JPH09322410A - Charge discharge control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the use time no matter what value the voltage of a secondary battery may be at, by deciding the delay time by means of a delay circuit without depending upon the power voltage of a secondary battery. SOLUTION: This circuit has such a constitution that this turns off a switch circuit after a certain delay time independently of power voltage when the overcharge and overdischarge detecting circuit and an overcurrent detecting circuit 8 detect the overdischarge and overcurrent, using a delay circuit 2 where the delay time is independent of power voltage for the charge and discharge control circuit of a secondary battery 9. Hereby, no matter what value the power voltage may be at, this detects precisely whether the overdischarge and overcharge condition of the secondary battery is temporary or not, this protracts the use time of a power unit using the secondary battery. Moreover, in the case of overcurrent condition, an excessive current flows only for a certain time independent of the power voltage, so this can prevent a large current from flowing for a long time to break down the load.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a charge / discharge control circuit capable of controlling charge / discharge of a secondary battery.

[0002]

2. Description of the Related Art As a conventional rechargeable power supply device using a secondary battery, a circuit as shown in FIG. 2 is known. That is, the secondary battery 9 is connected to the external terminal VDD or VSS via the switch circuit 10. Further secondary battery 9
An overcharge / discharge / overcurrent detection circuit 8 is connected to. The overcharge / discharge / overcurrent detection circuit 8 has a function of detecting the voltage and current of the secondary battery 9, and the voltage of the secondary battery 9 is in an overcharged state (state in which the voltage is higher than a predetermined high voltage value. ), Or over-discharged state (where the voltage is lower than the specified voltage value) and overcurrent state (when the current is higher than the specified current value)
Is detected. The output signal of the overcharge / discharge / overcurrent detection circuit 8 is the input signal of the delay circuit 2, and the delay circuit 2 outputs the output signal after a delay period of a certain time t. The output signal of the delay circuit 2 is the input signal of the control circuit 1, and when the secondary battery 9 is in the overcharged state, the overdischarged state or the overcurrent state, the control circuit is turned off. There is a signal from 1.

Without the delay circuit 2, in the case of a load that requires a large current in a pulsed manner, such as a motor, the large current and the internal resistance of the battery cause the voltage of the secondary battery to temporarily drop and overcharge. When the over-discharge detection unit of the discharge / over-current detection circuit 8 detects the over-discharged state, the control circuit 1 operates to turn off the switch circuit 10. Therefore, at this time, even if a large current flows through the secondary battery 9 and the battery voltage is still dischargeable, the power supply device using the secondary battery cannot be used. By using the delay circuit 2, the charge / discharge control circuit of FIG. 2 has a certain delay period from the detection of the over-discharged state to the turning off of the switch circuit 10. Therefore, when the amount of current decreases and the voltage of the secondary battery 2 returns to the normal state within the delay period, the switch circuit 10 turns off.
The power supply circuit using this charge / discharge control circuit can be continuously used without FF.

Further, due to a load that instantaneously requires a large current, an overcurrent detector of the overcharge / discharge / overcurrent detection circuit 8 detects an overcurrent due to a temporary large current flow, and the switch circuit is detected. It is prevented that the load that requires a large current momentarily becomes unusable due to turning OFF 10.

Further, for example, in the case of a Li secondary battery, there is a case where a voltage exceeding the overcharge voltage is applied to VDD with a rectangular wave when charging (hereinafter referred to as pulse charge). Even in the charging state, pulse charging can be performed by delaying a certain time after the overcharge detection unit of the overcharge / discharge / overcurrent detection circuit detects overcharge.

That is, this charge / discharge control circuit is used in the secondary battery 9
By controlling the switch circuit 10 between the external terminal and the external terminal, excessive charging of the secondary battery 9 and excessive reduction of the storage capacity of the secondary battery due to energy supply to the load of the secondary battery 9 are prevented. Furthermore, by placing the delay circuit 2 between the output of the overcharge / discharge / overcurrent detection circuit 8 and the input of the control circuit 1, it is possible to use a load that instantaneously flows a large current and realize pulse charging.

[0007]

However, in the conventional charge / discharge control circuit using the delay circuit 2 as shown in FIG. 2, the delay time t depends on the power supply voltage. That is, when the overcharge / discharge / overcurrent detection circuit 8 detects overcharge / overdischarge / overcurrent, the output signal of the overcharge / discharge / overcurrent detection circuit 8 turns on the transistor 7.
The current flows through the resistor 5 and the resistor 5 charges the capacitor 6. When the voltage V2 of the capacitor 6 becomes higher than the voltage V3 of the reference voltage circuit 11, the output of the comparator 4 reverses and becomes the input of the control circuit 1. The delay time t at this time is as follows.

Since the voltage of V2 is V2 = VDD (1-exp (-(1 / CR) t)) ----- (1), V3 = VDD (1-exp (-(1 / CR)) t)) -------- When (2), the output of the comparator is inverted.

The delay time t, that is, the time t until the comparator 4 is inverted is t = -CRln ((VDD-V3) / VDD) --- (3), and the delay time t depends on the power supply voltage VDD. And change. If the delay time changes from a predetermined value, the following problems occur. That is, when a load that instantaneously uses a large current is connected to a power supply device that uses a secondary battery, a large current temporarily flows and the voltage of the secondary battery temporarily decreases. When the load current decreases, the voltage of the secondary battery returns to above a predetermined voltage, but when the delay time becomes short, the switch circuit turns off before the voltage of the secondary battery returns, and a power supply device using this secondary battery Although it is still in a state where it can be discharged, it cannot be used. Further, if the load is abnormal and an excessive current is flowing, if the delay time becomes long, the load may be heated and destroyed before the switch circuit 10 is turned off.

[0010]

In order to solve the above-mentioned problems, the present invention uses a delay circuit which does not depend on a power supply voltage for a charging / discharging control circuit of a secondary battery, and uses an overcharge / discharge detection circuit / overcharge detection circuit. When the current detection circuit detects overcharge / discharge / overcurrent, the switch circuit is turned off after a certain delay time that does not depend on the power supply voltage.

When overcharging / discharging / overcurrent is detected, the switch circuit is turned off after a delay time that does not depend on the power supply voltage.
Since it is accurately detected whether the overcharged state is temporary, the usage time of the power supply device using the secondary battery is extended. Further, in the case of an overcurrent state, an excessive current flows only for a fixed time that does not depend on the power supply voltage, so that it is possible to prevent a large current from flowing for a long time and destroying the load.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of a charge / discharge control circuit of the present invention. External terminal VSS or VD
A secondary battery 9 is connected to D via a switch circuit 10 and an overcharge / discharge / overcurrent detection circuit 8. Switch circuit 10
When the resistance value of the overcharge / discharge / overcurrent detection circuit 8 is ideally 0, the external terminal VDD outputs the highest potential of the secondary battery, and VSS outputs the lowest potential.

When the overcharge / discharge / overcurrent detection circuit 8 detects overcharge / overdischarge / overcurrent, the overcharge / discharge / overcurrent detection circuit 8 is detected.
The output signal of turns off the transistor 7, and the current flowing through the resistor 5 charges the capacitor 6. The charging voltage V2 of the capacitor 6 is connected to the non-inverting input terminal of the comparator 4. The inverting input terminal of the comparator 4 has VD
Resistors R1 and R2 for dividing the power supply voltage between D-VSS
The voltage divided by the voltage dividing circuit 3 is connected. When the voltage V2 of the capacitor 6 becomes higher than the voltage V1 obtained by dividing the power supply voltage by the voltage dividing circuit 3, the output of the comparator 4 is reversed. The output of the comparator 4 is an input of the control circuit 1, and the output signal of the control circuit 1 controls the switch circuit 10.

At this time, the delay time is V1 = (R2 / (R1 + R2)) VDD-(4) when the resistors of the voltage dividing circuit 3 are R1 and R2, respectively.

The voltage V2 can be expressed by the equation (1). The output of the comparator is inverted when V1 = V2 −−−−−−− (5), so equations (1), (4), and (5)
From the formula, (R2 / (R1 + R2)) = (1-e (-1 / CR) t)-(6) Therefore, t = -CRln (R1 / (R1 + R2))-(7), and the delay time t is It does not depend on the power supply voltage VDD. That is, the delay circuit 2 outputs the output signal to the control circuit 1 after a delay time that does not depend on the power supply voltage.

The control circuit 1 receives the output of the delay circuit 2 as an input and outputs a signal for controlling the switch circuit 10 connected in series with the secondary battery 9. When the output of the control circuit 1 is input as an input signal, the switch circuit 10 turns off and the secondary battery 9
Prohibit charging and discharging. As described above, since the delay time depends only on the capacitance of the capacitor 6 and the resistors R, R1, and R2, the capacitance value and the resistance value are determined by considering the specified values of the overdischarge voltage, the overcharge voltage, and the overcurrent. It is also possible to obtain a desired delay time by making an appropriate selection.

[0017]

According to the charge and discharge control circuit of the present invention, the output of the overcharge and discharge detection and overcurrent detection section outputs a signal through a delay circuit having a delay time that does not depend on the power supply voltage, and the output of the delay circuit is switched. By using it as an input of a control circuit for controlling the circuit, it is possible to supply a charge / discharge control circuit which has a long usage time and a low risk regardless of the value of the secondary battery voltage.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an embodiment of a charge / discharge control circuit of the present invention.

FIG. 2 is a circuit block diagram of a conventional rechargeable power supply device.

[Explanation of symbols]

 1 Control circuit 2 Delay circuit 3 Voltage division circuit 4 Comparator 5 Resistor 6 Capacitor 7 Transistor 8 Overcharge / discharge / overcurrent detection circuit 9 Secondary battery 10 Switch circuit 11 Reference voltage circuit

Claims (1)

[Claims] 1. An overcharge / discharge detection circuit and an overcurrent detection circuit for detecting an overcharge / overdischarge / overcurrent state of a power source using a secondary battery, and an overcharge / discharge detection circuit and an overcurrent detection circuit. In a charging / discharging control circuit, which comprises a delay circuit for delaying the signal of (1) and a control circuit which inputs and processes an output signal of the delay circuit and outputs a signal for controlling charging / discharging. A charge / discharge control circuit characterized by being able to determine the delay time without depending on the power supply voltage.