KR101315115B1 - Battery charger digital control circuit and method and battery charger system - Google Patents

Abstract

The digitally controlled battery charger includes a power converter, a voltage sensor, a current sensor, a mode selector and a digital controller. The voltage sensor and the current sensor respectively sense the voltage of the rechargeable battery and the current flowing through the rechargeable battery. The mode selector selects a feedback signal from either the output of the voltage sensor or the output of the current sensor. The digital controller receives the selected feedback signal and generates a pulse width modulated signal for the power converter. In addition, the digital controller can dynamically adjust its coefficients so that when the battery charger operates in different battery charging stages, the control loop can maintain a stable system.

Description

Battery charger digital control circuit and method and battery charger system

This application claims the benefit of priority for US provisional application 61 / 438,067, "Battery Charger Digital Control Circuit and Method," filed Jan. 31, 2011, and all disclosures of that US provisional application are herein incorporated by reference. Incorporated by reference in the application.

Rechargeable batteries come in a variety of forms, including nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, lithium-ion batteries, lithium-ion polymer batteries, lithium-air batteries, and lithium iron phosphate batteries. It includes. Rechargeable batteries are used to store electrical energy. On the other hand, the battery charger is used to bring the rechargeable battery back to a charged state after the rechargeable battery is exhausted.

Different types of rechargeable batteries may use different charging methods. For example, when a lithium-ion polymer battery is charged from a depleted state to a full charged state, according to the charging profile of the lithium-ion polymer battery, the lithium-ion polymer battery is pre-conditioning phase. ), Initially charge at low current. After the battery voltage reaches the minimum charge voltage threshold, the battery charge cycle enters a current regulation phase in which the battery is charged with constant current. In this current control step, the voltage of the battery continues to increase until the voltage reaches a certain control voltage. The battery charge cycle then enters the voltage regulation phase by changing the battery charger from a constant current source to a constant voltage source. During the voltage control phase, the battery voltage is maintained at a certain voltage. Thus, the charging current gradually decreases. If the charge current is less than the specified current value, the battery charge cycle is completed.

Two types of battery chargers are known and commonly used. A linear regulator based battery charger includes an active device that acts like a variable resistor. By lowering the voltage in the active device, the linear regulator based battery charger can adjust one of its output voltage and output current. Conversely, a switching regulator based battery charger controls its output voltage or current by adjusting a duty cycle that controls the turn-on period of the charger's switching element. Compared with linear regulator based battery chargers, switching regulator based battery chargers usually provide a high efficiency charging process.

United States Patent Publication 20090237959 (Published: 2009. 09. 24) United States Patent Publication 20090237966 (Published: 2009. 09. 24)

For a more complete understanding of the present invention and its effects, reference is made to the following detailed description in conjunction with the accompanying drawings.
1 illustrates a digital controlled battery charger according to one embodiment.
2 shows a simplified block diagram of an embodiment of a digitally controlled battery charger.
3 shows a simplified block diagram of a digitally controlled battery charger according to another embodiment.
4 shows a simplified block diagram of a digitally controlled battery charger according to another embodiment.
5 shows a simplified block diagram of an example of a current winding used in a battery charger.
Unless otherwise indicated, the corresponding numbers and signs used in the different drawings generally indicate corresponding parts. The drawings are drawn to clearly show the relevant parts of the various embodiments, and are not necessarily drawn to scale.

The preparation and use of the presently preferred embodiments are described in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be implemented in a wide variety of specific details. The specific embodiments discussed herein are merely illustrative of specific recipes and uses and do not limit the scope of the invention.

The present invention will be described in connection with the preferred embodiment of the specific item, which is a buck switching regulator based battery charger. However, the present invention can also be applied to various battery chargers having different power topologies.

First, a digital control battery charger according to an embodiment will be described with reference to FIG. 1. The digitally controlled battery charger includes a power converter 104, a voltage sensor 106, a current sensor 108, a mode selector 100, and a digital controller 102. Include. The power converter 104 receives a control signal from the digital controller 102. The voltage sensor 106 and current sensor 108 are connected to the output of the power converter 104 and sense the voltage across the rechargeable battery 110 connected to the output of the power converter and the current flowing through the rechargeable battery, respectively. do. Both the output of the current sensor 108 and the output of the voltage sensor 106 are sent to the mode selector 100 and based on the control signal from the digital controller 102 in the mode selector 100, the mode selector 100. A logic control unit (not shown) selects one of two input signals and sends the selected signal to the digital controller 102. As shown in FIG. 1, the digital controller 102 receives an external signal from external registers 120 at a first input, a control signal from the mode selector 100 at a second input, and a third signal. It is set to receive some operating parameters from the power converter 104 at the input. Based on these three input signals, digital controller 102 generates a pulse width modulated (PWM) signal and controls power converter 104 accordingly.

The power converter 104 converts the input voltage (not shown, shown in FIG. 2) into a regulated output voltage for charging the rechargeable battery 110. Thus, in response to the PWM signal generated from the digital controller 102, the power converter 104 regulates the output voltage. As is known, the operation of power converter 104 is within the skill of one of ordinary skill in the art having ordinary skill in the art, and therefore the operation of power converter 104 will not be described in detail. While the preferred embodiment of the power converter 104 is a buck switching mode converter, the present invention is a boost switching mode converters, buck-boost switching mode converters. It can also be applied to other power topologies such as linear regulators, forward converters, full bridge converters, half bridge converters, and the like. The invention can also be applied to various derivatives of the power converter described above. For example, since the forward isolated converter is derived from a step-down switching mode converter, the scope of the present invention can be extended to the forward isolated converter.

In the constant current phase of the charging cycle, the current flowing through the rechargeable battery 110 is used as feedback to control the operation of the battery charger. The current sensor 108 is used to generate a current sense signal proportional to the current flowing through the rechargeable battery 110 using various current sensing techniques. The current sensor 108 may be implemented by connecting a sense resistor in series with the rechargeable battery 110. Also, if the amplitude of the current sense signal is too small, the sense resistor is connected across the inputs of the operational amplifier (not shown, shown in FIG. 2), and the operational amplifier allows the current sense signal to subsequent circuitry. It can be amplified in proportion to the possible level. Similarly, Hall effect devices, magneto resistive sensors, current sense integrated circuits or the like can be used to sense the current flowing through the rechargeable battery 110. have.

In the constant voltage phase of the charge cycle, the voltage across the rechargeable battery 10 is used as feedback to control the operation of the battery charger. The voltage sensor 106 is used to sense the voltage across the rechargeable battery 110 and to proportionally convert the voltage into a signal acceptable to subsequent circuits. Although a preferred embodiment of the voltage sensor 106 is a resistive divider connected between two terminals of the rechargeable battery 110, capacitive dividers, voltage dividers formed of various transistors. Other voltage sensing techniques, such as voltage sensing integrated circuits or the like, are within the scope of the present invention.

In the charging cycle, the battery charger first provides a constant current, and then provides a constant voltage after the rechargeable battery 110 reaches the threshold voltage. The mode selector 100 is used to select an input signal (eg, the voltage sensed from the voltage sensor 106) and send the selected signal to the digital controller 102. Although the mode selector 100 shown in FIG. 1 is a separate device, the mode selector may be an integral part of the digital controller 102. In addition, the signal selection process may be performed in hardware or software, or a combination thereof. However, in a preferred embodiment, the function is performed by a process such as executing a computer program in a digital signal processor or a central processing unit in accordance with code or software such as computer program code.

The digital controller 102 may receive an external signal from external registers 120. According to one embodiment, the external register may comprise a bank of registers in communication with the digital controller via a digital interface (eg, I2C, SPI or UART). Alternatively, the external signal may be a dynamic system configuration adjustment signal from a user or a system management unit. The external signal can be used to program various parameters of the digital controller 102. The external signal may include a battery parameter that includes an open circuit voltage, a charging current limit, and an equivalent load resistance. In addition, the digital controller 102 can retrieve the operating parameters of the power converter 104 and receive feedback from the mode selector 100. The operating parameter includes an input voltage connected to the power converter, an operating temperature of the power converter, an input current of the power converter, an output current of the power converter, an output voltage of the power converter, an input ripple voltage of the power converter. It may be selected from the group consisting of the output ripple voltage of the power converter. Based on these three signals, digital controller 102 generates a digital PWM signal for controlling power converter 104. Operation of the digital controller 102 will be described in detail with reference to FIG. One useful feature of the digital controller 102 is that the digital controller 102 can be configured to dynamically adjust the control loop compensation parameters as the battery charger enters another charging phase. Moreover, dynamic adjustment via digital control loops can provide dynamic compensation for possible process variations. This dynamic regulation also reduces the hardware cost of the battery charger since one controller (eg, digital controller 102) can handle both constant current charging and constant voltage charging. .

2 shows a simplified block diagram of a digitally controlled battery charger according to one embodiment. According to one embodiment, the power converter 104 is a buck switching mode comprising a P-channel field effect transistor (P-FET, Q1) connected in series with the N-channel field effect transistor (N-FET, Q2). mode converter). A junction point between P-FET Q1 and N-FET Q2 is connected to rechargeable battery 110 through a filter formed by output inductor Lo and output capacitor Co. The gates of the P-FET Q1 and the N-FET Q2 are connected to a driver 210, which receives the digital PWM signal from the digital controller 102, and converts the digital PWM signal into a minimum dead time ( Convert into two complementary gate signals with dead time. As is known, the driver 210 not only generates two complementary gate signals from the digital PWM signal received by the driver 210, but also the driver 210 turns on or turns the switching element of the power converter 104. When turned off, it provides enough current to increase sink and source capability. Q1 and Q2 may be implemented in other types of devices, such as J-FETs, HEX-FETs, bi-polar transistors, as known to those skilled in the art.

In the implementation of this embodiment, a sense resistor (Rs) is used to sense the current flowing through the rechargeable battery 110. Rs is connected in series to the rechargeable battery 110. Operational amplifier 212 has two inputs connected to two terminals of Rs. The gain of the operational amplifier 212 is adjusted so that the output voltage of the operational amplifier 212 is in the same range as the output of the voltage sensor 106. As a result, the feedback signal from the voltage sensor 106 and the feedback signal from the current sensor 108 are referenced when the mode selector selects any of them and sends the selected signal to the digital controller 102. voltage, wherein the selected signal will be compared to the reference voltage.

The charging cycle of the rechargeable battery includes at least two stages, namely a constant current stage and a constant voltage stage. The mode selector 100 is used to select a legitimate feedback signal during these two charging stages. This function can be performed in hardware or software. For example, the ORING circuit can pass a high amplitude feedback signal through the mode selector 100 and block the low amplitude feedback signal from reaching the digital controller 102. . Alternatively, the mode selection function can be integrated into the digital controller 102, where a computer program can compare two input signals to select a signal with high amplitude.

The digital controller 102 includes a sigma delta analog-to-digital converter (ADC) 202, a decimator 204, a digital filter 206 and a digital PWM generator 208. It includes. The sigma delta ADC 202 can be a simple switched capacitor design that eliminates the common mode of the incoming signal while still providing the differential gain required for conversion to the digital domain. have. According to one embodiment, the sigma delta ADC 202 receives a feedback signal from the mode selector 100 and compares the feedback signal with a reference voltage VREF. In addition, the sigma delta ADC 202 converts the difference between the reference voltage VREF and the feedback signal into a digital code. The sigma delta ADC 202 may be replaced with a sigma delta modulator including a differential amplifier and an ADC.

The decimator 204 is configured to perform two functions. First, the decimator 204 is used to reduce the sampling rate of the digital signal from the sigma delta ADC 202. By employing this technique, the Shannon-Nyquist sampling theorem criterion is maintained, while the data rate of the size of the data size at the output of the decimator 204. data) is reduced. The decimator 204 also provides an anti-aliasing filter in which quantization noise is reduced, thus improving the resolution of the signal at the output of the decimator 204. The decimator 204 uses a simple digital counter, in which the number of logic ones output from the sigma delta ADC 202 is counted during the previous period and a new digital code is generated based on the number of logic. Can be implemented.

The digital filter 206 is used to position the compensation poles and zeros so that the loop response of the constant current control and the constant voltage control of the battery charger is controlled. In other words, after adding extra poles and zeros through the digital filter 206, the control loop of battery charging has a phase margin of greater than 60 degrees. As is known, when the battery charger is in the constant current charging phase, the transfer function of the battery charger is a second-order system. In particular, the transfer function comprises two conjugate poles and one zero. As is known, in order to ensure that the secondary system has a phase margin of greater than 60 degrees, in an analog battery charger, the resistors and capacitors are connected via three poles and two zeros through an error amplifier. configured to provide zero. As with the analog counterpart, the digital filter 206 provides three poles and two zeros so that the loop response of the battery charger has a phase margin of greater than 60 degrees. According to one embodiment, the digital filter 206 has two conjugate poles of a transfer function such that the phase lag caused by the two conjugate poles is mitigated. It provides two zeros at the frequency of. The pole may be located at a frequency above the crossover frequency so that high frequency noise is attenuated.

On the other hand, when the battery voltage reaches the threshold voltage, the battery charger enters the constant voltage step. The battery charger under the constant voltage stage exhibits a transfer function similar to the secondary system described above with respect to the constant current stage. In summary, the constant current charging step and the constant voltage charging step share a similar transfer function even though the pole and zero are at different frequencies. This inherent feature means that both charging stages can share a digital filter, such as a recursive filter. As the battery charger enters a different charging stage, the digital filter 206 can compensate for the control loop by dynamically adjusting its coefficients, thus compensating zero and The pole can be adjusted. An advantage of the digital filter 206 is that two charging stages of the battery charger can share the same filter configuration. In addition, the control loop can be tuned in response to any one of an external signal and a change in operating conditions of the battery charger, such that the control loop can provide a stable system as well as a fast transient response. .

The digital PWM generator 208 receives a digital code from the digital filter 206 and generates a constant frequency PWM signal. The digital PWM generator 208 may be implemented using a digital counter (not shown). This digital counter allows the digital PWM generator 208 to output a logic high state until the digital counter counts to a value equivalent to the digital code from the digital filter 206. The output of the digital PWM generator 208 then remains at a logic low state until the next switching cycle. The output of the digital PWM generator 208 is connected to the driver 210, which generates two gate pulses to drive the step-down converter shown in FIG. The operation of controlling the step-down transducer via PMW control is known in the art and thus is not discussed here.

3 shows a simplified block diagram of a digitally controlled battery charger according to another embodiment. The battery charger shown in FIG. 3 is similar to the embodiment of FIG. 2 but includes only one voltage feedback loop. 4 shows a simplified block diagram of a digitally controlled battery charger according to another embodiment. The battery charger shown in FIG. 4 includes one current feedback loop. The operation of a voltage mode battery charger or current mode battery charger is known in the art and thus is not discussed here. Both Figures 3 and 4 show that the scope of the present invention can be applied to a single-loop battery charger as well as to a dual-loop battery charger. Those skilled in the art will recognize many variations, substitutions and alterations.

FIG. 5 shows a schematic diagram of the current sensor 108 shown in FIG. 4. According to one embodiment, the current sensor 108 includes a sense resistor (Rs), an operational amplifier 502, a resistor (R1), a current sense voltage setting resistor (Rset) and a transistor ( 504). The sense resistor Rs is connected in series to the rechargeable battery 110. The resistor R1, the transistor 504, and the current sense voltage setting resistor Rset are connected in series. The operational amplifier 502 has a positive input connected to the junction between the resistor R1 and the transistor 504, negative connected to the junction between the current sense resistor Rs and the rechargeable battery 110. Has an input and an output connected to the gate of the transistor 504.

As is known in the art, the voltage across sense resistor Rs is equal to the voltage across resistor R1. As shown in FIG. 5, the current flowing through the resistor R1 is approximately equal to the current flowing through the current sensing voltage setting resistor Rset. As a result, the voltage across the resistor R1 can be expressed as follows.

Where Vset is the voltage across the current sense voltage setting resistor Rset. Similarly, the voltage across the sense resistor Rs can be expressed as follows.

Where I _SNS is the current flowing through the sense resistor Rs. Since the voltage across the sensing resistor Rs is the same as the voltage across the resistor R1, Vset may be expressed as follows.

From the above equation, Vset is proportional to the current sense voltage across the sense resistor Rs. Also, the range of Vset can be adjusted by changing the value of Rset. One advantage of the current sensor 108 shown in FIG. 5 is that the current sensor 108 can generate a current sensing signal (eg , Vset) in the same order as the voltage feedback signal. This aspect is characterized in that, the current feedback loop and the voltage feedback loop, the ADC (for example, FIG sigma delta ADC (202) shown in Fig. 2) it allows to share and reference voltage.

While embodiments of the present invention and their advantages have been described in detail, it should be appreciated that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not limited to the specific embodiments of the process, machine, manufacture and composition, means, methods and steps of the materials described in the specification. Those skilled in the art can, from the disclosure of the present application, process or machine that are to be developed or later developed that can perform substantially the same functions or obtain substantially the same effects as the corresponding embodiments described herein. It will be readily understood that the preparation, composition and composition of the materials, means, methods and steps may be useful according to the disclosure. It is therefore intended that the appended claims cover such processes, machines, manufacture and compositions of matter, means, methods and steps within the scope of the claims.

Claims (10)

A mode selector configured to receive both a current sense signal and a voltage sense signal;
An analog-to-digital converter (ADC) coupled between the mode selector and the digital controller;
The digital controller configured to generate a digital pulse width modulated (PWM) signal;
A decimator coupled between the ADC and the digital filter;
Configured to add a plurality of poles and zeros to increase the phase margin of the power converter, wherein a group of coefficients is enabled when the current sensing signal is selected, The digital filter, wherein a second coefficient group is enabled when the voltage sensing signal is selected; And
And a digital PWM generator for receiving a digital signal from the digital filter and converting the digital signal into the PWM signal. 2. The digital control circuit of claim 1 wherein the mode selector selects an input signal and sends the input signal to the ADC. 2. The digital control circuit of claim 1 wherein the ADC comprises a sigma delta modulator and is configured to receive a reference voltage and a feedback signal from the mode selector. delete A power converter having an output coupled to the rechargeable battery;
A current sensor configured to sense a current flowing through the rechargeable battery;
A voltage sensor configured to sense a voltage across the rechargeable battery; And
Including digital control circuitry,
The digital control circuit includes a mode selector configured to receive both a current sense signal from the current sensor and a voltage sense signal from the voltage sensor;
An analog-to-digital converter (ADC) coupled between the mode selector and the digital controller;
The digital controller configured to generate a digital pulse width modulated (PWM) signal to control the power converter;
A decimator coupled between the ADC and the digital filter;
The digital filter configured to add a plurality of poles and zeros to increase the phase margin of the power converter; And
A digital PWM generator receiving the digital signal from the digital filter and converting the digital signal into a PWM signal,
The power converter is a step-down switching mode converter, a boost switching mode converter, a step-down switching mode converter, a linear regulator, a forward converter, a full bridge converter and a half bridge converter. Selected from the group consisting of,
The current sensor is selected from the group consisting of a sense resistor, a hall effect element, a magnetoresistive sensor and a current sense integrated circuit. The method of claim 5, wherein
A sense resistor connected in series with said rechargeable battery;
A current sense amplifier having two inputs across the sense resistor; And
And a driver coupled between the digital controller and the power converter. delete Sensing a current flowing through the rechargeable battery and converting the current into a current sense signal;
Sensing a voltage across two terminals of the rechargeable battery and converting the voltage into a voltage sensing signal;
Determining a selection signal from the current sensing signal and the voltage sensing signal and sending the selection signal to a digital controller;
Receiving operating parameters from a power converter;
Receiving an external signal;
Generating a digital pulse width modulated (PWM) signal in response to the operating parameter and the external signal; And
Transmitting the PWM signal to the power converter coupled to the rechargeable battery,
The operating parameter includes an input voltage connected to the power converter, an operating temperature of the power converter, an input current of the power converter, an output current of the power converter, an output voltage of the power converter, an input ripple voltage of the power converter. Is selected from the group consisting of output ripple voltage of the power converter,
The external signal comprises a battery parameter comprising an open circuit voltage, a charging current limit, and an equivalent load resistance. The method of claim 8,
Comparing the selection signal with a reference voltage and converting an error between the selection signal and the reference voltage into a digital code using an analog-to-digital converter (ADC);
Compensating the digital control loop by adding multiple poles and zeros through the digital filter,
Reducing the data size using a decimator coupled between the ADC and the digital filter, and
Transmitting the PWM signal to a driver to control the power converter. delete

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