JPH0970145A - Constant-voltage charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize heating from a series control element by cutting off the series control element for a specified period of time immediately after power-on using a power-on detecting section, and detecting short-circuit between charging terminals through a voltage sensor. SOLUTION: When a charger is connected to a commercial power supply 1 with its charging terminals 40, 41 short-circuited with each other, the voltage of a direct-current power supply 60 is sharply increased. A power-on detecting section 10 is fed with this abrupt variation in voltage, and short-circuits the output of an error amplifier 7 to the negative line of the charger for a specified period of time. As a result, a pre-amplifier 9 controlled through the output of the error amplifier 7 interrupts a current passed through a series control element 6. At this time, a direct-current power supply 60 is virtually brought under no load, and the output of the direct-current power supply 60 is maximized. Since the charging terminals 40, 41 are in a state close to short circuit, the potential difference between the voltage of the direct-current power supply 60 and the voltage of the positive charging terminal 40 exceeds a predetermined value. Therefore, a voltage sensor 8 switches on, and the pre-amplifier 9 interrupts a current passed through the series control element 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage charger that charges a secondary battery such as a lead storage battery until the voltage reaches a constant voltage.

[0002]

2. Description of the Related Art Conventionally, as one of the methods for charging a sealed small lead-acid battery, constant-current charging in which a constant current value is applied at the initial stage of charging, the terminal voltage of the battery gradually rises to a set voltage When it reaches, a constant voltage charging method is used in which charging is performed by switching to constant voltage charging that maintains this set voltage. FIG. 2 is a diagram showing a configuration of a conventional charger that charges a secondary battery by the above charging method. The configuration will be described below with reference to FIG. 1 is commercial power supply, 2
Is an isolation transformer for step-down, 3 and 4 are rectifying diodes, 5 is a smoothing capacitor, 20 is a voltage regulator, 30 is a backflow preventing diode, and 40 and 4
Reference numeral 1 is a positive and negative charging terminal, and 50 is a secondary battery such as a sealed lead acid battery that is charged by this charger. The power supplied from the commercial power source 1 is stepped down to a voltage corresponding to the charging voltage of the battery by the insulating transformer 2, and then the diode 3
Rectified by 4 and 4, and smoothed by the capacitor 5. The voltage regulator 20 is set so that a voltage equal to the charging terminal voltage of the secondary battery 50 can be supplied to the secondary battery 50. The diode 30 is connected to prevent the reverse flow of current from the secondary battery 50 to the charger side. During the period when the secondary battery 50 is in the initial charging, the secondary battery 5
The charging terminal voltage of 0 is low, and the voltage regulator 2
The output voltage of 0 is forcibly suppressed to the voltage of the charging terminal of the secondary battery 50. As a result, the voltage regulator 20 loses its control ability to hold its output voltage at the voltage of the charging terminal. The voltage regulator 20 outputs the maximum current that can be supplied to the secondary battery 50 and charges it. The charging current applied to the secondary battery 50 is
For the difference between the voltage obtained by adding the voltage equivalent to the drop voltage of the backflow prevention diode 30 to the set voltage of the regulator 20 and the terminal voltage of the battery 50, and the output impedance of the charger viewed from the charging terminal side. Dependent. Therefore, as the charging of the secondary battery 50 progresses and the voltage of the charging terminal rises, the charging current gradually decreases. When the charging current reaches a substantially constant value, charging is completed. At this point, voltage regulator 20
The potential difference between the input and output of is sufficiently large, and the voltage regulator recovers its control function and outputs a constant voltage.

[0003]

However, in the above-mentioned conventional charger, when a situation occurs such that both ends of the charging terminal are short-circuited, an excessive current is loaded into the charging circuit, and the voltage regulator 20. Power consumption becomes large. For this reason, a large voltage regulator that can withstand an excessive current load has been required.

In view of the above problems, the present invention detects a low voltage between charging terminals and stops the charging current.

[0005]

In order to achieve the above object, a constant voltage charger of the present invention includes a DC power supply obtained by rectifying and smoothing an AC voltage, and a DC power supply between the DC power supply and a battery to be charged. The connected serial control element, an error amplifier that compares the output of the serial control element with a reference voltage, and the difference between the voltage of the DC power supply and the voltage of the battery to be charged exceeds a predetermined value. Connected to the DC power supply, a preamplifier connected between the series control element and the error amplifier and controlled by the output of the error amplifier and the output of the voltage sensor. The power-on detector detects the power-on of the charger and generates an output for a predetermined time. In this configuration, the output of the power-on detection unit stops the output of the error amplifier for the predetermined time and shuts off the series control element via the preamplifier. During this period, the voltage sensor determines whether the voltage between the charging terminals exceeds a predetermined value, and the determination result is positively fed back to the series control element via the preamplifier.

[0006]

In the constant voltage charger of the present invention, the series control element is cut off within a certain period of time immediately after the start of operation, so that the DC power supply is in a no-load state during this period and its output voltage becomes high. At this time, if the charging terminals are short-circuited or if the voltage becomes extremely low, the difference from the voltage of the DC power source exceeds a predetermined value. At the same time that the voltage sensor detects this, positive feedback is made to the series control element via the preamplifier, so that the series control element maintains the cutoff state. Therefore, the power consumption of the series control element is very small even though the charging terminals are short-circuited. On the other hand, if a normal battery is connected between the charging terminals,
Initially, a large current flows, but the series control element operates in the saturation region. Therefore, the heat generation in the series control element is small, and a small element is possible.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The constant voltage charger of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of a constant voltage charger according to the present invention. Reference numeral 60 is a DC power supply composed of an insulating transformer 2 for stepping down the voltage supplied from the commercial power supply 1, rectifying diodes 3, 4 and a smoothing capacitor 5, and 6 is a DC power supply 60 and a secondary battery 5.
A serial control element connected between 0 and 7, an error amplifier 7 for comparing the output of the serial control element 6 and a reference voltage, and 8 for the voltage of the DC power supply 60 and the voltage of the secondary battery 50 which is the battery to be charged. Voltage sensor for measuring the difference between the measured value and a predetermined voltage value, 9 is a preamplifier connected between the series control element 6 and the error amplifier 7, and 10 is a DC power supply 6
A power-on detection unit that is connected to 0, detects the power-on state of the charger, and generates an output for a predetermined time,
Reference numeral 30 is a backflow preventing diode for preventing backflow of current from the secondary battery 50 to the charger side, 40 and 41 are positive and negative charging terminals, and 50 is a secondary battery. The DC power supply 60 is
The electric power supplied from the commercial power source is stepped down to a voltage corresponding to the charging voltage of the battery by the insulating transformer 2, rectified by the diodes 3 and 4, and smoothed by the capacitor 5. The error amplifier 7 is set so that a voltage equal to the charging voltage is supplied to the secondary battery 50.

Next, the operation of the constant voltage charger according to the present invention will be described. When the charger is connected to the commercial power supply 1, the voltage of the DC power supply 60 rises sharply. Power-on detection unit 10
Receives a rapid voltage change in the DC power supply 60 and short-circuits the output of the error amplifier 7 to the negative line of the charger for a predetermined time. As a result, the preamplifier 9 controlled by the output of the error amplifier 7 cuts off the current flowing through the series control element 6. The DC power supply 60 becomes almost unloaded due to the current interruption of the series control element 6, and the output voltage of the DC power supply 60 becomes maximum. On the other hand, the secondary battery 5 in a normal state
When 0 is connected to the charging terminals 40 and 41, the secondary battery 5
0 has some terminal voltage. Therefore, the potential difference between the DC power supply 60 and the positive charging terminal 40 does not exceed a predetermined value, and the voltage sensor-8 does not generate a detection signal. When the power-on detection unit 10 finishes generating the output for a predetermined time, the output short circuit of the error amplifier 7 is recovered, and the current starts flowing in the series control element 6. Secondary battery 50
While the battery is not sufficiently charged, the terminal voltage of the secondary battery 50 is low and the output voltage of the series control element 6 is forcibly suppressed to the terminal voltage of the secondary battery 50. Therefore, the series control element 6 operates in the saturation region. The DC power source 60 outputs the maximum current that can be supplied, and the secondary battery 50
To charge. The charging current flowing through the secondary battery 50 was seen from the difference between the voltage obtained by adding the voltage drop of the backflow prevention diode 30 to the voltage set by the error amplifier 7 and the charging terminal voltage of the secondary battery 50, and from the charging terminal. It depends on the output impedance of the charger. Therefore, the charging of the secondary battery 50 progresses and the charging current gradually decreases as the charging terminal voltage increases. The voltage at the charging terminal reaches a substantially constant value and charging is completed. At this time, the error amplifier 7 functions as a constant voltage control function, and a constant voltage is output between the charging terminals 40 and 41. Further, the series control element 6 operates in the saturation region most of the time, and its heat generation is extremely small.

Next, the case where the charging terminals 40 and 41 are short-circuited will be described. When the charger is connected to the commercial power supply 1, the voltage of the DC power supply 60 rises sharply. The power-on detector 10 receives this abrupt voltage change and short-circuits the output of the error amplifier 7 to the negative line of the charger for a predetermined time. As a result, the error amplifier 7
The preamplifier 9, which is controlled by the output of, shuts off the current through the series control element 6. The DC power supply 60 becomes almost unloaded due to the current interruption of the series control element 6, and the output voltage of the DC power supply 60 becomes maximum. Since the charging terminals 40 and 41 are in a state close to a short circuit, the potential difference between the voltage of the DC power supply 60 and the voltage of the positive charging terminal 40 exceeds a predetermined value, and the voltage sensor-8 becomes conductive. The preamplifier 9 operates so as to cut off the current flowing through the series control element 6. Even after the power-on detector 9 finishes generating the output for the predetermined time, the voltage sensor 8 continues to be conductive, and the series control element 6 is no longer recovered from the cutoff state. As a matter of course, in this case, the series control element 6 hardly generates heat.

The capacitor 11 connected to the control electrode of the series control element 6 is connected so as to delay the operating speed of the series control element 6 as compared with the operating speeds of the voltage sensor 8 and the preamplifier 9. . If the charging terminals 40 and 41 are short-circuited after a sufficient time has passed since the charger was connected to the commercial power source 1, the function of the power-on detection unit 10 cannot be used, but delay due to the capacitor is caused. Thus, the series control element 6 can be turned off.

[0011]

The constant voltage charger according to the present invention shuts off the series control element for a certain period of time immediately after power-on by the function of the power-on detector, and detects a short circuit between charging terminals by the voltage sensor. This makes it possible to suppress the heat generation in the series control element to an extremely low level, and it becomes possible to use a small and inexpensive element as the series control element, and the practical effect thereof is extremely great.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a constant voltage charger according to the present invention.

FIG. 2 is a configuration diagram of a conventional constant voltage charger.

[Explanation of symbols]

 1 Commercial Power Supply 2 Insulation Transformer 3, 4 Rectifying Diode 5 Smoothing Capacitor 6 Series Control Element 7 Error Amplifier 8 Voltage Sensor-9 Preamplifier 10 Power-on Detector 11 Capacitor 20 Voltage Regulator 30 Backflow prevention diode 40, 41 Charging terminal, 50 Secondary battery 60 DC power supply

Claims (2)

[Claims] 1. A DC power supply for rectifying and smoothing an AC voltage,
A series control element connected between the DC power supply and a rechargeable secondary battery, an error amplifier for comparing the output of the series control element with a reference voltage, the voltage of the DC power supply and the secondary battery A voltage sensor that detects that the difference from the voltage exceeds a predetermined value, and is connected between the series control element and the error amplifier and is controlled by the output of the error amplifier and the voltage sensor. Preamplifier,
Connected to the DC power supply, detects the power-on of the charger,
The power-on detector for generating an output for a predetermined time, and the output of the error amplifier is stopped for a predetermined time by the output of the power-on detector, and the preamplifier is turned on. A constant voltage charger characterized in that the output of the voltage sensor is positively fed back to the series control element via the preamplifier while shutting off the series control element via the preamplifier. 2. The constant voltage charger according to claim 1, wherein a capacitor element is connected to a control electrode of the series control element.