KR20140120025A - Charging circuit for rechareable battery, battery charger with the same and charging method for rechareable battery - Google Patents

Abstract

The present invention relates to a charging circuit for a rechargeable battery, a charger, and a charging method. The present invention is to change a PWM signal outputted from a control part into a direct current value which changes linearly without a ripple before the PWM signal is applied to a switch device. By this feature, a current outputted from the switch device is outputted with a direct current wave without a ripple, thereby having no need to have a separate buck circuit or a smoothing circuit.

Description

TECHNICAL FIELD [0001] The present invention relates to a secondary battery charging circuit, a charger having the secondary battery charging circuit, and a charging method for the secondary battery. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charging circuit, a charger having the secondary battery charging circuit, and a secondary battery charging method. More particularly, the present invention relates to a rechargeable secondary battery such as a lithium battery, A secondary battery charging circuit capable of supplying a stable charging power, a charger having the same, and a secondary battery charging method.

Description of the Related Art [0002] Portable electronic devices such as portable telephones, PHS (Personal Handy Phone) terminals, PDAs (Personal Digital Assistants), and personal computers are often used as secondary batteries, such as lithium batteries, which have excellent discharge characteristics and are rechargeable.

Conventionally, in a portable electronic device using a lithium battery as a secondary battery, charging is performed by constant current control at the initial stage of charging, and then charging is performed by constant voltage control.

The conventional portable electronic device disclosed in Patent Document 1 includes a constant current control circuit supplied with DC voltage from the AC adapter and controlling the constant current and a constant voltage control circuit controlling the constant voltage. In the initial state of charging, the constant current control transistor of the constant current control circuit is first controlled to charge the battery with a constant current. When the battery voltage rises up to a predetermined value by the constant current charging, the constant-current control is switched from the constant-current control to the constant-voltage control by the constant-voltage control circuit, the constant-voltage control transistor is controlled to charge the battery up to a constant voltage, Control is terminated. However, when the constant current charging circuit and the constant voltage charging circuit are separately provided as disclosed in Patent Document 1, the circuit becomes complicated.

Recently, a method of using one charging circuit as a constant current charging circuit and a constant voltage charging circuit by using a PWM (Pulse Width Modulation) method has been proposed. As a charging dedicated chip, a CCCV (Constant Current Constant Voltage) . The use of such a charge-only chip necessitates a complicated peripheral circuit configuration in order to implement the application function provided by the charge-only chip, which increases the number of components and thus increases the product cost and makes it difficult to miniaturize the product. Furthermore, the PWM control method provided in the CCCV chipset used in the conventional secondary battery charging circuit is driven by using a square wave having a frequent ON / OFF characteristic with a controlled pulse width. In order to supply the power supplied by the PWM control signal to the secondary battery, the ripple-free DC-type waveform must be deformed. Figure 1 is an example of a conventional second-order pre-charging circuit using a CCCV chipset providing a PWM waveform. Specifically, a chip dedicated to charging a lithium secondary battery of model AN10338 supplied by Philips, Inc. is used, and the circuit diagram shown in FIG. 1 is an example of a sample charging circuit provided by a chip supplier. Only the portion for processing the PWM control signal in the circuit diagram of Fig. 1 will be described. The PWM control signal is outputted from the pin 8 of the CCCV chipset 10 as shown in FIG. 1, and the corresponding control signal turns on / off the auxiliary switch element 11, whereby the main switch element 13 On / off. The waveform output to the output terminal of the main switch element 13 has a square wave form that is turned on / off. The output of the square wave is converted into a DC waveform with ripple removed by a buck converter, and then supplied to the secondary battery. The buck converter is a circuit composed of a Zener diode, a coil 21 and a capacitor 23. The PWM waveform output to the output terminal of the main switch element 13 is applied to the coil 21. [ The output of the square wave is converted into a DC waveform in which the ripple is present by using the inductor characteristics of the coil 21 (charging and discharging of energy in the AC current) (the ripple means a superimposed AC component in the DC bias) . A small-capacity capacitor 23 is installed to remove such ripple outputted from the coil 21 to generate a DC waveform from which the ripple is removed, and then supplies it to the + terminal of the secondary battery. At this time, since the coil 21 has a function of storing energy, the main switch element 13 is turned off and the energy temporarily stored in the coil 21 is supplied to the secondary battery 13 while the output value of the main switch element 13 is maintained in the off state. As shown in FIG. Of course, another method for making a square wave into a DC power source without ripple is to provide a smoothing capacitor for smoothing a square wave at the output terminal of the main switch element 13. In order to make a square wave into DC, It is difficult to obtain a DC without a complete ripple.

That is, in the secondary charging circuit employing the conventional PWM control method, in order to remove the ripple from the PWM waveform output from the main switching element and supply the charging power to the secondary battery even in the state where the switching element is turned off, There is a problem that the circuit becomes complicated.

Patent Document 1: Japanese Patent Application Laid-Open No. 8-106926 (published on Apr. 23, 1996)

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method and apparatus for generating a PWM control signal by using a general purpose CPU without using a CCCV dedicated chip, A secondary battery charging circuit for controlling a switching element after conversion, a charger having the secondary battery charging circuit, and a secondary battery charging method.

The above object of the present invention is achieved by a secondary battery charging circuit for charging a secondary battery using a direct current supplied from an external device, the secondary battery charging circuit comprising: a charging voltage detector for detecting a voltage between both terminals of the charging battery; A charging current detector for detecting a current value; a charging step for determining a charging step using the charging voltage inputted from the charging voltage detecting part and the charging current inputted from the charging current detecting part, and generating a PWM control signal for controlling the determined charging step A level converter for converting the direct current into a direct current having no ripple proportional to the duty ratio after receiving the PWM control signal; And the current amplifying the current flowing through the collector terminal of the auxiliary switching element It can be achieved by a secondary battery charging circuit comprising a main switching element to the supply from the external apparatus to the secondary battery as much.

It is still another object of the present invention to provide a level control apparatus and a control method thereof, which are provided with a case, a general-purpose control section for generating a PWM control signal in a case, a level conversion section for converting and outputting a DC current without inputting a PWM control signal, An auxiliary switch element for outputting a current value amplified in accordance with a direct current outputted from the converting section to a collector terminal and a main switch element for outputting a current value amplified in accordance with a current value flowing through a collector terminal of the auxiliary switch element to a collector terminal Which can be accomplished by a secondary battery charger.

It is still another object of the present invention to provide a secondary battery charging method for charging a secondary battery using a direct current supplied from an external device, comprising the steps of: detecting a charging voltage between both terminals of the charging battery; A second step of determining one charging step among a plurality of charging steps using a charging voltage and a charging current, a third step of generating a PWM control signal according to the charging step determined in the second step, A fourth step of converting the PWM control signal generated in the third step into a direct current having no ripple proportional to a duty ratio; and a fourth step of converting the amount of current amplified according to the direct current of the fourth step from the external device to the secondary battery And a fifth step of charging the secondary battery by charging the secondary battery.

The secondary transient charging circuit and the charger according to the present invention can generate the PWM control signal without using the CCCV dedicated chip provided by the semiconductor manufacturer and omit the components not necessary for the charging operation, . ≪ / RTI >

Conventionally, a technique adopted in the secondary battery charging circuit is required to repeatedly turn on / off the main switch element by a PWM control signal, so that ripples are generated. To eliminate such ripple, a buck circuit or a smoothing capacitor composed of an inductor and a capacitor element . However, the secondary battery charging circuit according to the present invention uses a method of controlling the main switch element after converting the PWM control signal output from the general-purpose controller into linearly varying uniform ripple-free DC waveforms. Therefore, a separate buck circuit or a smoothing circuit can be removed between the main switch element and the charging terminal of the secondary battery, so that the circuit configuration is simplified and the production cost of the charger can be reduced.

Figure 1 is an example of a conventional second-order pre-charging circuit using a CCCV chipset providing a PWM waveform.
2 is an example of a secondary battery charging circuit according to an embodiment of the present invention.
3 is a graph showing charging current and charging voltage for explaining the charging step of the battery according to the present invention.
4 is a waveform diagram showing a DC current value converted in accordance with a PWM control signal input to the level converting section 30. Fig.
5 is a graph of a current-voltage characteristic that ideally shows a saturated region curve of a general pnp transistor.

In the following, preferred embodiments, advantages and features of the present invention will be described in detail with reference to the accompanying drawings.

2 is an example of a secondary battery charging circuit according to an embodiment of the present invention. The secondary battery charging circuit shown in FIG. 2 includes a USB socket unit 15, an overvoltage protection unit 10, a reference voltage generation unit 20, a level conversion unit 30, an auxiliary switch device Tr2, a main switch device 50 A charging voltage detecting section 60 and a charging current detecting section 70, a battery connecting terminal section 80, and a general-purpose control section 90.

The USB socket 15 is a socket for receiving USB power from an external device. As an external device, a variety of power sources for supplying power by a USB method can be used. For example, a USB terminal of a personal computer or an adapter that converts 100V to 220V commercial power into DC power may be used. Generally, since the power source of 5V and 500mA is supplied from the USB terminal of the personal computer, the current supply amount is small and it takes much time to charge. On the other hand, in the case of an adapter that converts a commercial power source to a DC power source, since an adapter that supplies a large amount of current such as a rated output voltage of 5 V and a rated output current of 2 A can be used, the charging time can be shortened. The USB socket 15 is composed of five pins as a whole. The + power is applied to pin 1, the pins 2 and 3 are used as data terminals, the pin 5 is grounded, Is reserved for preliminary use.

The overvoltage protection unit 10 is a protection unit for blocking an instantaneous high voltage from the external power supply in order to protect the internal circuit elements. The reference voltage generation unit 20 generates a reference voltage, 5V) to a DC voltage suitable for driving the internal circuit elements. For example, when the internal circuit elements are constituted by elements driven with drive voltages of 3.5 V and 4.7 V, it is a circuit section that converts the 5 V voltage input from the USB socket 15 to 3.5 V and 4.7 V.

The voltage converted by the reference voltage generator 20 is supplied to the general-purpose controller 90 and used as an operating power for operating the general-purpose controller 90. The charging voltage detecting unit 60 detects a charging voltage value between the positive terminal and the negative terminal of the battery to be charged. The charging current detecting unit 70 detects a charging voltage value between the positive terminal and the negative terminal of the battery to be charged . For reference, in order to minimize the power consumption by the charging current detector 70, the resistors r8 and r9 have a very small resistance value.

The general-purpose control unit 90 receives the operating power from the reference voltage generator 20 through the pin, receives the charged voltage value from the charging voltage detector 60 through the pin 3, After receiving the charging current value flowing between both terminals of the charging battery from the charging current detector 70 through the pin 5, the PWM (Pulse Width Modulation) control signal corresponding to each step of CCCV charging is outputted through the pin 2 . Here, the reason why the general-purpose control unit 90 is not referred to as the control unit 90 but the term 'general-purpose' is attached is a term used for distinguishing from the charge-only chipset for the secondary battery supplied from the semiconductor chip manufacturer. Therefore, the general-purpose control unit 90 is not a control unit developed to be used for a special purpose, but a general-purpose control unit such as a CPU (Central Processing Unit) in which a user can freely implement a series of programs for performing appropriate operations in a memory provided therein, (Micro Processor), a microcomputer (Micom), and the like.

The level converter 30 converts the PWM control signal output from the general-purpose controller 90 into a DC current level having no ripple at a predetermined level. The auxiliary switch element Tr2 converts the output signal of the level converter 30 And outputs the amount of current amplified to the collector according to the DC current value (DC current value). The main switch element 50 outputs the current value amplified by the collector terminal according to the current value determined by the auxiliary switch element 50 and the current flowing to the collector terminal of the main switch element 50 forms the charge current Iout do. An npn type transistor is used as the auxiliary switching element Tr2, and a pnp type transistor is used as the main switching element Tr1. The battery connection terminal portion 80 is a terminal portion for connecting with a secondary battery receiving a charging current.

Hereinafter, the circuit operation will be described. In the circuit operation description, the USB socket unit 15, the overvoltage prevention unit 10, the reference voltage generation unit 20, the charge voltage detection unit 60, the charge current detection unit 70, and the battery connection terminal unit 80 It is not a core matter of the present invention, and is a commonly known circuit, and thus a detailed description thereof will be omitted. The charging step of the battery includes a preliminary charging step, a constant current charging step, and a constant voltage charging step. 3 is a graph showing charge current and charge voltage for explaining the charging step of the battery according to the present invention. 3, Iout represents a charging current applied to the charging cell, and Vout represents a charging voltage applied to both terminals of the charging battery. First, the charging step of the battery will be described with reference to FIG. It is assumed that the secondary battery to be charged has a rated voltage of 700 mA and 4.2V.

In the preliminary charging step, when the voltage (Vstart) remaining in the rechargeable battery is detected to be 3 V or less, a small amount of charge current (Ipre) is applied until the inter-terminal voltage of the rechargeable battery becomes 3 V , ≪ / RTI > 65mA). The pre-charging step may be omitted if the voltage between both terminals of the charging battery remains at least 3 V in the initial stage of charging.

The constant current charging step is a step for progressing the rapid charging and continuously applying a considerable amount of charging current (Ireg, 350mA) until the voltage of both terminals of the charging battery reaches 4.2V (Vreg).

When the terminal voltage of both terminals of the charged battery reaches 4.2V by the constant current charging step, the constant voltage charging step is carried out to gradually decrease the charging current while maintaining the both terminal voltage of the charging battery at 4.2V and to reach the full charging state. In the constant voltage charging step, when the time for which the charging current is maintained at 60 mA or less is continued for a predetermined time (for example, 50 minutes), it is determined that the buffering transition has occurred and the charging is terminated. When the lithium ion battery is used as the rechargeable battery, the battery temperature rises when the battery is overcharged. By detecting the rise in the ambient temperature of the battery, the full charge or overcharge state can be detected and the charge can be terminated. However, in recent years, most battery manufacturers have added an overcharge prevention circuit inside the battery pack to prevent the explosion of the lithium ion battery, thereby preventing the occurrence of overcharging. Therefore, a temperature sensor for detecting the ambient temperature of the battery There is no need to install.

After receiving the output values of the charging voltage detector 60 and the charging current detector 70, the general-purpose controller 90 determines the current battery state and selects one of the steps of the preliminary charging step, the constant current charging step, and the constant voltage charging step And generates a PWM control signal for charging the battery. The PWM control signal is input to the level converting unit 30, and the level converting unit 30 converts the PWM control signal into a DC current value without ripple. 4 is a waveform diagram showing a DC current value converted in accordance with a PWM control signal input to the level converting unit 30. In FIG. As shown in FIG. 4, the PWM signal outputs square waves having different amplitudes, and the level converting unit 30 receives the rectangular waves and converts them into DC current values without ripples. That is, the PWM square waves shown in Figs. 4 (a), 4 (b) and 4 (c) are rectangular waves having amplitudes of Wa, Wb and Wc, respectively. Here, Wc> Wa> Wb, 4 (c), 4 (a) and 4 (b), the duty ratio is lowered. The level converter 30 outputs the DC currents Ia, Ib and Ic after receiving the PWM control signals. It can be seen that Ic> Ia> Ib holds, and the duty ratio of the input PWM control signal It can be seen that the direct current output is proportional. That is, the level converting unit according to the present invention has a function of converting an input PWM control signal into a linear DC direct current and outputting it. Here, the linearity means that the DC current value linearly proportional to the amplitude of the PWM control signal is converted and output. As shown in FIG. 4 (d), when a PWM signal whose amplitude gradually increases is applied, the level converting unit 30 outputs a linearly increasing DC current.

The DC current from which the ripple is removed from the level converter 30 is transmitted to the auxiliary switch element Tr2 through the resistor r2. When the base current value (the current value outputted from the level converter) is applied to the base terminal, the auxiliary switch element Tr2 configured as an npn transistor type has a collector current value amplified in proportion to the base current value at the collector terminal. This will be described using a pnp type transistor saturation region curve. The pnp type transistor saturation region curve and the npn type transistor saturation region curve have the same shape in the characteristic graph only in the voltage polarity difference between the base and the emitter. 5 is a graph of a current-voltage characteristic that ideally shows a saturation region curve of a general pnp transistor. When the voltage Vbe between the base and the emitter exceeds the threshold voltage, the switch is turned on and enters the saturation state. In this saturation state, as shown in Fig. 5, a collector current value (Ic) proportional to the base current value Ib flowing in the base flows to the collector terminal. The collector current value versus the base current value is referred to as a current gain, which is typically represented by the symbol hFE as shown in Equation (1), and hFE is a value determined at the time of manufacturing the transistor.

The collector current value Ic flowing through the collector terminal of the auxiliary switching element Tr2 becomes the base current value of the main switching element Tr1 and therefore the base current value of the main switching element Tr1 in the emitter- An amplified collector current value is formed. This is the same as that described for the operation of the auxiliary switch element with reference to Fig. The collector current value of the main switch element Tr1 is lost through the part of the charge voltage detector 60, but it can be regarded almost equal to the charge current Iout since the amount of the dead-time is extremely small.

As described above, in the secondary battery charging circuit according to the present invention, it can be seen that the auxiliary switch element and the main switch element are used while varying the amplification factor according to the current value output from the level converter 30 during charging of the battery. Let's explain this by charging step. In the constant-current charging step, the general-purpose control unit 90 outputs a PWM control signal having a high duty ratio. The auxiliary switch element Tr2 and the main switch element Tr1 are operated at almost the maximum amplification factor so that the auxiliary switching element Tr2 and the main switching element Tr1 are almost inactivated, Is operated at a substantially fixed amplification rate, and is always maintained in the on state. In the constant voltage charging step, the PWM signal output from the general-purpose control unit 90 is a control signal having a variable duty ratio. The duty ratio varying in this manner is outputted as the DC current value whose value is linearly changed in the level converting section 30, so that the auxiliary switching element Tr2 and the main switching element Tr1 are controlled by the level converting section 30 in accordance with the DC current value And the current supplied from the external device is supplied to the rechargeable battery while varying the amplification factor. In the preliminary charging step, charging is performed while the amplification rates of the auxiliary switching element Tr2 and the main switching element Tr1 are different, similar to the constant voltage charging step.

On the other hand, in the conventional secondary battery charging circuit, the auxiliary switch element and the main switch element are always operated with a fixed gain regardless of the charging step. In the secondary battery charging circuit using the conventional PWM control method, since the PWM control signal is directly applied to the auxiliary switch element, the maximum value of the current flowing to the base terminal of the auxiliary switch element is always applied the same value regardless of the charging step. It simply repeats the on / off operation frequently. Therefore, in the state where the amplification factor of the auxiliary switch element and the main switch element is fixed, the power supply waveform output from the main switch element has a square wave form repeating on / off. Therefore, An additional circuit such as a capacitor is required, but it can be seen that the charging circuit according to the present invention does not require an additional circuit.

The secondary battery charging circuit shown in FIG. 2 is installed in the housing, the USB socket 15 connected to the external device and the USB device is partially exposed to the outside, and the battery connection terminal is exposed to the outside of the housing The charger according to the present invention is completed.

The charging method of the secondary battery according to the present invention will be summarized in steps. A method for charging a secondary battery according to the present invention includes a first step of detecting a charging voltage between both terminals of a charging battery and a charging current charged in the charging battery, A third step of generating a PWM control signal in accordance with the charging step determined in the second step, a third step of generating a PWM control signal generated in the third step by a DC current without linearly proportional to the ripple, And a fifth step of controlling and outputting the current input from the external device according to the direct current of the fourth step. The amplifying operation of the fifth step is composed of an auxiliary switch element and a main switch element. When the DC current of the fourth step is input to the base of the auxiliary switch element, the amplifier current is amplified and outputted by the collector current, And the main switch element forms an amplified current according to the base current so that the amount of current input from the external device can be controlled and supplied to the charger.

While the preferred embodiments of the present invention have been described and illustrated above using specific terms, such terms are used only for the purpose of clarifying the invention, and it is to be understood that the embodiment It will be obvious that various changes and modifications can be made without departing from the spirit and scope of the invention. Such modified embodiments should not be understood individually from the spirit and scope of the present invention, but should be regarded as being within the scope of the claims of the present invention.

10: Overvoltage protection section 15: USB socket section
20: reference voltage generator 30: level converter
Tr2: auxiliary switch element 50: main switch element
60: charging voltage detector 70: charging current detector
80: Battery connection terminal part 90: General purpose control part

Claims (8)

A secondary battery charging circuit for charging a secondary battery using a direct current supplied from an external device,
A charging voltage detector for detecting a voltage between both terminals of the rechargeable battery,
A charging current detector for detecting a current value charged in the charging battery,
A general-purpose control unit for determining a charging step using a charging voltage inputted from the charging voltage detecting unit and a charging current inputted from the charging current detecting unit, and generating a PWM control signal for controlling the determined charging step,
A level converter for converting the PWM control signal into a direct current having no ripple proportional to a duty ratio after receiving the PWM control signal,
An auxiliary switching element in which the current amplified in accordance with the direct current outputted from the level converting part flows from the collector terminal to the emitter terminal and
And a main switch element for supplying the amount of current amplified by the current flowing through the collector terminal of the auxiliary switch element from the external device to the secondary battery.
The method according to claim 1,
Wherein the auxiliary switch element and the main switch element perform an amplifying operation in a saturation region.
3. The method according to claim 1 or 2,
The charging step of the universal control unit includes a constant current charging step and a constant voltage charging step,
Wherein the auxiliary switch element and the main switch element are maintained in the on state at all times in the constant current charging step.
3. The method according to claim 1 or 2,
Wherein an npn type transistor is used as the auxiliary switching element, a pnp type transistor is used as a main switching element, a current outputted from the output terminal of the level converting portion is inputted to the base terminal of the auxiliary switching element, And a current flowing to the collector of the device is coupled to form a current flowing to the base terminal of the main switch device.
5. The method of claim 4,
Wherein the emitter terminal of the main switch element is connected to a power terminal input from the outside, and the collector terminal of the main switch element is connected to the positive terminal of the rechargeable battery.
The case,
Wherein the case is provided with a secondary battery charging circuit according to any one of claims 1 to 5.
A secondary battery charging method for charging a secondary battery using a direct current supplied from an external device,
A first step of detecting a charging voltage between both terminals of the charging battery and a charging current charged in the charging battery,
A second step of determining one charging step among a plurality of charging steps using the charging voltage and the charging current;
A third step of generating a PWM control signal according to the charging step determined in the second step,
A fourth step of converting the PWM control signal generated in the third step into a ripple-free DC current proportional to a duty ratio;
And a fifth step of supplying the amplified current amount from the external device to the secondary battery according to the direct current of the fourth step.
8. The method of claim 7,
The charging step of the second step includes a constant current charging step and a constant voltage charging step,
Wherein the supplying of the amount of current amplified in accordance with the direct current in the fifth step from the external device to the secondary battery is provided by using a transistor and the transistor is always kept in the on state in the constant current charging step A secondary battery charging method.

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