JPH03139120A - Battery overdischarge prevention circuit - Google Patents

Abstract

PURPOSE:To prevent the overdischarge of a battery by conducting a control transistor through a trigger pulse from a control terminal and by causing the control transistor to maintain its conductive state through the terminal voltage of the battery not lower than a certain value. CONSTITUTION:When a control transistor Tr2 is conducted by a trigger pulse from a control terminal Tc and a series transistor Tr1 is conducted thereby, an output terminal voltage is generated in an output terminal Tb1 so that both control transistor Tr2 and series transistor Tr2 are stabilized in a conductive state and can supply a load L with power. When the discharge of a battery B proceeds and the terminal voltage of the battery B lowers to a certain value and less, the output terminal Tb1 voltage on the output side of the series transistor Tr1 lowers also so that the control transistor Tr2 detects the voltage and is placed in a cutoff state and consequently the series transistor Tr1 also changes from the conductive state to the cutoff state. Thus, it is possible to separate the load L automatically and to prevent the overdischarge of the battery B.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a battery over-discharge prevention circuit for appropriately preventing over-discharge of a secondary battery such as a lead-acid battery.

BACKGROUND ART Storage batteries that can be repeatedly charged and discharged are called secondary batteries and are widely used, in contrast to primary batteries that cannot be recharged and reused.

The most common secondary batteries are lead-acid batteries and alkaline batteries, typified by nickel-cadmium batteries.The former, in particular, is cheaper than the latter, so it is difficult to transport cars, ships, etc. It is widely used not only for mounting equipment, but also as a mobile power source for various small portable electrical devices such as television receivers and radio receivers.

Problems to be Solved by the Invention Although lead-acid batteries can be conveniently used as mobile power sources, they have a major drawback of being susceptible to overdischarge. That is, as the discharge progresses, both lead oxide, which is an anode material, and lead, which is a cathode material, become lead sulfate (Pb3O).
4) and become immobile, and as a result of overdischarging beyond a certain level, it becomes impossible to recharge.

Therefore, it is preferable to use lead-acid batteries in combination with an appropriate overdischarge prevention circuit, and it is recommended that the load be automatically disconnected when the discharge progresses beyond a certain level. There was no known simple overdischarge prevention circuit that could be used in combination with lead-acid batteries.

Therefore, in view of the actual state of the prior art, an object of the present invention is to provide a battery overdischarge prevention circuit that can be easily incorporated into various small portable devices by combining a series transistor and a control transistor. It is in.

Means for Solving the Problems The configuration of the present invention to achieve the object is as follows: An input terminal connected to a battery (any secondary battery mainly including a lead-acid battery; the same shall apply hereinafter) and an output connected to a load. It is equipped with a series transistor interposed between the terminal and a control transistor that supplies a base current to the series transistor, and the control transistor is made conductive by a trigger pulse from the control terminal, and is made conductive by a terminal voltage of the battery exceeding a certain value. Its gist is to maintain the state.

Note that the base of the control transistor may be connected to the output terminal via a constant voltage element.

In this configuration, the series transistors are supplied with a base current by the control transistor, and the control transistor can control the conduction/blocking state. On the other hand, the control transistor is made conductive by a trigger pulse from the control terminal, and when the series transistor becomes conductive, an output terminal voltage is generated at the output terminal. From then on, both the control transistor and the series transistor are stabilized in a conductive state. Can power the load.

As the battery discharge progresses and the battery terminal voltage drops below a certain value, the output terminal voltage on the output side of the series transistor also drops, so the control transistor detects this and enters the cutoff state, so that the series transistor The transistor also switches from a conductive state to a cut-off state. That is,
By appropriately selecting the operating voltage of the control transistor at this time, it is possible to automatically disconnect the load and prevent over-discharge of the battery.

By connecting the base of the control transistor to the output terminal via a constant voltage element, by selecting a constant voltage element,
Since the operating voltage at which the control transistor changes from a conductive state to a cutoff state can be arbitrarily changed, it is possible to appropriately set the protection level of the battery.

Example Examples will be described below with reference to the drawings.

The battery overdischarge prevention circuit 10 includes a series transistor T.
ri and a control transistor Tr2 (first
figure).

The series transistor Tri is a power transistor of a predetermined current capacity including any type of GTO, FET, etc., and is interposed in series between the input terminal Tal and the output terminal Tbl. However, batch 1. It is assumed that IB is connected between the input terminal Tal and the common terminal Ta2, and the load is connected between the output terminal Tbl and the common terminal Tb2. Further, the common terminals Ta2 and Tb2 are connected by a common return line k.

A resistor R1 is connected between the emitter and base of the series transistor Tri, and a control transistor Tr2 is connected between the base of the series transistor Tri and the common return wire via a resistor R2.

The base of the control transistor Tr2 is connected to the series transistor Tri(7) via the Zener diode D1 and the resistor R3.
The collector of the series transistor Tri is connected to the output terminal Tbl. Note that from the connection point between Zener diode D and resistor R3, control terminal T
c is drawn out and connected to the common retrace line k via the capacitor C1. Further, the base of the control transistor Tr2 is connected to the common retrace line k via a resistor R4.

Generally, the terminal voltage VB of batch 'JB changes as shown in FIG. 2 as the discharge time t elapses.

That is, at the beginning of discharging, the terminal voltage VB only gradually decreases, but after a certain period of time to has elapsed and the terminal voltage VB becomes less than a certain value Vo, it rapidly decreases, and battery B This will lead to overdischarge.

On the other hand, in FIG. 1, when a positive trigger pulse is applied to the control terminal Tc, the control transistor Tr2 can be made conductive, whereby the control transistor Tr2 supplies the base current of the series transistor Tri, and the series transistor Tri can be made conductive. That is, power supply to the load can be started by a trigger pulse from the control terminal Tc.

At this time, even after the loss of the trigger pulse, the control transistor T
r2, in order for the series transistor Tri to be stable in a conductive state, V>Vd +VR3+VBE, ■=Output terminal voltage Vd: Zener voltage of Zener diode D VB3: Voltage drop of resistor R3 VBE2: Pace emitter of control transistor Tr2 voltage conditions are required.

The terminal voltage VB of battery B is the series transistor Tri
Assuming the emitter-collector voltage of VECI, VB =
V+VEC1, so if the discharge progresses and the terminal voltage VB decreases, and the condition of VB - VECI > Vd + Vr13 + VBE2 no longer holds true, the control transistor Tr2 and the series transistor Tri operate from the conductive state to the cut-off state,
The load can be automatically disconnected. That is, for the terminal voltage VB = Vo just before battery B reaches overdischarge, Vd < Vo - (VECI +VBE2 +VR3)
If the rating of Zener diode D is selected such that can accurately prevent overdischarge.

In the above explanation, the capacitor CI inserted between the control terminal Tc and the common retrace line is connected to the input terminal Tal,
Due to intrusion noise from the output terminal Tbl, control terminal Tc, etc., the control transistor Tr2 and the series transistor Tri
This is a noise prevention capacitor to prevent erroneous conduction.

Since the series transistor Tri conducts a load current corresponding to the load, a transistor having a sufficiently large current carrying capacity is used.

Further, the emitter-collector voltage L'[voltage VBCI is preferably as small as possible in order to reduce the loss within the series transistor Tri, and therefore it is preferable to use a PNP transistor as the series transistor Tri.

However, it goes without saying that NPN transistors can also be used by changing some of the circuits.

Note that since the Zener diode D defines the operating voltage of the control transistor Tr2 by its Zener voltage Vd, it may be replaced with any other constant voltage element.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, by combining a series transistor and a control transistor,
Since it is possible to detect that the terminal voltage of the battery has decreased below a certain value and switch the series transistor from a conductive state to a cutoff state via a control transistor, over-discharge of the battery can be reliably prevented, and Since the overall configuration is extremely simple, it has the excellent effect of being easily incorporated into any small portable device that uses a battery.

[Brief explanation of the drawing]

Figures 1 and 2 show examples, Figure 1 is an overall circuit diagram,
FIG. 2 is an example of the discharge characteristics of a battery. B...Battery VB...Terminal voltage Vo...Constant value 'r'al...Input terminal Tbl...Output terminal Tc...Control terminal Tri...Series transistor Tr2...Control transistor

Claims (1)

[Claims] 1) A series transistor interposed between an input terminal connected to a battery and an output terminal connected to a load, and a control transistor supplying a base current to the series transistor, the control transistor A battery overdischarge prevention circuit is characterized in that it becomes conductive in response to a trigger pulse from a control terminal, and maintains the conductive state in response to a terminal voltage of the battery exceeding a certain value. 2) The battery overdischarge prevention circuit according to claim 1, wherein the base of the control transistor is connected to an output terminal via a constant voltage element.