JPH08275402A - Electromagnetic induction coil drive circuit - Google Patents

Abstract

PURPOSE: To assure safe operations when an object such as coin is placed on an electromagnetic induction coil or there has been a change in input power by varying an oscillating frequency of an oscillating circuit for driving a semiconductor switching element and controlling the ON-time of the semiconductor switching element. CONSTITUTION: Frequency changes in response to the fluctuation in a voltage between drain and source of an FETQ2. Moreover, a differential effect is created by applying its output through an integrating circuit comprising a resistor R16, a diode D1, and a capacitor C6, and a control is so made that the OFF-time determined by an oscillating circuit becomes longer than the OFF-time of the FETQ2. Thus, if a metal object such as a coin is placed on an electromagnetic induction coil T1 at the side of a power sending portion 1, the voltage between the drain and source of the FETQ2 rises so that the ON-time of the FETQ2 is suppressed and the input power is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery (rechargeable battery) used as a power source for a cordless telephone, a portable device, etc., by transmitting electric power by electromagnetic induction so as to be contactless (with electrical connection). The present invention relates to a drive circuit of an electromagnetic induction coil for charging in the case of a non-use) and a charging device using the drive circuit, the charging device being incorporated in a cordless telephone, a portable device or the like.

[0002]

2. Description of the Related Art Non-contact type chargers that have been conventionally used in electric toothbrushes and the like apply a circuit for a switching regulator to an electromagnetic induction coil in an RCC circuit (ringing choke converter circuit) or a Royer oscillator circuit. The electric power is transmitted from the electromagnetic induction coil on the power transmitting unit side to the power receiving coil on the power receiving unit side by electromagnetic induction by driving. And
In the case of direct input of a commercial AC power supply (DC114V after rectification is used as it is in case of AC100V), it is difficult to stabilize the operation in the self-excited oscillation circuit at high frequency, so that the oscillation frequency of the oscillation circuit becomes 30 to 100 kHz In addition, the inductance of the electromagnetic induction coil used as the oscillation coil was set.

However, for example, a non-contact type charger is incorporated in a device such as a cordless telephone which has a multi-channel communication band at 12.5 kHz per band.
When contactless charging is performed at an oscillation frequency of 100 kHz, a problem arises that a harmonic of the oscillation frequency interferes with the call signal as noise.

In order to avoid the influence of the harmonic noise as described above, it is necessary to raise the oscillation frequency. However, the Hartley type and Colpitts type oscillation circuits which have been conventionally used as a high frequency oscillation circuit are applied at the signal level. However, in principle, stable switching operation cannot be performed, resulting in large loss of active components, and efficient charging cannot be expected in consideration of application to a charging device.

Further, when the energy transmitted from the electromagnetic induction coil on the power transmission section side increases due to the fluctuation of the input voltage, the constant current circuit built in the power receiving side apparatus generates a large amount of heat. May cause damage to the. Especially when applied to a telephone, this heat generation significantly reduces the commercial value.

In order to solve such a problem, Japanese Patent Application No.
-322971 has been proposed.

In this proposal, a self-excited Colpitts oscillator circuit is configured on the power transmission unit side to stably oscillate at high frequency, and the power transmission unit side is used by using this oscillation circuit as a drive circuit. The electromagnetic induction coil can be excited. Then, by exciting the electromagnetic induction coil on the power receiving unit side, power can be transmitted in a non-contact manner to the electromagnetic induction coil that is the power receiving coil on the power receiving unit side. In this method, since the oscillation at high frequency is stable, the harmonics of the oscillation frequency interfere with the call signal as noise.

Further, since the input power adjusting circuit is incorporated in the power transmitting unit side, the input power is limited accordingly even when an abnormal situation occurs due to fluctuation of the input voltage,
For example, it has become possible to suppress damage to equipment due to heat generation.

[0009]

By the way, when the power receiving coil on the power receiving unit side is not placed on the electromagnetic induction coil on the power transmitting unit side, such as when using a cordless telephone, metal such as coins is erroneously transmitted. If placed on the electromagnetic induction coil on the side of the unit, an eddy current is generated inside a metal such as a coin to generate heat, and the device may be damaged due to abnormal heat generation in the power transmission unit.

However, the input power cannot be sufficiently limited by the conventional general RCC circuit (ringing choke converter circuit), the Royer oscillator circuit, the oscillator circuit proposed in Japanese Patent Application No. 6-329271, and the like. Therefore, it is difficult to prevent possible damage to the device and the like.

Therefore, an object of the present invention is to operate safely even when a metal such as a coin is placed on the electromagnetic induction coil on the side of the power transmission unit, and even if the input power changes due to input fluctuations or the like. It is to provide a drive circuit for an electromagnetic induction coil that operates in the above manner.

Further, as a "charging device for charging a secondary battery (rechargeable battery) by non-contact (without electrical connection) by transmitting electric power by electromagnetic induction", a cordless telephone, a portable device, etc. It is a second object of the present invention to provide a charging device of this type in which harmonics of the oscillating frequency do not interfere as noise with respect to the call signal even when incorporated into the charging device.

[0013]

In order to solve the above-mentioned problems, the present invention is to connect a magnetic flux generating electromagnetic induction coil on the power transmitting section side to a semiconductor switching element, and to form a waveform on the other end of the semiconductor switching element. In an electromagnetic induction coil drive circuit in which a capacitor is equivalently connected in parallel with an electromagnetic induction coil so that a semiconductor switching element performs a switching operation by connecting an oscillation circuit through the circuit and a resonant circuit is formed with the electromagnetic induction coil. By detecting the peak value of the voltage generated in the switching element when the semiconductor switching element is turned off and comparing it with the reference voltage obtained by rectifying and smoothing a part of the energy generated by the oscillation, the semiconductor The oscillation frequency of the oscillation circuit that drives the switching element is changed to It is configured to control the time.

Further, according to the present invention, in the switching operation of the semiconductor switching element, the ON time of the pulse for driving the switching element is shorter than the ON time of the switching element.

Further, according to the present invention, the peak value of the voltage when the semiconductor switching element is turned off is detected by using the passive element.

[0016]

In the drive circuit of the electromagnetic induction coil of the present invention and the charging device using the drive circuit, a semiconductor switching element such as a field effect transistor (hereinafter referred to as FET) is switched by an external oscillator on the power transmission section side. Let Then, an electromagnetic induction coil for generating a magnetic flux is connected in series to the FET so that the electric power from the commercial AC power source is converted into a magnetic flux by the electromagnetic induction coil and sent to the power receiving unit side. Here, the description will be advanced especially when a FET is used as a semiconductor switching element.

Since a capacitor is connected between the drain and source of the FET and constitutes a resonance circuit together with the electromagnetic induction coil, the oscillation waveform is shaped to be close to a sine wave, and spurious noise is reduced. be able to.
Therefore, even when the charging device is incorporated in a cordless telephone, a portable device, or the like, there is no adverse effect that harmonics of the oscillation frequency interfere as noise in the call signal.

In the resonance type electromagnetic induction coil drive circuit constructed as described above, the OFF time of the FET is a resonance formed by the inductance of the electromagnetic induction coil and the capacitance of the capacitor connected between the drain and source of the FET. Determined by the resonant waveform of the circuit.

In order to operate safely even when a metal such as a coin is placed on the electromagnetic induction coil on the side of the power transmission unit and to operate safely even when the input power changes due to input fluctuations, etc. In order to suppress the power, it is necessary to reduce the ON time of the FET to reduce the input power. In order to reduce the ON time of the FET, increase the operating frequency of the FET, or increase the resonance frequency of the resonance circuit formed by the inductance of the electromagnetic induction coil and the capacitance of the capacitor connected between the drain and source of the FET. It is necessary.

By the way, in order to increase the resonance frequency, it is necessary to use a voltage variable capacitor,
Control is difficult because the resonance current is also large.

Therefore, when the above-mentioned abnormal state occurs,
Paying attention to the increase in the voltage between the drain and source of the FET when it is off, comparing the voltage of this part with the reference voltage obtained by rectifying and smoothing a part of the energy generated by the oscillation, FET drain,
When the source-to-source voltage rises, the frequency of the FET drive oscillation circuit is raised and the ON time of the FET is controlled to be small to suppress the input power.

However, as already mentioned, the OF of the FET is
Since the F time is constant, if the frequency is simply increased, the drain current will flow while the voltage between the drain and the source remains, resulting in a large loss of the FET and heat generation. Get up. In addition, the driving waveform of the FET is distorted, which leads to generation of harmonic noise.

In order to solve such a problem, therefore, the output from the oscillation circuit is passed through a differentiating circuit, waveform shaping is performed as necessary, and the ON time of the pulse for driving the FET is determined from the ON time of the switching element. It is necessary to control it so that it becomes shorter.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a drive circuit for an electromagnetic induction coil and a charging device using the drive circuit according to the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an overall structure of a drive circuit for an electromagnetic induction coil and a charging device using the drive circuit. In FIG. 1, the charging device includes a power transmission unit 1 and a power reception unit 2 that receives electric power by electromagnetic induction.

As shown in FIG. 1, the electromagnetic induction coil T1 is driven by a switching operation F to drive the electromagnetic induction coil.
The ETQ2 is connected, and the electromagnetic induction coil T1 and the capacitors C1 and C2 that form a resonance circuit are connected between the drain and the source of the FETQ2, and the electromagnetic induction coil T1 is connected.
The power from the commercial AC power source directly connected to 1 is converted into a corresponding magnetic flux and sent to the power receiving unit 2 side.

On the other hand, the voltage between the drain and the source of the FET Q2 is taken out by the resistors R7 and R8 connected between the drain and the source of the FET Q2, and is rectified by the rectifying section composed of the diode D2, the capacitor C3 and the resistor R9, and then the operational amplifier IC2. Is added to the positive terminal of. A reference voltage is input to the negative terminal side of the operational amplifier IC2, and its differential amplification output is composed of a varicap diode D5, a capacitor C5, a Schmitt inverter IC3, and a resistor R15. Oscillation circuit 3 (hereinafter referred to as VCO)
Is input to Therefore, the frequency changes in accordance with the change in the drain-source voltage of the FET Q2. Further, the output thereof is passed through an integrating circuit composed of a resistor R16, a diode D1 and a capacitor C6, and a waveform is shaped by the buffer IC1 so as to have a differential effect.
The OFF time determined by the oscillation circuit is controlled to be longer than the OFF time of TQ2.

Therefore, when a metal such as a coin is placed on the electromagnetic induction coil T1 on the power transmission section 1 side, the voltage between the drain and source of the FET Q2 rises, so this FET
The ON time of Q2 is suppressed and the input power becomes small. For this reason, the electric power supplied to the metal such as the coin is also reduced, and the metal such as the coin does not generate heat and does not cause a dangerous state such as smoking or ignition. In addition, even when the input power changes due to input fluctuations, the FE
Since the voltage between the drain and source of TQ2 rises, the increase in input power is suppressed and the device operates safely.

On the power receiving portion 2 side, Japanese Patent Application No. 6-3292
In the same manner as described in 71, the power transmitted by the electromagnetic induction coil T1 is received by the power receiving coil T2, and the voltage generated across the power receiving coil T2 is
The resonant circuit formed by the inductance of the power receiving coil T2 and the capacitor C8 rectifies the voltage increased by a multiple of Q obtained by the resonant circuit by the rectifier circuit including the diode D7 and the capacitor C9, and then the secondary battery through the constant current circuit. It is configured to charge the BAT.

Up to now, the case where the FET is used as the semiconductor switching element has been described as an example, but the invention is not limited to this, and a bipolar transistor can be used.
Further, in the present embodiment, the circuit including the varicap diode and the Schmitt inverter is used for the VCO 3, but the Schmitt circuit may be configured by using the NAND gate as shown in FIG. As described above, if the VCO can be configured, the operation of the electromagnetic induction coil drive circuit according to the present invention can be stably operated regardless of which circuit is used. Further, if the gain of the feedback circuit including the VCO is sufficient, it is obvious that the electromagnetic induction coil drive circuit according to the present invention can be configured except the operational amplifier IC2.

[0031]

As described above, the drive circuit for the electromagnetic induction coil and the charging device using the drive circuit according to the present invention are provided when a metal such as a coin is placed on the electromagnetic induction coil on the power transmission side. However, there is no danger of ignition and smoke due to safe operation, and safe operation is possible even when input power changes due to input fluctuations and the like. .

As a "charging device for non-contact (without electrical connection) charging of a secondary battery (rechargeable battery) by transmitting electric power by electromagnetic induction", a cordless telephone, a portable device, etc. Even if it is incorporated into, there is no harmful effect that harmonics of the oscillating frequency are mixed into the call signal as noise and interfere.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overall structure of a drive circuit for an electromagnetic induction coil and a charging device using the drive circuit according to an embodiment of the present invention.

FIG. 2 VCO configuration example

[Explanation of symbols]

1. 1. The power transmission section in the embodiment of the non-contact power transmission device according to the present invention. 2. The power receiving unit in the embodiment of the non-contact power transmission device according to the present invention. VCO department

Claims (3)

[Claims] 1. In an electromagnetic induction coil drive circuit of a non-contact power transmission device for transmitting electric power from a power transmission unit side to a power reception unit side in a non-contact state, a magnetic flux generating electromagnetic induction on the power transmission unit side is applied to a semiconductor switching element. A coil is connected, and an oscillation circuit is connected to the other end of the semiconductor switching element through a waveform shaping circuit to cause the semiconductor switching element to perform a switching operation, and a capacitor is connected to form an electromagnetic induction coil and a resonance circuit. An electromagnetic induction coil drive circuit comprising:
The peak value of the voltage when FF is detected is detected, and the oscillation frequency of the oscillation circuit that drives the semiconductor switching element is changed.
An electromagnetic induction coil drive circuit characterized by controlling an ON time of a semiconductor switching element. 2. In a switching operation of a semiconductor switching element, a pulse for driving the switching element is turned on.
The electromagnetic induction coil drive circuit according to claim 1, wherein the time is shorter than the ON time of the switching element. 3. The electromagnetic induction coil drive circuit according to claim 1, wherein the peak value of the voltage when the semiconductor switching element is turned off is detected by using a passive element.