JP3499744B2 - Electronic device 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 a charging circuit for electronic equipment, and more particularly to a power supply circuit for electronic equipment using a secondary battery.

[0002]

2. Description of the Related Art Secondary batteries (rechargeable batteries) are used in electronic devices.
Is often used as a power source. As a method of charging the secondary battery, power is supplied to the electronic device by an AC adapter or a DC adapter that only converts the power from the primary power source, and a charging control circuit is inserted between the secondary battery and the voltage converter. The general method is to control. The charge control circuit is a kind of voltage stabilizer, and includes a series dropper type and a switching regulator type.

Portable electronic devices are required to be small and lightweight. Portable electronic devices generally use batteries as a power source. A secondary battery is often used as this battery, and a charger for charging the secondary battery is also required to be downsized.

FIG. 9 is a conceptual diagram of a conventional device. In the figure, 1 is an input power source, 2 is a voltage converter for receiving power from the input power source 1 and generating an output voltage of V1, 10
Is an electronic device to which the voltage converter 2 is connected, and for example, a portable terminal or the like is used.

As the primary power source 1, an AC commercial power source or a DC power source, specifically, an automobile battery is used.
In the electronic device 10, 3 is a charge control circuit that stabilizes its output voltage, 4 is a secondary battery, and 5 is a load circuit that is supplied with operating power from the charge control circuit 3 or the secondary battery 4.

The voltage converter 20 is called an AC adapter or a DC adapter, and converts the voltage of the primary power source 1 into a DC power source required for electronic equipment. In the electronic device 10, a secondary battery 4 to be charged and a charge control circuit 3 that controls charging of the secondary battery are provided.

[0007]

When a series dropper type voltage stabilizer is used as the charge control circuit, the difference between the output voltage of the voltage converter 2 and the battery voltage is added to the charge control circuit 3, and the secondary battery is used. When 4 is in a discharged state and the battery voltage is low, the voltage difference is added to the charge control circuit 3 and heat is generated.

Further, when the switching regulator type is used as the charge control circuit 3, since the current flowing through the load is turned on / off, there is a problem that noise is generated when the current is turned on / off. Further, the switching regulator type has a problem that the voltage conversion efficiency is poor and the power consumption increases when the number of battery cells is small and the voltage is low.

As for the charging characteristics of the secondary battery, the voltage is low when the battery is empty, and the battery voltage rises with charging.
When charging is performed with the configuration shown in FIG. 9, the power consumption of the charge control circuit 3 is maximum when the battery is empty, and for safety, the charge control circuit 3 is designed to allow this maximum power, and is downsized. Was difficult.

The present invention has been made in view of the above problems, and an object thereof is to provide a charging circuit for an electronic device which consumes less power and is suitable for miniaturization.

[0011]

(1) FIG. 1 is a block diagram showing the principle of the present invention. The same parts as those in FIG. 9 are designated by the same reference numerals. In the figure, 20 is a voltage converter with a drooping characteristic, which is connected to the input power supply 1 and has a drooping characteristic according to the output current. Reference numeral 10 denotes an electronic device, and the electronic device 10
In FIG. 3, 3 is a charge control circuit for controlling charging of the secondary battery 4, 4 is a secondary battery, and 5 is a load circuit to which power is supplied from the charge control circuit 3 or the secondary battery 4.

[0012]

[0013]

[0014]

(1) According to the configuration of the present invention , a voltage stabilizing function is added to the voltage converter 20, and the drooping start point voltage of its own drooping characteristic is stabilized by the charging control circuit 3 provided in the subsequent stage. If the lowest voltage is set, the lowest voltage for the stabilizing operation is guaranteed as the voltage given from the voltage converter with drooping function 20 to the charge control circuit 3 in the subsequent stage.

[0016]

(2) Further, the battery 4 of the electronic device 10
The differences, if to switch the current supply capability of the voltage converter 20, the difference of the battery of the electronic device 10,
When batteries with different capacities are used in the same device, the charging time can be adjusted approximately.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a diagram showing a characteristic example of the present invention. In the figure, the vertical axis represents voltage and the horizontal axis represents current. In the figure, f1 is a voltage converter 20 with drooping characteristics.
, F2 represents the characteristics of the charge control circuit 3. The output voltage of the voltage converter 20 with the drooping characteristic gradually decreases until the current becomes i1. When the current exceeds i1, the voltage drops sharply, exhibiting a drooping characteristic. On the other hand, the output voltage of the charge control circuit 3 maintains the output voltage V2 until the voltage converter 20 with the drooping characteristic exhibits the drooping characteristic. When the voltage converter 20 with the drooping characteristic starts to droop, the output voltage thereof also decreases in conjunction with this.

According to this embodiment, since the voltage converter with drooping characteristic 20 has the drooping characteristic, the charging control circuit 3 is heated before the charging control circuit 3 generates heat when the secondary battery 4 is charged. The input voltage V1 of V.sub.1 decreases. As a result, the output voltage V2 of the charging control circuit 3 is also reduced, heat generation is stopped, and the charging control circuit 3 can be downsized.

FIG. 3 is a diagram showing an example of charging characteristics of a battery.
In the figure, the vertical axis represents voltage or current, and the horizontal axis represents time.
V1 is the output voltage of the voltage converter 20 with drooping characteristic,
Indicates the output voltage of the charging control circuit 3. Time t = 0
From t to t = t1, in the constant current mode, current is injected into the secondary battery 4 at a constant rate during this period, and the output voltage thereof gradually rises. Here, when the output voltage V1 of the voltage converter 20 with drooping characteristic reaches a predetermined value at time t1, the constant current mode until then becomes the constant voltage mode, and the output voltage V2 of the charging control circuit 3 becomes constant. V
The difference between 1 and V2 is taken by the transistor of the series dropper, for example. In the constant voltage mode, the charging current gradually decreases as shown in the figure.

According to this embodiment, the charging control circuit 3 is provided with the output voltage stabilizing function so that the secondary battery 4 can be stably charged and the load circuit 5 can be supplied with a stable voltage. You can

Further, the present invention is characterized in that the current supply capacity of the voltage converter 20 with the drooping characteristic is made smaller than the current supply capacity of the charge control circuit 3. According to this embodiment, in order to make the current supply capability of the voltage converter 20 with drooping characteristic smaller than the current supply capability of the charge control circuit 3, the charging control circuit 3 has the capability of the voltage converter 20 with drooping property. No more current is supplied,
The heat generation of the charge control circuit 3 can be suppressed.

Further, a voltage stabilizing function is added to the voltage converter 20 having the drooping characteristic, and the drooping start point voltage of the drooping characteristic of itself is set to the minimum voltage at which the charging control circuit 3 provided in the subsequent stage stabilizes. be able to.

According to this embodiment, the charge control is performed by setting the output voltage of the voltage converter 20 with the drooping characteristic immediately before the start of drooping to a value at which the charge control circuit 3 in the subsequent stage operates as a series drop. The minimum voltage for the circuit 3 to operate normally as a stabilized power supply is guaranteed.

FIG. 4 is a diagram showing an embodiment of the charging control circuit. Q1 is a transistor that functions as a series dropper. That is, the input voltage V1 and the output voltage V
By taking charge of the difference of 2 between the collector and the emitter of the transistor Q1, the output voltage V2 is kept constant.

The output voltage V2 gives a charging current to the secondary battery 4. The output voltage at this time is taken out from the voltage dividing point of the resistors R8 and R9 and given to the positive input of the error amplifier AMP2. The reference voltage VREF is applied to the negative input of the error AMP2, and the AMP2 outputs a signal based on the difference between the output voltage and the reference voltage via the diode D2 to the transistor Q2.
Give to the base of. Finally, when the positive input and the negative input of AMP2 become equal, the circuit becomes stable and the output voltage V2 takes a constant value. That is, the series regulator transistor Q1 is connected to the transistor Q2, and adjusts the voltage applied to its emitter and collector according to the base potential of the transistor Q2.

Here, the charge control circuit 3 can be provided with an overcurrent drooping characteristic. When an overcurrent flows through the load, the voltage drop across the resistor R3 increases, the output of AMP1 goes high, and the base potential of the transistor Q2 rises via the diode D1. As a result, the transistor Q1
Is turned off and the drooping characteristic is obtained.

According to this embodiment, since the charging control circuit 3 also has the overcurrent drooping characteristic, an excessive charging current is supplied to the secondary battery even when an unexpected voltage converter is connected. It can be prevented from flowing.

FIG. 5 is a diagram showing an embodiment of a voltage converter with a drooping characteristic. In a normal operating state, the switching transistor Q11 is driven by the drive circuit 22 driven by the PWM circuit 21, and the switching transistor
AC voltage is generated on the secondary side. The generated AC voltage is rectified and smoothed by the circuit including the diode D11 and the capacitor C12, and becomes the DC voltage V1.

The DC voltage V1 is divided by the voltage dividing circuit of the resistors R16 and R17 and input to the differential amplifier U2 as a monitor signal indicating the output voltage. The differential amplifier U2 is
The difference voltage between the output voltage and the reference voltage Vref1 is amplified and given to the PWM circuit 21 via the diode D12. Figure 6
[FIG. 7] is an explanatory diagram of a PWM control operation. A sawtooth wave f4 as shown in the drawing is generated, and the differential amplifier U2 gives a voltage as shown by L in the drawing. Sawtooth wave f4 and this level L
And a pulse P corresponding to the comparison result is output. By changing the duty of this pulse, the output voltage V1 is held constant.

By the way, when an overcurrent flows through this circuit,
The voltage drop of the resistor R13 becomes large. This voltage drop is
It enters one input of the differential amplifier U1. On the other hand, the reference voltage Vref2 is applied to the other input. When the voltage drop is large, the differential amplifier U1 outputs a high-level signal and gives it to the PWM circuit 21. As a result, the PWM circuit 2
1 stops the operation, and the drive circuit 22 turns on the transistor Q11.
Is turned off, and the output voltage V1 becomes 0.

FIG. 7 shows another characteristic example of the present invention. The vertical axis represents voltage and the horizontal axis represents current. V1 indicates the output characteristic of the voltage converter with the drooping characteristic, and V2 indicates the characteristic of the charge control circuit 3. This example shows a case where both V1 and V2 have drooping characteristics according to the current.

According to the present invention, the current supply capability of the voltage converter can be switched depending on the battery of the electronic device 10. According to this, when the batteries having different capacities are used in the same device due to the difference in the batteries of the electronic devices, the charging time can be almost matched.

FIG. 8 is a diagram showing a characteristic example of the present invention. In the figure, the horizontal axis indicates time, and the length of the figure is 10 minutes. The vertical axis represents the input voltage f5, the secondary battery voltage f6, and f7.
Is the input current. During the charging period, the input current is f7 in the figure.
As shown in, the current is injected into the secondary battery.
Then, when the charging period ends, the constant voltage mode is set, and 2
The secondary battery supplies power. When the secondary battery discharges and the battery voltage drops, the charging period starts again.

[0035]

As described in detail above, according to the present invention, (1) a voltage stabilizing function is added to the voltage converter, and
Of the drooping start point voltage of the drooping characteristic of the
By setting the lowest voltage for the circuit to stabilize,
From the voltage converter with the lower function to the charging control circuit in the subsequent stage
Guaranteed minimum voltage for stable operation
To be done.

[0036]

[0037]

[0038]

[0039]

(2) Furthermore, by switching the current supply capacity of the voltage converter depending on the battery of the electronic device, the batteries of different capacities can be used in the same device due to the battery of the electronic device. In this case, the charging time can be almost adjusted.

As described above, according to the present invention, it is possible to provide a charging circuit for electronic equipment which consumes less power and is suitable for miniaturization.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing a characteristic example of the present invention.

FIG. 3 is a diagram showing an example of charging characteristics of a battery.

FIG. 4 is a diagram showing an embodiment of a charge control circuit.

FIG. 5 is a diagram showing an embodiment of a voltage converter.

FIG. 6 is an explanatory diagram of a PWM control operation.

FIG. 7 is a diagram showing another example of characteristics of the present invention.

FIG. 8 is a diagram showing a characteristic example of the present invention.

FIG. 9 is a conceptual diagram of a conventional device.

[Explanation of symbols]

1 input power, 3 Charge control circuit 4 secondary battery 5 load circuit 10 electronic devices 20 Voltage converter with drooping characteristic

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G05F 1 / 445,1 / 56 G05F 1 / 613,1 / 618 H02M 3/00-3/44 H02J 1 / 00-7/36 H02H 7/00-7/20

Claims (2)

(57) [Claims] 1. A voltage converter for charging a secondary battery built in an electronic device or a secondary battery connected to an electronic device, the voltage converter receiving a voltage from an input power source and converting the voltage into a predetermined voltage. A charging control circuit for charging the secondary battery in response to the output of the voltage converter is provided , and a voltage stabilizing function is added to the voltage converter so that the voltage droops by itself.
The charging control circuit provided in the latter stage changes the characteristic drooping start point voltage.
A charging circuit for electronic equipment, which is characterized by a minimum voltage that stabilizes the voltage . 2. The voltage varies depending on the battery of the electronic device.
2. The charging circuit for an electronic device according to claim 1 , wherein the current supply capacity of the converter is switched .