JP3082537B2 - Charger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charger for rapidly charging a battery pack having a backflow prevention diode.

[0002]

2. Description of the Related Art In recent years, as a battery pack for a rechargeable battery such as a lithium secondary battery or a nickel cadmium storage battery, a backflow prevention diode is provided in a battery pack for the purpose of protecting a short circuit between a positive electrode terminal and a negative electrode terminal for charging the battery pack. Are often used. In addition, the main charge control method of the charger for rapidly charging the battery pack is an absolute voltage control method that detects and controls that the battery voltage has reached a certain set voltage, or a voltage drop after the peak of the battery voltage. A method of performing charging control by detecting a battery voltage, such as a -ΔV control method of detecting and controlling, is often used.

A charger for rapidly charging a battery pack having a backflow prevention diode according to a conventional method will be described below.

FIG. 2 is a circuit block diagram of a conventional charger using a DC power supply as an input. In FIG. 2, reference numeral 1 denotes an input DC power supply, reference numeral 2 denotes a current control unit for controlling a charging current at a constant current, and reference numeral 3 denotes a charging control unit for detecting battery voltage to detect completion of charging of the battery. 4 is a battery pack, 5 is a backflow prevention diode built in the battery pack, and 6 is a battery. 7 and 8 are discharge terminals of the battery pack.

[0005] The operation of the charger configured as described above will be described. First, a DC input is applied from a DC power source to a charger, and a rapid charging current, which has been converted to a constant current by a current control unit, flows into a battery pack of 4 and a battery of 6 through a backflow prevention diode of 5. Start quick charging. Simultaneously with the start of the rapid charging, the charging control unit 3 reads the output voltage of the charger as a voltage obtained by adding the forward voltage of the backflow prevention diode 5 to the battery voltage 6 and starts detecting the completion of charging of the battery. When the charging of the battery advances and the battery voltage drop indicating the completion of charging or the battery voltage reaches a certain set voltage is detected by the charging control unit (3), a charge end signal is output to the current control unit (2) and the rapid charging current is output. Is switched to the trickle current or gradually reduced, and the rapid charging of the battery ends. The charged battery pack is connected to the main device serving as a discharge load, and discharged through the discharge terminals 7 and 8.

[0006]

However, in the above-mentioned conventional configuration, the voltage detected by the charge control unit 3 is not the battery voltage of 6, but the output voltage of the charger, that is, the battery voltage of 6. This is the voltage obtained by adding the forward voltage of the backflow prevention diode. However, an accurate battery voltage is required for detecting the completion of charging, and therefore, the conventional charging control unit regards the forward voltage of the backflow prevention diode as a certain constant voltage and adds the certain voltage to the original charging control voltage. The voltage value is set as the charge control voltage. If the backflow prevention diode is a Schottky barrier diode, about 0.4 V is usually used for this constant voltage.

However, the forward voltage of the backflow prevention diode has a temperature characteristic. When the temperature of the backflow prevention diode is low, the forward voltage is high, and when the temperature is high, the forward voltage is low. . For this reason, when the ambient temperature at the time of charging is low, the forward voltage of the backflow prevention diode becomes higher than a fixed voltage added to the charge control voltage, and the difference voltage becomes an error in the charge control voltage for the battery. As a result, the charge control is performed at a voltage lower than the original charge control voltage for the battery itself. Also, when the ambient temperature during charging is high, the forward voltage of the backflow prevention diode is lower than the fixed voltage added to the charging control voltage, so that the battery itself does not have its own charge control The charge control is performed at a voltage higher than the voltage.

Further, the forward voltage of the backflow prevention diode has a dependency on the forward current. When the forward current is small, the forward voltage is low, and when the forward current is large, the forward voltage is low. Will be higher. For this reason, in the case of a charger in which the rapid charging current is switched between the large rapid charging current and the small rapid charging current in order to rapidly charge the two large and small batteries, the charging control is performed with the large rapid charging current flowing. When the voltage is set, the forward voltage of the backflow prevention diode decreases at the time of a small rapid charging current, so that the charging control is performed at a voltage higher than the original charging control voltage for the battery itself. Conversely, if the charging control voltage is set in the state where the small rapid charging current is flowing, the charging control will be performed at a voltage lower than the original charging control voltage at the time of the large rapid charging current.

As described above, in the conventional method, when a battery pack provided with a backflow prevention diode is rapidly charged, there is a problem that an error occurs in the charge control voltage depending on the ambient temperature or the magnitude of the rapid charging current. I was

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a charger which does not cause an error in the charge control voltage even when the ambient temperature or the magnitude of the rapid charging current changes.

[0011]

In order to solve these problems, a charger for rapidly charging a battery pack provided with a backflow prevention diode according to the present invention is provided with a current line through which a rapid charging current flows. It provided with a resulting blocking diode similar diode as the output diode of the charger, provided a voltage detection circuit for outputting a voltage obtained by subtracting twice the voltage of the forward voltage of the output diode from the anode potential of the output diode The battery charge completion detection is performed by reading the output voltage of the voltage detection circuit as a battery voltage into a charge control unit.

[0012]

The voltage detected by the charge control unit of the charger having the above structure is obtained by adding the forward voltage of the backflow prevention diode and the forward voltage of the output diode of the charger to the battery voltage. This is a voltage obtained by subtracting twice the voltage. If exactly the same diode is used for the backflow prevention diode and the output diode , the change in the ambient temperature during charging and the change in the forward voltage of the backflow prevention diode due to the switching of the rapid charging current will be caused by the forward direction of the output diode. The voltage has the same value as the change in voltage, and the forward voltage of the two always has the same voltage value.

Therefore, the voltage detected by the charging control unit is always equal to the battery voltage, and the charging control can be performed accurately without being affected by the ambient temperature during charging or the magnitude of the rapid charging current.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the circuit block diagram shown in FIG. Note that the circuit block diagram of the present embodiment shown in FIG. 1 has basically the same configuration as the conventional circuit block diagram shown in FIG. 2, so the same components are denoted by the same reference numerals.

In FIG. 1, 1 is an input DC power supply, 2 is a current control unit for controlling the charging current at a constant current, and 3 is a charging control unit for detecting the battery voltage and detecting the completion of charging of the battery. 4 is a battery pack, 5 is a backflow prevention diode built in the battery pack, and 6 is a battery. 7 and 8 are discharge terminals of the battery pack. Reference numeral 9 denotes an output diode of the charger, which is exactly the same as the backflow prevention diode 5. Reference numeral 10 denotes a voltage detection circuit that detects the forward voltage of the output diode 9 and outputs a voltage obtained by subtracting twice the forward voltage of the output diode from the anode potential of the output diode. And 13 having the same resistance value.

The operation of the charger configured as described above will be described. First, a DC input is applied from a DC power source to a charger, and a rapid charging current, which is made constant by a current control unit, flows into a battery pack 4 through an output diode 9 and a backflow prevention diode 5 , The rapid charging of the battery 6 is started. At the same time as the start of quick charge, 3
The charging control unit reads the voltage output from the voltage detection circuit unit and starts detecting the completion of charging of the battery. When the charging of the battery advances and the battery voltage drop indicating the completion of charging or the battery voltage reaches a certain set voltage is detected by the charging control unit (3), a charge end signal is output to the current control unit (2) and the rapid charging current is output. Is switched to the trickle current or gradually reduced, and the rapid charging of the battery ends. The charged battery pack is connected to the main device serving as a discharge load, and discharged through the discharge terminals 7 and 8.

In the charger according to the present embodiment, the voltage detected by the charge control unit 3 is a voltage obtained by adding the forward voltage of the backflow prevention diode 5 and the forward voltage of the output diode 9 to the battery voltage 6. Is a voltage obtained by subtracting twice the forward voltage of the output diode 9 from. Since the backflow prevention diode of No. 5 and the output diode of No. 9 are completely the same diode, the change of the forward voltage of the backflow prevention diode No. 5 accompanying the change of the ambient temperature during charging or the switching of the quick charge current is 9 The voltage value becomes the same as the change in the forward voltage of the output diode, and the forward voltage of both the output voltages always becomes the same.

Therefore, the voltage detected by the charge control unit is always equal to the battery voltage, and the charge control can be performed accurately without being affected by the ambient temperature during charging or the magnitude of the rapid charging current. is there.

[0019]

As described above, in the charger of the present invention, a diode similar to the backflow prevention diode provided in the battery pack is provided as the output diode of the charger, and the anode potential of the output diode is provided. A voltage detection circuit for outputting a voltage obtained by subtracting twice the forward voltage of the output diode from the output diode, and reading the output voltage of the voltage detection circuit as a battery voltage to obtain the ambient temperature during charging and the rapid charging current. The charge control can be performed accurately without being affected by the magnitude of the charge.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a charger according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram of a conventional charger.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Current control part 3 Charge control part 4 Battery pack 5 Backflow prevention diode 6 Battery 7 Battery pack discharge terminal 8 Battery pack discharge terminal 9 Output diode 10 Voltage detection circuit 11 Operational amplifier 12 Resistor 13 Resistor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36 H01M 10/42-10/48 301

Claims (1)

(57) [Claims] 1. A charger for charging a battery pack provided with a backflow prevention diode, wherein a diode similar to the backflow prevention diode provided in the battery pack is connected to a current line through which a rapid charging current flows, by an output diode of the charger. And a voltage detection circuit for outputting a voltage obtained by subtracting twice the forward voltage of the output diode from the anode potential of the output diode, and a charge control unit using the output voltage of the voltage detection circuit as a battery voltage. A battery charger that detects the completion of charging of a battery by reading the data into the battery charger.