q, the damper diode D ₅ whose anode is connected to the collector of this transistor Q, the smoothing capacitor Cd connected between the cathode of this damper diode D ₅ and the ground, and the base of the transistor Q. It is composed of a control circuit COM that supplies φ.

The main circuit of the control circuit COM is constituted by a microcomputer and outputs a control pulse φ having a frequency of 15 KHz or more.

 Next, the operation of this active filter will be described.

In a half cycle in which the potential of the connection point between the diodes D ₁ and D ₂ of the commercial AC is positive, the transistor Q
Turns on, diode D ₁ -reactor L-transistor Q
- the closed circuit of the diode D ₄ is formed a current to the reactor L
I _L flows. Then, when the control pulse φ is at the low level, the transistor Q is turned off and the previous closed circuit is opened,
Reactor L generates a back electromotive force in an attempt to maintain the previous electrical state. The voltage obtained by adding the counter electromotive force of the reactor L and the output of the bridge rectifier circuit exceeds the charging voltage of the smoothing capacitor Cd for a longer period compared to the capacitor input type rectifier circuit, and is smoothed via the damper diode D _5. Charge the capacitor Cd.

Further, in the half cycle of the connection point potential of the diode D ₁ and D ₂ of the commercial AC is negative, the control pulse φ is the transistor Q is turned on when the high level, the diode D ₃ - reactor L- transistor Q- diode D ₂ a closed circuit is formed current I _L flows through the reactor L and. Then, when the control pulse φ becomes the low level and the transistor Q is turned off and the previous closed circuit is opened, a counter electromotive force is generated in the reactor L as before, and the counter electromotive force and the bridge rectification circuit output are generated. The smoothed capacitor Cd is charged by the added voltage.

In the above active filter, the control pulse φ from the control circuit COM controls the on / off of the transistor Q. That is, the control pulse φ controls the coil current I _L flowing through the reactor L.

The active filter shown in FIG. 6 employs a control system in which the coil current is detected by the auxiliary winding (1). The auxiliary winding (1) is magnetically coupled to the reactor L and wound, and detects the polarity of the coil current I _L flowing through the reactor L. That is, while the transistor Q is on and the coil current I _L is flowing, and the energy is accumulated in the reactor L, a negative voltage is output from the auxiliary winding (1), the transistor Q is off, and the energy of the reactor L is reduced. A positive voltage is output from the auxiliary winding (1) during the period when is discharged, and the auxiliary winding (1) becomes zero voltage when the coil current I _L becomes zero.
This waveform is shown in FIG. The control circuit COM detects this zero voltage, outputs a control pulse φ for the next fixed period, and supplies a coil current I _L to the reactor L.

(C) Problems to be Solved by the Invention The above active filter device has the following problems.

Firstly, the reactor L needs to wind the auxiliary winding (1), and the reactor L has a complicated structure, resulting in a high price.

Secondly, the number of turns of the auxiliary winding (1) is set by the control circuit COM.
It is necessary to match the output voltage with the secondary output voltage, which complicates the design of the active filter.

Thirdly, when the difference between the rectified voltage of the rectifier circuit and the charging voltage becomes small, the output voltage of the auxiliary winding (1) becomes very small, and the control circuit COM cannot be operated normally.

(D) Means for Solving the Problems The present invention has been made in view of the above various problems, and an active circuit that solves the conventional problems is provided by providing a detection circuit that detects the coil current by the output voltage of the reactor. It realizes a filter device.

(E) Operation According to the present invention, since the output voltage V _C at one end on the output side of the reactor L is directly detected by the detection circuit, the reverse of the reactor L generated when the energy accumulated in the reactor L is released. The fall of the rectified voltage V _AC of the rectifier circuit can be reliably detected from the output voltage V _DC of the electromotive force, and the control circuit can output the control pulse φ by the detection output of the detection circuit, thus controlling the switching of the switching element.

(F) Example An active filter device according to the present invention will be described in detail with reference to FIGS. 1 to 5.

As shown in FIG. 1, the active filter of the present invention includes a bridge rectifier circuit including diodes D _{1 to} D ₄ , a reactor L having one end connected to a positive DC output terminal of the bridge rectifier circuit, and another reactor L A transistor Q ₀ whose collector and emitter are connected between the end and ground, a damper diode D ₅ whose anode is connected to the collector of this transistor Q ₀ , and which is connected between the cathode of this damper diode D ₅ and ground It is composed of a smoothing capacitor Cd and a control circuit COM that supplies a control pulse φ to the base of the transistor Q ₀ , and a detection circuit DEC that detects the output voltage V _C at the other end of the reactor L, which is a feature of the present invention.

The main circuit of the control circuit COM is constituted by a microcomputer and outputs a control pulse φ having a frequency of 20 KHz or more outside the audible range.

The detection circuit DEC, which is a feature of the present invention, has an output voltage of a counter electromotive force generated when the energy accumulated by the coil current I _L flowing when the transistor Q ₀ is turned on in the reactor L is released.
The fall from V _DC (see FIG. 3) to the rectified voltage V _AC (see FIG. 3) is detected to detect that the coil current I _L has disappeared.

The embodied detection circuit of the present invention will be described with reference to FIG. This detection circuit is connected between a series circuit of a capacitor C and a resistor R ₁ connected to the other end of the reactor L, a transistor Tr whose base is connected to the resistor R ₁ , and a collector of the transistor Tr and a power supply V _CC. Load resistor R ₃ , the output terminal connected to the collector of the transistor Tr and outputting the detection output signal V _S , the earth line connecting the emitter of the transistor Tr, the base of the transistor Tr, the capacitor C and the resistor R ₁ It is composed of a diode D and a resistor R ₂ connected in series between the points.

FIG. 4 is another embodied detection circuit of the present invention,
The feature is that an operational amplifier OP is used instead of the transistor Tr. Two bleeders connected between the power supply voltage V _CC and the ground line are connected to the + input terminal of the operational amplifier OP from the other end of the reactor L via a series circuit of a capacitor C and a resistor R _1. The reference voltage (threshold voltage) is input with a resistor.

Next, the operation of the active filter according to the present invention will be described. Since the basic operation is the same as that of the conventional one shown in FIG. 6, its explanation is omitted here. Here, the detection circuit DEC will be mainly described with reference to FIG.

Coil current I _L flowing through the reactor L is accumulated energy in the reactor L and the transistor Q ₀ flows during the on-time to release the energy transistor Q ₀ is accumulated in the reactor L does not flow during the off period. As a result, the coil current I _L is the saw-tooth waveform. Therefore, the output voltage V _C of the output side of the reactor L
The transistor on period during becomes 0V of Q _0, the transistor Q ₀ off at the same time as the back electromotive force is added to the rectified voltage V _AC generated in the reactor L and the output voltage V _DC next back EMF of the reactor L stored energy back to the rectified voltage V _AC are all released, returns to 0V with on of the transistor Q ₀ in. The base potential V _B of the transistor Tr of the detection circuit DEC is such that the accumulated current of the capacitor C is discharged through the transistor Q ₀ , the diode D, the resistor R ₂ and the base-emitter junction of the transistor Tr while the transistor Q ₀ is on. Therefore, the output voltage V _C of the reactor L is raised to 0.6 V or more by the output voltage V _C of the reactor L via the series circuit of the capacitor C and the resistor R ₁ when the transistor Q ₀ is turned off, and the output voltage V _C of the reactor L is V _DC. During the period, the capacitor C is charged and the time constant of the capacitor C and the resistor R ₁ slightly decreases, but it is maintained at 0.6 V or more, and the output voltage V _C of the reactor L is V _DC.
From falling below 0.6V with the fall of the V _AC, but further swings below 0V by falling with differential waveform from the output voltage V _C is V _AC of the reactor L to 0V returns to 0V soon.
Therefore, the detection output voltage V _S of the detection circuit DEC is
Is 0.6 V or more, that is, the output voltage V _{C of the} reactor L is low level only during the output voltage V _DC of the counter electromotive force, and is high level in other periods. This detection output voltage V _S is immediately input to the control circuit COM, the control pulse φ detects the rising from low to high level, the next pulse is output, and the transistor Q ₀ is turned on.

Therefore, the detection circuit DEC of the present invention detects the fall of the output voltage V _C of the reactor L from V _DC to V _AC when all the stored energy of the reactor L is released and the coil current I _L becomes 0. Therefore, the disappearance of the coil current can be reliably detected.

Further, referring to FIG. 5, a specific structure of an embodiment in which the above-described active filter device is mounted on a hybrid integrated circuit board made of an insulating metal substrate except for the reactor L and the smoothing capacitor Cd will be described.

The circuit pattern with diagonal lines is the ground pattern, and the circuit board consists of a small signal circuit block corresponding to the blank part in the upper half of the drawing and a large signal circuit corresponding to the lower half of the drawing. It is divided into two current circuit blocks. In this embodiment, the control pulse φ is supplied from the small signal circuit block to the large current circuit block, the wiring from the output side of the reactor L to the detection circuit DEC, or the large current circuit block is supplied to the small signal circuit block. The wiring of the emitter potential of the transistor Q ₀ is formed so as to bypass a part of the ground pattern,
For example, a transistor is not limited to this.
The wiring of the emitter potential of Q ₀ may be connected to a predetermined position of the small signal circuit block by a bonding wire (jumping wire connection).

Further, this ground pattern is connected to the aluminum substrate by a bonding wire W at a position closest to the emitter of the transistor Q ₀ through which a high frequency and large current flows, so that the aluminum substrate potential becomes equal to the ground pattern potential.

The large-current circuit block, the diode D ₁ to D ₄ constituting the bridge rectifier circuit, a damper diode D _5, the transistor Q ₀ is surface-mounted through a heat sink, further limiting the emitter current of the transistor Q _0, also An emitter resistance R for measuring the value is formed. These elements are arranged so that a large current does not flow in the ground pattern portion dividing the small signal circuit block and the large current circuit block. The external lead terminals for connecting the large current circuit block and the external circuit and the external lead terminals of the small signal circuit block are arranged on the opposite peripheral edges of the circuit board so that the mutual coupling is loose.

Further, since the distance between the externally connected smoothing capacitor Cd and the damper diode D ₅ has a great influence on the charging / discharging ability of the smoothing capacitor Cd, the damper diode D ₅ should be close to the terminal indicated by V ⁺ in FIG. Will be placed. Further, for the same reason, the terminal indicated by V ⁺ and the ground terminal GND are arranged adjacent to each other.

The small signal circuit block, a control circuit COM and L ^- a detection circuit DEC is mounted to be connected to the pattern.

(G) Effects of the Invention According to the present invention, the following various effects are obtained.

First, since the coil current I _L of the reactor _L is detected by the output voltage V _C of the reactor L, there is an advantage that the auxiliary winding which is conventionally required can be eliminated and the structure of the reactor L can be simplified. Also, the matching design between the auxiliary winding and the control circuit COM is not necessary.

Secondly, in the present invention, since the coil current I _L is detected at the fall of the output voltage V _C of the reactor L from the charging voltage V _DC to the rectified voltage V _AC , the charging voltage V _DC is normally stabilized. Therefore, there is an advantage that detection can be performed extremely accurately.

Thirdly, in the present invention, since the output voltage V _C of the reactor L is directly detected, even if the difference between the charging voltage V _DC and the rectified voltage V _AC becomes small, the detection output is far higher than the detection by the auxiliary winding. It has an advantage that a large voltage can be taken.

Fourth, since the auxiliary winding is not used in the present invention, the detection circuit can be mounted on the same hybrid integrated circuit board.
It has the advantage that a very small hybrid integrated circuit can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram illustrating an active filter device according to the present invention, and FIG. 2 is one detection circuit DE used in the present invention.
FIG. 3 is a circuit diagram illustrating C, FIG. 3 is a waveform diagram illustrating the operation of the active filter device of the present invention, FIG. 4 is a circuit diagram illustrating another detection circuit DEC used in the present invention, and FIG. FIG. 6 is a top view illustrating a state in which the active filter device of FIG. 1 is mounted on a hybrid integrated circuit board, FIG. 6 is a circuit diagram illustrating a conventional active filter device, and FIG. 7 is a waveform diagram illustrating an operation of the conventional active filter device. Is. L ...... reactor, D ₁ ~D ₆ ...... diode, Cd ...... smoothing capacitor, Q ₀ ...... transistor, COM ...... control circuit, DEC
.... Detection circuit.

Claims (3)

(57) [Claims] 1. A rectifier circuit, a reactor having one end connected to a positive output end of the rectifier circuit, a switching element connected between the other end of the reactor and a ground, the reactor and the switching element. A diode whose anode is connected to the connection point of, and a capacitor connected between the cathode of this diode and the ground, and after converting the AC voltage into the DC voltage by the rectifying circuit, the switching element An active filter device for intermittently flowing a coil current to a reactor, a detection circuit for detecting an output voltage of the reactor between an output end of the reactor and a control terminal of the switching element, and an output of the detection circuit. And a control circuit for generating an output for controlling the switching element at the control terminal. It is detected that the output voltage of the reactor to which the voltage generated by the counter electromotive force of the reactor generated when the chinging element is turned off has dropped to the input terminal voltage of the reactor, and the output thereby is provided to the control circuit. An active filter device characterized by outputting. 2. A rectifier circuit, a reactor having one end connected to the positive output end of the rectifier circuit, a switching element connected between the other end of the reactor and the ground, the reactor and the switching element. A diode whose anode is connected to the connection point of, and a capacitor connected between the cathode of this diode and the ground, and after converting the AC voltage into the DC voltage by the rectifying circuit, the switching element An active filter device for intermittently flowing a coil current to a reactor, a detection circuit for detecting an output voltage of the reactor between an output end of the reactor and a control terminal of the switching element, and an output of the detection circuit. And a control circuit for generating an output for controlling the switching element at the control terminal, wherein the detection circuit is a reference voltage. The output voltage of the reactor is compared with that for applying the result to the control circuit, and the output of the reactor to which the voltage generated by the counter electromotive force of the reactor generated when the switching element is turned off is added by this comparison. An active filter device characterized in that it detects that the voltage has dropped to the input terminal voltage of the reactor and outputs the output thereby to the control circuit. 3. The active filter device according to claim 1, wherein the rectifier circuit, the switching element, the diode, the control circuit, and the detection circuit are mounted on the same hybrid integrated circuit board.