JPH04145842A - Constant-current charging circuit for battery - Google Patents

Abstract

PURPOSE:To eliminate the need of a current limiting resistance having an excessive allowable power value from the title circuit so as to make the constitution of the circuit simpler by supplying an electric current to a battery by means of a current supplying means through the second switching element. CONSTITUTION:When a charging signal is raised to a high level by means of a command from a CPU, etc., transistors Tr10 and Tr20 are turned on. When the transistor Tr20 is turned on, a charging current ICHARGE starts to flow between the collector and emitter of a transistor Tr30, since a voltage difference is produced between the collector voltage of the transistor Tr20 and the positive pole of a battery. When the electric current flows through a resistance R50, a voltage VR50 is generated and, when the voltage VR50 exceeds the saturated voltage VBE40sat across the base and emitter of a transistor Tr40, the transistor Tr40 is turned on. The value of the resistance R50 is set so that the transistor Tr40 can be turned on when an electric current larger than the necessary charging current ICHARGE flows through the resistance R50.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a battery constant current charging circuit for charging a battery in, for example, a portable type serial printer that can be driven by a battery.

(Prior Art) Today, portable type printers that can be driven by batteries are used as serial printers such as inkjet printers and thermal printers.

Batteries used in such printers include rechargeable N1-CD batteries, and a charging circuit for the batteries is built into the printer.

As a charging circuit built into such a printer, a quasi-constant current charging circuit is used due to cost constraints and the like.

FIG. 2 shows a quasi-constant current charging circuit for a battery in such a serial printer.

In the figure, a charging signal input terminal l connected to an output terminal of a CPU (not shown) is connected to the base of a drive NPN transistor Trl via a resistor R1. Further, the resistor R1 is provided to ensure the base current necessary to drive the transistor Trl.

The emitter of the transistor Tri is grounded, and the collector is connected to the base of the PNP transistor Tr2 via a resistor R2. This transistor Tr2 is a transistor for taking out the battery charging current ■cHARGE, and the power supply voltage Vcc is applied to its emitter.
A resistor R3 is connected between the emitter and the base. Note that the resistor R2°R3 is a bias resistor of the transistor Tr2.

The collector of the transistor Tr2 is connected to the positive terminal of the battery 2 to be charged via a resistor R4 for limiting battery charging current and a diode D1 connected in the forward direction. Further, the negative terminal of the battery 2 is grounded. Note that the diode D1 is a diode for protecting discharge current from the battery 2 (preventing backflow).

Next, the operation of the charging circuit having the above configuration will be explained.

FIG. 3 is a timing chart showing the charging operation.

To explain the charging operation using the timing chart of FIG. 3, first, when the charging signal shown in FIG. 3(a) becomes high level by a command from the CPU (not shown), the transistor Tri is turned on (see FIG. 3(a)). b)).

As a result, the base current from Tr2 sinks, and the transistor Tr2 is turned on (FIG. 3(C)).

When the transistor Tr2 turns on, the battery charging current ICIIAIIGE flows to the battery 2 via the resistor R3 and the diode D1 (Fig. 3(d)).
).

The charging current I CHARGE at this time is expressed by the following equation.

I c++ARat□ (VCC-VCE2-VF-V
BAT) / R4-(1) VCC: Power supply voltage Vcg2: t' Collector-emitter saturation voltage of transistor Tr2 VF: Forward voltage of diode D1 VBAT: Voltage across the battery R4: Resistance value of resistor R4, that is, voltage of battery 2 Charging current I CHARGE is resistance R
It will flow through 4.

(Problems to be Solved by the Invention) However, if the battery 2 becomes unusable due to, for example, its lifespan or over-discharge, the situation may be similar to that in which both ends of the battery 2 are short-circuited.

When such a situation occurs, in the conventional charging circuit described above, I CHARGE becomes extremely large, as is clear from the fact that VBAT=O in equation (1).

As a result, the current limiting resistor R4 will generate abnormal heat.

Therefore, in the above charging circuit, the resistor R4 has a sufficiently large allowable power value, and is configured to cope with abnormal current.

However, the use of the resistor R4 with such a large allowable power value increases costs and requires a large mounting area, which hinders cost reduction and miniaturization.

(Means for Solving the Problem) The battery constant current charging circuit of the first invention has a first battery that becomes conductive when a current of a predetermined value or more flows through a connected battery.
a switching element, a second switching element that becomes non-conductive due to conduction of the first switching element, and current supply means for supplying current to the battery via the second switching element. be.

The battery constant current charging circuit of the second invention is provided with a monitoring circuit that determines that the battery is disconnected when the first switching element is non-conductive for a predetermined period of time or more. It is.

(Function) In the battery constant current forward circuit of the present invention, the current supply means supplies current to the battery via the second switching element. When a current of a predetermined value or more flows through the battery, the first switching element becomes conductive, and this conduction causes the second switching element to become non-conductive.

Therefore, when a current exceeding a predetermined value flows through the battery, the second switching element becomes non-conductive, thereby stopping the current supply to the battery.

Further, when the current supply to the battery is stopped, the first switching element becomes non-conductive and the second switching element becomes conductive.

By repeating such operations, the battery charging current is maintained at a constant value.

Therefore, a current exceeding a predetermined value does not flow through the current limiting resistor to the battery, and its allowable power value can be small.

Further, when a monitoring circuit is added, if the first switching element is non-conductive for a predetermined period of time or more, the monitoring circuit determines that the battery is disconnected.

Therefore, it is possible to prevent charging errors due to the battery not being installed or poor contact.

(Example) In the following, the invention will be explained in detail using illustrations and examples.

FIG. 1 is a circuit diagram showing a battery constant current charging circuit of the present invention.

In the figure, a charging signal input terminal 10 connected to an output terminal of a CPU (not shown) or the like is connected to the base of a transistor TrlO via a resistor RIO, and the emitter of the transistor Trio is grounded.

Further, the collector of the transistor Trio is connected to the base of the transistor Tr20 via a bias resistor 20. A power supply voltage ■ is applied to the emitter of this transistor Tr20. C is applied, and a bias resistor R30 is connected between its emitter and base.

The above-described circuit constitutes a current supply means, and these configurations are similar to conventional circuits.

The collector of the transistor Tr20 is connected to the collector of an NPN transistor Tr30, which is a second switching element, and is also connected to the base of the transistor Tr30 via a resistor 1140. Further, the emitter of the transistor Tr30 is connected to the positive terminal of the battery 20 via a forward-connected diode DIO,
The base is connected to the collector of NPN I-transistor Tr40.

The negative terminal of the battery 20 is grounded via a resistor R50, and the base of the transistor T r 40, which is the first switching element, is connected to the connection point between the resistor R50 and the negative terminal of the battery 20. The emitter of a transistor Tr40 is connected between and ground.

A monitoring circuit 30 is connected between the collector and emitter of the transistor Tr40. This monitoring circuit 30 is composed of a timer circuit, etc., and is connected to the collector of the transistor Tr40.
Emitter voltage■. This is a circuit that monitors changes in E40. That is, the monitoring circuit 30 detects the voltage V. A function that monitors E4° and determines that if the voltage V'CE40 is the off-state voltage of the transistor Tr40 and does not change for a predetermined period of time or more, the charging operation is not being performed, such as that the battery 20 is disconnected. This is a circuit with

Next, the operation of the battery constant current charging circuit having the above configuration will be explained.

FIG. 4 is a timing chart showing the operation of each part.

First, when the charging signal shown in FIG. 4(a) becomes high level (time t1) by a command from a CPU (not shown), etc., the transistors Trio and Tr20 are respectively turned on, as in the conventional case (see FIG. 4). (b)+' (C)).

Then, when the transistor Tr20 is turned on, a voltage difference is generated between the collector voltage of the transistor Tr20 and the positive electrode of the battery 20, so that a charging current I CHARGE flows between the collector and emitter of the transistor Tr30 (FIG. 4(d)).

When this current flows into the resistor R5'O, the voltage V uso
(Fig. 4(e)), this voltage VRI,O is the base-emitter saturation voltage V of the transistor T r 40.
When BE40sat is exceeded, transistor T r 4
0 is turned on (FIG. 4(f), time t2).

Therefore, the value of resistor R50 is determined by the required charging current I CHA
The transistor Tr40 is set to turn on when a current equal to or higher than RGE flows, and this relationship is shown in equation (2).

R50=VBE4o58t/■clIAR6E[Ω]
(2) When the transistor Tr40 is turned on, the collector-emitter saturation voltage V CE40 of the transistor Tr40 is applied to the base of the transistor Tr30. , at will be applied. In this case, since the base current is not supplied to the transistor Tr30, the transistor Tr30
is in an off state (FIG. 4(g), time t2).

When the transistor Tr30 is turned off, the transistor Tr30 turns off.
Since the collector current of 30 stops flowing, the charging current I
CHARGE also stops flowing.

Then, since the charging current ICIIARGE stops flowing, the voltage across the resistor R50 becomes ov, so the base-emitter voltage of the transistor Tr40 becomes O■, and the transistor Tr40 is turned off.

When the transistor Tr40 turns off, the resistor R40
Since the base current flows through the transistor Tr30, the transistor Tr30 is turned on. The base current at this time is expressed by the following equation.

Ia=(Vcc-VcE□o-VaE3osat-V
p-VaAT-VoEaosat)/R40...(3
) R40=Vcc-(Vctzo+Vngzogat"V
r+VaAy+Vol:4osat)/IB...
(4) Therefore, resistor R40 is set to the value shown by equation (4).

However, VCC: Power supply voltage V BE30tat: Base-emitter saturation voltage of l' transistor Tr30 VCE20: Collector-emitter voltage of transistor Tr20
Emitter saturation 1 voltage ■F, diode Dlo forward ■ Voltage drop VBAT: Voltage across the battery VaE4ogat: Base-emitter saturation voltage of transistor Tr40 When the transistor Tr30 is turned on, its collector current flows, so the charging current starts again. It will flow.

The above transistor Tr30. Constant current charging of the battery 20 is performed by repeating the on/off operation of the Tr 40 (section from t2 to t3 in FIG. 4).

Next, a charging operation when the battery 20 is not installed will be described.

When the charging signal becomes high level, the transistor Tr10
．． ．． Tr20 is turned on, and voltage Vcc-VCE20 is applied to the collector of transistor Tr30.

However, in this case, since the battery 20 is not installed, no potential difference occurs between the collector of the transistor Tr20 and the positive electrode of the battery 20, and therefore the transistor Tr3
The current passed between the collector and emitter of 0, that is, the charging current I CHARGE does not flow.

Therefore, the transistor Tr40 also remains in the off state,
The collector-emitter voltage of the transistor Tr40, ie, the input voltage of the monitoring circuit 30, is VCCVCE20.

The monitoring circuit 30 monitors this input voltage, and if this voltage does not change for a certain period of time, it determines that the battery 20 is not installed, and displays a battery no alarm (not shown) or the like.

Therefore, it is possible to know not only whether the battery 20 is not installed, but also whether the battery 20 is uncharged due to poor contact or disconnection of the battery terminals.

In the above embodiment, the first. Although a transistor is used as the second switching element, the second switching element is not limited to this. For example, it may be configured with a silice or the like.

(Effects of the Invention) As described in detail above, according to the present invention, the first switching element is conductive when a current of a predetermined value or more flows through the battery, and the first switching element is non-conductive when the first switching element is conductive. Since the charging current is supplied to the battery through the second switching element, there is no need for a current limiting resistor with an excessive allowable power value, and it is possible to use a current limiting resistor with a small power value. Since only a resistor is required and the circuit configuration is simplified, costs can be reduced and the size can be reduced, and there are advantages in terms of mounting.

In addition, since the second invention includes a monitoring circuit, it is possible to know if the battery is not attached or if the battery is disconnected due to poor contact at the terminal, etc., and it is possible to prevent charging errors, etc. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a battery constant current charging circuit of the present invention, Fig. 2 is a circuit diagram of a conventional battery charging circuit, Fig. 3 is a timing chart of a conventional battery charging circuit, and Fig. 4 is a circuit diagram of a battery of the present invention. 3 is a timing chart of a constant current charging circuit. Tr10. Tr20・-transistor, Tr30・・
- Second switching element (transistor), Tr40... first switching element (transistor), R50... resistor, 20... battery, 30... monitoring circuit.

Claims (2)

[Claims] (1) a first switching element that becomes conductive when a current of a predetermined value or more flows through a connected battery; a second switching element that becomes non-conductive due to conduction of the first switching element; A battery constant current charging circuit comprising: current supply means for supplying current to the battery via the switching element. (2) The battery constant current charging circuit according to claim 1, further comprising a monitoring circuit that determines that the battery is disconnected when the first switching element is non-conductive for a predetermined period of time or more. .