JPH08103028A - Non-contact charger - Google Patents

Abstract

(57) [Summary] [Purpose] Minimize heat generation and enable downsizing design. [Structure] When the device to be charged 5 is placed on the charging stand 1, a magnetic field is emitted from the coil 4 of the charging stand 1 and the coil L1 of the device to be charged 5
Then, the magnetic flux is received, and the circuit of the transistor Q2 is operated at a constant current to charge the secondary battery E. At the time of rapid charging, the transistor Q1 is turned on and resonates with the oscillation frequency from the charging stand 1. During trickle charging (a mode in which a minute current is passed through the battery E), L1 resonance is obtained by the capacitor C4 and the impedance of the diode D2 for flowing in the opposite direction between the V _{CE of the} transistor Q1 and the emitter / collector of Q1 and the capacitor C3. , Suppresses power consumption and heat generation of the transistor Q1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contactless charger for charging a device having a secondary battery or the like from a charging stand.

[0002]

2. Description of the Related Art FIG. 3 shows the structure of a conventional contactless charger. In FIG. 3, 1 is a charging stand, 2 is a rectifying circuit composed of a rectifying diode bridge, 3 is an oscillation circuit for electromagnetic induction, and 4 is a coil for supplying electromagnetic induction. 5
Is a charger, E is a secondary battery (nickel battery), L
Reference numeral 1 is an electromagnetic induction receiving coil, C2 is a resonance capacitor, Q1 is a transistor for varying the impedance, D2 is a diode for flowing a reverse current between the emitter and collector of the transistor Q1, and D1 is a rectifying diode. C1 is a smoothing capacitor, R1 is a bias resistor of the transistor Q1, Q2 is a constant current transistor, and 6 is a charge control CPU, which controls to switch the charging current of the secondary battery E between quick charging and trickle charging. . Q3 and Q4 are transistors which are turned on / off by a control signal of the CPU 6.

Next, the operation of the above conventional example will be described.
In FIG. 3, when the device to be charged 5 is placed on the charging stand 1, 2
When the secondary battery E is not charged, the CPU 6 outputs the charge control signal a of "L", the transistor Q4 is turned on, the transistor Q3 is also turned on, and the constant current circuit is
When the resistance R3 << R2, V _c ≉V _BE , and the rapid charging current I ₁ ≉V _BE / R3 // R4 is controlled so that the current flows from the collector of the transistor Q2 through the resistor R1 and the transistor Q2. The V _{BE of} Q1 is controlled, and the transistor Q1 operates so that I ₁ can flow. Here, when the oscillation frequency of the charging stand 1 is f ₀ , the values of the coil L1 and the capacitor C1 of the charger are f≈1 / 2
Resonance is set at π√ (L1 · C2) (L1
It is assumed that the internal resistance R _S is small). FIG. 4A is an equivalent circuit at the time of this rapid charging, and since a large amount of current flows to the secondary battery E at the time of rapid charging, the transistor Q1 is almost in the ON state. Therefore, the power consumption of the device to be charged 5 at the time of rapid charging is as follows.

[0004]

[Equation 1]

Next, when the secondary battery E is fully charged and trickle charging for compensating for self-discharge, the charge control signal a from the CPU 6 becomes "H", the transistor Q4 is turned off, and the transistor Q3 is also turned off. The trickle charge current I ₂ ≈V _BE / R3 is charged in the secondary battery E. At this time, the transistor Q1 is designed so that constant power is supplied from the charging stand 1 when I ₁ >> I ₂ and output power can be obtained during quick charging, as can be seen from FIG. 4B. Unnecessary power during trickle charging is consumed by the transistor Q1. Therefore, the power consumption of the device to be charged 5 during trickle charging is as follows.

[0006]

[Equation 2]

FIG. 5 is an equivalent circuit relating to resonance, in which a magnetic flux is generated from the coil 4 of the charging stand 1 and the energy stored in the coil L1 of the charger 5 is represented by (1/2) LI ² . The flowing current is as follows.

[0008]

(Equation 3) Maximum current when ωL = 1 / ωC

[0009]

[Equation 4] Flows,

[0010]

(Equation 5) The voltage of can be taken out.

When the resonance point shifts to f ₁ ,

[0012]

(Equation 6) Is applied to V _C , and the output voltage decreases as compared with f ₀ at the time of resonance.

FIG. 6 shows the voltage levels that can be taken out from the charging stand 1 by the device to be charged 5. When the resonance frequency of the to-be-charged device 5 matches the oscillation frequency of the charging stand 1, the maximum voltage V
_C (f ₀ ) is obtained, but f _{0 of the} device to be charged is shifted and f _{1 is changed.}
In case of, only the voltage shown in (Equation 6) can be obtained.

[0014]

However, in the above-mentioned conventional non-contact charger, when the trickle is charged, as shown in FIG.
As can be seen from the above, unnecessary power is consumed in the transistor Q1.

[0015]

(Equation 7) Heat generation (I _C × V _CE + V _F · I _F ) occurs, and especially in the case of a small charged device, the case becomes hot and a transistor with a large power is required, which requires a large mounting area, There is a problem that it hinders the miniaturization design of the charger.

[0016] The present invention solves such a conventional problem, and an object thereof is to provide an excellent non-contact charger which is miniaturized and suppresses heat generation as much as possible.

[0017]

In order to achieve the above-mentioned object, the present invention divides a resonance capacitor into two, one is connected to both ends of an electromagnetic induction receiving coil, and the other is an impedance. A control capacitor is connected in series with a transistor, and both ends thereof are similarly connected to both ends of an electromagnetic induction receiving coil.

[0018]

Therefore, according to the present invention, by connecting the capacitor for impedance control to both ends of the coil for electromagnetic induction reception of the device to be charged, it is possible to reduce the alternating current flowing through the capacitor for resonance during trickle charging. Further, it is possible to suppress the heat generation of the device to be charged and further enable the downsizing design.

[0019]

FIG. 1 shows the configuration of an embodiment of the present invention, the charging stand 1 is the same as the conventional example shown in FIG. 3, and in the charged object 5, the capacitor C3 is connected to the coil L1. It is similar to the circuit of FIG. 3 except that it is connected in parallel. With this change, the condenser C2 in FIG. 3 is shown as C4 in FIG.

Next, the operation of the above embodiment will be described. Since the values of the capacitors C4 and C3 resonate with the oscillation frequency of the charging stand, f ₀ ≈1 / 2π√ {(L1 × (C4
+ C3)} is satisfied, and the basic operation is the same as the conventional example.

At the time of rapid charging, the transistor Q1 is turned on, V _CE becomes V _{CE (SAT)} , the equivalent circuit of FIG. 2 (a) is obtained, and the rapid charging current I ₁ is charged to the secondary battery E. It The power consumption is only the heat generation corresponding to the internal resistance R _S of the coil L1 as in the conventional example.

Next, during trickle charging, as shown in FIG.

[0023]

(Equation 8) Is consumed by the transistor Q1.

Here, the current passing through the capacitor C4,

[0025]

[Outside 1] In FIG. 4 (b) of the conventional example,

[0026]

[Outside 2] If the value of the condenser C4 is determined to be 1/2 of

[0027]

[Equation 9] , And the power consumption of the impedance control transistor Q1, the impedance of the V _CE is,

[0028]

[Outside 3] Assuming the same in

[0029]

[Equation 10] Therefore, it can be suppressed to 1/4 of the conventional example.

In the above embodiment, a field effect transistor FET is used instead of the transistor Q1 to obtain the same effect. Also condensers C4, C3
An optimal circuit considering the temperature rise can be realized by determining the optimal value of the capacity of the device according to the charging specifications of the device to be charged.

[0031]

As is apparent from the above embodiment, the present invention divides the resonance capacitor into two, one is connected to both ends of the electromagnetic induction receiving coil, and the other is an impedance control capacitor. As it is connected in series to the transistor and both ends are connected to both ends of the electromagnetic induction receiving coil in the same way, it is possible to suppress the heat generation of the transistor during trickle charging without changing the resonance frequency, and a compact design Has the effect of enabling

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of a non-contact charger according to an embodiment of the present invention.

FIG. 2A is an equivalent circuit diagram during rapid charging in the embodiment. FIG. 2B is an equivalent circuit diagram during trickle charging in the embodiment.

FIG. 3 is a circuit diagram of a main part of a non-contact charger in a conventional example.

FIG. 4A is an equivalent circuit diagram during rapid charging in the conventional example. FIG. 4B is an equivalent circuit diagram during trickle charging in the conventional example.

FIG. 5 is a resonance equivalent circuit diagram in a conventional example.

FIG. 6 is a voltage level characteristic diagram in a conventional example.

[Explanation of symbols]

 1 Charging stand 2 Rectifier circuit 3 Oscillation circuit 4 Electromagnetic induction supply coil 5 Charged device 6 CPU for controlling secondary battery charging current L1 Electromagnetic induction receiving coil C4 First capacitor C3 Second capacitor Q1 Impedance variable circuit Transistor Q2 Constant current circuit transistor E Rechargeable battery (NiCd battery)

Claims (2)

[Claims] 1. A charging stand for charging is provided with a rectifying circuit, an oscillation circuit for electromagnetic induction, and a coil for supplying power, and a charged device is resonant with an electromagnetic induction receiving coil and an oscillation frequency of the charging stand. A first capacitor and a second capacitor for connecting a variable impedance circuit using a transistor to the first capacitor in series, and controlling the variable impedance circuit to a constant current circuit for charging a secondary battery. And a non-contact charger in which the second capacitor is connected to both ends of the electromagnetic induction receiving coil. 2. The value of the first and second capacitors is C
4, C3, the value of the coil for electromagnetic induction power reception is L1, and the oscillation frequency of the charging stand is f ₀ , C4, C3
The contactless charger according to claim 1, wherein the value of is set to f ₀ ≅1 / 2π√ {L1 × (C4 + C3)}.