JPH0458765A - Active filter unit - Google Patents

Abstract

PURPOSE:To realize simplification of structure, accurate detection, increase of detected output voltage and miniaturization of hybrid integrated circuit by providing a circuit for detecting a coil current based on an output voltage from a reactor. CONSTITUTION:A coil current IL flows into a reactor Land stores energy therein during ON interval of a transistor Qo and the energy is discharged during OFF interval of the transistor Qo. A detecting circuit DEC detects rising of output voltage VC of the reactor L to VAC from VDC which represents the voltage level at a time point when the reactor L is discharged perfectly and the coil current IL goes to O, and thereby extinction of coil current can be detected reliably. Since the coil current IL of the reactor L is detected based on the output voltage VC, conventional auxiliary winding can be obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an active filter device, and particularly to an active filter device equipped with a reactor current detection circuit.

〉Conventional technology In recent years, active filters have attracted attention as a noise countermeasure for rectified power supplies. - A boat fishing active filter will be explained with reference to FIG.

This active filter consists of a reactor L1 whose one end is connected to the positive DC output terminal of a bridge rectifier circuit consisting of diodes D, ~D4, and a bridge rectifier circuit.
A transistor Ql whose collector and emitter are connected between the other end and the ground, a damper diode D1 whose anode is connected to the collector of this transistor Q, and a smoothing capacitor Cd which is connected between the cathode of this damper diode D6 and the ground. and a control circuit COM that supplies a control pulse to the base of the transistor Q.

The main circuit of the control circuit COM is constituted by a microcomputer and outputs control pulses 4 having a frequency of 15 KHz or higher.

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

In the half cycle when the potential at the connection point of commercial AC diodes DI and Dl is positive, 15KH is output from the control circuit COM.
When a control pulse with a frequency equal to or higher than z is at a high level, transistor Q is turned on, and a closed circuit of diode D, reactor L, transistor Q, and diode D4 is formed, and a current I flows through reactor L.

flows. When the control pulse φ is at a low level, the transistor Q is turned off and the previously closed circuit is opened, and the reactor L attempts to maintain the previous electrical state and generates a back electromotive force. The voltage calculated by the back electromotive force of the reactor L and the bridge rectifier circuit output exceeds the charging voltage of the smoothing capacitor Cd for a long period of time compared to the capacitor input type rectifier circuit, and the damper diode D,
The smoothing capacitor Cd is charged via the smoothing capacitor Cd.

In addition, in the half cycle in which the potential at the connection point of the commercial AC diode D, tori is negative, when the control pulse is at a high level, the transistor Q is turned on, and the diode D, - reactor L
A closed circuit of - transistor Q - diode D is formed so that t current I flows through the reactor.

flows. Then, when the control pulse≠ becomes low level and the transistor Q is turned off, the previously closed circuit is opened.
As before, a back electromotive force is generated in the reactor, and the smoothing capacitor Cd is charged with a voltage that is the sum of the back electromotive force and the output of the bridge rectifier circuit.

In the above active filter, the on/off of the transistor Q is controlled by the control pulse φ from the control circuit COM. That is, this control pulse≠ controls the coil current flowing through the reactor.

In the active filter shown in Fig. 6, the auxiliary winding (1)
A control method that detects the coil current is adopted. The auxiliary winding (1) is magnetically coupled and wound around the reactor,
The polarity of the coil current IL flowing through the reactor L is detected.

In other words, during the period when the transistor Q is on, the coil current flows, and energy is stored in the reactor L, a negative voltage is output from the auxiliary winding (1), and the transistor Q
During the period when the reactor L is turned off and the energy of the reactor L is released, no positive voltage is output from the auxiliary winding (1), and when the fill current IL becomes zero, the auxiliary winding (1) becomes zero voltage.

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 causes a coil current IL to flow through the reactor.

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

First, it is necessary to wind the auxiliary winding (1) around the reactor L, resulting in a complicated structure of the reactor L, resulting in a high price.

Second, the control circuit COM sets the number of turns of the auxiliary winding (1).
It is necessary to match the output voltage and the secondary output voltage, and there is a problem that the design of the active filter becomes complicated.

Thirdly, the rectified voltage of the rectifier circuit and the charging 'f/l! When the difference between the voltage and the voltage becomes small, the output voltage of the auxiliary winding (1) becomes very small, and there is a problem that the control circuit COM cannot operate normally.

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

(*) Effect According to the present invention, since the output voltage vc at one end of the output side of the reactor L is directly detected by the detection circuit, the back electromotive force of the reactor L is generated when the energy stored in the reactor L is released. It is possible to reliably detect the fall of the rectified voltage vAC of the rectifier circuit from the output voltage VDC of the detection circuit, and a control pulse can be outputted from the control circuit using the detection output of the detection circuit, and the switching of the switching element can be controlled.

Example) An active filter device according to the present invention is shown in FIGS. 1 to 5.
This will be explained in detail with reference to the drawings.

The active filter of the present invention, as shown in FIG.
A bridge rectifier circuit consisting of diodes D and D4, a reactor L1 whose one end is connected to the positive DC output terminal of the bridge rectifier circuit, a transistor Q whose collector and emitter are connected between the other end of this reactor L and the ground, respectively. A damper diode D5 whose anode is connected to the collector of this transistor Q, and this damper diode D6
smoothing capacitor C connected between the cathode and ground of
d and the control circuit COM that supplies a control pulse ≠ to the base of the transistor Q0, and a reactor L that is a feature of the present invention.
■ Output voltage at the other end. It consists of a detection circuit DEC that detects.

The main circuit of the control circuit COM is constituted by a microcomputer, and outputs a control pulse φ having a frequency of 20K) Iz or higher, which is outside the audible range.

The detection circuit DEC, which is a feature of the present invention, converts the rectified voltage VAc from the output voltage VDC (see Fig. 3) of the back electromotive force generated when the accumulated energy is released by the coil current IL flowing in the reactor L when the transistor Q0 is on. (See FIG. 3) is detected, and it is detected that the coil t[IL is gone.

An embodiment of the detection circuit of the present invention will be described with reference to FIG. This detection circuit consists of a series circuit of a capacitor C and a resistor R1 connected to the other end of the reactor L, a transistor Tr whose base is connected to the resistor R1, and a transistor Tr.
collector and source V. A load resistor Rs connected between C, an output terminal connected to the collector of the transistor Tr and outputting the detection output signal V, an earth line connecting the emitter of the transistor Tr, the base of the transistor Tr, the capacitor C, and the resistor. It consists of a diode D and a resistor R1 connected in series between the connection points of R0.

FIG. 4 shows another embodiment of the detection circuit of the present invention, which is characterized in that an operational amplifier oP is used in place of the transistor Tr. Reactor L is connected to the input terminal of the operational amplifier OP.
It is connected from the other end through a series circuit of capacitor C and resistor R1, and the reference voltage (threshold voltage) is input to the - input terminal through two bleeder resistors connected between the power supply voltage v0° and the ground line. ing.

Next, the operation of the active filter according to the present invention will be explained. Since the basic operation is the same as the conventional one shown in FIG. 6, the explanation here will be omitted. Here, the detection circuit D
This will be explained with reference to FIG. 3, focusing on EC.

The coil current IL flowing through the reactor L is the transistor Q0.
flows during the on period and stores energy in the reactor, and transistor Q0 does not flow during the on period and releases the energy stored in the reactor.

As a result, the coil current pattern □ has a sawtooth wave shape. Therefore, the output voltage on the output side of reactor L is ■.

is 0 during the ON period of the transistor Q0, and at the same time as the transistor Q0 is turned off, a back electromotive force is generated in the reactor and is added to the rectified voltage VAC, resulting in the output voltage VW of the back electromotive force. When all the energy stored in the reactor L is released, the voltage returns to the rectified voltage vAc, and returns to OV when the transistor Q0 is turned on. The base potential 8 of the transistor Tr of the detection circuit DEC is the accumulated charge of the capacitor C when the transistor Q is on.
0, the diode D1 is discharged through the resistor R2 and the base-emitter junction of the transistor Tr, so it is OV, and when the transistor Q0 is turned off, the output voltage of the reactor L becomes ■. The output voltage V of the reactor L is raised to 0.6 or more through the series circuit of the capacitor C and the resistor R1. During the period of vDc, the capacitor C is charged and the time constant of the capacitor C and resistor R1 slightly decreases, but it is maintained at 0.6 V or higher, and the output voltage of the reactor L becomes ■.

is 0.6 with the fall from vDo to VAC.
V, and further the output voltage vc of reactor L becomes VA
With the fall from c to Ov, the differential waveform swings below Ov, but eventually returns to Ov. Therefore, the detected output voltage vS of the detection circuit DEC is during the period when the transistor Tr is 0.6V or more, that is, the output voltage Vc of the reactor L is the output voltage (2) of the back electromotive force. It is at a low level only during this period, and is at a high level during other periods. This detected output voltage 5 is immediately input to the control circuit COM, and when the rise of the control pulse 4 from low to high level is detected, the next pulse is output, turning on the transistor Q-.

Therefore, the detection circuit DEC of the present invention detects the output voltage V of the reactor L when all the stored energy in the reactor L is released and the current IL flowing through the coil becomes 0.

Since the fall of V DC to V AC is detected, it is possible to reliably detect that the coil current has disappeared.

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

The circuit pattern with diagonal lines is the ground pattern, and the circuit board has a part of the ground pattern.
It is divided into two parts: a small signal circuit block corresponding to the blank space in the road half of the drawing, and a large current circuit block corresponding to the lower half of the drawing. In this embodiment, the wiring for 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 wiring from the large current circuit block to the small signal circuit block. The wiring for the emitter potential of the transistor Q0 is planned to be formed so as to bypass a part of the ground pattern.
The present invention is not limited to this, and for example, the wiring for the emitter potential of the transistor Q0 may be connected to a predetermined position of the small signal circuit block by a bonding wire (jumping wire connection).

Furthermore, 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 through which a high frequency and large current flows, thereby making the aluminum substrate potential equal to the ground pattern potential.

In the large current circuit block, diodes D, ~D4, a damper diode D5, and a transistor Q, which constitute a bridge rectifier circuit, are surface mounted via a heat sink, and further limit the emitter current of the transistor Q0 and change its value. The emitter resistor R for measurement can now be formed. These elements are arranged so that a large current does not flow into the ground pattern portion that divides the small signal circuit block and the large current circuit block. The external lead terminals that connect the large current circuit block and the external circuit and the external lead terminals of the small signal circuit block are arranged on opposite peripheral edges of the circuit board so that they are loosely coupled to each other.

Also, since the distance between the externally connected smoothing capacitor Cd and the damper diode D6 greatly affects the charging and discharging ability of the smoothing capacitor Cd, the damper diode D is placed close to the terminal shown by vl in FIG. Ru. Furthermore, for the same reason, the terminal indicated by V'' and the ground terminal GND can be placed adjacent to each other.

The J% signal circuit block is equipped with a control circuit COM and a detection circuit DEC that can be connected to the L- pattern.

(g) Effects of the invention According to the present invention, the following various effects are achieved.

First, since the coil voltage a I L of the reactor L is detected using the output voltage Vc of the no-after L, the auxiliary winding that was conventionally required can be eliminated, and the structure of the reactor L can be simplified. Further, matching design between the auxiliary winding and the control circuit COM becomes unnecessary.

Second, in the present invention, since the coil current is detected by the fall of the output voltage vc of the reactor L from the charging voltage VDc to the rectified voltage vAc, the charging voltage VDc is normally stabilized, so it is extremely It has the advantage of being able to perform accurate detection.

Thirdly, in the present invention, the output voltage V of the reactor L.

Since it directly detects the charging voltage VDC and rectified voltage V
Even if the difference from AC becomes small, it has the advantage of being able to obtain a much larger detection output voltage than detection using an auxiliary winding.

Fourth, since the present invention does not use an auxiliary winding, the detection circuit can be mounted on the same hybrid integrated circuit board, which has the advantage of realizing an extremely compact hybrid integrated circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram explaining an active filter device according to the present invention, and FIG. 2 is a detection circuit DE used in the present invention.
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. 5 is a circuit diagram illustrating the operation of the active filter device of the present invention. 6 is a circuit diagram illustrating the conventional active filter device, and FIG. 7 is a waveform diagram illustrating the operation of the conventional active filter device. It is. L...Reactor, Cd...Smoothing capacitor, COM...Control circuit, D1-D6...Diode, Qo...Transistor, DEC...Detection circuit.

Claims (3)

[Claims] (1) A rectifier circuit, a switching element, a reactor, a diode for extracting a charging voltage from the reactor, a capacitor charged with the charging voltage, and a control circuit for controlling switching of the switching element, and the rectifier circuit controls the AC power supply. In an active filter device configured to intermittently flow a coil current to the reactor using the switching element after converting it into a rectified DC voltage, detecting the output voltage of the back electromotive force of the reactor that occurs when the switching element is turned off. 1. An active filter device comprising: a detection circuit for applying a detection output to the control circuit. (2) The detection circuit is formed by a series circuit of a capacitor and a resistor, and detects a fall of the back electromotive force of the reactor to the output voltage rectified voltage, and turns off the switching element. The active filter device described. (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.