JPH0787682A - battery charger - Google Patents

Abstract

(57) [Abstract] [Purpose] Automatically cancels the input offset voltage of the output current output circuit that detects and controls the output current of the switching regulator, enabling accurate and arbitrary battery charging. . [Configuration] A switching regulator 17 is configured to control a switching pulse width of the converter 4 by applying a DC voltage to a primary winding of a transformer 3 via a converter circuit 4 that performs a switching operation. The control means 26 controls the data sent to the D / A converter 33 according to the data value detected by the output voltage of the switching regulator 17 and A / D converted by the A / D converter 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger which is a device having a charging function for a household AC adapter.

[0002]

2. Description of the Related Art In recent years, compact personal computers, home video cameras, and the like have been miniaturized, and by using a battery as a power source, they can be carried anywhere and are becoming popular. It is believed that battery-powered devices will increase and that rechargeable batteries, which are economically advantageous, will be used in the future.

However, a rechargeable battery is required to have an optimum charging function in order to prolong its service life and to fully charge the battery and bring out its battery capacity. Its function is as follows.

A. Can be fully charged in a short time. b. A sufficient amount of discharge can be taken out.

C. Can be fully charged at each temperature. d. Does not overcharge.

A conventional example of the above-mentioned battery charger will be described below with reference to FIG.

As shown in the figure, the AC voltage input from the power cord 1 is converted into a DC voltage by the rectifying / smoothing circuit 2, one end of the output of the DC voltage is added to the primary winding of the transformer 3, and the other end is a converter. The circuit 4 switches the DC voltage. As a result, an AC output corresponding to the winding ratio with the primary winding is generated from the secondary winding of the transformer 3, and is rectified by the rectifier 5 to obtain the secondary side output voltage. This secondary side output voltage is detected by the output voltage / output current control circuit 6, and the control signal 7 is transmitted to the converter circuit 4 via a photo coupler or the like so as to become a specified voltage, and the switching pulse width is controlled to control the secondary side output. Keep the voltage constant. This controlled secondary output voltage is supplied from the terminal 8 to the device 9 such as a video camera.

Next, the battery charging circuit controls the secondary side output voltage by the transistor 10, and its output is supplied with the charging current to the + side of the battery 12 via the battery charging terminal 11. The negative side of the battery 12 is used as a circuit ground via the terminal 13 and the charging current charged in the battery 12 is connected to the other end of the secondary winding of the transformer 3 through the current detection resistor 14. Then, whether or not the battery 12 is connected is input from the battery charging terminal 11 to the microcomputer (hereinafter, referred to as a microcomputer) 16 through the detection signal line 15, and the A / D converter of the microcomputer 16 determines whether the battery 10 is connected to the transistor 10. To conduct. For the constant current required to charge the battery 12, the terminal voltage of the current detection resistor 14 is input to the output current control circuit of the output voltage / output current control circuit 6, and the converter circuit 4 is supplied via the control signal 7.
Was controlled to obtain the secondary side output voltage required for constant current.

[0009]

In such a conventional battery charger, since the current detecting resistor 14 uses a low resistance so as not to give it to the output voltage, the potential difference between both ends becomes several mV, and this voltage detected by the current is detected. Is amplified by the operational amplifier in the output voltage / output current control circuit 6, variations in the input offset voltage of the operational amplifier and the current detection resistor 1
4. There was a problem that variations in bias resistance cannot be ignored. Therefore, there has been adopted a method of using an expensive operational amplifier with a small input offset voltage, or canceling it by including a variation in each resistance with a volume. Furthermore, there are many circuit components such as the output voltage / output current control circuit 6 and the microcomputer 16, which makes it difficult to reduce the size.
There is a problem that the accuracy of charging the battery 12 is poor and the cost cannot be reduced.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly accurate, compact and inexpensive battery charger.

[0011]

In order to achieve the above object, the present invention applies a DC voltage to a primary winding of a transformer through a converter circuit that performs a switching operation, and rectifies a secondary winding voltage of the transformer. A switching regulator that detects the output DC voltage or current and controls the switching pulse width of the converter to keep the secondary output voltage or current constant, and a reference current energizing means for flowing a reference current from the output voltage of the switching regulator. An A / D conversion means for detecting the output voltage of the switching regulator and A / D converting it;
Of the switching regulator by controlling the control means for controlling the data to be sent to the D / A conversion means according to the D / A converted data value and the output current detecting section for detecting the output DC current by the output of the D / A conversion means. A state control means for controlling the state, wherein the control means gradually controls the state of the switching regulator by the output of the D / A conversion means to obtain the reference current, and exceeds the designated output voltage. The data or the previous value to the D / A conversion means at this time is stored, and the current required for output from the reference current is controlled by adjusting the data to the D / A conversion means. Is used as a means for solving the problem.

Further, the control means of the first problem solving means rapidly changes the state of the switching regulator up to a certain output voltage by the output of the D / A conversion means in order to obtain the reference current, and gradually controls thereafter. A value obtained by returning one step from the data value to the D / A conversion means when the output voltage exceeds the specified output voltage, or the output voltage specified by the A / D conversion means data in the state before and after the elapse of a certain time. The second problem solving means is to select and store which one is closer to the current, and to control the current required for output from the reference current by adjusting the data to the D / A conversion means.

[0013]

According to the first means for solving the above problems, the present invention provides:
Data obtained by detecting the output voltage of the switching regulator and A / D converting it, and detecting the output current by the D /
The A-converted voltage can be adjusted to control the switching regulator, the output voltage can be detected and the A / D converted data can be controlled to match, and the input offset voltage of the operational amplifier of the switching regulator output current control circuit can be automatically adjusted. You can cancel it.

Further, according to the second problem solving means, the D / A
Even if the change in the output voltage of the switching regulator per step of the conversion means is large, the control accuracy can be improved.

[0015]

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. The same components as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown in the figure, the switching regulator 17 includes a transformer 3, a converter circuit 4, a rectifier 5,
The output voltage output current control circuit 6 and the like are configured. The output voltage output current circuit 6 is configured by an output voltage control circuit 18 and an output current control circuit 19, and the output voltage control circuit 18 is
A voltage obtained by dividing the secondary side output voltage rectified by the rectifier 5 by the resistors 20 and 21 and the voltage of the reference power supply 22 are compared, and the output is regulated by the photocoupler 23 as the control signal 7 Input to the converter circuit and control the switching pulse width. The secondary output voltage controlled in this way is supplied from the terminal 8 to the device 9 such as a video camera.

The charging circuit of the battery 12 controls on / off of the secondary side output voltage by the transistor 10 and supplies a charging current to the battery 12 through the battery charging terminal 11. Whether the battery 12 is connected or not is determined by connecting the battery charging terminal 11 to the A / D via the detection signal line 24.
It is connected to the converter (A / D conversion means) 25, the output of the A / D converter 25 is input to the control means 26 for determination, and the result is input to the transistor 10 via the control line 27 to make it conductive. .

The constant current required to charge the battery 12 is
The terminal voltage of the current detection resistor 14 is divided by the resistors 29 and 30 and the resistors 31 and 32 which form the output current detection unit 28 and input to the output current control circuit 19, and by the output of the output current control circuit 19. The switching pulse width of the converter circuit 4 is controlled via the photo coupler 23. Here, in the current control, assuming that the charging current of the battery 12 is 1.3 A, when the resistance value of the current detection resistor 14 is 0.05Ω, the terminal voltage Vr of the current detection resistor 14 is: Vr = 1.3 A × 0 0.05 Ω = 0.065 V = 65 mV, and in order to operate so that the differential input terminal voltage of the output current control circuit 19 becomes 0 V at the voltage Vr or higher, the voltage division ratio between the resistors 29 and 30 and the resistors 31 and 32 is set. It needs to be set up and working.

Next, the fully charged battery 12
Requires a charging current of about 0.1 A to be supplied as a supplement to self-discharge. The terminal voltage Vr of the current detection resistor 14 at this time is Vr = 0.1 A × 0.05 Ω = 0.005 V = 5 mV, but when amplified by the operational amplifier of the output current control circuit 19, the terminal voltage Vr is equal to the input offset voltage of the operational amplifier. Resistance 29,
Dispersion between 30 and resistors 31 and 32 cannot be ignored.

Therefore, in the present invention, the data from the control means 26 is converted into an analog voltage by the D / A converter (D / A conversion means) 33, and the resistor 3 constituting the state control means 34 is formed.
The input voltage of the operational amplifier of the output current circuit 19 can be slightly changed by connecting to the connection point of the resistors 29 and 30 for voltage division via 5 and 36. Here, the D / A converter 33
The analog voltage value output by the output voltage is the resistance 37,
The voltage divided by 38 is input to the control means 26 via the A / D converter 25, and the control means 26 determines.

The above operation is suitable for producing a reference current. That is, first, the transistor (reference current conducting means) 39 is turned on as a reference current of the output current, and a current is passed through the bleeder resistor 46. At this time, the secondary side output voltage is Vc
c, the reference current is Is, and the resistance value of the bleeder resistor 40 is Rb
Then, since Is = Vcc / Rb, the secondary side output voltage Vcc is converted into the A / D converter 25.
The reference current Is is uniquely determined by the measurement. This means that the operational amplifier input offset voltage of the output current control circuit 19, the resistors 29 and 30, the resistors 31 and 32, and the current detection resistor 1 that constitute the output current detection unit 28.
Since item 4 does not come in, it is canceled by the D / A converter 33.

The control means 26 obtains the reference current by
The state of the switching regulator 17 is gradually controlled by the output of the D / A converter 33, and the data or the previous value to the D / A converter 33 when the specified output voltage is exceeded is stored and output from the reference current. The current required for the above is controlled by adjusting the data to the D / A converter 33.

In the above structure, the operation will be described with reference to FIGS. 2 to 4. After the offset correction shown in FIG. 2 is started, the transistor 1 is initially set in step a.
0 is turned off, and input data (Y = 8 is input to the D / A converter 33.
0, a value at which the secondary side DC voltage Vcc becomes high) is turned on, the transistor 39 is turned on, and a current is passed through the bleeder resistor 40 (point a in FIG. 3). Next, in step b, Y = Y + 2 (addition value 2 shortens the processing time and is changed according to the variation tolerance of parts), and data is input to the D / A converter 33. Then, in step c, the secondary side output voltage is divided by the resistors 37 and 38, and the voltage Vo is divided by the A / D converter 25.
Is converted into data X with, and this data X is converted into 2 in step d.
Whether the output voltage on the secondary side is 10 V or less is determined. If NO, the process returns to step b, and if YES, the process proceeds to step e. In step e, Y = Y + 1 is set, and the D / A converter 33
Enter data into.

Next, in step f, the secondary side output voltage is divided by the resistors 37 and 38, the voltage Vo is converted into the data X by the A / D converter 25, and in step g, the data X is converted into the secondary side. Whether the output voltage is 7 V or less is determined. If NO, the process returns to step e, and if YES, the process proceeds to the next step h. When the data X becomes 7V or less, Y = Y- in step h.
Set to 1. This is because the response of the secondary side output voltage is the control means 26.
This is because it is slower than the processing of (1) to prevent overcorrection. Then, in step i, the Y value is stored. The Y value (denoted as Y0) at this time is the offset correction value, and the reference current Is is obtained. Next, in step j, the transistor 39 is turned off to complete the offset correction.

Next, when a constant current of 1.0 A is applied to the battery 12, in step k, Y = Y0 + y (1.
0). y (1.0) is the reference power source of the D / A converter 33, the resistors 35 and 36, the resistors 29 and 30, and the current detection resistor 1
The value determined by 4 is shown in FIG. Then, in step 1, the transistor 10 is turned on, and the battery 1
Charging to 2 starts.

3A shows the characteristics of the bleeder resistance 41 of 35 ohms, and FIG. 3B shows the characteristic of 100 ohms.
In (B), the change in the secondary side output voltage per step of the D / A converter 33 is large, and the accuracy of the reference current Is decreases. On the contrary, if the bleeder resistance 40 is small, the processing time becomes long.

(Embodiment 2) Next, another embodiment of the present invention will be described.

The control means 26 shown in FIG. 1 of the first embodiment gradually controls the state of the switching regulator 17 by the output of the D / A converter 33 in order to obtain the reference current, and when the specified output voltage is exceeded. The data or previous value of the D / A converter 33 is stored, and the reference current is obtained by controlling the current required for output from the reference current by adjusting the data to the D / A converter 33. Therefore, the output of the D / A converter 33 causes the state of the switching regulator 17 to change rapidly up to an output voltage, and then gradually controlled,
A value obtained by returning one step from the data value of the D / A converter 33 when the output voltage exceeds the specified output voltage or the data of the A / D converter 25 in the state before and after the elapse of a certain time, One of the two is selected and stored, and the current required for output from the reference current is controlled by adjusting the data to the D / A converter 33. The other structure is the same as that of the first embodiment.

The operation of the above structure will be described with reference to FIG. 5. To improve the accuracy of the reference current Is,
It is necessary to increase the detection accuracy of the secondary side output voltage Vcc (7V = D / A converter data X0) at that time. The processing from step a to step g after the start of the offset correction in FIG. 5 is the same as that of the above-mentioned embodiment, so the description thereof is omitted.

In step g, if the data X is 7 V or less in the secondary side output voltage, the process proceeds to step m, and in step m,
The timer waits until the secondary output voltage Vcc stabilizes, and then in step n, the secondary output voltage is converted into data X1 by the A / D converter 25 and stored. Then, in step o, Y2 = Y-1, and the Y value is returned by one step, and D
Input data to the / A converter 33. Then, in step p, the timer again waits until the secondary side output voltage Vcc stabilizes, and then in step q, the secondary side output voltage is converted into data X2 by the A / D converter 25 and stored.

Next, in step r, X2-X0 <X
The value close to the data X0 of the A / D converter 25 having the secondary side output voltage Vcc = 7V is selected by 0-X1, and the process proceeds to step s or step t, and it is determined whether it is the Y2 value or the Y value corresponding to the result. And remember. The Y value (denoted as Y0) at this time is the offset correction value, and the reference current Is is obtained. Then, the process proceeds to step u to turn off the transistor 39 and complete the offset correction.

Next, when a constant current of 0.1 A is applied to the battery 12, Y = Y0-y (0.1
A). Here, y (0.1 A) is the D / A converter 3
The values determined by the reference power supply No. 3, the resistors 35 and 36, the resistors 29 and 30, and the current detection resistor 14 are shown in FIG. Then, in step w, the transistor 10 is turned on to start charging the battery 12.

By the above processing, the secondary output voltage Vcc
The detection accuracy of (7V = D / A converter data X0) is approximately doubled, and the accuracy of the reference current Is is also improved to approximately 2. When a charging current of about 0.1 A is supplied as a supplement to the self-discharge of the battery 12 that has been charged, when Y of FIG.
= Y0−y (0.1) and y (0.1) may be subtracted, and the accuracy is improved as much as it is closer to the reference current. This is D / A
All the circuits such as the converter 33 and the output current control circuit 19 are linear, and if the data of the D / A converter 33 is determined,
It has the characteristic that the charging current is uniquely determined, for example 0.0
Highly accurate charge current control from 1A to 1A can be freely programmed.

[0034]

As is apparent from the above embodiments, according to the present invention, in order to obtain the reference output current, the state of the switching regulator is gradually controlled by the output of the D / A conversion means, and the designated output voltage is changed. Since the data or the previous value to the D / A conversion means when it exceeds is stored, the current required for output from the reference output current is controlled by adjusting the data to the D / A conversion means. The output voltage of the switching regulator is detected, and the D / A converted voltage is controlled by the control means to be adjusted, and the output voltage is accurately detected and controlled by the A / D conversion means, and the operational amplifier of the output current control circuit of the switching regulator is used. The offset of the output current control circuit is canceled, and the accuracy of the input offset voltage of the operational amplifier of the output current control circuit and the resistance of each resistor of the output current detection unit is reduced It is a good battery charge. Further, since the volume can be eliminated, the manufacturing process time can be shortened and the reliability can be improved, and further, a one-step IC can be realized and the cost can be reduced.

Further, in order to obtain the reference output current, the state of the switching regulator is rapidly changed up to a certain output voltage by the output of the D / A conversion means, and then gradually controlled.
Which of the output voltages specified by the A / D conversion means data before and after the step of returning from the data value of the D / A conversion means when the output voltage exceeds the specified value by one step or after a predetermined time has elapsed Is selected and stored, and the current required for output from the reference output current is controlled by adjusting the data to the D / A conversion means, so that the accuracy of the reference output current can be improved, More accurate battery charging is possible.

[Brief description of drawings]

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

[Fig. 2] Flow chart of the battery charger

FIG. 3 is a diagram showing a relationship of a secondary side output voltage with respect to a D / A conversion means of the battery charger.

FIG. 4 is a diagram showing a relationship of D / A conversion output data with respect to a battery charging current of the battery charger.

FIG. 5 is a flowchart of a battery charger according to another embodiment of the present invention.

FIG. 6 is a block diagram of a conventional battery charger.

[Explanation of symbols]

 3 transformer 4 converter circuit 17 switching regulator 25 A / D converter (A / D conversion means) 26 control means 28 output current detection unit 33 D / A converter (D / A conversion means) 34 state control means 39 transistor (reference) Current energizing means)

Claims (2)

[Claims] 1. A switching pulse width of the converter, which detects the output DC voltage or current obtained by applying a DC voltage to a primary winding of a transformer through a converter circuit that performs a switching operation, and rectifying a secondary winding voltage of the transformer. To regulate the secondary side output voltage or current to a constant value, reference current conducting means for flowing a reference current from the output voltage of the switching regulator, and A / D for detecting the output voltage of the switching regulator.
A / D conversion means for converting, control means for controlling data sent to the D / A conversion means by the data value A / D converted by the A / D conversion means, and output by the output of the D / A conversion means A state control means for controlling an output current detection section for detecting a direct current to control a state of the switching regulator, wherein the control means uses the output of the D / A conversion means to obtain the reference current. The state of the switching regulator is gradually controlled, and the data or the previous value to the D / A conversion means when the specified output voltage is exceeded is stored, and the current required for output from the reference current is changed to the D / A. A battery charger that controls the data to the conversion means. 2. The control means D / for obtaining a reference current
The state of the switching regulator is quickly changed to a certain output voltage by the output of the A conversion means and then gradually controlled, and one step is returned from the data value to the D / A conversion means when the specified output voltage is exceeded. A value, or which of the output voltages specified by the A / D conversion means data before and after that after a certain time has elapsed is selected and stored,
2. The battery charger according to claim 1, wherein the current required for output from the reference current is controlled by adjusting the data to the D / A conversion means.