JPH04320506A - Active filter device - Google Patents

Abstract

PURPOSE:To securely detect a current which flows to a reactor irrelevantly to variation in temperature by detecting the current which flows to the reactor by a detecting circuit equipped with a metallic resistance body and applying the detection output to a control circuit. CONSTITUTION:A damper diode D5 charges the charging voltage of the reactor L in a capacitor Cd. A control circuit COM controls the switching of a transistor Q0. The rectifying circuit composed of diodes D1-D4 converts an AC source voltage into a rectified AC voltage and then the TR Q0 supplies a coil current to the reactor L intermittently. At this time, the detecting circuit DEC equipped with the metallic resistance body which is low in resistance temperature coefficient(TCR) as a detection resistance detects the current flowing to the reactor L directly. Consequently, the current which flows to the reactor L can securely be detected irrelevantly to the variation in temperature. Further, auxiliary winding can be omitted and the TR Q0 can be controlled with the detection output of a detecting circuit DEC through control pulses phi of the control circuit COM.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter device, and more particularly to an active filter device for controlling current flowing through a reactor.

0002

2. Description of the Related Art In recent years, active filters have been attracting attention from the viewpoint of countermeasures against noise in rectified power supplies. A general active filter will be explained with reference to FIG. This active filter consists of a bridge rectifier circuit consisting of diodes D1 to D4, 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 respectively connected between the other end of this reactor L and the ground. a damper diode D5 whose anode is connected to the collector of the transistor Q, a smoothing capacitor Cd connected between the cathode of the damper diode D5 and the ground, and a control pulse φ to the base of the transistor Q. Consists of circuit COM.

The main circuit of the control circuit COM is constituted by a microcomputer or the like, and outputs a control pulse φ having a frequency of 15 KHz or more. Next, the operation of this active filter will be explained. During the half cycle in which the potential at the connection point of commercial AC diodes D1 and D2 is positive, the control circuit CO
When the control pulse φ with a frequency of 15 KHz or higher output from M is at a high level, transistor Q is turned on, and diode D1 - reactor L - transistor Q - diode D
A closed circuit of 4 is formed and current IL flows through reactor L. Then, 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 connect the previous electrical state and generates a back electromotive force. The voltage obtained by adding the back 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 long period of time compared to a capacitor input type rectifier circuit, and is transferred to the smoothing capacitor Cd via the damper diode D5. Charge the CD.

[0004] Furthermore, in the half cycle in which the potential at the connection point between the commercial AC diodes D1 and D2 becomes negative, when the control pulse φ is at a high level, the transistor Q is turned on and the diode D3 is turned on.
- Reactor L - Transistor Q - A closed circuit of diode D2 is formed, and current IL flows through reactor L. Then, when the control pulse φ becomes low level and the transistor Q is turned off and the previous closed circuit is opened, a back electromotive force is generated in the reactor L as before, and the back electromotive force and the bridge rectifier circuit output are Smoothing capacitor Cd is charged by the added voltage.

[0005] 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 φ controls the coil current IL flowing through the reactor L. The active filter shown in FIG. 4 employs a control method in which coil current is detected by an auxiliary winding (1). The auxiliary winding (1) is magnetically coupled and wound around the reactor L, and detects the polarity of the coil current IL flowing through the reactor L. In other words,
During the period when the transistor Q is on and the coil current IL flows and energy is stored in the reactor L, the auxiliary winding (1
) outputs a negative voltage, and during the period when the transistor Q is turned off and the energy of the reactor L is released, a positive voltage is output from the auxiliary winding (1), and when the coil current IL becomes zero, the auxiliary winding Line (1) has 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 the coil current IL to flow through the reactor L.

[0006]

SUMMARY OF 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 and high cost. Secondly, it is necessary to match the setting of the number of turns of the auxiliary winding (1) with the control circuit COM and the secondary output voltage, making the design of the active filter complicated.

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, making it impossible to operate the control circuit COM normally. There is.

[0008]

[Means for Solving the Problems] The present invention has been made in view of the various problems mentioned above, and has solved the conventional problems by providing a detection circuit that detects the current flowing in the reactor using a metal resistor. This realizes an active filter device.

[0009]

[Operation] According to the present invention, since the current flowing through the reactor is directly detected by a detection circuit equipped with a metal resistor with a low temperature coefficient of resistance (TCR) as a detection resistor, it is possible to
It eliminates the need for an auxiliary winding, can reliably detect current in response to changes in the current detection level regardless of temperature changes, and can output control pulses φ from the control circuit using the detection output of the detection circuit. Switching of switching elements can be controlled.

0010

[Example] Fig. 1 shows an active filter device according to the present invention.
This will be explained in detail with reference to FIGS. The active filter of the present invention has diodes D1 to D as shown in FIG.
4, a reactor L whose one end is connected to the positive DC output terminal of the bridge rectifier circuit, a transistor Q0 whose collector and emitter are respectively connected between the other end of this reactor L and the ground, and this transistor Q.
0, a smoothing capacitor Cd connected between the cathode of the damper diode D5 and the ground, and a control circuit C that supplies a control pulse φ to the base of the transistor Q0.
OM, which is a feature of the present invention, is composed of a detection circuit DEC equipped with a metal resistor having a low temperature coefficient of resistance (TCR) as a detection resistor for detecting the current flowing through the reactor.

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, which is outside the audible range. The detection circuit DEC, which is a feature of the present invention, causes a coil current I0 flowing in the reactor L when the transistor Q0 is on to be passed through a detection resistor R0 made of a metal resistor, and generates a voltage signal obtained by the voltage drop. When the voltage signal is equal to or less than a predetermined value determined by the control circuit, that is, a sine wave level synchronized with the power supply voltage, the transistor Q0 is turned on and current is caused to flow through the reactor L. When this current reaches a predetermined set level, transistor Q0 is turned off based on the output signal of operational amplifier OP, cutting off the current flowing through reactor L. In this way, the transistor Q0 is repeatedly turned on and off in order to cause a sinusoidal current to flow.

An embodiment of the detection circuit of the present invention will be described with reference to FIG. This detection circuit consists of a detection resistor R0 made of a metal resistor connected to the emitter of the transistor Q0 and the ground line to detect the current flowing through the reactor L, and a positive input terminal connected to the connection point between the detection resistor R0 and the transistor Q0. the operational amplifier OP, the resistor R1 connected between the detection resistor R0 (ground line side) and the negative input terminal of the operational amplifier OP, and the negative terminal of the operational amplifier OP and the operational amplifier OP.
A resistor R2 is connected between the output terminals of the resistor R2. Note that the operational amplifier OP can be omitted when the voltage detected by the detection resistor R0 is large.

As the detection resistor R0, a metal resistor having a low temperature coefficient of resistance (TCR) is used. Specifically, a nickel-plated resistor is used as the detection resistor R0. Since nickel plating has an extremely lower TCR than metals such as copper and Ag, it is possible to detect a somewhat constant current regardless of temperature changes. Nickel plating has a small fusing current value, but by increasing the area or thickness, it is possible to detect a certain amount of current.

As mentioned above, nickel-plated resistors have the disadvantage that the area must be increased or the plating must be thickened in order to detect a certain amount of current, but metals such as copper and Ag Since the TCR is extremely high, it cannot be used as a detection resistor, so the current flowing through the reactor L cannot be reliably detected regardless of temperature changes, and a nickel-plated resistor is indispensable.

Next, referring to FIG. 3, a detailed structure of an embodiment in which the above-described active filter device, excluding the reactor L and 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 small signal circuit block corresponding to the blank area in the upper half of the drawing and a large signal circuit block corresponding to the lower half of the drawing by a part of the ground pattern. It is divided into two current circuit blocks. In this embodiment, the control pulse φ is wired from the small signal circuit block to the large current circuit block, the control pulse φ is wired from the output side of the reactor L to the detection circuit DEC, or the control pulse φ is supplied from the large current circuit block to the small signal circuit block. Transistor Q0
The wiring for the emitter potential of the transistor Q0 is formed so as to bypass a part of the ground pattern, but the wiring is not limited to this. For example, the wiring for the emitter potential of the transistor Q0 is formed to bypass a part of the ground pattern. It may be connected to the position by a bonding wire (jumping wire connection).

Furthermore, this ground pattern is suitable for high frequencies,
It is connected to the aluminum substrate by a bonding wire W at a position closest to the emitter of the transistor Q0 through which a large current flows, thereby making the aluminum substrate potential equal to the ground pattern potential. In the large current circuit block, diodes D1 to D4, a damper diode D5, and a transistor Q0, which constitute a bridge rectifier circuit, are surface mounted via a heat sink, and further limit the emitter current of the transistor Q0 and measure its value. Detection resistor R for
0 is 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.

Furthermore, an externally connected smoothing capacitor Cd
The distance between the damper diode D5 and the smoothing capacitor Cd
The damper diode D5 is placed close to the terminal designated V+ in FIG. 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 includes
Although not shown, a control circuit COM and a detection circuit DEC in which a metal resistor having a low temperature coefficient of resistance (TCR) is connected to the detection resistor R0 are mounted.

[0018]

[Effects of the Invention] As detailed above, according to the present invention,
Since the coil current of the reactor L is detected using a metal resistor with a low TCR, there is an advantage that an auxiliary winding as in the conventional method is unnecessary and the structure of the reactor L can be simplified. Further, matching design between the auxiliary winding and the control circuit COM is also unnecessary.

Furthermore, in the present invention, since a metal resistor with a low TCR is used as the detection resistor, detection can be performed reliably regardless of temperature rise changes. As a result, the reliability of the active filter device itself is improved. Furthermore, in the present invention, since the auxiliary winding is not required, the detection circuit can be mounted on the same hybrid integrated circuit board, and an extremely miniaturized hybrid integrated circuit device can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram illustrating an active filter device according to the present invention.

FIG. 2 is a circuit diagram illustrating a detection circuit DEC used in the present invention.

FIG. 3 is a top view illustrating a state in which the active filter of the present invention is mounted on a hybrid integrated circuit board.

FIG. 4 is a circuit diagram illustrating a conventional active filter device.

FIG. 5 is a waveform diagram illustrating the operation of a conventional active filter device.

[Explanation of symbols]

L Reactor D1~D5 Diode Cd Smoothing capacitor Q0 Transistor COM Control circuit DEC detection circuit R0 Detection resistor

Claims (4)

[Claims] 1. A rectifying circuit, a switching element, a reactor, a diode for extracting charging voltage from the reactor, a capacitor charged with the charging voltage, and a control circuit for controlling switching of the switching element, An active filter device configured to convert a power source into a rectified alternating current voltage and then intermittently cause a coil current to flow through the reactor using the switching element,
An active filter device comprising: a detection circuit including a metal resistor for detecting a current flowing through the reactor; and applying a detection output from the detection circuit to the control circuit. 2. The detection circuit includes an operational amplifier to which one end of the low-resistance metal detection resistor and a + input terminal are connected, and an operational amplifier connected between the other end of the low-resistance metal detection resistor and a − input terminal of the operational amplifier. 2. The active filter device according to claim 1, further comprising a resistor connected between the negative input terminal and the output terminal of the comparator. 3. The active filter device according to claim 1, wherein a nickel-plated resistor is used as the metal resistor. 4. The active filter device according to claim 1, wherein the rectifier circuit, the switching element, the diode, and the control circuit are mounted on the same hybrid integrated circuit board.