JP3838708B2 - Lithium ion power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium ion power supply apparatus having a lithium ion power supply monitoring IC that detects overdischarge and overcurrent of a lithium ion battery and promotes overdischarge and prevents overcurrent discharge.
[0002]
[Prior art]
Due to its characteristics, the lithium-ion power supply has a built-in protection IC called a lithium-ion power supply monitoring IC for stable operation, and overdischarge detection and overcurrent detection among the protection functions are delayed to prevent external noise. A circuit is added.
[0003]
FIG. 5 shows a principal block diagram of a conventional lithium ion power supply device (referred to as “battery pack”). In the figure, 1 is a lithium ion power source comprising one or a plurality of lithium ion batteries, 2 is a discharge control FET, 3 is a FET control circuit, 4 is a first comparator, 5 is a first delay circuit, and 6 is a second. A comparator, 7 is a second delay circuit, 8 is an OR circuit, 9 is a + terminal, 10 is a-terminal, and 11 is an external load.
[0004]
The first comparator 4 monitors the voltage of the lithium ion power supply 1, and when the voltage becomes equal to or lower than the predetermined voltage _Vref1, it becomes a high level output, and this output passes through the first delay circuit 5 for a predetermined time T1. After elapse, the signal is input to the OR circuit 8. In response to this, the FET / OFF signal is output from the OR circuit 8 to the FET control circuit 3 (the output of the OR circuit 8 becomes high level). When the FET control circuit 3 inputs the FET / OFF signal, the discharge control FET 2 is turned off, so that the discharge control FET 2 is turned off and the overdischarge promotion of the lithium ion power source 1 is prevented.
[0005]
The second comparator 6 monitors the amount of current flowing from the lithium ion power supply 1 by converting it into a voltage by the ON resistance of the discharge control FET 2. When the voltage becomes equal to or higher than the predetermined voltage V _ref2 , the output becomes a high level. The signal is input to the OR circuit 8 through the second delay circuit 7 after a predetermined time T2 has elapsed. In response to this, the FET / OFF signal is outputted from the OR circuit 8 to the FET control circuit 3 (the output of the OR circuit 8 becomes high level), the discharge control FET 2 is turned off by the FET control circuit 3, and the lithium ion power source 1 is turned on. Overcurrent discharge is prevented.
[0006]
When an overcurrent occurs, the voltage of the lithium ion power supply 1 is lowered due to the internal impedance of the lithium ion power supply 1 and may be erroneously determined as being in an overdischarge state. Therefore, the first delay circuit 5 It is necessary to make the delay time T1 in the second delay circuit T2 longer than the delay time T2 in the second delay circuit 7.
[0007]
[Problems to be solved by the invention]
As described above, since the delay time at the time of overdischarge detection is different from the delay time at the time of overcurrent detection, in the prior art, as in a delay circuit for overdischarge detection and a delay circuit for overcurrent detection, 2 Since two delay circuits are provided, the cost is increased and a capacitor is included as a component of the delay circuit, which leads to an increase in the area of the IC chip and the board on which the IC chip is mounted. That meant limiting the size of the lithium-ion battery and reducing its power capacity.
[0008]
In addition, because the delay time in the delay circuit varies due to variations in the capacitance of the capacitors, the relationship between the inherent delay times in the two delay circuits is reversed, and overdischarge and overcurrent cannot be accurately detected. there is a possibility.
[0009]
Therefore, an object of the present invention is to provide a lithium ion power supply device that can realize cost reduction and IC chip area reduction, and can detect overdischarge and overcurrent more accurately.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a lithium ion power supply device of the present invention controls a lithium ion power supply composed of a lithium ion battery, a discharge control FET connected in series to a lithium ion power supply and a load, and the discharge control FET. An FET control circuit, an overdischarge detection circuit for detecting an overdischarge of a lithium ion power supply, and an overcurrent detection circuit for detecting an overcurrent, and when the overdischarge is detected by the overdischarge detection circuit , or A lithium ion power supply device in which the discharge control FET is turned off when an overcurrent is detected by the overcurrent detection circuit, and the discharge control FET is turned off from the overdischarge detection circuit and the overcurrent detection circuit via an OR circuit. signal is inputted to, and delayed by a delay time of the signal, a delay circuit that outputs to the FET control circuit, overdischarge detecting the delay time It is is provided with a variable delay circuit so as to be longer than the time of overcurrent detection.
[0011]
With the above configuration, if the delay time of the delay circuit is controlled so that the time when overdischarge is detected is longer than the time when overcurrent is detected, the number of delay circuits can be reduced, so that the cost can be reduced. At the same time, the IC chip area can be reduced.
[0012]
In addition, since one delay circuit provides a delay time when overdischarge is detected and a delay time when overcurrent is detected, even if the delay time of the delay circuit varies, the relationship between the two delay times does not reverse. Overdischarge and overcurrent can be accurately detected.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a main part of a lithium ion power supply apparatus according to an embodiment of the present invention. The same parts as those of the prior art in FIG.
[0014]
The FET control circuit 3 inputs the output of the delay circuit 101, but when the output of the delay circuit 101 is not output (at a low level), the discharge control FET2 is turned on, and the output of the delay circuit 101 is the FET / OFF signal ( In the case of high level), the discharge control FET 2 is turned off.
[0015]
Reference numeral 101 denotes a delay circuit capable of switching the delay time between two types of T1 and T2 (T1> T2). The output of the OR circuit 8 is used as the first input, and the output of the second comparator 6 is used as the second input. input. The delay circuit 101 does not operate when the first input is at a low level, and the output is at a low level. Accordingly, neither overdischarge nor overcurrent is detected, and when it is normal, the discharge control FET 2 is turned on and the external load 11 is driven.
[0016]
On the other hand, when the first input becomes high level, the output of the delay circuit 101 switches to high level after a delay time that switches according to the state of the second input has elapsed. When the second input is at a low level, that is, when no overcurrent is detected, the delay time is T1, and when the second input is at a high level, that is, when an overcurrent is detected, The delay time is T2.
[0017]
Therefore, when at least one of overdischarge and overcurrent is detected, the discharge control FET 2 is turned off after the delay time T1 or T2 has elapsed, and overdischarge is promoted and overcurrent discharge is prevented. The delay time at the time of discharge detection is longer than the delay time at the time of overcurrent detection, and it is possible to accurately detect overdischarge and overcurrent.
[0018]
A specific configuration example of the delay circuit 101 is shown in FIG. In the figure, 21 is a first input terminal, 22 is a second input terminal, CC1, CC2, CC3, and CC4 are constant current sources that output currents I1, I2, I3, and I4 (I3> I4), respectively. Q1, Q2 and Q6 are PNP transistors, Q3, Q4 and Q5 are NPN transistors, SW1, SW2 and SW3 are switch circuits, KSW is a changeover switch circuit, R1 and R2 are resistors, C is a capacitor, CV is a constant voltage source It is.
[0019]
The transistors Q1 and Q2 form a differential pair. The base of the transistor Q1 is connected to the connection point between the constant current source CC1 and the capacitor C via the switch circuit SW1, and the base of the transistor Q2 is the switch circuit SW3. And connected to a connection point between the two constant current sources CC3 and CC4 and the resistor R1 via the changeover switch circuit KSW. A constant current source CC2 is connected to the emitter side of the transistors Q1 and Q2 via the switch circuit SW2, and the input side of the current mirror circuit composed of the transistors Q3 and Q4 is connected to the collector side of the transistors Q1 and Q2. (The collector of the transistor Q3) and the output side (the collector of the transistor Q4) are connected to each other.
[0020]
The base of the transistor Q5 is connected to a connection point between the collectors of the transistors Q2 and Q4, and a constant voltage source CV is connected to the collector with a resistor R2 as a load. The base of the transistor Q6 is connected to the connection point between the resistor R2 and the collector of the transistor Q5, the constant voltage source CV is connected to the emitter, and the collector of the transistor Q6 serves as the output terminal of the delay circuit 101.
[0021]
The first input and the second input, which are inputs of the delay circuit 101, are input from the first input terminal 21 and the second input terminal 22, respectively. The first input from the first input terminal 21 is given to the switch circuits SW1, SW2, and SW3. When the first input becomes high level, the switch circuits SW1, SW2, and SW3 are turned on. Yes. The changeover switch KSW is supplied with the second input from the second input terminal 22, and the changeover switch KSW is switched to the constant current source CC3 side when the second input is at the low level. Is switched to the constant current source CC4 side.
[0022]
With the configuration as described above, it operates only during detection of overdischarge or overcurrent, and when the base voltage of the transistor Q1 exceeds the base voltage of the transistor Q2, an output appears at the collector of the transistor Q6. However, since the base voltage of the transistor Q2 rises steeply, the base voltage of the transistor Q1 gradually rises with time due to the action of the capacitor C, so that a delay time is provided.
[0023]
When the resistance value of the resistor R1 is R1, the base voltage of the transistor Q2 is I3 · R1 when overdischarge is detected, I4 · R1 when overcurrent is detected, and I3> I4. The overdischarge detection time is higher than the overcurrent detection time, and therefore the delay time when overdischarge is detected is longer than the delay time when overcurrent is detected (see FIG. 4).
[0024]
Even if there is a variation in the capacitance of the capacitor C, the delay time during overdischarge detection and overcurrent detection varies in the same direction, so the relationship between the two delay times will not be reversed. Overcurrent can be accurately detected.
[0025]
For example, in this embodiment, when one lithium ion battery is connected (voltage of one lithium ion battery≈3.6V), I4 · R1 is set to 2.3V, and I3 · R1 is set to 3.5V. , T2 is set to be longer than T1 by about 10 ms.
[0026]
The present invention is not limited to the above-described embodiment, and may be a lithium ion power source in which a charge control FET is inserted between the discharge control FET 2 and the negative terminal 10.
[0027]
As for the delay circuit, the connection of the constant current sources CC3 and CC4 for generating the base voltage of the transistor Q2 in FIG. 2 may be as shown in FIG. 3. In this case, the changeover switch KSW is set to the second input high. It may be set to OFF when the level is ON and ON when the level is low.
[0028]
【The invention's effect】
As described above, according to the lithium ion power supply device of the present invention, since one delay circuit can be provided, the cost can be reduced, the IC chip area can be reduced, and Since one delay circuit provides a delay time for overdischarge detection and a delay time for overcurrent detection, even if the delay time of the delay circuit varies, the relationship between the two delay times does not reverse. Discharge and overcurrent can be detected accurately.
[Brief description of the drawings]
FIG. 1 is a block diagram of a lithium ion power supply device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration example of a delay circuit in a lithium ion power supply device according to an embodiment of the present invention.
FIG. 3 is a diagram showing a configuration example of a delay circuit in a lithium ion power supply device according to an embodiment of the present invention.
FIG. 4 is a diagram for explaining a difference in delay time between overdischarge detection and overcurrent detection.
FIG. 5 is a block diagram of a conventional lithium ion power supply device.
[Explanation of symbols]
1 Lithium ion power supply 2 Discharge control FET
3 FET control circuit 4 1st comparator 5 1st delay circuit 6 2nd comparator 7 2nd delay circuit 8 OR circuit 9 + terminal 10-terminal 11 External load 21 1st input terminal 22 2nd input terminal CC1, CC2, CC3, CC4 constant current source Q1, Q2, Q6 PNP type transistors Q3, Q4, Q5 NPN type transistors SW1, SW2, SW3 switch circuit KSW changeover switch circuit R1, R2 resistor C capacitor CV constant voltage source 100 lithium ion power supply monitoring IC
200 Lithium ion power supply (power pack)

Claims (1)

A lithium-ion power source comprising a lithium-ion battery;
A discharge control FET connected in series with a lithium ion power source and a load;
An FET control circuit for controlling the discharge control FET;
An overdischarge detection circuit for detecting an overdischarge of a lithium ion power supply, and an overcurrent detection circuit for detecting an overcurrent ;
A lithium ion power supply device in which a discharge control FET is turned off when an overdischarge is detected by an overdischarge detection circuit or when an overcurrent is detected by an overcurrent detection circuit,
A delay circuit that inputs a signal for turning off the discharge control FET from the overdischarge detection circuit and the overcurrent detection circuit via an OR circuit, delays the signal by a delay time, and outputs the delayed signal to the FET control circuit, A lithium ion power supply apparatus comprising a delay circuit that varies the delay time so that the time when overdischarge is detected is longer than the time when overcurrent is detected.

Images