JPS5833778B2 - Jiyuden Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit having a function of correcting fluctuations in charging capacity due to fluctuations in power supply voltage.

One type of charging circuit is one that compares the terminal voltage of the battery to be charged with the fully charged battery voltage inside the circuit, and stops charging when the two match.

In general, the appropriate value of the fully charged battery voltage of a battery tends to decrease as the battery temperature rises, so the temperature characteristics of the thermistor and PN junction are used to change the fully charged battery voltage in accordance with the battery temperature. Several charging circuits have been in existence for some time.

However, in conventional charging circuits of this type, when the temperature rises due to self-heating of the charging circuit, a temperature difference occurs between the thermosensor and the battery due to the difference in heat capacity, and even though there is no large change in battery temperature, There is a drawback that the battery voltage drops after charging is completed, making it impossible to charge the battery to a sufficient capacity.

On the other hand, although the above self-heating is mainly caused by an increase in charging current due to an increase in power supply voltage, there is another drawback that is caused by fluctuations in charging current directly affecting battery voltage.

In other words, since the battery has internal resistance, the battery voltage fluctuates due to fluctuations in the charging current due to fluctuations in the input voltage of the charging circuit, and charging may stop even though the battery has not been charged to a sufficient capacity. be.

The present invention has been proposed in view of the above points, and aims to provide a charging circuit that eliminates the above two drawbacks caused by fluctuations in power supply voltage.

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

The drawings show embodiments of the present invention, and in the drawings Wl,
W2 is the primary transformer that operates at commercial frequency.

This is the secondary coil.

Diode D2. D3 performs full-wave rectification of the transformer output using the center tap method, and provides pulsating direct current to the charging circuit.

SCR is a charging current switch, B is a battery to be charged, R7 is a resistor that limits (stabilizes) charging current and acts as a heating element, transistor T1 operates to transmit battery voltage VB to battery voltage detection stage transistor T2, When the charging power source is not working, the battery voltage VB detection section prevents the battery from discharging.

R1 is a bias resistance of transistor T1.

The diode D1 and the resistor R2 form a voltage dividing circuit to provide a base signal for the transistor T2, and the fully charged battery voltage VBf is set by the voltage dividing ratio.

Furthermore, the diode D1 functions to increase the base current when the temperature rises due to the temperature characteristics of the PN junction, and has the function of advancing the turn-on timing of the transistor T2 and lowering the fully charged battery voltage to an appropriate value.

Transistor T3. T4 is a simple amplifier stage, and transistor T5 is a buffer stage, which controls the gate current of the SCR according to the switching operation of transistor T4.

Note that the resistor R2 is thermally coupled to the resistor R7, for example, the resistor R7 is located near the resistor R2,
The resistor R2 easily receives the heat of the resistor R7, and is configured so that the temperature of the resistor R2 increases when the charging current is large.

Said resistor R2 is a temperature sensitive resistor with a negative temperature coefficient of resistance, for example a thermistor.

Next, the operation of the present invention will be explained in detail.

When commercial power is applied, a half-wave sinusoidal voltage is applied every half cycle.

When the sine wave rises, the transistor T1 is forward biased and becomes conductive, and the battery voltage 8 is transmitted to the lower two transistor stages.

Here, the fully charged battery voltage VBf is the voltage when the battery voltage divided by the diode D1 and resistor R2 and applied to the base of the transistor T2 reaches the rising voltage between the base and emitter of the transistor and turns on. Therefore, when VB < VB f, transistor T2 is off, transistor T3 is off, and transistor T
4 is off, transistor T5 is on, and the SCR is fired and charged during its half cycle.

Conversely, when VB≧VBf, transistor T2 is turned on,
Transistor T3 is off, transistor T4 is on, transistor T5 is off, the SCR is not fired, and charging is stopped.

This operation is continued every half cycle, and charging is performed until VB"VBf is reached.

Generally, the value of the fully charged battery voltage VBf is mainly determined by the diode D1. Determined by the temperature of transistor T2,
If there is no increase or decrease in charging current, diode D1. The temperature of the transistor T2 is equal to the ambient temperature, and at the same time, the temperature of the transistor T2 is equal to the battery temperature.

However, when the charging element and the battery to be charged are built into the same case, such as in a rechargeable razor, when the charging current increases or decreases due to fluctuations in the power supply voltage, the charging element, especially the SCR and the resistor R7. The amount of heat generated by the diode D1. The temperature rise value of the transistor T2 portion increases or decreases.

Since the battery to be charged has a larger heat capacity than other circuit elements, the change in temperature rise is small, creating a temperature difference with the diode D and the transistor T2 as temperature sensing elements.

Before implementing the present invention, that is, when the resistor R2 is a normal resistor and there is no thermal feedback by the resistor R7, the fully charged battery voltage VBf determined by the diode D1 and the transistor T2 depends on the temperature of the battery voltage. Since it has a negative temperature coefficient, it is suitable for diode D1. If the temperature rise in the transistor T2 portion is large, the fully charged battery voltage Bf will be lower than when the power supply voltage is low, charging will be completed earlier, and the charging capacity will not be secured.

On the other hand, from another perspective, battery voltage VB is a function of temperature as well as charging current, and even if the battery voltage VB is at the same charging capacity, it differs depending on the charging current value at that time.

That is, as the charging current increases, the battery voltage VB also increases by the voltage drop across the internal resistance.

Therefore, when the power supply voltage is high, the fully charged battery voltage VBf is (
If the charging current is high (high charging current), sufficient charging capacity cannot be secured compared to when the power supply voltage is low.

At this time, as in the embodiment of the present invention shown in the drawings, a temperature-sensitive resistor having a negative temperature coefficient is used as the resistor R2, and by transmitting the heat of the resistor R7 to this, the resistor R2 increases as the power supply voltage increases. is heated, the resistance value decreases, and the diode D1
The forward voltage drop increases, and the fully charged battery voltage VBf increases.

As a result, the fully charged battery voltage VB against power supply voltage fluctuations
Correction of f is performed, and charging to a sufficient capacity is performed regardless of the level of the power supply voltage.

In the illustrated embodiment, the resistor R7 and the resistor R2 are thermally coupled, but the same effect can be obtained by using the SCR as a charging current switch as a heating element and thermally coupling the SCR and the resistor R2. You can expect it.

Furthermore, in the illustrated embodiment, the temperature dependence of the charged battery voltage VBf is mainly determined by the base-emitter impedance of the diode D1 and the transistor T2, but the diode D1 is replaced with a simple resistor, and the resistor R2 is Even when using a sensitive resistor and determining the temperature dependence of the charged battery voltage VBf mainly by the base-emitter impedance of the resistor R2 and the transistor T2, the heat received from the resistor R7 or SCR as a heating element to the resistor R2 can be adjusted to achieve the same effect.

As described above, the present invention makes it possible to correct the charged battery voltage due to power supply voltage fluctuations, and achieves effects such as eliminating fluctuations in charging capacity due to power supply voltage fluctuations.

[Brief explanation of drawings]

The drawings illustrate embodiments of the invention. Wl...Primary coil, W2...Secondary coil, Dl
...diode, D2. D3...- rectifier diode,
B...Battery to be charged, R2...Temperature sensitive resistor, T1
．． T,...-transistor.

Claims (1)

[Claims] 1 It has a transistor that inputs the voltage of the battery to be charged to the base via a voltage dividing circuit, and charging is performed by turning on and off a charging current control element connected in series with the battery to be charged by turning on and off the transistor. In the charging circuit, the resistance between the base and emitter of the voltage dividing circuit is a temperature-sensitive resistor, and a heating element connected in series with the battery to be charged is placed close to the temperature-sensitive resistor. A charging circuit characterized by changing the voltage of a fully charged battery in response to fluctuations in power supply voltage by changing the resistance of a resistor.