JP2546098Y2 - Charging circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a charging circuit suitable for a cordless telephone handset, for example.

[0002]

2. Description of the Related Art A cordless telephone handset generally has a built-in rechargeable battery such as a nickel-cadmium battery (hereinafter simply referred to as a "rechargeable battery") to which charging power is supplied from a charging stand. Has become. In FIG.
A conventional example of such a cordless telephone handset is shown. In the figure, a charging circuit 12 and
Other communication circuits 14 are provided, and the communication circuit 14 is mainly configured by a control microcomputer 16. The communication circuit 14 includes a modem, a dial circuit, and the like for communicating with the master unit (not shown).

On the other hand, the charging stand 18 is provided with a charging power supply circuit 20 connected to a commercial power supply, and supplies power to the charging circuit 12 of the slave unit 10 via charger contacts 22A, 22B, 22C, 22D. Is supplied.

The charger contact 22A is connected to a resistor R
1, a diode D1 and a switch S are connected to the input side of the communication circuit 14. The charger contact 22B is connected to the ground on one side, and is connected to the input side of the microcomputer 16 via the resistor R2 on the other side. The anode side of the diode D1 is connected to the cathode side of the Zener diode D2 and the microcomputer side of the resistor R2.
Further, between the cathode side of the diode D1 and the ground,
Rechargeable battery B is connected.

Next, the operation of the conventional charging circuit 12 will be described. When handset 10 is placed on charging stand 18, charger contacts 22A, 22B, 22
When C and 22D come into contact with each other, a voltage is applied from the charging power supply circuit 20 to the charging circuit 12 of the child device 10, and power is supplied. This voltage is connected to a resistor R1, a diode D1
Are applied to the rechargeable battery B via each of them, and the charging is performed. The power of the rechargeable battery B is supplied to the communication circuit 14 via the switch S which is normally turned on. Note that the zener diode D2 is provided to limit an excessive voltage from being applied to the communication circuit 14 when the rechargeable battery B is removed.

In this case, the charging current for the rechargeable battery B is set to 0.1 to 0.2 C by selecting the value of the resistor R1 in order to prevent damage due to overcharging.
(C is the capacity of the battery and is represented by Ah).

Note that the resistance R2 is determined by
This is for detecting whether or not it is placed above and informing the microcomputer 16. For example, when there is an incoming call and the bell is ringing, handset 10 is
8, the fact is notified to the microcomputer 16 via the resistor R 2, and the off-hook control processing is performed by the communication circuit 14.

At the end of the call, the slave unit 10 is
When it is placed on the upper side, the fact is notified to the microcomputer 16 via the resistor R2, and the control processing of the on-hook is performed in the communication circuit 14. The switch S is, for example, a switch that is turned off at the time of shipment from a factory and turned on when the user uses the switch. As described above, conventionally, the rechargeable battery B of the child device 10 is charged on the charging stand 18.

[0009]

However, as the life of the rechargeable battery B approaches, even if the battery is fully charged, the talk time becomes insufficient and the battery runs out during the call. When the life of the rechargeable battery B has expired, it is necessary to replace it.
If a spare rechargeable battery is not prepared, the child device 10 cannot be used.

On the other hand, recently, the communication circuit 14
Cordless telephones provided with a direct power supply jack for directly supplying power to a telephone. The present invention pays attention to these points, and an object of the present invention is to provide a charging circuit capable of favorably performing direct power supply by a direct power supply jack and charging a rechargeable battery.

[0011]

SUMMARY OF THE INVENTION The present invention provides a dedicated charger for charging a rechargeable battery that supplies power to a circuit to be supplied, and directly supplies power to the circuit to be supplied from an external adapter. A charging circuit having a direct power feeding jack for obtaining a charging output based on an input of the direct power feeding jack in consideration of a charging voltage when the rechargeable battery is fully charged. A filter for absorbing input fluctuation of a direct power supply jack and outputting the fluctuation to the supply target circuit is provided. According to a main aspect of the present invention, there is provided switching means for connecting only one of the external adapter and the dedicated charger to the power supply circuit.

[0012]

According to the present invention, the input of the direct power supply jack is
On the other hand, while power is supplied directly to the supply target circuit,
On the other hand, it is also supplied to the rechargeable battery. At this time, a charging voltage in consideration of the charging voltage when the rechargeable battery is fully charged is output from the power supply circuit to the rechargeable battery, and charging is rapidly performed while preventing overcharging. In addition, since the ripple component of the direct power supply jack input is absorbed by the filter, high-quality power is supplied to the supply target circuit even when there is no rechargeable battery.

Further, according to the main aspect of the present invention, in order to prevent the external adapter and the dedicated charger from being connected at the same time and the power supply circuit from being damaged, either one of the adapters is connected. Switching is performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the charging circuit according to the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals are used for components that are the same as or correspond to those in the above-described conventional example. <First embodiment>

First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a charging circuit 32 of the slave unit 30 according to the first embodiment. In the figure, a charger contact 22A is connected to a resistor R1.
Is connected to the anode side of the diode D3. The anode side of the diode D3 is connected on one side to the resistor R3, and is connected on the other side to the microcomputer 16 side of the resistor R2.

Further, the cathode side of the diode D3 is directly connected to one terminal 34A of the power feeding jack 34 and the collector of the NPN transistor Q. The cathode side is also connected to the base of the transistor Q via the resistors R4 and R5. The other terminal 34B of the direct power feeding jack 34 is connected to the ground.

A Zener diode D4 is connected between the connection point of the resistors R4 and R5 and the ground, and the base of the transistor Q is connected to the ground via a capacitor C. The emitter of the transistor Q is connected on one side to one end of the switch S, and on the other side to the positive side of the rechargeable battery B. The rest of the configuration and the charging stand 18 are the same as in the above-described conventional example.

Next, the overall operation of this embodiment will be described with reference to FIG. When charging rechargeable battery B on charging stand 18 In this case, the elements shown in FIG. 2A mainly operate. The voltage applied to the charge contact 22A from the charging power supply circuit 20 of the charging stand 18 (see FIG. 4) is supplied to the base of the transistor Q via the resistors R1 and R3, so that the transistor Q conducts (see FIG. 4). 2 (A) See arrow FA). Accordingly, the rechargeable battery B is charged via R1 → D3 → Q collector → emitter (see arrow FB).

Note that the charging current at this time is also determined by the resistor R1 although it is affected by the _{hfe of} the transistor Q and the resistor R3. Therefore, by appropriately setting the value of the resistor R1, the charging current can be limited to a desired value.

In the state where the rechargeable battery B is present,
When power is supplied by the jack 34, the direct power supply jack 34 is connected to an AC adapter (not shown) for obtaining a required DC voltage from a commercial power supply. In this case, the element shown in FIG.

[0021] the base of the transistor Q, the voltage V _Z which is limited by the Zener diode D4 is applied via a resistor R5 (Fig. 2 (B) refer to arrow FC). As a result, the transistor Q conducts and the direct power supply jack 34
The rechargeable battery B is charged by the AC adapter connected to the power supply (see arrow FD), and power is supplied to the communication circuit 14 (see arrow FE).

In this operation, the transistor Q
The emitter voltage V _e, the base-emitter voltage _V be
When, a _{V e = V Z -V be V} Z = V e + V be ................................................... (1). Assuming that V _be = 0.6 V, the emitter of the transistor Q does not exceed V _e = V _Z -0.6 V. Thus, in the present embodiment, a value obtained by adding 0.6 V to the voltage (corresponding to V _e ) when the rechargeable battery B is fully charged is set as V _Z. Therefore, the rechargeable battery B can be rapidly charged while preventing overcharging.

In the absence of the rechargeable battery B, the power supply
When power is supplied by the jack 34, the basic operation in this case is the same as that described above. However, the effect of absorbing the ripple current contained in the output of the AC adapter by the rechargeable battery B cannot be expected. For this reason, a ripple filter circuit is formed by the resistor R5, the capacitor C, and the transistor Q, whereby the amount of ripple in the power supplied to the communication circuit 14 indicated by the arrow FE is reduced favorably.

Next, a specific example of setting the circuit constants of the main part will be described. Conditions for Power Reduction in Direct Power Supply For example, an AC adapter having relatively low impedance is connected to the direct power supply jack 34. Therefore, when the rechargeable battery B is completely discharged, a considerably large current may flow as a charging current.

As described above, in order to supply power to the rechargeable battery B or the communication circuit 14, it is necessary to make the transistor Q conductive. For this purpose, the voltage supplied directly to the power supply jack 34 is, for example, -10
It is necessary to set the resistor R4 and the zener diode D4 so that a sufficient base current can be supplied to the transistor Q even when the power is at the lowest value of%.

Here, if the rating of the rechargeable battery B is 600 m
Assuming that Ah is 3.6V, about 4.1 at full charge.
It becomes 4.2V. Therefore, the base of transistor Q
Assuming that the emitter-to-emitter voltage V _be = 0.6 V, from the equation (1), V _Z = (4.1 to 4.2) + 0.6 = 4.7 to 4.8 V (2)

The output of the AC adapter is 9 V, 100 mA
In general, at the time of -10% power reduction, 10
The output voltage is about 8 V with a 0 mA load. From now on V
_{If Z} is subtracted, a voltage of about 3 V remains at both ends of the resistor R4.

On the other hand, the h _fe of the transistor Q is set to 100 to 3
00 and then, as to ensure the charging current of 0.1 C = 60 mA even at reduced voltage, when obtaining the base current _{I B, I B = 0.1C /} h femin = 60/100 = 0.6mA ......... (3) That is, the voltage across the resistor R4 is about 3 V, and the current is 0.6 mA. Therefore, its value is: R4 _MAX = 3 / 0.6 = 5KΩ ... (4), and R4 cannot be made larger than 5 KΩ.

On the other hand, in the case of overpower of + 10% of the normal case, the AC adapter is connected directly to the power supply jack 34 with the switch S OFF and the rechargeable battery B not set. , A current flows as shown by an arrow FF in FIG.
The power consumption of the Zener diode D4 is determined by the value of the resistor R4. _Assuming that the maximum allowable power of the Zener diode D4 is 100 mW, since V _Z = 4.7 V, the current is I _ZMAX = 100 / 4.7 = 20 mA... (5). This current will flow through the resistor R4. Therefore, assuming that the voltage of the AC adapter at the time of overload and no load is about 12 V, R4 _MIN = (12−4.7) / 20 = 365Ω ............ (6)

Therefore, the resistor R4 needs to be set in a range of about 400Ω to 5KΩ. However, R4 = 400
When Ω, h _fe = 300, the maximum value I _C of the charging current indicated by the arrow FD in FIG.
Therefore, I _C = I _B · h _fe = {(9−V _Z ) / 400} · 300 = {(9−0.6) / 400} · 300 = 6.3A... ………… (7)

Therefore, in this embodiment, a resistor R5 is inserted to limit the charging current. However, R4 +
R5 <5KΩ must be satisfied. R4 + R5 = 2.7K
If Ω, I _C = {(9−0.6) / 2700} · 300 ≒ 0.9A (8), and the charging current is 1.5 C or less even in the worst condition, so that there is no fear of damaging the rechargeable battery B. Further, when a current of 0.9 A is actually taken out from the AC adapter, the voltage drops, so that there is no more worry in practical use.

As described above, according to the present embodiment, the power supply circuit from the direct power supply jack 34 considers the rechargeable battery voltage at full charge, the presence / absence of a load, the presence / absence of a rechargeable battery, and the power fluctuation on the AC adapter side. Therefore, power supply by the direct power supply jack 34 is performed favorably.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same reference numerals are used for components similar or corresponding to those in the first embodiment. In the above-described first embodiment, it is assumed that the slave unit 30 is further returned to the charging stand 18 (see FIG. 4) in a direct power supply state, that is, in a state where the plug of the external adapter is inserted into the direct power supply jack 34.

Then, the charging power supply circuit 2 of the charging stand 18
0 is connected to the charging circuit 42 via the charger contacts 22A to 22D. For this reason, the charging voltage is applied to the charger contacts 22A and 22B, and the transistor Q is completely turned on. Therefore, there is a possibility that an excessive current flows through the transistor Q and the transistor Q is destroyed. The present embodiment is improved so as not to cause such inconvenience. The direct power supply jack 34 and the charger contacts 22A and 22B are distinguished from each other and can be switched.

FIG. 3 shows a charging circuit 42 of a slave 40 according to the second embodiment. In the figure, a charger contact 22A is connected to the anode side of a diode D3 via a resistor R1, as in the previous embodiment.
The cathode side of the diode D3 is
Is connected to one terminal 44A and the collector of an NPN transistor Q. The other terminal 44B of the direct power feeding jack 44 is connected to the resistor R2 and the ground.

Further, the direct power supply jack 44 is further provided with another terminal 44C, which constitutes a switch together with the terminal 44B. That is, when a plug (not shown) is not directly inserted into the power feeding jack 44, the terminals 44B and 44C are connected and turned on,
When inserted, terminals 44B and 44C are separated and OF
It becomes F. The terminal 44C is connected to the charger contact 2
2B. In addition, other configurations and the charging stand 1
8 is the same as in the above embodiment.

Next, the operation of the second embodiment configured as described above will be described.
When charging is performed using the charging stand 18 without using the power supply, the terminals 44B and 44C of the direct power feeding jack 44 are turned ON. For this reason, the charger contact 22B is connected to the ground side of the charging circuit 42, and the charging power supply circuit 20 of the charging stand 18 is connected to the charging circuit 42 to enable charging.

On the other hand, when direct power is supplied by the direct power supply jack 44, a plug of an AC adapter (not shown) is inserted into the direct power supply jack 44. Therefore, terminal 4
4C is separated from the terminal 44B and the charger contact 2
2B is in a state in which nothing is electrically connected. Therefore,
Even if child device 40 is placed on charging stand 18 in this state, charging power supply circuit 20 is not connected to charging circuit 42.

As described above, according to the present embodiment, a jack with a switch is used as the direct power supply jack 44, and one of the charger contacts is connected to the switch portion. For this reason, either charging by the charging stand 18 or charging by the direct power supply jack 44 is switched and performed, and both are not performed simultaneously. Therefore, destruction of the transistor Q of the charging circuit 42 due to simultaneous charging is favorably prevented.

The present invention is not limited to the above embodiment, but includes, for example, the following. (1) The circuit configuration and each numerical value shown in the above-described embodiment are examples, and may be appropriately set so as to achieve the same operation. (2) The above embodiment is an example in which the present invention is applied to a cordless telephone handset, but does not prevent application to other devices having a rechargeable battery.

[0041]

As described above, the charging circuit according to the present invention has the following effects. (1) Based on the input of the direct power supply jack, a charge output considering the charge voltage at the time of full charge of the rechargeable battery is obtained, and this is supplied to the rechargeable battery. It can be carried out.

(2) Since the input fluctuation of the power supply jack is directly absorbed by the filter, high-quality power supply can be performed to the supply target even when there is no rechargeable battery. (3) Since the charging by the direct power supply and the charging by the charger are automatically switched and only one of them is performed, the destruction of the charging circuit is prevented well.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing the operation of the embodiment.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating an example of a conventional charging circuit.

[Explanation of symbols]

14: communication circuit (supplied circuit), 16: microcomputer, 18: charging stand (dedicated charger), 20: charging power supply circuit, 22A to 22D: charger contact, 30, 40: slave unit, 32, 42 ... Charging circuit, 34 ...
Direct power supply jack, 44: direct power supply jack (switching means), B: rechargeable battery, C: capacitor (power supply circuit, filter), D3: diode, D4: zener diode (power supply circuit), Q: NPN transistor (power supply circuit) , Filters), R1, R2 ... resistors, R3, R4 ... resistors (feeding circuit), R5 ... resistors (feeding circuit, filter), S ... switches, FA to FF ... arrows indicating power feeding.

Claims (2)

(57) [Scope of request for utility model registration] 1. A dedicated charger for charging a rechargeable battery that supplies power to a supply target circuit, and a direct power supply jack for directly supplying power to the supply target circuit from an external adapter. The charging circuit includes a power supply circuit for obtaining a charging output in consideration of a charging voltage when the rechargeable battery is fully charged based on an input of the direct power supply jack, and the power supply circuit absorbs an input fluctuation of the direct power supply jack. And a filter for outputting to the supply target circuit. 2. The charging circuit according to claim 1, further comprising switching means for connecting only one of the external adapter and the dedicated charger to the power supply circuit.