JPH1070847A - Charging device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent occurrence of overshoot in charging voltage. A DC-DC converter and a control circuit for controlling the operation of the converter are provided. The DC-DC converter 10 includes a pulse modulation circuit 11, a circuit M1, Q1, D1, 13 for converting an input DC voltage into a predetermined DC output voltage VDC by an output pulse thereof, and a resistor for dividing the output voltage VDC. R2 and R4. Resistors R2, R4
Is fed back to the pulse modulation circuit 11 as its modulation input to stabilize the DC output voltage VDC to a predetermined value. The control circuit 20 controls the conversion operation of the DC-DC converter 10 to supply the output voltage VDC intermittently to the rechargeable battery BATT for a predetermined period. A capacitor C1 for changing the rise of the DC output voltage VDC is connected in parallel to the resistor R2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a charging device.

[0002]

2. Description of the Related Art For example, when charging a lithium ion battery, charging is generally performed with charging characteristics as shown in FIG. 3 in consideration of the characteristics of the battery. That is, for example, 2
In the case of a lithium-ion battery pack in which two battery cells are connected in series, charging is performed at a constant current until the terminal voltage reaches the specified voltage 8.4V, and thereafter, charging is performed at a constant voltage. .

In order to perform charging with such characteristics, a charging device for a lithium ion battery is configured as shown in FIG. 4, for example.

[0004] That is, in FIG. 4, reference symbol BATT indicates a lithium-ion battery for which the charging is performed. In FIG. 4, two lithium-ion battery cells are connected in series. Charging terminals T11, T
Connected to 12.

Reference numeral 10 denotes a switching type D.
3 shows a C-DC converter. And this converter 1
0, the transformer M1 is connected between the power supply terminal T1 and the ground.
And the drain-source of the switching FET (Q1) is connected in series. Further, a PWM modulation circuit 11 formed as a one-chip IC is provided, a voltage at a terminal T1 is supplied to the PWM modulation circuit 11, and a PWM pulse PPWM of a predetermined frequency is extracted from an output terminal OUT.

The pulse PPWM is applied to the NOR circuit 1
2, the current is supplied to the gate of the FET (Q1), and the current flowing through the primary coil of the transformer M1 is switched, so that an alternating voltage is extracted to the secondary coil of the transformer M1. The alternating voltage is rectified by the diode D1 and smoothed by the smoothing circuit 13. The smoothing circuit 13 outputs the DC voltage VDC.

The output terminal of the smoothing circuit 13 is connected to a charging terminal T11 through a current limiting resistor R1, and the charging terminal T12 is connected to ground. A resistor R2 and a variable resistor R3 are connected between the terminal T11 and the ground.
And a resistor R4 are connected in series, and a resistor R1
Is connected in parallel between the base and emitter of the transistor Q2 for current detection, and its collector is connected to the connection point of the resistors R2 and R3.

Then, the divided voltage VDIV is output from the variable resistor R3.
The divided voltage VDIV is supplied to the input terminal IN of the modulation circuit 11 as a modulation input to form a feedback loop. Thus, the duty ratio of the pulse PPWM is changed according to the voltage VDIV, and the voltage VDV
IV is stabilized to the reference value VREF.

Then, at this time, the voltage VDC is changed by the resistor R
Since the battery BATT is supplied to the battery BATT through 1, the battery BATT is charged by the voltage VDC.

Here, when the remaining amount of the battery BATT is small, the charging current ICHG flowing through the resistor R1 is large.
When the voltage exceeds the emitter-to-emitter voltage (= approximately 0.6 V), the transistor Q2 is turned on, and the voltage VDC is reduced by the resistors R3, R4
, And becomes a voltage VDIV.

At this time, the voltage VDIV is set to the specified value VR.
Since the voltage is stabilized at EF, the voltage VDC is also stabilized at a predetermined constant value. Therefore, when the remaining amount of the battery BATT is small, the current ICHG becomes substantially constant because the voltage VDC is constant.
Battery BATT is charged with a constant current.

When charging proceeds and the remaining amount of the battery BATT increases, the charging current ICHG flowing through the resistor R1 decreases.
, The transistor Q2 is turned off, and the terminal voltage VBATT of the battery BATT is divided by the resistors R2 to R4 to become the voltage VDIV.

At this time, the voltage VDIV is set to the specified value VR.
Since the voltage is stabilized at EF, the terminal voltage VBATT of the battery BATT is also stabilized at 8.4 V, for example. Therefore, when the remaining amount of the battery BATT is large, the charging voltage is constant at 8.4 V, and the battery BATT is charged at a constant voltage.

As described above, in this charging apparatus, charging is performed according to the charging characteristics shown in FIG. 3. In this charging apparatus, detection of the start and end of charging, the presence or absence of the battery BATT, and the like are further performed. This is realized by the microcomputer 20.

That is, a microcomputer 20 formed as a one-chip IC is provided, and resistors R5 and R6 and a collector and an emitter of a switching transistor Q3 are connected in series between the terminal T11 and the ground. The voltage VDET obtained at the connection point between the resistors R5 and R6 is supplied to the analog input port (built-in A / D
Converter) connected to A / D.

Further, a predetermined control signal DCTL is output from the output port D1 of the microcomputer 20, and this signal DCTL is supplied to the base of the transistor Q3 and to the OR circuit 12.

In this case, the control signal DCTL is always
As shown in FIG. 5A, for example, the signal is a signal that alternately repeats the “L” level and the “H” level at a cycle of one second. Therefore, during the period TL of DCL = "L", the pulse PPWM from the modulation circuit 11 is supplied to the FET (Q1) through the OR circuit 12.
And the transistor Q3 is turned off. If the battery BATT is connected to the terminals T11 and T12,
This battery BATT is charged during the period TL.

Further, during the period TH in which DCCTL = "H", FE
T (Q1) is turned off, DC voltage VDC is no longer output, and transistor Q3 is turned on. Therefore, if nothing is connected to the terminals T11 and T12,
The voltage VDET during the period TH becomes 0.

However, if a battery BATT is connected to the terminals T11 and T12, the battery
Since the battery BATT is charged to L, the voltage of the battery BATT is divided by the resistors R5 and R6, and the divided voltage becomes the voltage VDET.

That is, if the battery BATT is not connected to the terminals T11 and T12, VDET = 0 during the period TH, and the battery BA
If TT is connected, VDET> 0 during the period TH.

Therefore, the microcomputer 20 can check whether the battery BATT is connected to the terminals T11 and T12 by checking the voltage VDET by the microcomputer 20.

The battery BATT is connected to the terminals T11 and T12, and when this is detected by the microcomputer 20, the charging of the battery BATT is started as described above. In this case, the control signal DCL is set to the level shown in FIG. As shown in (2), for example, TL is changed to 30 seconds, and the above-described charging is executed during this period TL. That is, the DC voltage VDC is output for each period TL, and charging is performed intermittently.

At the time of charging, the voltage VDET is applied during the period TH.
Is checked to determine whether or not this voltage VDET has reached a voltage corresponding to a prescribed charge end voltage. If not, charging is continued, but if reached, charging is terminated. . Also, during the period TH, VD
If ET = 0, since the battery BATT has been disconnected from the terminals T11 and T12, the signal DCTL is again in the state of FIG. 5A.

Thus, in this charging device, FIG.
The charging is performed according to the charging characteristics described above, the start and end of charging, the presence or absence of the battery BATT, and the like are also detected, and processing corresponding to each is performed.

[0025]

As can be seen from the charging characteristics shown in FIG. 3, a considerably large charging current, for example, a charging current of 200 to 300 mA flows near the start of charging. However, near the end of charging, the charging current is small and the load becomes light.

When the load changes as described above, converter 10 is designed with a heavy load as a target so as to withstand the heavy load.
For this reason, when the load is light, that is, when charging is considerably advanced, as shown in FIG. 6, at the start of the period TL, an overshoot occurs in the DC voltage VDC.

This overshoot occurs when charging progresses.
It occurs every time the period TL starts, and its peak value reaches 15 V or more. Therefore, the applied voltage exceeds the specified voltage for the battery BATT, which causes an extremely large stress, which is not preferable. In some cases, it can cause problems such as ignition.

The present invention is intended to solve such a problem.

[0029]

According to the present invention, D
A DC-DC converter; and a control circuit for controlling the operation of the DC-DC converter. The DC-DC converter is configured to convert an input DC voltage to a predetermined value by a pulse modulation circuit and an output pulse of the pulse modulation circuit. It has a circuit for converting to a DC output voltage, and first and second resistors for dividing the DC output voltage, and the divided voltages from the first and second resistors are supplied to the pulse modulation circuit. The DC output voltage is fed back as a modulation input to stabilize the DC output voltage to a predetermined value, and the control circuit controls the conversion operation of the DC-DC converter so that the DC output voltage is intermittently charged for a predetermined period. Supplied to the battery,
A charging device is provided in which a capacitor for changing the rise of the DC output voltage is connected in parallel to the first resistor.

As a result, the voltage supplied to the rechargeable battery is soft-started, and there is no overshoot.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a DC-DC converter 10 and a microcomputer 20 are configured as described above, and a capacitor C1 is connected in parallel with a resistor R2.

According to such a configuration, in the period TL, the voltage V2 at the connection point between the capacitor C1 and the resistor R3 is obtained.
Is rapidly raised to the voltage VBATT through the capacitor C1, and the voltage VD
IV also rises. Then, the rise of the voltage VDC is equivalent to the case where the output voltage VDC rises from the specified value for the modulation circuit 11, so that the modulation circuit 11 operates to change the duty ratio of the pulse PPWM to lower the voltage VDC. . Therefore, as shown in FIG. 2, at the start of the period TL, the voltage VDC is almost zero.

However, as the period TL elapses, the capacitor C1 is gradually charged, and accordingly, the voltage V2 is gradually decreased, and the voltage VDIV is also gradually decreased. Therefore, as shown in FIG. 2, at the start of the period TL, the voltage VDC gradually increases even if it is almost 0, and stabilizes to the specified value.

Therefore, as shown in FIG.
At the start of the period TL, a clean soft start rises and no overshoot occurs.

Thus, according to this charging device, the battery BA
Even when charging is performed intermittently to detect the state of TT, if the charging current is small, the charging voltage VDC
No overshoot occurs.

Therefore, no stress is applied to the battery BATT, and no trouble such as ignition occurs. Moreover, for this purpose, it is only necessary to add the capacitor C1, which is extremely simple and inexpensive.

In the above description, the battery BATT is a lithium-ion battery. However, the charging current greatly changes as the battery BATT is charged, and the battery BATT is intermittently charged every period TL. If it is a charging device that detects or checks etc., the battery BATT
The present invention is applicable regardless of the type of.

[0038]

According to the present invention, it is possible to prevent the occurrence of overshoot in the charging voltage. Moreover, for that purpose, it is only necessary to add one capacitor, which is simple and inexpensive.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the present invention.

FIG. 3 is a waveform chart for explaining the present invention.

FIG. 4 is a connection diagram for explaining the present invention.

FIG. 5 is a waveform chart for explaining the present invention.

FIG. 6 is a waveform chart for explaining the present invention.

[Explanation of symbols]

10 = DC-DC converter, 11 = PWM modulation circuit,
12 = NOR circuit, 13 = smoothing circuit, 20 = microcomputer

Claims (4)

[Claims] A DC-DC converter; and a control circuit for controlling the operation of the DC-DC converter. The DC-DC converter includes a pulse modulation circuit, and an input pulse output from the pulse modulation circuit. A circuit for converting the DC voltage to a predetermined DC output voltage; and a first and second resistor for dividing the DC output voltage, wherein the divided voltage from the first and second resistors is: The pulse modulation circuit is fed back as its modulation input to stabilize the DC output voltage to a predetermined value, and the control circuit controls the conversion operation of the DC-DC converter, so that the DC output voltage is increased by a predetermined period. While being supplied intermittently to the rechargeable battery, a capacitor for changing the rise of the DC output voltage is connected in parallel to the first resistor. Collector. 2. The charging device according to claim 1, wherein a state of the rechargeable battery is detected during a period between intermittent supply of the DC output voltage to the rechargeable battery. Charging device. 3. The charging device according to claim 2, wherein the converting circuit is a switching system, and the pulse modulation circuit is a PWM modulation circuit. 4. The charging device according to claim 3, wherein when the charge amount of the rechargeable battery has not reached a predetermined value, the charging by the DC output voltage is a constant current charging, A charging device in which when the charged amount reaches a predetermined value, the charging by the DC output voltage is a constant voltage charging.