JPH11332113A - Power control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a voltage drop generated by a reverse current preventing diode for a battery power source, and to reduce power consumed by a transistor connected in parallel with this reverse current preventing diode, by providing a change-over switch which short-circuits the reverse current preventing diode by turning the transistor on when only a battery power source is being used, and turns the transistor off when not so. SOLUTION: At a cut-off time of an AC adaptor 3, the contact between terminals a and b of the switch 39 of a connector 4 with a switch is made, and the contact between terminals b and c is opened, and a battery 6 is connected to a DC/DC converter 24 through the contact between the terminals b and a of the switch 39. Meanwhile, the contact between the terminals a and b of the switch 39 is opened, and the contact between the terminals b and c is made, and an AC power source 1 is connected to the DC/DC converter 24 through a diode 26, when the AC adoptor 3 is connected to the connector 4 with a switch. At this time, service interrupt is detected by a source voltage monitoring IC 31, when power supplying service of the AC power source 1 is interrupted, and a transistor 9 connected in parallel with a reverse current preventing diode 8 is turned on via the use of a MOSFET transistor 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a power supply control circuit, and more particularly to an improvement in power consumption due to short-circuit of a diode for preventing a backflow of a primary battery and prevention of battery leakage due to overdischarge of the battery. The present invention relates to a possible power supply control circuit.

[0002]

2. Description of the Related Art Conventionally, in a device such as a portable information terminal device using a main power supply with a primary battery, when an AC adapter is connected from the outside, a diode for preventing backflow from the battery is provided in a battery supply line. By the way, as for the discharge characteristics of a battery, for example, the continuous discharge curve of each constant current load of one alkaline battery at room temperature, the voltage of the discharge curve decreases as the load current increases, as shown in FIG.

In addition, the relationship between the forward current and the voltage of the Schottky barrier diode does not show a negligible voltage drop as compared with the battery voltage as shown in FIG. For this reason, a method for suppressing the voltage drop of the battery supply line has been studied. For example, there is a method as disclosed in Japanese Patent Laid-Open No. 9-308129. FIG. 4 is a block diagram of a conventional circuit,
FIG. 5 shows a time chart thereof, and FIG. 6 shows a voltage drop state of the backflow prevention diode during use on the anode side and the cathode side.

First, the circuit operation of FIG. 4 will be described with reference to a time chart of FIG. Period 50 in FIG.
Reference numeral 1 denotes a state where the battery 6 is set. During the period 502, the control unit 19, the load 25, and the signal 104 communicate with each other about the increase and decrease of the load current. To "H" level,
The output signal of the AND circuit 18 becomes "H" level and the MOS
The gate of the FET 15 is driven, the MOSFET 15 is turned on, and the base current of the transistor 9 flows according to the magnitude of the load current to turn on the transistor 9.

During a period 503, when the load current becomes larger, the control section 19 sends a signal 102 to the AND circuit 17, and
The MOSFET 14 is turned on to increase the base of the transistor 9. During the period 504, when the load current further increases, the MOSFET 13 is turned on in the same manner, the base current of the transistor 9 is increased, and the voltage drop between the emitter and the collector of the transistor 9 is controlled so as not to be increased by the load current.

During the period 505, the load current slightly decreases,
The signal 103 of the control unit 19 is set to the “L” level and the MOSF
Turn off ET13. During the period 506, since the load current further decreases, the signal 102 of the control unit 19 is set to the “L” level to turn off the MOSFET 14. The period 507 is a state where the load current increases again and the MOSFET 14 is turned on.

During the period 508, the load current further increases again, and M
The OSFET 13 is turned on. Period 509 is A
When C adapter 3 is connected to connector 4, diode 2
The AC adapter power is supplied to the DC / DC converter 24 through 6. At this time, the AC adapter voltage monitoring IC 5
Detects the AC adapter voltage and transmits the "L" level to the AND circuits 16, 17 and 18 by the signal 100,
The FETs 13, 14, and 15 are turned off, and the transistor 9 is turned off.

[0008] With respect to the change in the voltage of 200 on the battery voltage side in FIG.
The DC / DC converter input side 201 is for reducing the voltage drop by the transistor 9, and 201 ′ indicates a voltage change when the transistor 9 is not provided.

[0009]

The above-mentioned prior art has the following problems. The first problem is the backflow preventing diode 8.
Since the voltage between the emitter and the collector of the transistor 9 connected in parallel is used in a saturated state, the base current of the transistor 9 increases, and the battery energy cannot be used efficiently.

The second problem is that the battery supply line is branched by the transistor 9 and current flows. The voltage between the emitter and the collector of the transistor 9 is about 0.1 V, and it is necessary to further reduce the voltage drop. is there. The third problem is that the control unit for controlling the base current of the transistor 9 and the MOSFE
The number of circuit components such as T was large, the ratio of the circuit components to the board area was large, and the control was complicated.

Another important fourth problem is as follows.
When the battery 6 is set in the apparatus and stored for a long period of time, the battery 6 is overdischarged, a safety valve is activated by gas generation inside the battery, a liquid leak occurs, and the equipment is corroded.
The reason is that although the battery voltage drops and the DC / DC converter stops operating, there is no means to stop the battery supply, and therefore dark current depending on the load impedance continues to flow.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a power supply for improving power consumption due to short-circuit of a diode for preventing backflow of a primary battery and preventing battery leakage due to overdischarge of the battery. It is to provide a control circuit.

[0013]

According to the present invention, a battery power supply and an AC adapter power supply for outputting a DC voltage higher than the output voltage of the battery power supply are provided with a backflow prevention diode connected to each power supply output side. In the power supply control circuit for selectively supplying a load via the power supply, when the battery power supply is used, the backflow prevention diode is short-circuited, and the PNP transistor having an emitter and a collector connected in parallel with the backflow prevention diode is turned off. Switch means for switching the backflow prevention diode to function effectively when the AC adapter power supply is connected; and loading the output of the AC adapter power supply and the output of the battery power supply via the backflow prevention diode. DC / DC supplied to
A power failure or disconnection of the AC adapter outlet is detected during the power supply from the AC adapter power supply and the AC adapter power supply, and the power supply is smoothly switched from the AC adapter power supply to the battery power supply, and a voltage close to the battery power supply voltage is supplied to the DC / DC converter. A diode short-circuit means for preventing backflow, and a battery voltage for detecting a drop in battery voltage and activating a relay drive monitoring means under a long-term storage state by mounting the battery power supply on the device to cut off the battery power supply from a load. A power supply control circuit is constituted by monitoring means and AC adapter power supply voltage monitoring means for monitoring a power failure or disconnection of the AC adapter outlet while power is being supplied from the AC adapter power supply.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a power supply control circuit according to the present invention will be described with reference to FIG. The power supply control circuit 30 is connected between the AC adapter 3 and the battery 6 and the DC / DC converter 24. The AC input power supply 1 side of the power supply control circuit 30 connects the AC adapter power supply voltage monitoring resistors 40 and 41 and the divided voltages of these AC adapter power supply voltage monitoring resistors 40 and 41 via the connector 4 with the switch 39. The detected AC adapter power supply voltage monitoring IC 31 and its output signal are connected to the gate of the MOSFET transistor 13 via the resistor 42, and the battery 6 power supply connected via the connector 7 is connected in parallel to the battery 6. Battery voltage monitoring I
C32, a relay drive IC (relay drive monitoring means) 33 for receiving the output signal, a latch relay 36 for opening and closing the battery power line, a push button switch 34 for closing the initial power line, and a latch relay 36 for opening and closing the battery supply line. It is constituted by a contact 38.

As shown in FIG. 2, the circuit of the AC adapter power supply voltage monitoring IC 31 has an output terminal formed by an emitter follower circuit employing transistors 55 and 57, and the transistor 57 is inserted into a base. It is configured to be held at the “L” level through the resistor 56 and turned on. Therefore, the power supply circuit M
The gate of the OSFET transistor 13 is at "L" level, the base voltage of the transistor 9 is at "H" level, and the transistor 9 is turned off.

Hereinafter, the circuit operation of FIG. 1 will be described with reference to the drawings. Normally, when the battery 6 is used as a main power source, the AC adapter 3 is disconnected. At this time, in the switch 39 of the connector 4 with a switch, the terminals a and b are short-circuited. AC adapter power supply voltage monitoring IC
The power supply 31 is turned off because the terminals b and c of the switch 39 are opened.

The circuit of the AC adapter power supply voltage monitoring IC 31 is a circuit as shown in FIG. 2, the output terminal is an emitter follower circuit, and the base of the transistor 57 is a resistor 56.
It is turned on because it is at the "L" level through. Therefore, the gate of the MOSFET transistor 13 of the power supply circuit is at the "L" level, so that the base voltage of the transistor 9 is at the "H" level, and the transistor 9 is off.

FIG. 3 is a time chart of the present invention, which will be described in detail with reference to FIG. During the period 401, since the battery 6 is set and the relay contact 38 is open,
The power supply circuit does not operate. During the period 402, when the push button switch 34 is pressed, the set coil of the latch relay 36 operates, the relay contact 38 closes, power is supplied from the battery 6, and the power is supplied to the DC / DC converter 24 through the terminal ba of the switch 39. Is done. DC / DC converter 24
Starts the operation and supplies the output voltage to the load 25.

During the period 403, even when the push button switch 34 is released, no current flows to the set coil of the latch relay 36, but the relay contact 38 is closed. DC /
Since the DC converter 24 is directly supplied with the voltage of the battery 6 and the base current of the transistor 9 does not flow, the loss of battery energy is greatly improved. In the period 404, when the AC adapter 3 is connected to the
9 is open between the terminals a and b, closed between the terminals b and c, and the power of the AC
It is supplied to a converter 24. At this time, AC adapter 3
Is set higher than the battery voltage.

During a period 405, when the AC input power supply 1 of the AC adapter 3 is out of power or the AC adapter outlet 2 is disconnected, the output voltage of the AC adapter is detected by the IC adapter 31 for monitoring the divided voltage of the resistors 40 and 41. When the voltage falls below the reference voltage 51 of the comparator 52 with hysteresis in the IC 31, the base of the transistor 55 is driven through the resistor 54, and the transistor 55 is turned on. When a current flows to the resistor 56 and the base voltage of the transistor 57 increases, the transistor 5
7 turns off.

The level of the signal line 100 of the power supply control circuit 30 becomes "H", and the gate of the MOSFET 13 is driven. The MOSFET 13 is turned on, the transistor 9 is turned on, and the battery 9 is supplied from the backflow prevention diode 8 to the transistor 9 from the battery 6. The current to be switched is switched. Thus, even when the power supply of the AC adapter 3 is stopped while the AC adapter 3 is connected to the connector 4, the supply to the DC / DC converter 24 can be smoothly switched at a voltage level close to the battery voltage. .

During the period 406, the AC input power supply 1 is restored, or the AC adapter 3 is connected to the outlet 2, and A
When the output voltage is supplied from the C adapter 3, the resistor 4
When the comparator 52 with hysteresis detects a voltage equal to or higher than the reference voltage 51 based on the divided voltages of 0 and 41, the base voltage of the transistor 55 becomes "H" level, the transistor 55 is turned off, the transistor 57 is turned on, and the MOSFET 13 of the power supply circuit is turned on. Gate becomes "L" level,
The MOSFET 13 turns off and the transistor 9 turns off. Power is supplied again from the AC adapter 3 to the DC / DC converter 24 through the diode 26.

During the period 407, the AC adapter 3 is connected to the connector 4
It is a case where it is further separated. During the period 408, when the battery 6 is exhausted and the battery voltage decreases, the DC / DC converter 2
4, the operation of the DC / DC converter stops, but the battery current flows to the load 25 through the internal coil and the diode 27 of the DC / DC converter 24, though the battery current is minute, and the state is left as it is. Then battery 6
Leads to overdischarge.

However, during the period 408, when the battery voltage monitoring IC 32 sends the "H" level signal to the relay drive IC 33 when the battery voltage falls below the specified voltage, the relay drive IC 33 turns on the reset coil of the latch relay 36, and Open the contact 38 and disconnect the battery supply line. During the period 409, the relay contact 38 is opened and the battery supply line is disconnected. Since the output voltage of the DC / DC converter 24 decreases, the latch relay 3
Since the reset coil 6 and the power supply of the relay drive IC 33 are supplied from the output voltage of the DC / DC converter 24, the operation is stopped.

A period 410 indicates a state where the battery is replaced with a new battery. During the period 411, the push button 34 is pressed again, the relay contact 38 is closed, and the supply of power from the new battery 6 is restarted.
The diodes 35 and 37 of the power supply control unit 30 prevent malfunction caused by noise generated when the coil of the latch relay 36 is turned on and off.

The resistor 42 is a pull-up resistor for determining the level of the gate voltage of the MOSFET 13. The constant current source 50 of the AC adapter power supply voltage monitoring IC 31 shown in FIG. 2 is for stabilizing the reference power supply 51, the resistor 53 is a pull-up resistor, and the resistor 54 is the base current of the transistor 55. It is a limiting resistor. Resistor 56
Is a drive resistor of the transistor 57.

[0027]

As described in detail above, when the AC adapter is not connected to the connector with the switch, the power supply control circuit according to the present invention closes the terminals a and b of the switch to prevent charging of the battery. Therefore, the backflow prevention diode is in a short state. Therefore, the power supply voltage of the AC adapter power supply voltage monitoring IC is cut off,
The gate voltage of the transistor is held at "L" level,
Turn off the transistor. As a result, the voltage drop of the backflow prevention diode is prevented, the base current of the transistor is stopped, and the power consumption is improved.

During long-term storage of the equipment,
If an alkaline battery is used as the secondary battery, the safety valve operates due to expansion of the active material inside the battery and gas generation when the battery reaches an overdischarged state, causing the strong alkaline solution inside to flow out and causing an overdischarged state. However, when the battery voltage monitoring IC reaches the specified voltage or less, this is detected and the relay drive I is detected.
A signal is sent to C to operate the small latching relay and open the relay contact, so that the load connected to the battery is cut off and overdischarging of the battery is prevented.

That is, a voltage higher than that of the DC / DC converter can be supplied, the battery can be used efficiently, the battery can be used for a long time, and a power failure or disconnection of the AC adapter outlet occurs during use of the AC adapter. Also, even when the mode is switched to the battery supply, the mode is smoothly switched to the battery supply, and a voltage close to the battery voltage can be supplied to the DC / DC converter.

When the battery voltage reaches the specified voltage or less, the battery voltage monitoring IC detects the battery voltage and opens the battery supply line to completely disconnect the battery from the load. Can be used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a power supply control circuit according to the present invention.

FIG. 2 is an IC circuit diagram for monitoring an AC adapter power supply voltage according to the present invention.

FIG. 3 is a time chart of an embodiment according to the present invention.

FIG. 4 is a block diagram of a conventional power supply control circuit.

FIG. 5 is a time chart of a conventional power supply control circuit.

FIG. 6 is a graph showing a change in input voltage of a battery power supply line of a conventional power supply control circuit.

FIG. 7 is a graph showing a continuous discharge curve at a constant current load of one alkaline battery cell at room temperature.

FIG. 8 is a graph showing a forward current and voltage characteristic curve of a Schottky barrier diode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC input power supply 2 AC adapter outlet 3 AC adapter 4 Connector with switch 6 Battery 7 Connector 8 Backflow prevention diode 9 Transistor 10 Resistor 13 MOSFET transistor 20 Capacitor 21 Inductance 22 Switching control IC 23 Capacitor 24 DC / DC converter 25 Load 26 Backflow prevention diode 27 Diode 30 Power supply control circuit 31 AC adapter power supply voltage monitoring IC 32 Battery voltage monitoring IC 33 Relay drive IC 34 Push button switch 35 Diode 36 Small latch relay 37 Diode 38 Relay contact 39 Switch 40 AC adapter power supply Voltage monitoring resistor 41 AC adapter power supply voltage monitoring resistor 42 Pull-up resistor 50 Constant current source 51 Reference voltage 52 Hysteresis Comparator with cis 53 Pull-up resistor 54 Resistor 55 Transistor 56 Resistor 57 Transistor

Claims (3)

[Claims] 1. A power supply for selectively supplying a battery power supply and an AC adapter power supply that outputs a DC voltage higher than an output voltage of the battery power supply to a load via a backflow prevention diode connected to each power supply output side. In the power supply control circuit, when the battery power supply is used, the backflow prevention diode is short-circuited, and a PNP transistor having an emitter and a collector connected in parallel with the backflow prevention diode is turned off.
When the AC adapter power supply is connected, switch means for switching the backflow prevention diode to function effectively, and an output of the AC adapter power supply and an output of the battery power supply via the backflow prevention diode to a load. DC /
A power supply control circuit, comprising: a DC converter; and an AC adapter power supply voltage monitoring means for monitoring a power failure or disconnection of an AC adapter outlet while power is being supplied from the AC adapter power supply. 2. The power supply control circuit detects a power failure or disconnection of an AC adapter outlet while power is being supplied from an AC adapter power supply, and smoothly switches from the AC adapter power supply to a battery power supply. 2. The power supply control circuit according to claim 1, further comprising a diode short-circuit means for preventing backflow supplied to the DC / DC converter. 3. A power supply control circuit for mounting a battery power supply to a device, detecting a drop in battery voltage and operating a relay drive monitoring means in a long-term storage state to shut off the battery power supply from a load. 3. The power supply control circuit according to claim 1, further comprising a battery voltage monitoring means.