JP2010213559A - Dc power supply and dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To run down completely the energy of a battery in a DC power supply with a dry battery serving as a power supply. <P>SOLUTION: The DC power supply includes a switching element (SW2) capable of shutting down a current running from a primary battery to a load; and a low-voltage detecting circuit (16) to detect the voltage of the primary battery, and to generate a signal and output it for controlling the switching element. In the DC power supply, the low-voltage detecting circuit outputs a controlling signal to keep the switching element (SW2) shut down when the voltage of the primary battery remains at a predetermined potential or below over a predetermined period of time or above. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a battery low voltage detection technique in a DC power supply using a dry battery as a power source. For example, the present invention is effective for low voltage detection in a boost type DC-DC converter that boosts the voltage of a dry battery and supplies it to a load. Regarding technology.

  Dry batteries may leak due to overdischarge. Therefore, in a DC power supply device using a dry cell as a power source, it is desirable to provide a low voltage detection circuit and a switch for detecting a decrease in the voltage of the dry cell and cutting off the current from the battery to the load. As an invention relating to a low voltage detection circuit for a battery, for example, there is one described in Patent Document 1. This prior invention prevents the battery from being consumed quickly due to the consumption current of the detection circuit. This is for avoidance and has a different purpose from the present invention.

  The present inventors considered and considered a circuit as shown in FIG. 5 as a low voltage detection circuit in a control circuit of a step-up DC-DC converter that boosts the voltage of a dry battery (hereinafter simply referred to as a battery). . The circuit of FIG. 5 includes a comparator CMP that receives the battery voltage Vbat. When the battery voltage becomes lower than 0.9 V, for example, compared to a reference voltage Vref such as 0.9 V, the battery and the load The current is cut off by turning off the switch element SW provided in the current path between the LD. A period T1 in FIG. 6 shows a change in potential of each part in this state. In FIG. 5, the load LD includes a DC-DC converter.

JP-A-9-325160

  In the circuit of FIG. 5, when the load current Iload increases as in the period T2 of FIG. 6, the output voltage Vbat of the battery decreases due to the internal impedance of the battery, so the comparator CMP detects the low voltage and the switch element SW Will be turned off. For this reason, in a system in which the load current is transiently increased or decreased, the switch element SW is immediately turned off upon detection of a low voltage due to an increase in the load current, and the battery energy cannot be used up sufficiently. .

  For example, in a DC power supply device that boosts the voltage of a battery with a DC-DC converter and supplies it to a system that becomes a load, the battery voltage decreases when the DC-DC converter is activated with the battery remaining low. A low voltage detection circuit detects this and interrupts the current to the DC-DC converter as a load. For this reason, the battery energy cannot be fully used, resulting in waste. Further, it has been clarified that there is a problem that when a system becomes inoperable despite energy remaining in a battery, a time in which the battery can be operated is shortened.

  An object of the present invention is to provide a low-voltage detection technique that can sufficiently use the energy of a battery in a DC power supply using a dry battery as a power source, thereby reducing waste.

  Another object of the present invention is to provide a low-voltage detection technique capable of extending the operating time of a single battery in a DC power supply apparatus using a dry battery as a power source.

  Still another object of the present invention is to provide a control technique for preventing repeated operation in which an output current is cut off or passed when a battery is exhausted and the voltage drops in a DC power supply using a battery as a power source. Is to provide.

  In order to achieve the above object, the present invention provides a switching element capable of interrupting a current flowing from a primary battery to a load, and a low voltage for detecting the voltage of the primary battery and generating and outputting a signal for controlling the switching element. In the DC power supply device including the detection circuit, the low voltage detection circuit outputs a control signal for shutting off the switch element when the voltage of the primary battery becomes equal to or lower than a predetermined potential for a predetermined time or more. It is composed.

  According to the configuration as described above, in the DC power supply device using the primary battery as a power source, the current is not cut off immediately when the battery voltage is lowered, but the current is supplied when the battery voltage is lower than the predetermined potential for a predetermined time or more. In order to cut off, the current is not cut off when the battery voltage is temporarily lowered, so that the battery energy can be used up sufficiently, thereby reducing waste.

  Another invention of the present application is directed to an inductor connected between a voltage input terminal to which a DC voltage from a primary battery is input and an output terminal to which a load is connected, a drive element for passing a current through the inductor, and an output A control circuit that generates and outputs a signal for controlling the drive element in accordance with the feedback voltage of the control circuit, wherein the control circuit includes a low voltage detection circuit that monitors the voltage of the primary battery. And the low voltage detection circuit is configured to cut off the current flowing through the inductor when it is detected that the voltage of the primary battery has become a predetermined potential or more for a predetermined time or more.

  According to the above configuration, in the DC-DC converter using the primary battery as a power source, the current is not cut off immediately when the battery voltage is lowered, but the current is turned off when the battery voltage is lower than the predetermined potential for a predetermined time or more. Therefore, when the battery voltage is temporarily lowered, the current is not cut off and the battery energy can be used up sufficiently, thereby reducing waste.

  Further, an inductor and a rectifying element are connected in series between a voltage input terminal to which a DC voltage from the primary battery is input and an output terminal to which a load is connected, and coupled to a connection node between the inductor and the rectifying element. A drive element for passing a current to the inductor; a control circuit for generating and outputting a signal for controlling the drive element in accordance with an output feedback voltage; and a switch element capable of interrupting a current passed from the primary battery to a load; In the step-up DC-DC converter, the control circuit monitors the voltage of the primary battery, and shuts off the switch element when the voltage of the primary battery becomes equal to or lower than a predetermined potential for a predetermined time or more. A low voltage detection circuit that generates and outputs a control signal is provided.

  In a step-up DC-DC converter, a high voltage required for driving a load can be obtained by boosting the voltage. If the input voltage (battery voltage) can be operated even if the input voltage (battery voltage) decreases, the battery energy can be used up accordingly. Will be able to.

  Further, in the step-up DC-DC converter, when a switch element that can cut off the current flowing from the primary battery to the load is not provided, the battery voltage is turned off when the drive element is turned off and the control for boosting is stopped. Is higher than the forward voltage of the rectifying device, current may flow through the inductor-rectifying device-load path, and the battery may be consumed. By shutting off, it is possible to prevent unnecessary battery consumption.

  Here, preferably, the control circuit is configured to stop driving of the drive element when the low voltage detection circuit detects that the voltage of the primary battery has become equal to or lower than a predetermined potential for a predetermined time or more. . As a result, when the battery voltage as the input voltage decreases, the converter can automatically stop the boosting operation, thereby preventing wasteful consumption of the battery.

  More preferably, the current interrupting switch element is constituted by a P-channel field effect transistor connected between the rectifying element and the output terminal. Although it is possible to use an N-channel field effect transistor as a switching element for interrupting current, in that case, it is necessary to apply a gate voltage higher than the battery voltage in order to reduce resistance when turned on. However, the current consumption of the control circuit increases, but by using a P-channel field effect transistor, a high voltage is not required for the control circuit, and the current consumption of the control circuit can be suppressed.

  Further, preferably, the control circuit includes a latch circuit that is provided at a subsequent stage of the low voltage detection circuit and latches an output of the low voltage detection circuit. As a result, once the battery voltage drops and the output of the low voltage detection circuit changes, the state is latched by the latch circuit, and then the battery voltage increases and the output of the low voltage detection circuit changes to the original state. However, since the output of the latch circuit does not change, the switch element for cutting off the current repeatedly turns on and off when the battery is depleted and the voltage drops, and the load current (output current) is cut off or passed. The operation can be prevented.

  According to the present invention, in a DC power supply using a dry battery as a power source, the battery energy can be used up sufficiently, thereby reducing waste. In addition, in a DC power supply device using a dry battery as a power source, there is an effect that it is possible to extend the time that can be operated by one battery. Furthermore, it is possible to prevent the output current from being cut off or repeated when the battery is consumed and the voltage is lowered.

It is a block block diagram which shows one Embodiment at the time of applying this invention to a step-up type DC-DC converter. It is a block block diagram which shows the modification of the DC-DC converter to which this invention is applied. It is a circuit block diagram which shows the specific structural example of the low voltage detection circuit in embodiment. It is a time chart which shows operation | movement of the low voltage detection circuit in the DC-DC converter of embodiment. It is a block block diagram which shows the structural example of the conventional low voltage detection circuit. It is a time chart which shows operation | movement of the conventional low voltage detection circuit. 2 is a time chart showing an operation when the battery is consumed and the voltage is lowered in the DC-DC converter of the embodiment of FIG. 1. FIG. 10 is a time chart showing an operation when the battery is considerably consumed and the voltage is lowered in the DC-DC converter of the second embodiment shown in FIG. 9. It is a block block diagram which shows the structure of the DC-DC converter of the 2nd Embodiment of this invention. It is a block block diagram which shows the modification of the DC-DC converter of 2nd Embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment in which the present invention is applied to a step-up DC-DC converter.

  The DC-DC converter of this embodiment includes a coil (inductor) L1 and a rectifying diode D1, which are connected in series between a voltage input terminal IN to which a DC voltage Vin from the battery 20 is input and an output terminal OUT. A driving transistor SW1 composed of an N-channel MOSFET (insulated gate field effect transistor) connected between a connection node between the coil L1 and the diode D1 and the ground point GND, and the driving transistor SW1 is controlled to be turned on / off. The switching control circuit 10, the smoothing capacitor C1 connected between the output terminal OUT and the ground point, etc. constitute a step-up type switching regulator.

  Further, a resistor voltage dividing circuit composed of resistors R1 and R2 in series is connected in parallel with the smoothing capacitor C1 between the output terminal OUT and the ground point, and the voltage divided by the resistors R1 and R2 is received. The switching control circuit 10 is configured to be applied to the feedback terminal FB.

  Further, in this embodiment, a current cutoff switch SW2 made of a P-channel MOSFET is connected in series with the diode D1 between the rectifying diode D1 and the output terminal OUT, and the voltage of the battery 20 Is provided with a low voltage detection circuit 16 for detecting whether or not the voltage drops below a predetermined potential (for example, 0.9 V), and the current cutoff switch SW2 is turned on and off by the output of the low voltage detection circuit 16 Has been. Here, when an alkaline battery is used as the battery 20, it is desirable to select a potential such as 0.9 V as the predetermined potential.

  Although not particularly limited, the switching control circuit 10 is formed as a semiconductor integrated circuit (hereinafter referred to as a power supply driving IC) on one semiconductor chip together with the driving transistor SW1 and the current cutoff switch SW2. The coil L1 and the smoothing capacitor C1 can be configured so as to be configured as discrete components and connected as external elements to the power supply driving IC.

  In the switching control circuit 10, the reference voltage Vref1 from the reference voltage circuit 11 is applied to the inverting input terminal, the voltage of the feedback terminal FB is applied to the non-inverting input terminal, and a voltage corresponding to the potential difference between the feedback voltage and the reference voltage Vref1 is applied. The error amplifier 12 to be output, the PWM (pulse width modulation) comparator 13 in which the output of the error amplifier 12 is input to the inverting input terminal, and the on / off drive of the driving transistor SW1 according to the output of the PWM comparator 13 It has a drive circuit (driver) 15 comprising an inverter that generates and outputs a signal. Between the PWM comparator 13 and the drive circuit 15, an AND gate G <b> 1 that receives an output of the PWM comparator 13 and a signal obtained by inverting the output of the low voltage detection circuit 16 is provided.

  The non-inverting input terminal of the PWM comparator 13 is supplied with a waveform signal from a waveform generation circuit 14 that has a built-in oscillator and generates a waveform signal (RAMP signal) such as a triangular wave or sawtooth wave of a predetermined frequency. When the output voltage is high according to the feedback voltage, control is performed such that the pulse width of the output drive pulse is narrowed, and when the feedback voltage is low, the pulse width is widened. The pulse signal generated by the PWM comparator 13 is supplied to the drive circuit 15 via the AND gate G1.

  Based on this pulse, the drive circuit 15 turns on the switch transistor SW1 to cause current to flow through the coil L1 and accumulates energy. By turning off SW1, energy is released from the coil, and rectified by the diode D1 and output to the output terminal. Electric charge is supplied to the connected capacitor C1 to generate an output voltage Vout obtained by boosting the input voltage from the battery. Further, the feedback control based on the voltages from the voltage dividing resistors R1 and R2 can keep the output voltage Vout constant even if the load fluctuates.

  FIG. 3 shows a specific configuration example of the low voltage detection circuit 16 in the present embodiment. As shown in FIG. 3, the low voltage detection circuit 16 is a voltage comparison circuit in which the voltage Vbat from the battery 20 is input to the non-inverting input terminal and a reference voltage Vref2 such as 0.9 V is input to the inverting input terminal. And an insensitive time setting circuit 62 that changes the output to a high level when the output of the comparator 61 maintains a low level for a predetermined time (hereinafter referred to as insensitive time). The insensitive time setting circuit 62 is, for example, a delay circuit DLY that delays the output of the comparator 61 by a time corresponding to the insensitive time Td, and NOR that takes the logical product of the signal delayed by the delay circuit and the output of the comparator 61. It can be constituted by the gate G2. For example, when an alkaline battery is used as the battery, the insensitive time is desirably set to about 10 to 50 milliseconds.

  Next, the operation of the DC-DC converter of FIG. 1 will be described with reference to FIG. In the low voltage detection circuit 16 of this embodiment, when the battery voltage Vbat becomes lower than the reference voltage Vref2 (timing t1 in FIG. 4) as in the period T3 in FIG. 4, the output of the comparator 61 changes to the low level. When this state lasts longer than the insensitive time Td, the output SD of the insensitive time setting circuit 62 changes to high level to turn off the current cut-off switch SW2, and the output voltage Vout falls accordingly. (Timing t2 in FIG. 4). Thereafter, when the battery voltage Vbat recovers to Vref2 or higher, the output CMPOUT of the comparator 61 changes to high level, and immediately the output SD of the insensitive time setting circuit 62 changes to low level, turning on the current cutoff switch SW2. Accordingly, the output voltage Vout rises (timing t3 in FIG. 4).

  On the other hand, when the battery voltage Vbat temporarily falls below the reference voltage Vref2 due to the increase in the load current Iload as in the period T4 in FIG. 4, it is insensitive if the state is shorter than the insensitive time Td. The output SD of the time setting circuit 62 is maintained at the low level without changing to the high level. Therefore, the current cutoff switch SW2 is not turned off, and the output voltage Vout does not fall. On the other hand, when the battery voltage Vbat falls below the reference voltage Vref2 due to the increase in the load current Iload as shown in the period T5 in FIG. 4, and the state lasts longer than the insensitive time Td, the insensitive time is set. The output SD of the circuit 62 changes to a high level to turn off the current cutoff switch SW2, and the output voltage Vout falls accordingly (timing t4 in FIG. 4).

  As described above, in the DC-DC converter according to the present embodiment, when the load current transiently increases and decreases repeatedly and the battery voltage temporarily decreases, the low voltage detection circuit 16 is immediately detected when the battery voltage decreases. However, the current cut-off switch SW2 is not turned off to cut off the current, so that the battery energy can be used up sufficiently.

  FIG. 2 shows a modification of the DC-DC converter. In this modification, the current cutoff switch SW2 is provided not between the diode D1 and the output terminal OUT but between the voltage dividing resistor R2 and the ground point, and as the current cutoff switch SW2, instead of the P-channel MOSFET. An N-channel MOSFET is used.

  Even when configured as in this modification, substantially the same effect as the DC-DC converter of the above-described embodiment can be obtained. The load 30 and the capacitor C1 are connected between the output terminal OUT and a connection node between the voltage dividing resistor R2 and the current cutoff switch SW2. Thereby, even when there is a constant current path inside the load, the current can be cut off. The capacitor C1 may be connected between the output terminal OUT and the ground point.

  Next, another embodiment of the present invention will be described. In the DC-DC converter of the above-described embodiment, it is possible to prevent the load current from being cut off when a large load current suddenly flows and the input voltage is temporarily reduced. However, when the battery is considerably consumed and the voltage is reduced, the apparent battery voltage is reduced due to the internal resistance of the battery, so that the current is cut off. Then, the internal resistance of the battery becomes invisible, the battery voltage rises, the low voltage detection circuit 16 detects it, the output SD changes, and the current cutoff switch SW2 is turned on. When the current flows, the battery voltage decreases again due to the internal resistance of the battery, and the low voltage detection circuit 16 detects this and turns on the current cutoff switch SW2. Therefore, as shown in FIG. 7B, there is a problem that SW2 is repeatedly turned on and off, and the operation of interrupting or flowing the load current Iload is repeated.

  FIG. 9 shows an embodiment of a DC-DC converter in which the above problems are eliminated. In this embodiment, an RS flip-flop 17 that functions as a latch circuit is provided at the subsequent stage of the low voltage detection circuit 16 in the embodiment of FIG. The output of the low voltage detection circuit 16 is input to the set terminal S of the flip-flop 17, and the enable signal that commands the operation / non-operation of the switching control circuit (power supply driving IC) 10 from the external terminal to the reset terminal R. A signal obtained by inverting SHDN by an inverter INV is input. The enable signal SHDN is set to a high level when the circuit is operated.

  With the configuration as described above, in the DC-DC converter shown in FIGS. 1 and 2, when the input voltage is lowered due to considerable battery consumption, the low-voltage detection circuit 16 has the battery voltage Vbat. When the output SD changes to high level once the decrease is detected and the predetermined delay time Td has elapsed, the state is latched by the flip-flop 17 and the current cutoff switch SW2 is turned off. Then, even if the battery voltage Vbat subsequently increases and the output of the low voltage detection circuit 16 changes to a low level, the output of the flip-flop (Latch) 17 does not change as shown in FIG. By repeatedly turning on and off, it is possible to prevent an operation in which the load current Iload is interrupted or passed.

  FIG. 10 shows a modification of the above embodiment. In this modification, an RS flip-flop 17 functioning as a latch circuit is provided at the subsequent stage of the low voltage detection circuit 16 in the DC-DC converter of FIG. Also in this modified example, as in the DC-DC converter of FIG. 9, once the output of the low voltage detection circuit 16 changes to a high level, the state is latched by the flip-flop 17 and then the battery voltage becomes high and low. Even if the output of the voltage detection circuit 16 changes to a low level, the output of the flip-flop 17 does not change. Therefore, the operation in which SW2 is repeatedly turned on and off and the load current Iload is interrupted or passed can be prevented. .

  Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment. For example, in the above embodiment, the PWM comparator 13 is provided after the error amplifier 12, but a PFM (pulse frequency modulation) comparator may be provided instead of the PWM comparator. The number of batteries as the input power supply is not limited to one, and the present invention can be applied to the case of two series, three series, two parallels, three parallels, or the like.

  In the above embodiment, the driving transistor SW1 and the current cutoff switch SW2 are described as being formed in the chip of the IC in which the control circuit 10 is formed. However, the driving transistor SW1 and the current cutoff switch SW2 are connected to the IC as external elements. You may comprise. Further, instead of using external elements as the resistors R1 and R2 for dividing the output voltage, these resistors may be formed inside the chip.

  Further, a logical sum (or logical product) of a terminal for inputting a control signal for controlling the operation (ON / OFF) of the IC from the outside of the chip and a control signal from the terminal and the output of the low voltage detection circuit 16 It is also possible to provide a logic gate that takes the following action so that the current cutoff switch transistor SW2 can be controlled to be turned on and off by either an external control signal or the output of the low voltage detection circuit 16.

  In the second embodiment, the latch circuit (17) for latching the output is provided immediately after the low voltage detection circuit 16. However, the low voltage detection circuit 16 is sandwiched by an inverter, a logic gate, or a logic circuit. A latch circuit may be provided at the subsequent stage. The latch circuit is not limited to the RS flip-flop, and any latch circuit can be used as long as it can latch a signal.

  In the above description, the case where the invention made by the present inventor is applied to the step-up DC-DC converter which is the field of use behind the present invention has been described. However, the present invention is not limited thereto, and the step-down DC-DC -It can be widely used for a DC power supply using a battery as a power source such as a DC converter.

DESCRIPTION OF SYMBOLS 10 Switching control circuit 11 Reference voltage circuit 12 Error amplifier 13 PWM comparator 14 Waveform generation circuit 15 Drive circuit (driver)
16 Low voltage detection circuit 17 Latch circuit (RS flip-flop)
20 Secondary battery (lithium ion battery)
30 Load 61 Voltage comparison circuit (comparator)
62 Insensitive time setting circuit L1 Coil (inductor)
C1 smoothing capacitor SW1 coil driving transistor (driving element)
SW2 Current cut-off switch (switch element)
R1, R2 output voltage dividing resistor

Claims (6)

A DC power supply device comprising: a switch element capable of interrupting a current flowing from a primary battery to a load; and a low-voltage detection circuit that detects a voltage of the primary battery and generates and outputs a signal for controlling the switch element. And
The low-voltage detection circuit outputs a control signal for turning off the switch element when the voltage of the primary battery becomes equal to or lower than a predetermined potential for a predetermined time or more. An inductor connected between a voltage input terminal to which a DC voltage from the primary battery is input and an output terminal to which a load is connected; a driving element for passing a current through the inductor; and the driving according to an output feedback voltage A control circuit for generating and outputting a signal for controlling the element, and a DC-DC converter comprising:
The control circuit includes a low voltage detection circuit that monitors the voltage of the primary battery, and when the low voltage detection circuit detects that the voltage of the primary battery has fallen below a predetermined potential for a predetermined time or more, A DC-DC converter characterized by interrupting a flowing current. An inductor and a rectifier element are connected in series between a voltage input terminal to which a DC voltage from the primary battery is input and an output terminal to which a load is connected, and coupled to a connection node between the inductor and the rectifier element. A drive element for passing a current through the inductor; a control circuit for generating and outputting a signal for controlling the drive element in accordance with an output feedback voltage; and a switch element capable of interrupting a current passed from the primary battery to the load. A step-up DC-DC converter comprising:
The control circuit includes a low voltage detection circuit that monitors the voltage of the primary battery and outputs a control signal that switches off the switch element when the voltage of the primary battery becomes equal to or lower than a predetermined potential for a predetermined time or more. A step-up DC-DC converter.   The control circuit is configured to stop driving of the drive element when the low voltage detection circuit detects that the voltage of the primary battery has become a predetermined potential or less for a predetermined time or more. The step-up DC-DC converter according to claim 3.   5. The step-up DC circuit according to claim 3, wherein the current interrupting switch element includes a P-channel field effect transistor connected between the rectifying element and the output terminal. DC converter.   6. The step-up DC according to claim 2, wherein the control circuit includes a latch circuit that is provided at a subsequent stage of the low voltage detection circuit and latches an output of the low voltage detection circuit. DC converter.

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