JPH0622467A - Charger - Google Patents

Abstract

PURPOSE:To perform reductions in number of components and a cost, to shorten a charging time and to reduce in size a charger. CONSTITUTION:In the step of charging, secondary side output voltage and current are detected by an output of a tertiary winding N3 of a transformer 20 and a current flowing to a resistor 7 inserted to a drain of a power MOSFET 5, and charging is controlled only by a primary side control without feeding back a secondary side by a PWM controller 22. A circuit configuration of a charger is simplified, and an output controller at the secondary side is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a secondary battery such as a lead battery.

[0002]

2. Description of the Related Art As a conventional charging device (or a small one is appropriately called as a charger), there is one as shown in FIG. 9, for example. The one shown in the figure is an example in which a so-called flyback converter system is adopted. In this figure, reference numeral 1 denotes an AC connector, which is an AC power source (for example, AC
100V). The AC power source (AC input) from the AC connector 1 is supplied to the rectification / smoothing circuit 3 via the input filter 2, where it is rectified (for example, pulsating current) and smoothed before being supplied to the primary side of the transformer 4. Power MOS
It is switched by the FET5.

The power MOSFET 5 has a P at its base.
PWM from WM (Pulse Width Modulation) control circuit 6
A pulse is applied and driven, and a switching operation is performed. As a result, the secondary side output of the transformer 4 is controlled. The PWM control circuit 6 is composed of a PWM control IC. A resistor 7 is inserted in the drain of the power MOSFET 5.

The transformer 4 has a power MOS on its primary side.
A predetermined output voltage is generated on the secondary side by being switched by the FET 5, and the secondary side output is rectified and
After being supplied to the smoothing circuit 8, rectified and smoothed to direct current, it is supplied to a secondary battery 11 such as a lead battery via a switch unit 9 and a backflow prevention diode 10 in sequence.

A charging current detecting resistor 12 is inserted on the negative electrode side of the secondary battery 11, and the potential at this point is taken out by the charging control circuit 13 and supplied to the output control circuit 14 as a charging current signal. . The charge control circuit 13 controls the operation of the switch unit 9 according to the state of the secondary battery 11. For example, when the secondary battery 11 is not attached (non-charged state), the switch unit 9 for charging is turned off. Alternatively, the switching unit 9 is turned on / off with a pulse having a predetermined cycle to supply a charging current to the secondary battery 11.

The output control circuit 14 is mainly composed of an error amplifier or the like, compares the rectified and smoothed secondary side output voltage and output current with a reference value, and outputs the error output via the photo coupler circuit 15 to PWM. Output to the control circuit 6. As a result, the rectified and smoothed secondary side output information is fed back to the primary side of the transformer 4 and subjected to PWM control (current feedback control), and a constant voltage / constant current charging output characteristic as shown in FIG. 10 is obtained. To be

According to such a charging output characteristic, for example, a state where the uncharged secondary battery 11 is attached to the charger is point a in the constant current region in the charging output characteristic, and when the battery terminal voltage increases due to charging. Then, the process proceeds to point b, the charging current gradually decreases, and the battery is fully charged at point c.

Further, the charging characteristics including the internal loss are as shown in FIG. 11, and each characteristic with respect to the charging time T is shown.

[0009]

However, in such a conventional charging device, the flyback converter system is adopted and the voltage of the secondary side output of the transformer in order to obtain constant voltage and constant current characteristics. Since the current is detected by the output control circuit using an error amplifier, etc., and the error output is compared with the reference voltage and fed back to the primary side, this method further reduces the number of parts and lowers the cost. There was a problem that it was difficult to convert.

Further, since the conventional device charges at a constant voltage and a constant current, it is difficult to increase the charging energy any more, and it is possible to meet the demand for shortening the charging time and reducing the size of the charger. I couldn't.

In recent years, even in a power supply device such as a charger for a small device such as a video camera, cost reduction by simplifying the circuit configuration and reducing the number of parts has become an important development subject, and the above-mentioned problems are caused. Is desired to be solved.

Therefore, an object of the present invention is to provide a charging device which can reduce the number of parts and cost and can shorten the charging time and the size.

[0013]

In order to achieve the above object, a charging device according to claim 1 rectifies an AC input and supplies it to a primary side of a transformer, and the primary side of the transformer is provided with a switching element. In a charging device having a control means for performing switching control to generate a predetermined charging output on the secondary side and controlling the operation of the switching element according to the charging state, an auxiliary winding is provided on the primary side of the transformer. At the same time, current detecting means for detecting the current flowing through the switching element is provided, and the control means obtains the charging current from the output of the current detecting means and obtains the secondary side output voltage of the transformer from the output of the auxiliary winding. Detects the state of charge,
The operation of the switching element is controlled according to the detection result.

In a preferred embodiment, a rectifying / smoothing circuit for rectifying / smoothing the output from the auxiliary winding provided on the primary side of the transformer is provided.

The control means is composed of a pulse width modulation control circuit, and performs PWM control of the switching element to control the secondary side output of the transformer so that the secondary battery is charged with constant power or constant voltage. Characterize.

The current detecting means is characterized by having a resistor for compensating the input voltage dependence of the constant power characteristic.

[0017]

In the present invention, the charging current is obtained from the output of the current detecting means, and the secondary side output voltage of the transformer is obtained from the output of the auxiliary winding provided in the transformer to detect the charging state. Then, the operation of the switching element is controlled (for example, PWM control) according to the detection result, and the secondary battery is charged with constant power or constant voltage by the secondary side output of the transformer.

Therefore, the charging of the secondary battery can be controlled only by controlling the primary side without feedback of the signal from the secondary side of the transformer, the circuit configuration of the charging device is simplified, the number of parts is reduced, and the cost is reduced. Is achieved. In addition, it is possible to charge the area that was previously charged with a constant current with constant power, and since more charging energy can be input in a short time, it is possible to charge for a shorter time with the same size, while the same size. With the charging time, the charging device can be made smaller.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a charging device according to the present invention, which is an example adopting a flyback converter system. In the description of this figure, the same components as those of the above-described conventional example are designated by the same reference numerals, and the duplicate description will be omitted.

In FIG. 1, reference numeral 20 denotes a transformer. The transformer 20 is provided with a tertiary winding N3 as an auxiliary winding in addition to the primary winding N1 and the secondary winding N2. Also, dots are added in the drawing to indicate the direction of the polarity of each winding. As is apparent from this polarity, the tertiary winding N3 is designed to correlate with the secondary winding N2 that outputs the secondary side voltage.

The output of the tertiary winding N3 is a rectifying / smoothing circuit 21.
To the PWM control circuit 22 after being rectified (for example, pulsating flow) and smoothed. Also, power M
A resistor 7 is inserted in the emitter of the OSFET 5,
The current Is flowing through the resistor 7 is detected as a charging current signal and input to the PWM control circuit 22.

Furthermore, the output of the input correction circuit 23 is input to the PWM control circuit 22, and the input correction circuit 23 has a resistor 43 for correcting the dependence of the constant power characteristic on the input voltage (described later). (See FIG. 2).

FIG. 2 shows a concrete circuit example of the rectification / smoothing circuit 21 and the input correction circuit 23, which is a characteristic part of this embodiment. The rectifying / smoothing circuit 21 shown in this figure is connected to the tertiary winding N3 of the transformer 20, and rectifies the output of the tertiary winding N3 by a diode 31, a smoothing capacitor 32, and a tertiary winding. A resistor 33 that divides the output of N3
And a variable resistor 34, and a tertiary winding N3
After rectifying and smoothing the output of, the resistance 33 and the variable resistance 3
The voltage is divided by 4 and output to the PWM control circuit 22. A resistor 35 is connected to the resistor 33 via a diode 53, and the resistor 35 is connected to the PW in the PWM control circuit 22.
It has a function as a starting resistance of the M control IC 22a.
The diode 53 has a backflow prevention function that facilitates starting, and the capacitor 44 is for smoothing.

On the other hand, the current Is flowing through the drain of the power MOSFET (switching element) 5 is taken out as a divided voltage value of the resistors 41 and 42 inserted at both ends of the resistor 7, detected as a charging current signal, and PWM controlled. Circuit 22
Is supplied to. Further, a resistor 43 and a capacitor 44 are connected to the connection point of the resistors 41 and 42, and these constitute the input correction circuit 23. The resistor 43 is for correcting the dependence of the constant power characteristic on the input voltage.
The resistor 7, the resistors 41, 42, the resistor 43, and the capacitor 44 constitute a current detecting means 50.

The PWM control circuit (control means) 22 has a PWM control IC 22a inside, and has a PWM control IC 22a.
C22a operates as a pulse-by-pulse protection circuit that exerts an overcurrent protection function. Then, the rectifying / smoothing circuit 21
Secondary output voltage of the transformer 20 is indirectly obtained from the output of the transformer 20, and the power MOSFET 5 is PWM-controlled to control the secondary output of the transformer 20 to control the secondary battery 11
Is charged with constant power and constant voltage.

A rectifier arranged on the primary side of the transformer 20.
The smoothing circuit 3 is composed of a diode 51 and a capacitor 52.

Description of Operation In the above configuration, when the secondary battery 11 is mounted on the charging device and AC input is supplied, the charging control circuit 13 turns on the switch unit 9 to supply the charging current to the secondary battery 11. Charging starts. Here, the charging control circuit 13 mainly confirms the decrease of the charging current and terminates the charging, or controls the pulse charging described later. Then, in the process of charging, the secondary side output voltage and the output current are respectively detected from the output of the tertiary winding N3 of the transformer 20 and the current flowing through the resistor 7 inserted in the drain of the power MOSFET 5, and 1 is detected without feedback. Charging is controlled only by the secondary control.

That is, in detail, the transformer 20-2
The secondary output voltage is detected by utilizing the correlation between the tertiary winding N3 and the secondary output winding N2, and appears as the output of the tertiary winding N3. The output of the tertiary winding N3 is rectified and smoothed by the diode 31 and the capacitor 32, divided by the resistor 33 and the variable resistor 34, and input to the PWM control circuit 22.

A current Is flowing through the drain of the power MOSFET 5 is inserted between both ends of the resistor 7 to form a resistor 41,
It is taken out as a divided voltage value of 42, detected as a charging current signal, and inputted to the PWM control circuit 22.

In the PWM control circuit 22, the PWM control I
C22a is operated as an error amplifier, and transformer 20
Power MOSFE so that the secondary side output voltage of
Control T5. Also, the charging output current is I for PWM control.
Using the overcurrent protection function of C22a, a charging output as shown in FIG. 3 can be obtained.

Now, assuming that the secondary battery 11 in the uncharged state is mounted on the secondary output of the transformer 20, the output voltage on the secondary side drops to the battery voltage indicated by A in FIG. At this time, the output voltage of the tertiary winding N3 also drops due to the correlation between the secondary output winding N2 and the tertiary winding N3. Therefore, the tertiary winding N
P of the PWM control circuit 22 to which the divided voltage output of 3 is input
Since the WM controlling IC 22a operates as an error amplifier, it is in an unbalanced state and tries to maximize the on-duty period of the output OUT.

As the on-duty period of the output OUT is expanded, the peak of the current Is flowing through the power MOSFET 5 also becomes high, and as shown in FIG.
When the voltage reaches 200 mV shown in FIG. 4, the latch circuit inside the IC is activated and the on-duty period of the output OUT is as shown in FIG.
As indicated by the shaded area,

Here, the energy PE transmitted to the secondary side of the transformer 20 by the switching control of the power MOSFET 5 is given by the following equation 1. PE = (1/2) × (LI ² · f) = [(Vin ² · Ton ² ) / 2L] × f (Equation 1) where L: primary side inductor I: primary side Current flowing in f: Frequency

From equation 1, the flyback converter is (1 /
2) It can be seen that the output P becomes constant if I of LIf is controlled to be constant. Since the on-duty period of the output OUT is thus limited, the energy PE transmitted to the secondary side of the transformer 20 is limited to a constant value.

That is, constant power charging is performed by the above-described overcurrent protection function (pulse-by-pulse current limit) until the terminal voltage of the secondary battery 11 reaches the portion B shown in FIG. 3 by charging. When the point B is reached, the pulse-by-pulse current limit is released thereafter, constant voltage charging is performed up to the point C, and when the point C is reached, the charging ends.

The one-dot broken line and the two-dot broken line shown in FIG. 3 correspond to the width of the charging area, and charging is performed within this range. That is, the dependence of the constant power characteristic on the input voltage of the transformer 20 is corrected by the resistor 43, and for example, when the input voltage is low, the charging region becomes a curve along the dashed line in FIG.
When the input voltage is high, the charging area becomes a curve along the two-dot broken line in FIG.

By inserting the resistor 43, a bias depending on the input voltage is applied to the terminal CL of the PWM control circuit 22, and even if the input voltage changes, it is controlled so as to have the characteristics shown by the solid line in FIG.

As described above, in this embodiment, unlike the conventional case,
The charging of the secondary battery 11 (which is also rapid charging) can be easily controlled only by the primary side control without feedback of the signal from the secondary side of the transformer 20. Therefore, the circuit configuration of the charging device is simplified, and accordingly, the output control circuit on the secondary side becomes unnecessary. Therefore, the number of parts can be reduced and the cost can be reduced.

Further, it becomes possible to perform constant power charging in a region which has been conventionally charged with a constant current, and a larger amount of charging energy can be put in a shorter time, so that it is possible to charge in a shorter time with the same size. . On the other hand, if the charging time is the same, the charging device can be made smaller.

FIG. 5 shows the charging characteristics of this embodiment. This charging characteristic will be described in comparison with the above-mentioned conventional characteristic. First, as shown in FIG. 11 in the conventional characteristic, the change of the internal loss starts to increase as the terminal voltage V of the battery gradually rises and becomes constant. It reaches a peak at the time of switching from the current charging area to the constant voltage charging area. Then, after entering the constant voltage mode (constant voltage charging region), the charging output (output Pout) starts to decrease as the charging current I decreases.

On the other hand, in this embodiment, as shown in FIG. 5, the constant current value is controlled so that the internal loss becomes constant in the constant current region. In other words, more charging current can be flowed without changing the power loss (internal loss).

Therefore, the circuit of this embodiment makes it possible to average the internal loss in the constant current region and supply the charging current to the secondary battery 11 without changing the peak value of the internal loss. As a result, efficient charging output can be obtained, and charging can be performed in a shorter time. On the other hand, if the charging time is the same, the charger can be made smaller.

In the PWM control circuit 22, if the pulse-by-pulse current limit continues, the complete latch is reached after a certain period of time (for example, after T1).
Further, for example, the PWM control circuit 22 uses a pulse-by-pulse protection circuit as a timer latch function (timed latch function).
In the minimum constant power region, the secondary side charging control circuit 13 may be provided with a timer for turning on / off the switch unit 9, and charging may be performed with an ON pulse of T1 or less.

An example of this is shown in FIGS. FIG. 6 shows the charging characteristics when the timer has the time delay function.
The meaning of C is the same as that shown in FIG. Further, FIG. 7 shows the relationship between the charging voltage and the charging current with respect to the charging time. Furthermore, FIG. 8 shows the waveform of pulse charging,
The shaded area in the figure shows the charging period, which is a cycle of several seconds or several tens of seconds.

[0045]

As described above, according to the present invention,
1 without feedback of the signal from the secondary side of the transformer
It is possible to easily control the charging of the secondary battery only by the secondary side control, simplify the circuit configuration of the charging device, and reduce the number of parts and cost.

Further, it becomes possible to perform constant power charging in a region which has been conventionally charged with a constant current, and more charging energy can be input in a short time, so that charging can be performed in a shorter time with the same size. On the other hand, if the charging time is the same, the charging device can be made smaller.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a charging device according to the present invention.

FIG. 2 is a detailed circuit diagram of a rectification / smoothing circuit and an input correction circuit in the same embodiment.

FIG. 3 is a diagram showing a charging characteristic in the example.

FIG. 4 is a diagram showing a duty waveform of a power MOSFET in the example.

FIG. 5 is a diagram illustrating internal loss of charging characteristics in the example.

FIG. 6 is a diagram showing a modified example of charging characteristics in the same embodiment.

FIG. 7 is a diagram showing a relationship between a charging voltage and a charging current with respect to a charging time when the timer latch function is provided in the embodiment.

FIG. 8 is a diagram illustrating a waveform of pulse charging in the example.

FIG. 9 is a block diagram of a conventional charging device.

FIG. 10 is a diagram illustrating a charging mode of a conventional charging device.

FIG. 10 is a diagram illustrating an internal loss of charging characteristics of a conventional charging device.

[Explanation of symbols]

 2 Input filter 3, 8 Rectification / smoothing circuit 5 Power MOSFET (switching element) 9 Switch part 10 Reverse current prevention diode 11 Secondary battery 12 Charging current detection resistor 13 Charge control circuit 20 Transformer 21 Rectification / smoothing circuit 22 PWM control circuit (control Means) 23 input correction circuit 50 current detection means N3 tertiary winding (auxiliary winding)

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[Procedure amendment]

[Submission date] February 24, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a charging device according to the present invention.

FIG. 2 is a detailed circuit diagram of a rectification / smoothing circuit and an input correction circuit in the same embodiment.

FIG. 3 is a diagram showing a charging characteristic in the example.

FIG. 4 is a diagram showing a duty waveform of a power MOSFET in the example.

FIG. 5 is a diagram illustrating internal loss of charging characteristics in the example.

FIG. 6 is a diagram showing a modified example of charging characteristics in the same embodiment.

FIG. 7 is a diagram showing a relationship between a charging voltage and a charging current with respect to a charging time when the timer latch function is provided in the embodiment.

FIG. 8 is a diagram illustrating a waveform of pulse charging in the example.

FIG. 9 is a block diagram of a conventional charging device.

FIG. 10 is a diagram illustrating a charging mode of a conventional charging device.

FIG. 11 is a diagram illustrating internal loss of charging characteristics of a conventional charging device.

[Explanation of Codes] 2 Input Filter 3, 8 Rectification / Smoothing Circuit 5 Power MOSFET (Switching Element) 9 Switch Section 10 Backflow Prevention Diode 11 Secondary Battery 12 Charging Current Detection Resistor 13 Charging Control Circuit 20 Transformer 21 Rectification / Smoothing Circuit 22 PWM control circuit (control means) 23 Input correction circuit 50 Current detection means N3 Third winding (auxiliary winding)

Claims (4)

[Claims] 1. An AC input is rectified and supplied to the primary side of a transformer, the primary side of the transformer is switching-controlled by a switching element to generate a predetermined charge output on the secondary side, and the transformer is charged. In a charging device having a control means for controlling the operation of the switching element according to the above, an auxiliary winding is provided on the primary side of the transformer, and a current detection means for detecting a current flowing through the switching element is provided. Determines the charging current from the output of the current detecting means, detects the secondary side output voltage of the transformer from the output of the auxiliary winding, detects the charging state, and controls the operation of the switching element according to the detection result. Charging device characterized in that 2. The charging device according to claim 1, further comprising a rectifying / smoothing circuit for rectifying / smoothing an output from an auxiliary winding provided on the primary side of the transformer. 3. The control means comprises a pulse width modulation control circuit, PWM-controls the switching element, and controls the secondary side output of the transformer to charge the secondary battery with constant power or constant voltage. The charging device according to claim 1, wherein: 4. The charging device according to claim 1, wherein the current detecting unit has a resistor that compensates for the input voltage dependency of the constant power characteristic.