JP3683053B2 - Power circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit that converts AC power into DC and supplies power to a load circuit, charges a backup battery, and supplies power from the battery to the load circuit when AC power is not input.
[0002]
[Prior art]
For example, some electronic circuit devices, such as notebook computers, include an AC / DC converter, a charging circuit, and a backup battery. When an AC power supply is input, the AC circuit is converted to a direct current to supply power to the load circuit. In addition, there is a type that employs a power supply circuit that trickle-charges a backup battery and supplies power from the battery to a load circuit when no AC power is input.
[0003]
In this type of equipment, there is a type in which a built-in backup battery is fixedly mounted by soldering or the like (not premised on battery replacement) and a battery can be freely attached and detached. In the latter type of device, of course, the power backup function using the battery does not work when the battery is not attached.
[0004]
[Problems to be solved by the invention]
Many of the devices provided with the backup battery as described above display the charge state of the battery with an LED lamp or the like (the lamp is lit when fully charged). However, in the past, even devices such as notebook personal computers in which the backup battery can be freely attached / detached, hardly display whether the battery is installed or removed.
[0005]
In the case of a device that is placed close to the user, such as a notebook computer or home video camera, and is always operated by being exposed to the human eye, whether or not a backup battery is installed is immediately determined from the appearance. As can be seen, there is no need to display the presence of a battery with an LED lamp.
[0006]
However, the situation is different in the case of the LAN concentrator previously developed by the present inventors. As is well known, a LAN concentrator is a device used to construct a system for connecting computers and exchanging data within a limited range such as in an office or a building. The widely used standard 10BASE-T uses a pair of unshielded wires similar to a normal telephone line, and its connection is very simple compared to other standard transmission lines. A concentrator called a hub (HUB) is commercially available, and a LAN can be constructed simply by connecting a jack at the end of a cable connected to a LAN board of a personal computer to the multiport connector of the concentrator.
[0007]
The present inventors recently developed a LAN concentrator equipped with the above-described power supply circuit including a backup battery. According to this, even if there is an accident that suddenly causes a power failure or accidentally disconnects the power plug, the function of the LAN concentrator is backed up by the built-in battery and carries out important information processing. Avoid serious damage to your computer network.
[0008]
If a LAN concentrator is installed in an office, etc. and necessary cable wiring is performed, the concentrator is “held from behind the edge” that supports the LAN and needs to be noticed by the user during normal times. There is no equipment. Therefore, it is usually installed in a suitable place, and it is not uncommon to install it under the floor of the free access floor together with wiring. Of course, the power remains on (originally there is no power switch).
[0009]
In the LAN concentrator used in such an environment, there is a risk of using the backup battery with the backup battery removed for some reason. Therefore, a function for notifying the user whether or not a backup battery is installed when the power is supplied to the apparatus is indispensable. Such a need may exist in addition to the LAN concentrator.
[0010]
By the way, as a method of detecting that a battery pack is mounted on the device body, a contact type sensor such as a limit switch, a photoelectric sensor, or a magnetic sensor is provided in the battery mounting portion, and the presence or absence of the battery pack is mechanically determined. Alternatively, a physical detection method is known. However, this method has a problem of high cost and is inferior in reliability.
[0011]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to add a simple circuit between a charging circuit and a backup battery, and thereby to reliably determine whether or not a battery is mounted. It is an object of the present invention to provide a power supply circuit that detects and informs the user by the sex.
[0012]
[Means for Solving the Problems]
The power supply circuit of the present invention basically has the following requirements (1) to (4) (Claim 1).
[0013]
(1) An AC / DC converter that converts AC power into DC power and supplies it to a load circuit, a backup battery that is detachably connected to a battery terminal, and the battery is charged by the output of the AC / DC converter And a system for supplying the output of the battery to the load circuit when there is no output of the AC / DC converter.
[0014]
(2) In a charging current path from the output of the AC / DC converter to the battery, a charging current detecting resistor a, a charging output adjusting transistor b, and a backflow preventing diode c in order of the charging current direction. And a MOS transistor d serving as a battery separation switch exist in series. An intermediate point between the diode c and the MOS transistor d is connected to the load circuit side, and the output of the battery is supplied to the load circuit by this system.
[0015]
(3) There is a gate drive transistor e for turning on and off the MOS transistor d and its control circuit, and the transistor e is turned on when a voltage higher than a predetermined value is present between the battery terminals. In response, the MOS transistor d is turned on.
[0016]
(4) A circuit for detecting and notifying that the transistor e or the MOS transistor d is in an on state.
[0017]
In the power supply circuit having the above requirements, in the second invention, there is a series circuit of a Zener diode and a resistor between the battery terminals, and the transistor e is turned on when the Zener diode is turned on. doing. In the third aspect of the invention, when both a condition that there is a voltage greater than a predetermined value between the battery terminals and a condition that a predetermined control signal is in a predetermined state are satisfied, the transistor e Is configured to turn on.
[0018]
Further, the fourth invention is characterized in that the following requirements (5) to (7) are provided in relation to the charging circuit.
[0019]
(5) A current limiting circuit for controlling the transistor b according to the magnitude of the voltage drop at the resistor a so that the charging current does not exceed a predetermined value, and detection at the output side of the transistor b And a voltage limiting circuit for controlling the transistor b so that the voltage does not exceed a predetermined value.
[0020]
(6) The circuit is configured such that the transistor f is turned on when the voltage obtained by appropriately dividing the voltage downstream of the resistor a by the resistor circuit exceeds a predetermined value, whereby the charging current is sufficient. Detects a fully charged state that has become smaller.
[0021]
(7) A circuit for lighting the LED lamp when the transistor f is turned on is provided.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
==== Overall Basic Configuration ====
A configuration of a power supply circuit according to an embodiment of the present invention is shown in FIG. Basically, this circuit converts a commercial AC power source 1 into a DC power source (15 volts) and supplies it to the load circuit 2, and a backup unit that is detachably connected to the battery terminals 4a and 4b. Battery 5, a system for charging battery 5 by the output of AC / DC converter 3, and a system for supplying output of battery 5 to load circuit 2 when there is no output from AC / DC converter 3. As a part of the load circuit 2, a state display circuit 6 for driving the LED lamp is included as will be described later.
[0023]
In the charging current path from the output of the AC / DC converter 3 to the battery 5, a charging current detection resistor R 3, a charging output adjustment transistor Q 1, a backflow prevention diode D 1, A MOS transistor Q2 serving as a separation switch exists in series. An intermediate point between the diode D1 and the MOS transistor Q2 is connected to the load circuit 2 via a backflow prevention diode D3, and the output of the battery 5 is supplied to the load circuit 2 by this system. There is a diode 4 for preventing backflow so that the discharge current of the battery 5 does not flow into the AC / DC converter 3 side.
[0024]
==== Configuration of Charging Circuit Portion ====
For a charge output adjusting transistor (also referred to as a main transistor) Q1, a transistor Q3 and a resistor R8 are connected in series between a base and a ground line, and a resistor R7 is connected between an emitter and a base. The charging current (collector current) flowing through the main transistor Q1 is adjusted by adjusting the base current of this path. A constant voltage Vr is applied from a constant voltage source (not included) (not shown) to the base of the transistor Q3, and a collector current always flows through Q3 (not constant). In the following description, it is assumed that the battery 5 is connected to the terminals 4a and 4b and the MOS transistor Q2 is turned on.
[0025]
A transistor Q6 and a resistor R2 are connected in series between the emitter of the transistor Q3 and the charging current upstream side of the current detection resistor R3. The base of the transistor Q6 is connected to the downstream side of the charging current of the current detection resistor R3 via the resistor R4. Therefore, as the charging current flowing through the resistor R3 increases and the voltage drop increases, the base-emitter voltage of the transistor Q6 increases and the collector current of Q6 (current flowing into the resistor R8) increases. As a result, the emitter potential of the transistor Q3 increases, the collector current of Q3 (base current of the main transistor Q1) decreases, and the charging current flowing through the main transistor Q1 decreases. The above configuration is the above-described current limiting circuit that controls the main transistor Q1 so that the charging current does not exceed a predetermined value.
[0026]
A resistor R9 and a transistor Q4 are connected in series between the collector of the main transistor Q1 and the emitter of the transistor Q3. Further, resistors R10 and R11 for detecting charging voltage are connected in series between the collector of the main transistor Q1 and the ground, and an intermediate point thereof is connected to the base of the transistor Q4. When the collector voltage (charge voltage) of the main transistor Q1 rises, the detection voltage at the resistors R10 and R11 (base potential of the transistor Q4) rises, and the collector current of Q4 (current flowing into the resistor R8) increases. As a result, the emitter potential of the transistor Q3 increases, the collector current of Q3 (the base current of the main transistor Q1) decreases, and the charging voltage decreases. The above configuration is the above-described voltage limiting circuit that controls the main transistor Q1 so that the charging voltage does not exceed a predetermined value.
[0027]
==== Full charge detection circuit ====
When the battery 5 is fully charged, the charging current is very small. This is detected by a full charge detection circuit. The resistors R5 and R6 are connected in series between the downstream side of the charging current of the current detection resistor R3 and the ground, and the transistor Q7 and the resistor R1 are connected in series between the upstream side of R3 and the ground. The midpoint of resistors R5 and R6 is connected to the base of transistor Q7.
[0028]
When the charging current flowing through the resistor R3 is larger than the specified value, the voltage drop due to R3 is large, so that the base-emitter voltage of the transistor Q7 is large and Q7 is on. At this time, the full charge detection signal {circle around (1)} taken out from the middle point of the transistor Q7 and the resistor R1 is at the H level. On the other hand, when the charging current flowing through the resistor R3 becomes equal to or less than the specified value, the base-emitter voltage of the transistor Q7 decreases and Q7 is turned off. Then, the full charge detection signal (1) becomes L level.
[0029]
The full charge detection signal {circle around (1)} is transmitted to the status display circuit 6; when the signal {circle around (1)} is H level, the LED lamp indicating charging is turned on, and when the signal {circle around (1)} is L level, Light.
[0030]
==== System for detecting whether battery 5 is mounted / not mounted ====
For the MOS transistor Q serving as a battery separation switch, a resistor R12 is connected between the source and the gate, and a gate drive transistor Q5 is connected between the gate and the ground. A Zener diode D2 and resistors R13 and R14 are connected in series between the battery terminals 4a and 4b, and a midpoint of the resistors R13 and R14 is connected to the base of the transistor Q5.
[0031]
Here, it is assumed that the battery 5 is not connected to the terminals 4 a and 4 b and the AC power source 1 is not input to the AC / DC converter 3. Since there is no power supply in this state, the MOS transistor Q2 and the gate drive transistor Q5 are naturally turned off.
[0032]
Assume that the AC power supply 1 is input to the AC / DC converter 3 without the battery 5. At this time, the output voltage (charging voltage) of the charging circuit is applied to the source side of the MOS transistor Q2, but since the MOS transistor Q2 is off, no charging voltage appears on the drain side of Q2. Therefore, Zener diode D2 remains off, so transistor Q5 also remains off. That is, the MOS transistor Q2 is not turned on.
[0033]
It is assumed that the battery 5 charged to some extent is connected to the terminals 4a and 4b. At this time, the output voltage of the battery 5 is applied to the series circuit of the Zener diode D2 and the resistors R13 and R14, D2 is turned on, and a base voltage for turning on the transistor Q5 is generated. When the transistor Q5 is turned on, the MOS transistor Q2 is turned on, and the output voltage (charging voltage) of the charging circuit appears at the drain of Q2. Thus, the battery 5 is trickle charged by the output of the charging circuit. In this state, when there is no input from the AC power supply 1 and there is no output from the charging circuit, the discharge current of the battery 5 flows to the load circuit 2 side through the MOS transistor Q2 and the diode D3. This is a backup state by the battery 5.
[0034]
By the way, the battery detection signal (2) is taken out from the base side of the transistor Q5. As described above, if the battery 5 is present, the battery detection signal {circle around (2)} is H level and the transistor Q5 is turned on. If the battery 5 is not present, the battery detection signal {circle around (2)} is at L level and the transistor Q5 is off. This signal (2) is transmitted to the status display circuit 6. When the signal (2) is at the L level, the LED lamp informing that there is no battery is lit, and when the signal (2) is at the H level, there is a battery. The LED lamp to notify turns on. Note that the presence or absence of the battery can be notified by other notification means such as a buzzer sound.
[0035]
FIG. 2 shows another embodiment of the present invention regarding a system for detecting whether or not the battery 5 is mounted. Instead of the Zener diode D2 in FIG. 1, a transistor Q8 is connected in FIG. A resistor R15 is connected between the base and emitter of the transistor Q8, and a control signal (3) from the control system included in the load circuit 2 is applied to the base of the transistor Q8 via the resistor R16. In this embodiment, both the condition that the battery 5 is connected and there is a voltage greater than or equal to a predetermined value between the terminals 4a and 4b and the condition that the predetermined control signal (3) is at the L level are satisfied. The gate drive transistor Q5 is turned on, and as a result, the MOS transistor Q2 is turned on.
[0036]
【The invention's effect】
According to the present invention, by adding a simple circuit between the charging circuit and the backup battery, it is possible to detect with high reliability whether or not the battery is mounted and notify the user. Compared to a conventional configuration in which the presence or absence of a battery is mechanically or physically detected by an appropriate sensor, the implementation cost is considerably reduced, and there is less fear of failure.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of only a main part of another embodiment in which a part of the embodiment is changed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC power supply 2 Load circuit 3 AC / DC converter 4a * 4b Battery terminal 5 Battery 6 Status display circuit R3 Charge current detection resistance a
Q1 Charge output adjustment transistor b
D1 Backflow prevention diode c
Q2 MOS transistor d serving as battery separation switch
Q5 Transistor e for gate drive

Claims (2)

A power supply circuit comprising the following requirements (1) to (4):
(1) An AC / DC converter that converts AC power into DC power and supplies it to a load circuit, a backup battery that is detachably connected to a battery terminal, and the battery is charged by the output of the AC / DC converter And a system for supplying the output of the battery to the load circuit when there is no output of the AC / DC converter.
(2) In a charging current path from the output of the AC / DC converter to the battery, a charging current detecting resistor a, a charging output adjusting transistor b, and a backflow preventing diode c in order of the charging current direction. And a MOS transistor d serving as a battery separation switch exist in series. An intermediate point between the diode c and the MOS transistor d is connected to the load circuit side, and the output of the battery is supplied to the load circuit by this system.
(3) There is a gate drive transistor e for turning on and off the MOS transistor d and its control circuit, and the transistor e is turned on when a voltage higher than a predetermined value is present between the battery terminals. In response, the MOS transistor d is turned on.
(4) A circuit for detecting and notifying that the transistor e or the MOS transistor d is in an on state.   2. The power supply circuit according to claim 1, wherein there is a series circuit of a Zener diode and a resistor between the battery terminals, and the transistor e is turned on when the Zener diode is turned on.

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