JP2002078249A - Power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify winding of a coil to a core by not requiring a detection coil. SOLUTION: An AC voltage is generated in capacitors C1, C2, for feedback and FETs Q1, Q2 are turned on and off alternately by supplying the AC voltage to convert to an AC current which is then given to feeding side coils L2, L3, and then the power is supplied to power receiving coils L4, L5 by means of the electromagnetic induction action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for supplying power from a power supply coil to a power receiving coil by electromagnetic induction.

[0002]

2. Related Background Art Conventionally, in this type of power supply device, as shown in, for example, Japanese Patent No. 2809433, the resonance frequency of a power receiving side coil is detected by a detection coil as induced electromotive force due to electromagnetic induction, and the induced electromotive force is detected. To supply an alternating current to the power supply side coil in accordance with the change in polarity of
And the second transistor are alternately switched.

[0003]

However, in the above device, a detection coil for detecting induced electromotive force is required in addition to the power supply side and power reception side coils, and the detection coil is combined with the power supply side coil. There is a problem that the winding around the core is complicated and takes a lot of trouble.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a power supply device which does not require a detection coil and can simply wind a coil around a core.

[0005]

According to the present invention, there is provided a resonance circuit comprising a power supply side coil and a capacitor, and a power receiving side coil, wherein electromagnetic induction is provided from the power supply side coil to the power receiving side coil. A first and second capacitors connected to both ends of the power supply side coil and generating an AC voltage in accordance with the induced electromotive force of the power supply side coil and the power receiving side coil; A power supply device comprising: a changing unit configured to change an AC frequency of power supplied to the power supply side coil according to the generated AC voltage.

That is, an AC voltage is generated by the first and second feedback capacitors, and the AC frequency of the power supplied to the power supply side coil is changed in accordance with the AC voltage, thereby eliminating the need for the detection coil. . Further, in the present invention, the changing unit is supplied with an AC voltage from a first and a second capacitor, and resonates with a capacitor of the resonance circuit to alternately supply a current to the power supply side coil. The first and second transistors are alternately turned on and off to convert the current into an alternating current, and the power is supplied to the power receiving side coil by electromagnetic induction.

[0007]

FIG. 1 shows a power supply device according to the present invention.
7 through FIG. FIG. 1 is a circuit diagram showing a circuit configuration of a first embodiment of a power supply device according to the present invention. In the figure, the power supply device of the present embodiment includes a power supply unit 10 and a power reception unit 20, and supplies power from the power supply unit 10 to the power reception unit 20 in a non-contact manner.

The power supply unit 10 includes a + input terminal (INPUT) connected to a positive electrode of a power supply (not shown) and a-input terminal (INPUT) connected to a negative electrode, an inductor L1 connected to a + input terminal, Starting resistors R1 to R4, power supply side resonance circuit 11, conversion circuit 12, power supply side resonance circuit 11, resistance R
Capacitors C1, C2 connected via R5 and R6 respectively
It is composed of The conversion circuit 12 constitutes the conversion means of the present invention, and the capacitors C1 and C2 constitute the first and second capacitors of the present invention.

The power supply side resonance circuit 11 includes a power supply side coil L
2 and L3, and a capacitor C3 connected in parallel with the power supply side coils L2 and L3. An inductor L1 is connected to a middle point a between the power supply side coils L2 and L3, and a power supply is provided via the inductor L1. Power is supplied from A conversion circuit 12 is connected in parallel to the ends of the power supply side coils L2 and L3, and a capacitor C1 is connected to an end of the power supply side coil L2 via a resistor R5. Is connected to a capacitor C2 via a resistor R6.

The conversion circuit 12 includes field-effect transistors (hereinafter, referred to as "FETs") Q1 and Q2 constituting the first and second transistors of the present invention connected in series. The midpoint b between the sources S of Q2 is grounded, and the drain D of the FET Q1.
Is connected to the drain D of the FET Q2 at the end of the feeding coil L2.
Are connected to the ends of the power supply side coil L2, respectively. The gate G of the FET Q1 is connected to the starting resistors R3 and R1.
Is connected to the + input terminal and the capacitor C2, and the gate G of the FET Q2 is connected to the starting resistor R
4, and connected to the + input terminal via R1 and to the capacitor C1.

The power receiving section 20 includes a power receiving side resonance circuit 21, a rectifier circuit 22, and a smoothing circuit 23. The power-receiving-side resonance circuit 21 includes a power-receiving-side coil L4, L5 and a capacitor C4 connected in parallel with the power-receiving-side coil L4, L5.
The middle point c between the power receiving side coils L4 and L5 is connected via a smoothing circuit 23 to a negative output terminal (OUT).

The rectifier circuit 22 includes a diode D3 connected to an end of the power receiving coil L4 and a diode D4 connected to an end of the power receiving coil L5.
3, D4 are connected to a + output terminal (OUT) via a choke coil L6 of the smoothing circuit 23, which will be described later. The smoothing circuit 23 includes a choke coil L6 connected to a positive output terminal.
And a smoothing capacitor C5 connected to the + output terminal and the-output terminal, respectively. A load (not shown) is connected to the + output terminal and the-output terminal.

Next, the operation of the contactless power supply device of the present embodiment will be described with reference to the waveform diagram of FIG. When the power is turned on, the starting resistors R1, R2, R3, R4 cause F
A voltage VGS is applied between the gate G and the source S of the ETQ1 and Q2 (see FIG. 2A), and the lower threshold voltage level is turned on first (in the case of a bipolar transistor, the current amplification factor is lower). The larger one is turned on first). In the present embodiment, a case will be described in which, for example, the FET Q1 is turned on first.

In this embodiment, during a period I shown in FIG. 2, the conduction between the drain D and the source S of the FET Q1 is established, and the inductor L1 and the power supply side coil are supplied from the + input terminal connected to the positive electrode of the power supply. A current IDS flows between the drain D and the source S of the FET Q1 via L2 (FIG. 2 (c)).
reference). The current IDS of the FET Q1 becomes a substantially rectangular wave due to the constant current action of the inductor L1. Since the FET Q1 is turned on, the drain potential VDS of the FET Q1 becomes the ground level. When the drain potential of the FET Q1 reaches the ground level, F
Since the voltage VGS between the gate G and the source S of the ETQ2 is turned off (see FIG. 2D), the FET Q2 maintains the off state.

A current flows through the parallel resonance circuit 11 composed of the power supply side coils L2 and L3 and the resonance capacitor C3 via the inductor L1, and the resonance capacitor C3 is charged and discharged by this current. This parallel resonance circuit 11
Supplies power to the rectifier circuit 22 in synchronization with the parallel resonance circuit 21 including the power receiving side coils L4 and L5 and the resonance capacitor C4.

Since the FET Q1 is in the ON state, the drain potential is kept at the ground level, and a current flows through the supply coil L2, so that the FET Q1 resonates in the parallel resonance circuit 11 and
The voltage VDS between the drain D and the source S of the ETQ2 becomes a sine wave due to this resonance (see FIG. 2E). When the above resonance lasts for a half cycle, the voltage VDS of the FET Q2 returns close to the ground level (see FIG. 2B). FETQ
When the voltage VDS of 2 goes to the ground level, the voltage VGS of the FET Q1 decreases via the resistor R6 and the capacitor C2, and the FET Q1 is turned off. With this, FET
The drain potential of Q1 rises, and the resistor R5 and the capacitor C1
AC voltage is applied to the gate G of the FET Q2 via
The voltage VGS of ETQ2 increases, and the FET Q2 is turned on.

Next, during a period II shown in FIG. 2, the drain D-source S of the FET Q2 is supplied from the + input terminal connected to the positive electrode of the power supply via the inductor L1 and the feeding coil L3.
During this time, a current IDS flows (see FIG. 2 (f)). FET Q2
Is turned on, the drain potential of the FET Q2 becomes the ground level, and the voltage VGS between the gate G and the source S of the FET Q1 is turned off (see FIG. 2A).
Maintain the off state.

A current flows through the FET Q2 through the parallel resonance circuit 11 via the inductor L1, and the voltage VDS between the drain D and the source S of the FET Q1 becomes sinusoidal due to the resonance action of the parallel resonance circuit 11. Wave voltage appears. After the resonance lasts for a half cycle, the FET Q2 is turned off and the FET Q1 is turned on. Thus, FET
Q1 and Q2 oscillate by alternately repeating on / off operations in periods I and II.

Next, in the parallel resonance circuit 21 on the power receiving side, induced electromotive force is generated in the power receiving side coils L4 and L5 by the magnetic flux of the power supply side coils L2 and L3, and the resonance capacitor C4 is charged and discharged by the induced electromotive force. Is done. In the rectifier circuit 22,
When an induced electromotive force is generated in the direction from the power receiving side coil L5 to L4, the diode D3 takes out the electromotive force generated in the power receiving side coil L4, and when the induced electromotive force is generated in the direction from the power receiving side coil L4 to L5, the diode D4 extracts the electromotive force generated in the power receiving side coil L5. The power rectified by the rectifying circuit 22 is smoothed by the smoothing capacitor C5 using the self-inducing action of the choke coil L6, becomes DC power, and is supplied to the load via the + output terminal and the-output terminal.

As described above, in the present embodiment, an AC voltage is generated from the feedback capacitors C1 and C2 connected to the power supply side coil in accordance with the induced electromotive force of the power supply side coil and the power reception side coil, and the FET Q1, Since power is supplied to the power receiving side while Q2 is turned on and off alternately and a self-excited push-pull operation is performed, the winding of the coil around the core can be simplified by eliminating the need for the detection coil.

Further, in the present embodiment, a ceramic capacitor having a low withstand voltage can be used as the feedback capacitor, so that the manufacturing cost can be reduced as compared with the conventional example. Further, in the conventional example, if the polarity of the detection coil and the polarity of the power supply side coil are not correctly connected, the voltage induced in the detection coil is reversed, and if the transistor Q1 is turned on and the transistor Q2 is turned off, the transistor Q1 is turned off. off,
A voltage is applied to each base in the direction of turning on Q2, and the on / off of the transistors Q1 and Q2 is reversed without waiting for a half cycle of resonance. Therefore, transistors Q1, Q2
Oscillation due to is not caused. Furthermore, in this circuit,
Normally, the input power supply is connected to the base of the transistor via the starting resistor, and the voltage is supplied to the transistor only at the time of starting, but if the oscillation does not occur as described above,
The voltage remains applied to the bases of both transistors Q1, Q2, and both transistors Q1, Q2 are simultaneously turned on. For this reason, a voltage is applied between the collector and the emitter of both transistors Q1 and Q2 while maintaining a low resistance, and a large current flows to destroy the transistors.

For this reason, in the conventional example, if the polarity of the power supply side coil or the detection coil is incorrectly connected at the time of manufacturing, for example, there is a problem that oscillation does not occur and the transistor is destroyed. On the other hand, in the circuit configuration of the present invention, an AC voltage is generated from the feedback capacitor to change the AC frequency of the power supplied to the power supply side coil. Can be operated.

In this embodiment, the FETs Q1 and Q2 are alternately turned on and off, and the oscillation cycle is determined by L1, L2, C1 and C2. If the gap widens, L1, L2, L
3, the mutual inductance of L4 becomes smaller, the oscillation cycle becomes faster, and the power supply is stabilized. In addition, since the oscillation cycle changes in response to a load change, stable power can be supplied to the load.

FIG. 3 shows the FE in the above circuit.
Gate-source voltage VGS and drain current IDS of TQ1
And measured waveforms of the drain-source voltage VDS. In the figure, the voltages VGS and VDS are not perfect sine waves but are distorted. This is because the input capacitance of the FET (the sum of the capacitance CGS between the gate and the source and the capacitance CGD between the gate and the drain) is large, so that it takes a long time to charge and discharge at the time of switching. Further, the gate voltage is AC-coupled by the feedback capacitor C1 and the input capacitance of the FET, so that when the gate voltage is off, the gate voltage drops to a negative value.

In the voltage VDS and the current IDS shown in FIG. 3, a switching loss occurs in a region of S1 and S2 where their waveforms intersect, and the FET may generate heat. Due to this loss, the transmission efficiency of the circuit is reduced, and it is necessary to attach a large radiator plate to the FETs Q1 and Q2 in order to remove heat, and the circuit configuration becomes large. Therefore, in the present invention, as shown in the second embodiment of FIG.
The diodes D1 and D2 are connected to the ground between each gate G and the source S to reduce the switching loss. In addition,
Here, the operation when the FET is turned on and off is represented by F
This will be described with reference to the actually measured waveform diagram of FIG. 5 taking ETQ1 as an example. In FIG. 5, Tc is the charging time of the input capacitance of the FET Q1, Td is the discharging time of the input capacitance, and Ton is the FE
The ON time of TQ1 and Toff similarly indicate the OFF time of FET Q1.

The electric charge charged in the gate-source capacitance CGS during the Ton period of the FET Q1 is equal to Ton during turn-off.
It is immediately discharged by the diode D1 during the period. For this reason, the Td time is shorter than that in FIG.
The ff time becomes longer. As a result, the area of the S1 region where the waveforms of the voltage VDS and the current IDS intersect was reduced, and the switching loss was reduced.

At the end of the Toff period and when turning on, it is necessary to charge the input capacitance of the FET. In the case of FIG. 3, the gate-source voltage VGS of the FET Q1 must rise from a negative value to turn on the gate. For this reason, it takes time to reach the gate-on voltage, and F
The charging time Tc of the input capacity of the ET also becomes longer. Therefore, in the case of the second embodiment shown in FIG. 4, as described above at the time of turn-off, the charge charged in the gate-source capacitance CGS by the diode D1 is immediately discharged, so that To
During the ff period, the gate-source voltage VGS is stabilized at the level of 0V. Therefore, at the time of turn-on, the FE
Time Tc to reach voltage VGS for turning on TQ1
Starts from the 0 V level, and is therefore shorter than when there is no diode D1. As a result, the voltage VDS and the current I
The area of the S2 region where the DS waveform intersects is reduced, and the switching loss is reduced.

In this embodiment, the FET Q1 has been described as an example. At this time, the switching loss of the FET Q2 is similarly reduced by the diode D2. As described above, in the present embodiment, the voltage VDS and the current IDS intersect with each other.
1, the switching loss is reduced in the region of S2, the heat generation of the FET is suppressed, and the temperature rise due to the above-mentioned heat generation was about 20 ° C., but in the present embodiment, it was reduced to about 10 ° C., so the transmission efficiency of the circuit was reduced. And the size of the heat sink can be reduced, and the size of the circuit can be reduced.

The present invention can also be used in a power supply circuit of a DC-DC converter of a self-excited sine wave push-pull circuit type, for example, as shown in a third embodiment of FIG. The difference between the circuit of the present embodiment and the first embodiment is that no capacitors are connected in parallel to the secondary side coils L4 and L5. In the case of the present embodiment, similarly to the case of the first embodiment, the primary-side FETs Q1, Q2
Are alternately turned on and off to maintain oscillation and supply power to the secondary side.

Further, the present invention can be used for a driving circuit of a lighting fixture such as a fluorescent lamp 30 as shown in a fourth embodiment of FIG. 7, for example. In the case of the present embodiment, an AC voltage is supplied to the secondary coil L4 by electromagnetic induction of the primary coils L2 and L3, and a voltage is applied between the two poles of the fluorescent lamp 30 to discharge the fluorescent lamp 30. Can begin.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention.

[0032]

As described above, according to the present invention, an AC voltage corresponding to the induced electromotive force of the power supply side coil and the power receiving side coil is generated by using the feedback capacitor, and the transistor is turned on and off alternately. Since power is supplied to the power receiving side,
Since the detection coil is not required, the winding of the coil around the core can be simplified.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of a first embodiment of a power supply device according to the present invention.

FIG. 2 is a waveform chart showing waveforms in main parts of the circuit shown in FIG.

FIG. 3 is a waveform diagram showing measured waveforms of a gate-source voltage VGS, a drain current IDS, and a drain-source voltage VDS of the FET Q1 in the circuit.

FIG. 4 is a circuit diagram showing a circuit configuration of a second embodiment of the power supply device according to the present invention.

5 is a waveform diagram showing measured waveforms of a gate-source voltage VGS, a drain current IDS, and a drain-source voltage VDS of the FET Q1 in the circuit shown in FIG.

FIG. 6 is a circuit diagram showing a circuit configuration of a third embodiment of the power supply device according to the present invention.

FIG. 7 is a circuit diagram illustrating a circuit configuration according to a fourth embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 power supply unit 11 power supply side resonance circuit 12 conversion circuit 20 power reception unit 21 power reception side resonance circuit 22 rectifier circuit 23 smoothing circuit 30 fluorescent lamp L2, L3 supply side coil L4, L5 power reception side coil C1, C2 feedback capacitor C3, C4 resonance Capacitor Q1, Q2 FET

Continued on the front page F term (reference) 5H007 BB03 CA02 CB06 CB09 CC32 DB03 GA01 5H730 AS11 BB35 BB61 DD04 DD13 DD22 FD24 XC01

Claims (2)

[Claims] 1. A power supply device, comprising: a resonance circuit including a power supply side coil and a capacitor; and a power reception side coil, wherein power is supplied from the power supply side coil to the power reception side coil by electromagnetic induction. First and second capacitors connected to both ends for generating an AC voltage according to the induced electromotive force of the power supply side coil and the power receiving side coil; and supplied to the power supply side coil according to the generated AC voltage. A power supply device comprising: a changing unit configured to change an AC frequency of electric power. 2. The first and second changing means are supplied with an AC voltage from the first and second capacitors and resonate with a capacitor of the resonance circuit to alternately supply a current to the power supply side coil. The power supply device according to claim 1, further comprising: