JP2009060683A - Charger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem, wherein when the output voltage of a direct-current power source, such as an AC adaptor or a car battery, connected to a charger body gets out of an allowable voltage range within which the charger body can operate normally, a fault or abnormal charging operation is caused in the charger and this can lead to damages to the direct-current power source itself due to abnormal charging. <P>SOLUTION: The charger includes: supply voltage detecting means 142 and 143, that detect that the input voltage Vin of a direct-current power source 200 supplied to an input terminal 131 is equal to or lower than the lower limit value of or equal to or higher than the upper limit value of an allowable voltage range, within which a charging power supply circuit portion 146 can normally operate; and a power supply interrupting means 141 that stops the charging operation of the charging power supply circuit portion 146, based on the detection signal from the supply voltage detecting means 142 and 143. When the supply voltage detecting means 142 and 143 detect a voltage equal to or lower than the lower limit value of or equal to or higher than the upper limit value of the input voltage Vin of the direct-current power source 200, the power supply interrupting means 141 makes the charging operation of the charging power supply circuit portion 146 stop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging device for charging a secondary battery such as a nickel cadmium battery, a nickel metal hydride battery, or a lithium ion battery, and in particular, as an input DC power source of the charging device, a plurality of types such as an AC adapter and a car battery are provided. The present invention relates to a charging device to which a power supply can be applied.

  Generally, a secondary battery such as a nickel cadmium battery, a nickel metal hydride battery, or a lithium ion battery is used as a power source for portable equipment such as a cordless electric tool. Some charging devices for charging these secondary batteries can be used outdoors. For example, there are devices that can charge a car battery as an input DC power source in a vehicle heading to a construction site. In addition, this type of charging apparatus is configured so that an external AC adapter is connected to convert an indoor commercial power source into a voltage close to the DC voltage of the car battery and can be used as an input DC power source. That is, a charging device to which a plurality of types of input power sources such as alternating current and direct current can be applied is well known.

  As disclosed in Patent Document 1 below, in a conventional charging device for charging a secondary battery using a storage battery (car battery) mounted on an automobile as a dedicated input power source, a voltage detection circuit is provided in the input power circuit of the charging device. If the battery voltage of the car battery drops below a predetermined value, the charging operation of the secondary battery by the car battery is interrupted so that the car battery can no longer drive the original electric circuit of the car. A technique of providing a charging operation blocking means is known.

Japanese Patent Laid-Open No. 9-37478

  In the charging device disclosed in Patent Document 1, when the output voltage of the car battery as a DC power source is a low voltage equal to or lower than a predetermined value, the charging circuit cutoff means has a protection function of preventing the car battery from being overdischarged.

  However, since the output voltage of the supply voltage from the car battery changes depending on the state of charge, if the charging device deviates abnormally from the input voltage range in which the charging device can operate normally, the charging device can cause failure or abnormal charging. There is sex. Similarly, when charging is performed using an inexpensive AC adapter that includes only a power transformer, a rectifier circuit, and a smoothing circuit as an input DC power supply of the charging apparatus, and does not include an output constant voltage circuit by feedback control, There has been a problem in that the output voltage of the AC adapter changes higher or lower than the allowable input range depending on the power supply voltage fluctuation of the power supply, that is, the power supply environment, causing a failure or abnormal charging of the charging device. In particular, in a charging device to which a plurality of types of power sources such as a car battery or an AC adapter can be applied, there is a problem that a DC power source having a voltage outside the allowable input range is easily connected by mistake.

  The technique disclosed in Patent Document 1 stops charging when the voltage is lower than the lower limit in the charging device, and restarts charging when the voltage is restored. Therefore, when using an inexpensive AC adapter as described above, the output voltage changes higher or lower than the allowable input range, and the voltage change that returns to the allowable input range is repeated. Along with the change, the charging operation is repeatedly stopped and started in a short cycle, which causes a problem that stable charging cannot be performed.

  Accordingly, an object of the present invention is to solve the above-described problems, and to provide a charging device that cuts off the charging operation of the charging power supply circuit when the connected DC power supply is a low voltage or a high voltage outside the allowable input range. There is.

  Another object of the present invention is to provide a charging apparatus to which a plurality of types of input DC power supplies can be applied, such as an AC adapter and a car battery.

  Of the inventions disclosed in the present application, the outline of typical ones will be described as follows.

  According to one aspect of the present invention, the secondary battery connected to the output terminal has a predetermined voltage based on an input voltage of a DC power source having an input terminal and an output terminal and connected to the input terminal. A charging device having a charging power supply circuit that operates so that a charging current or a predetermined charging voltage can be fed, wherein the input voltage of the DC power supplied to the input terminal can operate the charging power supply circuit normally. Supply voltage detecting means for detecting that the voltage is lower than the lower limit value or higher than the upper limit value with respect to the allowable voltage range, and charging the charging power supply circuit based on the detection signal of the supply voltage detection means A power shut-off means for stopping operation; and the supply voltage detecting means detects that the input voltage of the DC power supply is lower than the lower limit value or higher than the upper limit value. If it, the power supply breaker is configured to stop the charging operation of the charging power supply circuit.

  According to another aspect of the present invention, the DC power source connected to the input terminal of the charging device is a converter that converts an AC voltage from a commercial power source into a DC voltage, or a storage battery mounted on an automobile. .

  According to still another feature of the present invention, the power shut-off means detects that the supply voltage detecting means is that the input voltage of the DC power supply is lower than the lower limit value or higher than the upper limit value. In this case, latching means for holding the detection signal is provided, and the charging operation of the charging power supply circuit is held in a stopped state by the latching means.

  According to still another aspect of the present invention, the charging power supply circuit includes a switching element that adjusts an output voltage by switching an input voltage of the DC power supply, and a switching power supply that includes switching control means that controls the switching element. The power supply cutoff means includes a circuit, and stops the charging operation of the switching power supply circuit by cutting off the drive power supply of the switching control circuit based on the detection signal of the supply voltage detection means.

  According to still another aspect of the present invention, the supply voltage detection unit includes a first supply voltage detection circuit including a first voltage detection element that is turned on when the input voltage is equal to or higher than the lower limit voltage; And a second supply voltage detection circuit including a second voltage detection element that conducts when the input voltage exceeds the upper limit voltage.

  According to still another feature of the present invention, a secondary battery having an input terminal and an output terminal and connected to the output terminal based on an input voltage of a DC power supply connected to the input terminal is provided with a predetermined value. A charging device having a charging power supply circuit that operates so as to supply a charging current or a predetermined charging voltage, wherein the input voltage of the DC power supplied to the input terminal can operate the charging power supply circuit normally. Power supply cutoff means for detecting that the voltage is lower than the lower limit value of the allowable voltage range, and for stopping the charging operation of the charging power supply circuit based on a detection signal of the supply voltage detection means. The power shut-off means holds the detection signal when the supply voltage detection means detects that the input voltage of the DC power supply is lower than the lower limit value. Has a pitch means, for holding the charge operation of the charging power supply circuit to the stopped state by said latch means.

  According to the present invention, when a DC voltage outside the allowable voltage range is supplied from the DC power supply to the charging device, the operation of the charging power supply circuit is shut off by the power shut-off means. Damage to the input DC power supply or the charged secondary battery can be prevented. In addition, when a car battery is used as the input voltage, overdischarge of the car battery can be prevented, and heat generation of components of the charging device can be prevented when a high voltage is input.

  According to the present invention, since the latch circuit is added to the power shut-off means, even if high-frequency noise is superimposed on the input DC power supply, the intrusion of the high-frequency noise is shut off by the operation of the latch circuit. It is possible to prevent malfunction such as overcharge of the circuit portion.

  According to the present invention, when the commercial power supply environment is bad and the input voltage of the AC adapter fluctuates, once the input voltage to the charging device becomes lower than the lower limit value, the charging operation is stopped by the latch means and the stopped state is maintained. Therefore, stable charging can be performed without repeating the start and stop of the charging operation with an inexpensive adapter.

  The above and other objects of the present invention, and the above and other novel features of the present invention will become more apparent from the following description of the present specification and the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that in all the drawings for explaining the embodiments, members having the same function are denoted by the same reference numerals, and repeated description is omitted.

  FIG. 1 is a configuration diagram of a charging device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of the charging device shown in FIG. In FIG. 1, the charging device 101 includes a power cutoff circuit unit 141 and a charging power source circuit unit 146, and a plurality of types of DC power sources 200 can be connected to an input terminal (connector) 131. In the present embodiment, in particular, an AC adapter (converter) 201 that converts commercial AC power to DC voltage, or a cigarette lighter socket 202 for supplying DC voltage from an automobile car battery is applicable as the DC power source 200. Is shown. Although not shown, the AC adapter 201 includes a step-down power transformer, a rectifier circuit, and a smoothing circuit that are electrically connected to a commercial AC power source. The AC-DC is a combination of the step-down power transformer and a relatively simple rectification and smoothing circuit. It is constituted by a converter. That is, the AC adapter 201 does not have a constant voltage control circuit that controls its output voltage to a predetermined value, and is an inexpensive adapter in which fluctuations in the commercial AC power supply appear directly as the output voltage. On the other hand, the cigarette lighter socket 202 has a relatively simple structure with a built-in fuse that blows against an overcurrent. The charging device 101 performs a normal charging operation when the input DC voltage Vin from the DC power source 200 is within an allowable voltage range of, for example, 8 to 22 V, and charging is performed when a DC voltage outside the allowable voltage range is input. The operation is stopped.

  A battery pack (secondary battery) 102 for charging is electrically connected to the output terminal 147. The battery pack 102 is composed of a single battery unit or a battery group in which a plurality of unit cells are connected in series. For example, a unit cell of a lithium ion secondary battery with a nominal voltage of 3.6V can be charged with a charging voltage of 4V.

  FIG. 2 shows a circuit block diagram of the charging apparatus 101 shown in FIG. The charging power supply circuit unit 146 includes a switching power supply circuit (step-down DC / DC converter) 148 including an input capacitor 121, a switching transistor (PNP transistor) 122, a rectifying diode 124, a choke coil 123, and a smoothing capacitor 125. And a switching control circuit 126, a constant voltage control circuit 127, a constant current control circuit 128, a charging current detection circuit 129, and a termination current detection circuit 130.

  The switching power supply circuit 148 is configured by a step-down DC / DC converter that steps down an input DC voltage in an allowable voltage range supplied to the input line 149 and converts it to an output voltage necessary for charging the secondary battery 102.

  The switching control circuit 126 is electrically connected to the base of the switching transistor 122, controls the drive pulse width of the transistor 122, adjusts the output voltage or output current of the switching power supply circuit 148, and controls the start and stop of charging. .

  The constant voltage control circuit 127 detects the battery voltage of the secondary battery 102, compares it with a reference voltage corresponding to a predetermined voltage value, performs calculation, and outputs the result to the switching control circuit 126. The constant voltage control circuit 127 is configured by connecting operational amplifiers (OP amplifiers) in multiple stages, for example.

  The constant current control circuit 128 compares the detection result (detection voltage) from the charging current detection circuit 129 that detects the charging current of the secondary battery 102 with a reference voltage corresponding to a predetermined reference current value, performs an operation, The result is output to the switching control circuit 126. The constant current control circuit 128 is configured by connecting, for example, operational amplifiers (OP amplifiers) in multiple stages.

  The termination current detection circuit 130 is a circuit that detects a predetermined charging current (end current) when the charging current drops in a short time from a constant constant current value at full charge. It is determined that charging is performed, and a charge stop signal is output to the switching control circuit 126.

  The power cutoff circuit unit 141 includes a low input voltage detection circuit 142, a high input voltage detection circuit 143, and a cutoff circuit 144.

  The low input voltage detection circuit (first supply voltage detection means) 142 includes a Zener diode 103, a digital transistor (a transistor with a built-in resistor) 104, a resistor 105, a diode 106, and an electrolytic capacitor 108. The low input voltage detection circuit 142 sets the lower limit value of the allowable input voltage range of the DC power supply 200 with the Zener voltage of the Zener diode 103. That is, when the input voltage Vin of the DC power supply 200 is equal to or higher than the Zener voltage of the Zener diode 103, the NPN type digital transistor 104 is turned on. Therefore, the low input voltage detection circuit 142 does not transmit a signal to the cutoff circuit 144. When Vin becomes a voltage lower than the Zener voltage of the Zener diode 103 (a voltage lower than the lower limit value of the allowable input voltage range), the digital transistor 104 is turned off, and a cutoff signal is input from the resistor 105 through the diode 106 to the cutoff circuit 144. The interruption circuit 144 stops or interrupts the operation of the charging power supply circuit unit 146 based on the detection interruption signal.

  The high input voltage detection circuit (second supply voltage detection means) 143 includes a Zener diode 114 and a diode 115. The upper limit value of the allowable voltage range of the input voltage Vin of the supply line 149 is set by the Zener voltage of the Zener diode 114. When the input voltage Vin of the supply line 149 becomes equal to or higher than the Zener voltage of the Zener diode 114 (a voltage exceeding the upper limit value of the allowable input voltage range), the cutoff signal is input to the cutoff circuit 144 through the diode 115.

  The cutoff circuit 144 includes a PNP type digital transistor 109, an NPN type digital transistor 120, N channel type FETs 107 and 113, a P channel type FET 118, resistors 110, 112, 116, 117 and 119, and a capacitor 111. Composed. When the cutoff circuit 144 receives from the diode 106 of the low input voltage detection circuit 142 or the diode 115 of the high input voltage detection circuit 143 an abnormality detection signal deviating from the lower limit or upper limit of the allowable input voltage range, the FET 107 Is turned on, so that the digital transistor 109 is turned on and the FET 113 is also turned on. As a result, since the ON signal is again input to the gates of the FETs 107 and 113 through the resistors 110 and 112, once the FETs 107 and 113 are turned on, the FETs 107 and 113 continue to maintain the ON state. That is, the N-channel FET 107 and the PNP digital transistor 109 constitute a latch circuit, and both hold the ON state by the detection signal input via the diode 106 or the diode 115. When the FET 113 is turned on, the digital transistor 120 is turned off. For this reason, the P-channel FET 118 that supplies the drive power to the switching control circuit 126 is turned off, the power supply line from the line 149 to the switching control circuit 126 is cut off, and the operation of the switching control circuit 126 is cut off. . When the operation of the switching control circuit 126 stops, the charging operation of the switching power supply circuit 148 including the PNP transistor 122 stops. In order to return the FET 107 and the transistor 109 held in the latched state to the OFF state, it is necessary to temporarily disconnect the AC adapter 201 or the cigarette lighter socket 202 serving as the DC power source 200 from the input terminal 131 of the charging device 101. It becomes.

  Here, by incorporating a latch circuit composed of the N-channel FET 107 and the PNP digital transistor 109 into the cutoff circuit 144, high-frequency noise (for example, a voltage higher than the upper limit of the allowable input voltage range from the DC power source 200 to the line 149) Even if the noise (MHz order noise) is superimposed, the FET 107 and the transistor 109 are instantly in a latched state, so that the abnormality detection signal can be detected by the latch and the charging operation of the charging power supply circuit unit 146 can be stopped. As a result, malfunction due to noise of the switching control circuit 146 and overcharge of the switching power supply circuit 148 can be prevented. Moreover, once the latch state is established, the start and stop of the charging operation accompanying the fluctuation of the input voltage is not repeated.

  Further, according to the present invention, an inexpensive charging device can be provided by using an inexpensive AC adapter 201. That is, as the AC adapter 201, as described above, one that does not have a constant voltage control circuit for controlling its output voltage to a predetermined voltage is used, and a relatively simple circuit configuration is realized by a transformer, a rectifier circuit, and a smoothing circuit. An inexpensive adapter can be used.

  When an inexpensive AC adapter is used, fluctuations in the commercial AC power supply appear directly in the output voltage, but in the state where the commercial AC power supply is near the lower limit of the allowable voltage range in which the commercial AC power supply can operate, the charging device 101 further uses the secondary battery. When the battery 102 is to be charged, the output voltage of the AC adapter 201 further decreases due to the charging current flowing through the secondary battery 102. As a result, when the input voltage to the charging device 101 falls below the lower limit value of the input voltage range in which the charging operation can be performed, according to the present invention, the latching means is provided. Therefore, unstable charging by the AC adapter can be prevented. On the other hand, in the conventional charging device as described above, the input voltage drops below the lower limit of the input voltage range in which the charging operation can be performed, and the charging current stops flowing when the charging is stopped. Return to within the allowable voltage range. When the voltage is restored, the secondary battery can be charged and charging is started again. Thereafter, charging is stopped again due to a decrease in the input voltage. As a result, since the start or stop of the charging of the secondary battery may be repeated in a short cycle, stable charging may not be possible.

  With the above configuration, when the input voltage Vin from the DC power supply 200 outputs a DC voltage that is lower or higher than the allowable input voltage range, the power cut-off circuit unit 141 stops or cuts off the charging operation of the charging power supply circuit unit 146. can do. When a DC power supply 200 having a voltage in an allowable input voltage range (for example, an allowable voltage range of 8 to 22 V) is connected to the input terminal 131, a secondary battery (for example, a lithium ion battery) is connected by the charging power supply circuit unit 146. ) 102 can be charged to a predetermined battery voltage (eg, 4V). In this case, even if high frequency noise exceeding the allowable input voltage range is superimposed, the latch circuit operates, so that it is possible to prevent malfunction of the charging power supply circuit unit 146 configured by the switching power supply circuit 148. Furthermore, once the input voltage Vin becomes equal to or lower than the lower limit value of the allowable input voltage, charging is stopped and stable charging can be performed because the state is maintained.

  Next, the operation of the charging apparatus 101 will be described with reference to the control flowchart shown in FIG.

  When the charging device 101 is supplied with a DC voltage from the AC adapter 201 or the cigarette lighter socket 202 as the DC power source 200 (see FIG. 1), first, the input voltage Vin of the line 149 is set to the lower limit (minimum value) of the allowable input voltage range. The low input voltage detection circuit 142 detects whether or not the input voltage is equal to or lower than the input voltage (step 301).

  When the detection result by the low input voltage detection circuit 142 is equal to or lower than the minimum input voltage which is the lower limit value in Step 301 (in the case of YES), the FET 118 is turned off (Step 310), and the cutoff circuit 144 is switched from the input line 149. The drive power supply to the control circuit 126 is cut off (step 311).

  In step 301, when the detection result by the low input voltage detection circuit 142 is equal to or higher than the minimum input voltage which is the lower limit value (in the case of NO), the input voltage Vin is set to the upper limit value of the allowable input voltage range by the high input voltage detection circuit 143. It is detected whether or not a certain maximum input voltage is exceeded (step 302). If the maximum input voltage which is the upper limit value of the allowable input voltage range is exceeded in step 302 (in the case of YES), the input voltage Vin becomes equal to or higher than the Zener voltage of the Zener diode 114. A cut-off signal is input. As a result, as in step 301, the FET 118 is turned off (step 310), and the power supply to the switching control circuit 126 is cut off (step 311).

  If the input voltage Vin is in the allowable input voltage range in step 302 (NO), it is checked whether or not the secondary battery (battery set) 102 is connected (inserted) to the charging device 101. In other words, it waits for the secondary battery 102 to be inserted into the charging device 101 (step 303).

  When the secondary battery 102 is connected in step 303, charging is started by the switching power supply circuit 148 including the transistor 122 (step 304).

  In step 304, the switching power supply circuit 148 converts the DC voltage Vin from the AC adapter 201 or the cigarette lighter socket 202 into a predetermined charging voltage Vo, and charges the secondary battery 102. In the charge control, charging is first performed so that a constant current value preset by the constant current control circuit 128 and the switching control circuit 126 is obtained. That is, constant current charging is performed. Thereafter, when the voltage of the secondary battery 102 reaches a preset voltage value, this time, charging is performed with a constant voltage value preset by the constant voltage control circuit 127 and the switching control circuit 126. That is, constant voltage charging is performed.

  On the other hand, during charging, the input voltage Vin from the AC adapter 201 or cigarette lighter socket 202 is always detected by the low input voltage detection circuit 142 and the high input voltage detection circuit 143 (steps 305 and 306). When the input voltage Vin is outside the allowable voltage range, a cutoff signal is input to the cutoff circuit 144, the power supply of the switching control circuit 126 is shut off, and the operation of the switching power supply circuit 148 is stopped.

  When the charge current reaches the end current set by the end current detection circuit 130 after the start of charging, it is determined that the battery is fully charged (step 307), and a stop signal is input to the switching control circuit 126 to stop charging (step 308). ).

  Next, it is determined whether or not the secondary battery (battery set) 102 has been removed from the charging device 101 (step 309). If it is determined in step 309 that the secondary battery 102 has been removed, the process returns to step 301.

  As is apparent from the above description of the embodiment of the present invention, according to the present invention, when a DC power supply having a voltage outside the allowable input voltage range is input to the charging device, the power supply shut-off means Since the operation is cut off, it is possible to prevent the charging apparatus main body from being broken or abnormally charged, and the input DC power source or the secondary battery to be charged is damaged. In addition, according to the present invention, since the latch circuit is added, the charging operation of the charging power supply circuit unit is stopped even if high frequency noise is superimposed on the input DC power supply. Etc. can be prevented from malfunctioning. Furthermore, it is possible to prevent an unstable charging operation in which charging is started or stopped in a short cycle based on a relatively inexpensive AC adapter usage environment.

  As mentioned above, although the invention made | formed by this inventor was demonstrated based on embodiment, this invention is not limited to the said embodiment, A various change is possible within the range which does not deviate from the summary. In the above embodiment, the case where the cutoff circuit 144 cuts off the supply of the driving DC power supply to the switching control circuit 126 and stops the operation of the switching power supply circuit 148 has been described, but the cutoff circuit 144 includes the supply voltage detection means 142 and The power supply line 149 of the input DC voltage Vin to the switching power supply circuit 148 may be cut off by 143.

The block diagram of the charging device which concerns on one Embodiment of this invention. The circuit block diagram of the charging device which concerns on embodiment shown in FIG. The control flowchart which concerns on operation | movement of the charging device which concerns on embodiment shown in FIG.

Explanation of symbols

101: Charging device 102: Battery pack (secondary battery)
103: Zener diode (for low input voltage detection)
104: Digital transistor (NPN type transistor) 105: Resistor 106: Diode 107: N channel type FET 108: Electrolytic capacitor 109: Digital transistor (PNP type transistor) 110: Resistor 111: Capacitor 112: Resistor 113: N channel Type FET
114: Zener diode (for high input voltage detection) 115: Diode 116, 117: Resistor 118: P channel type FET 119: Resistor 120: Digital transistor (NPN type transistor) 121: Electrolytic capacitor 122: Power transistor (PNP type) Transistor) 123: Choke coil 124: Diode 125: Electrolytic capacitor 126: Switching control circuit 127: Constant voltage control circuit 128: Constant current control circuit 129: Charging current detection circuit 130: Termination current detection circuit 131: Input terminal (connector)
141: Power cut-off circuit unit 142: Low input voltage detection circuit (first supply voltage detection means)
143: High input voltage detection circuit (second supply voltage detection means) 144: Cut-off circuit 146: Charging power supply circuit unit 147: Output terminal 148: Switching power supply circuit (step-down DC / DC converter) 149: Feed line 200: DC Power supply 201: AC adapter 202: Cigarette lighter socket

Claims (6)

A predetermined charging current or a predetermined charging voltage can be supplied to a secondary battery connected to the output terminal based on an input voltage of a DC power source having an input terminal and an output terminal and connected to the input terminal A charging device having a charging power supply circuit that operates as follows:
Detecting that the input voltage of the DC power source supplied to the input terminal is lower than a lower limit value or higher than an upper limit value with respect to an allowable voltage range in which the charging power supply circuit can normally operate. Further comprising power supply cutoff means for stopping supply operation of the charging power supply circuit based on a detection signal of the supply voltage detection means, comprising supply voltage detection means;
When the supply voltage detecting means detects that the input voltage of the DC power supply is lower than the lower limit value or higher than the upper limit value, the power shutoff means stops the charging operation of the charging power supply circuit. A charging device characterized by being configured as described above.   2. The charging device according to claim 1, wherein the DC power source connected to the input terminal is a converter that converts an AC voltage from a commercial power source into a DC voltage, or a storage battery mounted in an automobile. .   When the supply voltage detecting means detects that the input voltage of the DC power supply is a voltage lower than the lower limit value or a voltage higher than the upper limit value, the power supply shutting means includes a latch means for holding the detection signal. 3. The charging device according to claim 1, wherein the charging unit holds the charging operation of the charging power supply circuit in a stopped state. 4. The charging power supply circuit comprises a switching power supply circuit comprising a switching element that adjusts an output voltage by switching an input voltage of the DC power supply, and a switching control means that controls the switching of the switching element,
The power supply cutoff means stops charging operation of the switching power supply circuit by shutting off a driving power supply of the switching control circuit based on a detection signal of the supply voltage detection means. Item 4. The charging device according to any one of Items 3.   The supply voltage detection means includes a first supply voltage detection circuit including a first voltage detection element that conducts when the input voltage is equal to or higher than the lower limit voltage, and the input voltage exceeds the upper limit voltage. 5. The charging device according to claim 1, wherein the charging device includes a second supply voltage detection circuit including a second voltage detection element that conducts in some cases. A predetermined charging current or a predetermined charging voltage can be supplied to a secondary battery connected to the output terminal based on an input voltage of a DC power source having an input terminal and an output terminal and connected to the input terminal A charging device having a charging power supply circuit that operates as follows:
Supply voltage detection means for detecting a voltage at which the input voltage of the DC power supply supplied to the input terminal is lower than a lower limit value of an allowable voltage range in which the charging power supply circuit can normally operate; Further comprising a power cutoff means for stopping the charging operation of the charging power supply circuit based on a detection signal of the means,
The power shut-off means has latch means for holding a detection signal when the supply voltage detection means detects that the input voltage of the DC power supply is lower than the lower limit value, and the latch means A charging device that holds a charging operation of the charging power supply circuit in a stopped state.

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