JP2007028802A - Protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection circuit capable of ensuring the safety of a user by promptly annunciating failure of a charger. <P>SOLUTION: This protection circuit includes: a transistor Q2 connected in series on a charging path of a secondary battery 3; a comparator A1 for detecting that a battery voltage Va reaches a predetermined over-charging protection voltage Ref1; a comparator A2 for detecting the battery voltage Va drops to a predetermined charging restart voltage Ref2; and a charge control section 13 which turns off the transistor Q2 when it is detected that the battery voltage Va has risen to a predetermined over-charging protection voltage Ref1 and turns on the transistor Q2 when the battery voltage Va drops to the charging restart voltage Ref2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a protection circuit for protecting a secondary battery.

  FIG. 4 shows a circuit diagram of a charging system to which a conventional protection circuit is applied. The charging system includes a protection circuit 100, a charging device 200, and a secondary battery 300. The protection circuit 100 includes comparators 101 to 103, a logic circuit 104, FETs 105 and 106, a resistor 107, and reference voltage sources 108 to 110. The protection circuit 100 and the secondary battery 300 constitute a battery pack.

  The comparator 101 compares the battery voltage Va of the secondary battery 300 with the overcharge protection voltage Vref1 (= 4.3 V), and detects whether or not the secondary battery 300 is overcharged. The comparator 102 compares the battery voltage Va with the overdischarge protection voltage Vref2, and detects whether or not the secondary battery 300 is overdischarged. The comparator 103 uses the overcurrent protection voltage Vref3 to detect whether or not an excessive discharge current (overcurrent) is flowing.

  When overcharge is detected by the comparator 101, the logic circuit 104 turns off the FET 106 and protects the secondary battery 300 from overcharge. In addition, when overdischarge is detected by the comparator 102, the logic circuit 104 turns off the FET 105 and protects the secondary battery 300 from overdischarge. Further, when an overcurrent is detected by the comparator 103, the logic circuit 104 turns off the FET 105 and protects the secondary battery 300 from the overcurrent.

  The charging device 200 is a DC / DC converter including a coil 207, a transistor 209, and the like. The charging control unit 205 performs constant voltage control so that the charging voltage Vb becomes the reference voltage Vref21 according to the comparison result between the voltage (charging voltage Vb) between the connection terminals 111 and 112 and the reference voltage Vref21 by the comparator 201.

  Further, the charging control unit 205 turns the transistor 209 on and off so that the charging current becomes a constant value according to the comparison result between the reference voltage Vref22 and the voltage drop Vc caused by the charging current in the resistor 210 by the comparator 202. To perform constant current control. The charging control unit 205 performs constant current control until the charging voltage Vb reaches the reference voltage Vref21, and performs constant voltage control after the secondary battery 300 reaches the reference voltage Vref21.

  FIG. 5 shows a timing chart of the charging system shown in FIG. 4, where (a) shows the battery voltage Va and (b) shows the charging current. Since the charging control unit 205 performs constant current control until the battery voltage Va reaches the reference voltage Vref21 (= 4.2V), the charging current maintains a constant value as shown in (b). You can see that On the other hand, since the charging control unit 205 performs constant voltage control after the battery voltage Va reaches the reference voltage Vref21, the battery voltage Va is maintained at a constant value as shown in (a). I understand.

FIG. 6 shows a timing chart of the charging system to which the poor charging device 200 in which the reference voltage sources 203 and 204 are unstable or the failed charging device 200 is applied, and (a) shows the battery voltage Va. , (B) shows the charging current. When the secondary battery 300 is charged using the poor charging device 200 or the failed charging device 200, the constant voltage control by the charging device 200 does not work well, so the secondary battery 300 has a fully charged voltage of 4.2V. It will be charged beyond the limit. When the battery voltage Va reaches the overcharge protection voltage Vref1 (= 4.3V), the FET 106 is turned off, the charging current is set to 0 as shown in (b), and the charging of the secondary battery 300 is stopped. As shown in (a), the battery voltage Va decreases. Patent Document 1 is known as a technique for protecting a secondary battery from overcharge and overdischarge.
JP-A-11-262270

  However, since the conventional protection circuit does not include means for notifying the user that the charging device 200 is out of order or inferior, there is a problem that the charging device 200 is continuously used. If such a charging apparatus 200 is continuously used, the protection circuit is promoted to breakage. Due to this breakage, the overcharge protection function of the protection circuit may not function and the secondary battery 300 may generate heat. is there. The user can finally recognize that the charging device 200 is out of order or inferior due to this heat generation, but this cannot ensure the safety of the user.

  An object of the present invention is to provide a protection circuit capable of promptly informing a failure of a charging device and ensuring the safety of a user.

  The protection circuit according to the present invention includes a switching means connected in series on a charging path of a secondary battery, a voltage detection means for detecting the voltage of the secondary battery, and the voltage of the secondary battery is overcharged by the voltage detection means. When it is detected that the voltage has risen to the protection voltage, the switching means is turned off, and it is detected by the voltage detection means that the voltage of the secondary battery has dropped to a charge resumption voltage lower than the overcharge protection voltage. And control means for turning on the switching means (claim 1).

  Further, in the above configuration, the control means starts a time measurement operation when the switching means is turned off, and performs a time measurement operation until a time-out time for detecting a full charge of the secondary battery elapses; When the voltage of the secondary battery decreases to the charge resumption voltage until the timeout time elapses, it is preferable to include a charge control unit that turns on the switching unit when the timeout time elapses ( Claim 2).

  Further, in the above configuration, the voltage detection unit compares the voltage of the secondary battery with the overcharge protection voltage, and compares the voltage of the secondary battery with the charge resumption voltage. 2 comparators (claim 3).

  In the above configuration, the first comparator has a positive terminal connected to the positive electrode of the secondary battery, the overcharge protection voltage applied to the negative terminal, an output terminal connected to the timing means, The comparator of 2 has a positive terminal connected to the positive electrode of the secondary battery, the charging resumption voltage is applied to the negative terminal, an output terminal is connected to the charge control means, and the time measuring means is the first comparator When a low-level signal is received, the timing operation is started, the timing control start signal is notified to the charging control means, and when the timeout time elapses after the timing operation is started, An operation end signal is notified, and the charging control means turns off the switching means when receiving the time measuring operation start signal from the time measuring means, and the time counting It is preferable to turn on the switching means when receiving said timing operation end signal from the stage.

  In the above configuration, it is preferable to further include a transmission means for transmitting electric energy from the contactless charging device to the secondary battery.

  According to the first aspect of the present invention, even when the voltage of the secondary battery exceeds the overcharge protection voltage because the secondary battery is charged using a charging device that does not function well with constant voltage control. Since the switching means is turned off by the control means, charging is stopped and the secondary battery is protected from overcharging. Then, when the battery voltage of the secondary battery decreases to the charging restart voltage, the switching means is turned on again and charging is restarted. Thereafter, when the battery voltage rises to the overcharge protection voltage, the switching means is turned off again, and the secondary battery is protected from overcharge. Thereby, since a charging current flows intermittently, the charge lighting lamp with which a charging device is provided can be blinked. As a result, it is possible to notify the user of the abnormality of the charging device to the user before the protection circuit is broken and the secondary battery generates heat, so that the abnormality of the charging device can be promptly notified and the safety of the user is ensured. can do.

  According to the invention described in claim 2, when a time-out time for detecting the full charge of the secondary battery is provided, and the voltage of the secondary battery falls to the charge restart voltage within the time-out time, the secondary battery is Since the switching means is turned on when it is determined that the battery is not fully charged, the switching means is intermittently turned on / off until the full charge state is reached, and the secondary battery is maintained at a voltage equal to or lower than the overcharge protection voltage. Can be charged. This can prevent the protection circuit from being damaged.

  According to the invention described in claim 3, it is possible to accurately detect whether the voltage of the secondary battery has increased to the overcharge protection voltage or whether the voltage of the secondary battery has decreased to the charge resumption voltage.

  According to the invention of claim 4, when the time measuring means receives a low level signal indicating that the voltage of the secondary battery has reached the overcharge protection voltage from the first comparator, the time measuring means performs a time measuring operation on the charge control means. The charging control means that receives the start signal and turns on the switching means can turn on the switching means quickly when the voltage of the secondary battery reaches the overcharge protection voltage.

  The second comparator outputs a low-level signal indicating that to the charge control means when the voltage of the secondary battery drops to the charge resumption voltage, while the time measurement means counts the time when the time measurement operation ends. Since the operation end signal is output to the charge control means, it is possible to accurately detect whether or not the voltage of the secondary battery has decreased to the charge resumption voltage before the timeout time elapses.

  According to invention of Claim 5, a secondary battery can be charged with a non-contact-type charging device.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a charging system to which a protection circuit according to Embodiment 1 of the present invention is applied. The charging system shown in FIG. 1 includes a protection circuit 1, a charging device 2, and a secondary battery 3. The protection circuit 1 and the charging device 2 constitute a battery pack. As the secondary battery 3, a rechargeable secondary battery such as a lithium ion secondary battery, a lithium polymer secondary battery, a nickel hydride secondary battery, or a nickel cadmium secondary battery is adopted.

  The protection circuit 1 includes comparators A1 to A5, reference voltage sources E1 to E4, transistors Q1 and Q2, a resistor R1, a control unit 10, and connection terminals T1 and T2. The comparator A1 has a negative terminal connected to the positive electrode of the secondary battery 3 and a positive terminal connected to the positive electrode of the reference voltage source E1. The comparator A <b> 2 has a − terminal connected to the positive electrode of the reference voltage source E <b> 2 and a + terminal connected to the positive electrode of the secondary battery 3. The comparator A3 has a negative terminal connected to the positive electrode of the reference voltage source E3 and a positive terminal connected to the positive electrode of the secondary battery 3. The comparator A4 has a negative terminal connected to the positive terminal of the comparator A5 and a positive terminal connected to the positive electrode of the reference voltage source E4.

  Each of the reference voltage sources E <b> 1 to E <b> 4 has a negative electrode connected to the negative electrode of the secondary battery 3. The negative electrode of the secondary battery 3 is connected to the source of the transistor Q1. The drains of the transistors Q1 and Q2 are connected to each other. The source of the transistor Q2 is connected to the connection terminal T2. The resistor R1 has one end connected to the source of the transistor Q2 and the connection terminal T2, and the other end connected to the minus terminal of the comparator A4 and the plus terminal of the comparator A5.

  The comparator A1 outputs a low level signal to the timer 11 when the battery voltage Va of the secondary battery 3 exceeds the predetermined overcharge protection voltage Ref1, and the timer A when the battery voltage Va is equal to or lower than the overcharge protection voltage Ref1. 11 outputs a high level signal. In the present embodiment, Ref1 = 4.3V is adopted as the overcharge protection voltage.

  The comparator A2 outputs a low level signal to the charge control unit 13 when the battery voltage Va becomes equal to or lower than a predetermined charge resumption voltage Ref2 (<Ref1), and when the battery voltage Va exceeds the charge resumption voltage Ref2, A high level signal is output to the charging control unit 13. In the present embodiment, Ref2 = 4.2V is adopted as the charge resumption voltage.

  The transistors Q1 and Q2 are n-channel field effect transistors, the transistor Q1 is a transistor for overdischarge and overcurrent protection, and the transistor Q2 is a transistor for overcharge protection.

  The comparator A3 outputs a low level signal to the discharge control unit 12 when the battery voltage Va becomes a predetermined overdischarge protection voltage Ref3 (<Ref2) or less, and the battery voltage Va exceeds the overdischarge protection voltage Ref3. In this case, a high level signal is output to the control unit 10. The comparator A4 detects that an overcurrent has flowed through the secondary battery 3 by short-circuiting the connection terminals T1 and T2 or connecting a low resistance, and notifies the discharge control unit 12 of it. The comparator A5 detects the current direction (charging or discharging) and notifies the control unit 10 of it.

  The connection terminals T1 and T2 are terminals for connecting the charging device 2 or a load device such as a mobile phone, a PDA, a power tool, and a notebook computer.

  The control unit 10 includes a timer 11, a discharge control unit 12, and a charge control unit 13. When the timer 11 receives a low level signal indicating that the battery voltage Va exceeds the overcharge protection voltage Ref1 from the comparator A1, the timer 11 starts a time measuring operation, and controls to control a time measuring start signal indicating the start of the time measuring operation. To the unit 13. In addition, the timer 11 ends the timekeeping operation and outputs a timekeeping operation end signal for notifying the end of the timekeeping operation to the charge control unit 13 when a predetermined time-out time has elapsed since the timer 11 started.

  The timeout time is a time set in advance for detecting whether or not the secondary battery is fully charged, and is, for example, 10 ms.

  The charging control unit 13 has a low level indicating that the battery voltage Va has become equal to or less than the charging resumption voltage Ref2 from the comparator A2 after receiving the timing operation start signal from the timer 11 and before receiving the timing operation end signal. When the signal is received, it is determined that the secondary battery 3 is not fully charged, a high level signal is output to the transistor Q2, the transistor Q2 is turned on, and charging is resumed. On the other hand, the charging control unit 13 is a low level signal indicating that the battery voltage Va has become equal to or lower than the charging restart voltage Ref2 from the comparator A2 after receiving the timing operation start signal from the timer 11 and before receiving the timing operation end signal. When the level signal is received, it is determined that the secondary battery 3 is fully charged, the transistor Q2 is continuously turned off, and charging is stopped.

  When receiving a low level signal from the comparator A3, the discharge control unit 12 outputs a low level signal to the transistor Q1 to turn off the transistor Q1 in order to protect the secondary battery 3 from overdischarge. Further, when the discharge control unit 12 receives a notification of overcurrent detection from the comparator A4, the discharge control unit 12 outputs a low level signal to the transistor Q1 to turn off the transistor Q1. In other cases, a high level signal is output to the transistor Q1 to turn on the transistor Q1.

  In the present embodiment, the comparator A1, the reference voltage source E1, the comparator A2, and the reference voltage source E2 correspond to an example of voltage detection means, the control unit 10 corresponds to an example of control means, and the transistor Q2 serves as an example of switching means. This corresponds to an example, and the timer 11 corresponds to an example of a time measuring unit.

  Next, the charging device 2 will be described. The charging device 2 is a DC / DC converter, and includes a charging control unit 21, a DC power source 22, comparators A21 and A22, reference voltage sources E21 and E22, a coil L1, a capacitor C21, a diode D21, and a transistor Q21.

  The comparator A21 compares the charging voltage Vb between the connection terminals T1 and T2 with a predetermined reference voltage Ref21 (= 4.2V). When the charging voltage Vb exceeds the reference voltage Ref21, the comparator A21 outputs a low level signal. When the charging voltage Vb is equal to or lower than the reference voltage Ref21, a high level signal is output to the charging control unit 21.

  The comparator A22 compares the voltage drop Vc of the resistor R2 due to the charging current with a predetermined reference voltage Ref22. If the voltage drop Vc exceeds the reference voltage Ref22, the comparator A22 outputs a low level signal to the charge control unit 21 and the voltage drop Vc. Is equal to or lower than the reference voltage Ref22, a high level signal is output to the charge control unit 21. In addition, the charging device 2 includes a light emitting diode LED1 that is turned on when a charging current is flowing and is turned off when the charging current is not flowing to notify a user whether charging is in progress.

  The charging control unit 21 sets the charging current to a constant value according to the comparison result between the reference voltage Ref22 by the comparator A22 and the voltage drop Vc due to the charging current at the resistor R2 until the charging voltage Vb reaches the reference voltage Ref21. A constant PWM control signal is generated and constant current control is performed. On the other hand, after the charging voltage Vb reaches the reference voltage Ref21, the charging control unit 13 generates a PWM signal such that the charging voltage Vb maintains the reference voltage Ref21, and performs constant voltage control. Further, when the charging current is flowing, the charging control unit 13 turns on the LED L1 as charging, and when the charging current is not flowing, the charging control unit 13 turns off the LED 1 as not charging.

  Transistor Q21 is a converter drive transistor composed of a P-channel field effect transistor. The diode D21 is a freewheeling diode, and the capacitor C21 is a smoothing capacitor.

  Next, the operation of the protection circuit 1 will be described. 2 shows a timing chart of the protection circuit 1, (a) shows the battery voltage Va, (b) shows the charging current, and (c) shows the lighting state of the light emitting diode LED1. First, when the charging device 2 is connected to the connection terminals T1 and T2, a charging current flows from the charging device 2 as shown in (b), and charging is started, the battery voltage Va is as shown in (a). Ascending in a smooth curve, the light emitting diode LED1 is turned on as shown in FIG.

  When the battery voltage Va reaches the overcharge protection voltage Ref1 (= 4.3V) (time T1), the comparator A1 outputs a low level signal to the timer 11, and the timer 11 receiving this signal performs a time measuring operation. At the same time, a timing operation start signal is output to the charging control unit 13. Upon receiving this signal, the charging control unit 13 outputs a low level signal to turn off the transistor Q2. As a result, the charging of the secondary battery 3 is stopped, the battery voltage Va decreases as shown in (a), the charging current becomes 0 as shown in (b), and the light emitting diode as shown in (c). LED1 is turned off.

  Next, since the charging control unit 13 has received a low level signal from the comparator A2 at time T2 prior to time T3 when the timing operation end signal has been received from the timer 11, the charging control unit 13 has a high level at the transistor Q2 at time T3. The signal is output. That is, when the battery voltage Va becomes equal to or lower than the charging resumption voltage Ref2 after the battery voltage Va rises to the overcharge protection voltage Ref1 and before the timeout time elapses, the charge control unit 13 determines that the timeout time has elapsed. Sometimes transistor Q2 is turned on and charging is resumed. Thereby, as shown to (c), light emitting diode LED1 lights up again.

  When the battery voltage Va reaches the overcharge protection voltage Ref1 (time T4), the transistor Q2 is turned off, so that the battery voltage Va decreases as shown in FIG. Then, at time T5 before time T6 indicating that the timeout time has elapsed, since the battery voltage Va has decreased to the charging resumption voltage Ref2, the charging control unit 13 turns on the transistor Q2 and resumes charging at time T6. . As a result, the light emitting diode LED1 is turned on again as shown in FIG.

  Thereafter, until time T7, the battery voltage Va drops to the charging resumption voltage Ref2 while the timeout period elapses, so that the transistor Q2 is intermittently turned on / off, and as shown in FIG. Flashes. Thereby, abnormality of a charging device can be alert | reported with respect to a user.

  At time T7, the transistor Q2 is turned off, and at time T9, the battery voltage Va drops to the charge resumption voltage. However, since the time T9 is a time after time T8 when the timeout time elapses, the charge control unit 13 determines that the secondary battery 3 is fully charged, continuously turns off the transistor Q2, and ends the charging. In this case, as shown in (c), it can be seen that the battery voltage Va is maintained at 4.2 V, and the secondary battery 3 is fully charged.

  As described above, according to the protection circuit 1 according to the first embodiment, since the secondary battery 3 is charged using the charging device 2 in which the constant voltage control does not function well, the battery voltage Va becomes the overcharge protection voltage. Even when Ref1 is exceeded, since the transistor Q2 is turned off by the charging control unit 13, charging is stopped and the secondary battery is protected from overcharging. Then, when the battery voltage Va decreases to the charging restart voltage Ref2 before the timeout time elapses, the transistor Q2 is turned on again, and the charging of the secondary battery 3 is restarted. Thereafter, when the battery voltage Va rises to the overcharge protection voltage, the transistor Q2 is turned off again, and the secondary battery 3 is protected from overcharge. Thereby, as a result of the charging current flowing intermittently, the light emitting diode LED1 included in the charging device can be blinked. As a result, the abnormality of the charging device 2 can be notified to the user before the protection circuit 1 is damaged and the secondary battery generates heat, and the abnormality of the charging device 2 can be promptly notified. Safety can be ensured.

(Embodiment 2)
Next, the protection circuit 1a according to the second embodiment will be described. FIG. 3 is a circuit diagram showing a charging system to which the protection circuit 1a is applied. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 3, the charging system includes a protection circuit 1 a, a charging device 2 a, and a secondary battery 3.

  The charging device 2a is a contactless charging device, and includes a coil L2a, a transistor Q21a, a light emitting diode LED1, a DC power supply 22a, a charging control unit 21a, and a magnetic body M. The charging device 2a includes a mounting portion for mounting a battery pack provided in the casing of the charging device 2a, and the magnetic body M and the coil L2a are disposed inside the mounting portion. .

  The protection circuit 1a further includes a coil L1a, a diode D2a, and a capacitor C1a with respect to the protection circuit 1 of the first embodiment. In addition, the housing of the battery pack including the protection circuit 1a and the secondary battery 3 includes a contact portion that comes into contact with the placement portion of the charging device 2a, and the coil L1a is disposed inside the contact portion.

  Therefore, when the contact portion of the battery pack comes into contact with the placement portion of the charging device 2a, the coil L2a and the coil L1a are magnetically coupled via the magnetic body M.

  The charge control unit 21a detects whether the secondary battery 3 is being charged by detecting a change in voltage due to electromagnetic induction in the coil L2a when the battery pack is placed on the placement unit. When it is detected that the secondary battery 3 is being charged, the light emitting diode LED1 is turned on. On the other hand, when it is detected that the secondary battery 3 is not being charged, the light emitting diode LED1 is turned off.

  The capacitor C1a is a smoothing capacitor, the diode D2a is a rectifier diode, the coil L2a is a primary side coil, the coil L1a is a secondary side coil, the transistor Q21a is a drive switch element of the charging device 2a, and charging control The unit 21a is a drive pulse signal generator that generates a PWM signal for turning on / off the transistor Q21a.

  When the transistor Q21a is driven by the charge controller 21a, the energy stored in the coil L2a is transmitted to the coil L1a via the magnetic body M, rectified by the diode D2a, smoothed by the capacitor C1a, and supplied to the secondary battery 3. And the secondary battery 3 is charged.

  As described above, according to the protection circuit 1a according to the second embodiment, the same effect as the protection circuit according to the first embodiment can be obtained, and the coil L1a, the diode D2a, and the capacitor C1a are provided. The secondary battery 3 can be charged by supplying the secondary battery 3 with the electric energy supplied by the contactless charging device.

  Since the protection circuit of the present invention can promptly notify the user of the abnormality of the charging device, it is useful as a drive source for mobile devices and electric tools.

1 is a circuit diagram showing a charging system to which a protection circuit according to an embodiment of the present invention is applied. The timing chart of a protection circuit is shown, (a) shows a battery voltage, (b) shows a charging current, (c) shows the lighting state of the light emitting diode. The circuit diagram of the charging system when a non-contact-type charging device is employ | adopted is shown. The circuit diagram of the charging system to which the conventional protection circuit was applied is shown. The timing chart of the charging system shown in FIG. 4 is shown, (a) shows the battery voltage Va, (b) shows the charging current. The timing chart of the charging system to which the poor charging device in which the reference voltage sources 203 and 204 are unstable or the failure charging device is applied is shown, (a) shows the battery voltage Va, and (b) shows the charging. Current is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Protection circuit 2, 2a Charger 3 Secondary battery 10 Control part 11 Timer 12 Discharge control part 13 Charge control part 21 21a Charge control part 22 22a DC power supply A1-A5 Comparator A21, A22 Comparator C21, C1a Capacitor D21, D2a Diode LED1 Light emitting diodes E1 to E5 Reference voltage sources E21, E22 Reference voltage sources L1, L1a, L2a Coil M Magnetic bodies Q1, Q2 Q21, Q21a Transistors R1, R2 Resistor Ref1 Overcharge protection voltage Ref2 Charge resumption voltage Ref21 Ref22 Reference voltage Ref3 Overcurrent protection voltage Va Battery voltage Vb Charging voltage Vc Voltage drop

Claims (5)

Switching means connected in series on the charging path of the secondary battery;
Voltage detection means for detecting the voltage of the secondary battery;
When the voltage detection means detects that the voltage of the secondary battery has risen to the overcharge protection voltage, the switching means is turned off, and the voltage detection means changes the voltage of the secondary battery to the overcharge protection voltage. And a control means for turning on the switching means when it is detected that the voltage has been lowered to a lower charge resumption voltage. The control means includes
A timing unit that starts a timing operation when the switching unit is turned off, and performs a timing operation until a time-out period for detecting a full charge of the secondary battery elapses;
Charge control means for turning on the switching means when the timeout time elapses when the voltage of the secondary battery drops to the charge resumption voltage until the timeout time elapses. The protection circuit according to claim 1.   The voltage detection unit includes a first comparator that compares the voltage of the secondary battery and the overcharge protection voltage, and a second comparator that compares the voltage of the secondary battery and the charge resumption voltage. The protection circuit according to claim 2. In the first comparator, a positive terminal is connected to a positive electrode of the secondary battery, the overcharge protection voltage is applied to a negative terminal, an output terminal is connected to the timing means,
In the second comparator, a positive terminal is connected to the positive electrode of the secondary battery, the charging resumption voltage is applied to a negative terminal, an output terminal is connected to the charge control unit,
When the time measuring means receives a low level signal from the first comparator, it starts a time measuring operation, notifies the charging control means of a time measuring operation start signal, and starts the time measuring operation before the time-out period. When the time elapses, the charging control means is notified of a timing operation end signal,
The charging control unit turns off the switching unit when receiving the timing operation start signal from the timing unit, and turns on the switching unit when receiving the timing operation end signal from the timing unit. The protection circuit according to claim 3.   The protection circuit according to claim 1, further comprising a transmission unit that transmits electric energy from the non-contact charging device to the secondary battery.

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