CONSTANT CURRENT CHARGING DEVICE

A constant current charging device is configured to charge a device to be charged and includes: a current regulating unit electrically coupled to the device to be charged and configured to provide a regulating current and a charging current according to a reference voltage; a current-to-voltage converting unit electrically coupled to the current regulating unit and configured to output a regulating voltage according to the regulating current; and a first operational amplifier electrically coupled to the current regulating unit, the current-to-voltage converting unit, and the device to be charged and configured to regulate the regulating current.

TECHNICAL FIELD OF DISCLOSURE

The present disclosure relates to the field of charging technologies, and more particularly to a constant current charging device.

BACKGROUND OF DISCLOSURE

A conventional charging device includes a constant current charging mode and a constant voltage charging mode. At the beginning of charging a battery, the charging device charges the battery in the constant current charging mode. When the battery is charged to a predetermined voltage, the charging device charges the battery in the constant voltage charging mode.

However, a current and a voltage provided by the conventional charging device are unstable. The unstable current or the unstable voltage not only affects charging efficiency of the battery but also decreases service life of the battery.

Therefore, there is a need to solve the above-mentioned problem in the prior art.

SUMMARY OF DISCLOSURE

An objective of the present disclosure is to provide a constant current charging device capable of solving the problem in the prior art.

The constant current charging device of the present disclosure includes: a current regulating unit electrically coupled to the device to be charged and configured to provide a regulating current and a charging current according to a reference voltage; a current-to-voltage converting unit electrically coupled to the current regulating unit and configured to output a regulating voltage according to the regulating current; and a first operational amplifier electrically coupled to the current regulating unit, the current-to-voltage converting unit, and the device to be charged and configured to regulate the regulating current.

The constant current charging device of the present disclosure can provide, by the current regulating unit, the current-to-voltage converting unit, and the first operational amplifier, the charging current which has a high current value and is controllable. Furthermore, the constant current charging device of the present disclosure can design the charging current according to channel width/length ratios of transistors of the current regulating unit. Finally, the constant current charging device of the present disclosure can provide, by the current regulating unit, the current-to-voltage converting unit, and the first operational amplifier, the charging current which is stable.

DETAILED DESCRIPTION OF DISCLOSURE

To make the objectives, technical schemes, and technical effects of the present disclosure more clearly and definitely, the present disclosure will be described in detail below by using embodiments in conjunction with the appending drawings. It should be understood that the specific embodiments described herein are merely for explaining the present disclosure, and as used herein, the term “embodiment” refers to an instance, an example, or an illustration but is not intended to limit the present disclosure. In addition, the articles “a” and “an” as used in the specification and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form. Also, in the appending drawings, the components having similar or the same structure or function are indicated by the same reference number.

Please refer toFIG. 1andFIG. 2.FIG. 1illustrates a block diagram of a constant current charging device in accordance with an embodiment of the present disclosure.FIG. 2illustrates a detailed circuit diagram of the constant current charging device inFIG. 1.

The constant current charging device is configured to charge a device30to be charged and includes a current regulating unit10, a current-to-voltage converting unit20, and a first operational amplifier OPAL

The device30to be charged of the present disclosure may be but not limited to a circuit required to be charged or a rechargeable battery.

The current regulating unit10is electrically coupled to a power source VDD and the device30to be charged and configured to provide a regulating current IBand a charging current ICaccording to a reference voltage VREF. The charging current ICis configured to charge the device30to be charged, and the charging current ICcan be M times of the regulating current IB. M is a positive integer. In detail, the current regulating unit10can control to increase or decrease the charging current IC. Furthermore, the current regulating unit10is further configured to adjust a charging voltage VCof the device30to be charged. In detail, the current regulating unit10can control to increase or decrease the charging voltage VC. The power source VDD may be a direct-current power source. The reference voltage VREFcan be adjusted according to requirements.

The current-to-voltage converting unit20is electrically coupled to the current regulating unit10and configured to output a regulating voltage VBaccording to the regulating current IB.

The first operational amplifier OPA1is electrically coupled to the current regulating unit10, the current-to-voltage converting unit20, and the device30to be charged and configured to regulate the regulating current IBaccording to the charging voltage VCinputted to the device30to be charged. The first operational amplifier OPA1includes an inverting input −, a non-inverting input +, and a first operational amplifier output O1. The inverting input − of the first operational amplifier OPA1is electrically coupled to the current regulating unit10and the current-to-voltage converting unit20. The non-inverting input + of the first operational amplifier OPA1is electrically coupled to the current regulating unit10and the device30to be charged. The first operational amplifier output O1of the first operational amplifier OPA1is electrically coupled to the current-to-voltage converting unit20.

As shown inFIG. 2, the current regulating unit10includes a first transistor T1, a second transistor T2, and a second operational amplifier OPA2.

The first transistor T1includes a first control terminal, a first input terminal, and a first output terminal. The second transistor T2includes a second control terminal, a second input terminal, and a second output terminal. The second operational amplifier OPA2includes an inverting input −, a non-inverting input +, and a second operational amplifier output O2.

The first control terminal is electrically coupled to the second control terminal. The first input terminal is electrically coupled to the power source VDD. The first output terminal is electrically coupled to the current-to-voltage converting unit20and the first operational amplifier OPAL The second input terminal is electrically coupled to the power source VDD. The second output terminal is electrically coupled to the first operational amplifier OPA1and the device30to be charged. The inverting input − of the second operational amplifier OPA2is electrically coupled to the reference voltage VREF. The non-inverting input + of the second operational amplifier OPA2is electrically coupled to the regulating voltage VB. The second operational amplifier output O2of the second operational amplifier OPA2is electrically coupled to the first control terminal and the control second terminal.

In the present embodiment, the first transistor T1and the second transistor T2may be P-type Metal-Oxide-Semiconductor Field-Effect Transistor (PMOSFET).

The current-to-voltage converting unit20includes a third transistor T3and a resistor R. The third transistor includes a third control terminal, a third input terminal, and a third output terminal. The third control terminal is electrically connected to the first operational amplifier output O1of the first operational amplifier OPAL The third input terminal is electrically connected to the inverting input − of the first operational amplifier OPAL One terminal of the resistor R is electrically connected to the third output terminal. The other terminal of the resistor R is electrically connected to the ground G.

In the present embodiment, the third transistor T3may be a PMOSFET.

An operating principle of the constant current charging device of the present disclosure will be described in detail as follows.

First, the regulating voltage VBis zero in an initial state. A voltage (equal to zero) of the non-inverting input + of the second operational amplifier OPA2is smaller than the reference voltage VREF. The second operational amplifier OPA2outputs a low voltage level. The charging voltage VCis zero in an initial state. Accordingly, a voltage inputted to the inverting input − of the first operational amplifier OPA1is greater than the charging voltage VC. The first operational amplifier OPA1outputs a low voltage level. The first transistor T1and the third transistor T3are turned on, and the regulating current IBis generated.

The charging current ICcan be M times of the regulating current IB. In detail, the charging current ICrelates to a channel width/length ratio (W1/L1) of the first transistor T1and a channel width/length ratio (W2/L2) of the second transistor T2. M is a ratio of the channel width/length ratio (W1/L1) of the first transistor T1to the channel width/length ratio (W2/L2) of the second transistor T2. W1 is a channel width of the first transistor T1, and L1 is a channel length of the first transistor T1. W2 is a channel width of the second transistor T2, and L2 is a channel length of the second transistor T2. A relationship between the charging current ICand the regulating current IB:

When the charging current ICis raised and the charging voltage VCis greater than the voltage inputted to the inverting input − of the first operational amplifier OPA1, the first operational amplifier OPA1outputs a high voltage level to decrease the regulating current IB. When the regulating voltage VBis close to the reference voltage VREF, the second operational amplifier OPA2outputs a high voltage level to decrease the charging current IC. When the regulating voltage VBis raised to the reference voltage VREF, the second transistor T2stops providing the charging current IC. That is, when the regulating voltage VBis equal to the reference voltage VREF, the charging current ICis zero.

In summary, the constant current charging device of the present disclosure can control to increase or decrease the charging current ICand control to increase or decrease the charging voltage VCby the current regulating unit10, the current-to-voltage converting unit20, and the first operational amplifier OPA1, thereby providing the charging current ICand the charging voltage VCwhich are stable. Furthermore, the constant current charging device of the present disclosure can provide, by the current regulating unit10, the charging current ICwhich has a high current value and is controllable.

Please refer toFIG. 3.FIG. 3illustrates a simulation diagram of the charging current ICand the charging voltage VCinFIG. 2.

In the simulation diagram ofFIG. 3, the power source VDD is 4 volts, the reference voltage VREFis 1 volt, the reference current IRFFis 100 microamperes, the charging current ICis 200 milliamperes, and the device30to be charged is a one farad capacitor.

It can be understood fromFIG. 3that the charging current ICcan rapidly provide a stable current of 200 milliamperes at about 2 seconds. When the charging voltage VCis raised gradually, the charging current ICis decreased gradually. When the charging voltage VCis raised to the power source VDD (4 volts), the charging current ICis decreased to zero.

It is noted that the charging current ICshown in negative values represents a definition of a current direction.

Please refer toFIG. 4.FIG. 4illustrates a simulation diagram of the regulating voltage VBand a voltage of the first operational amplifier output O1inFIG. 2.

It can be understood fromFIG. 4that the voltage of the first operational amplifier output O1is raised to the power source VDD (4 volts) gradually, the regulating voltage VBis decreased to 0 volts gradually.

Please refer toFIG. 5.FIG. 5illustrates a block diagram of a constant current charging device in accordance with another embodiment of the present disclosure.

A difference between the constant current charging device inFIG. 5and the constant current charging device inFIG. 1is that the constant current charging device inFIG. 5further includes a voltage regulating unit40. The voltage regulating unit40is electrically coupled between the power source VDD and the current regulating unit10and configured to adjust the charging voltage VC. In detail, the voltage regulating unit40can control the charging voltage VCof the device30to be charged to any one voltage excluding the power source VDD. The voltage regulating unit40may be but not limited to a low-dropout (LDO) regulator or a booster.

Please refer toFIG. 6.FIG. 6illustrates a block diagram of a constant current charging device in accordance with yet another embodiment of the present disclosure.

A difference between the constant current charging device inFIG. 6and the constant current charging device inFIG. 1is that the constant current charging device inFIG. 6further includes a voltage detecting unit50. The voltage detecting unit50is electrically coupled between the power source VDD and the current regulating unit10and configured to adjust the charging voltage VC. In detail, the voltage detecting unit50can control the charging voltage VCof the device30to be charged to any one voltage excluding the power source VDD. The voltage detecting unit50may be but not limited to a comparator.

The constant current charging device of the present disclosure can provide, by the current regulating unit, the current-to-voltage converting unit, and the first operational amplifier, the charging current (as shown inFIG. 3) which has a high current value and is controllable. Furthermore, the constant current charging device of the present disclosure can design the charging current according to the channel width/length ratios of the transistors of the current regulating unit. Finally, the constant current charging device of the present disclosure can provide, by the current regulating unit, the current-to-voltage converting unit, and the first operational amplifier, the charging current (as show inFIG. 3) which is stable.

While the preferred embodiments of the present disclosure have been illustrated and described in detail, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present disclosure is therefore described in an illustrative but not restrictive sense. It is intended that the present disclosure should not be limited to the particular forms as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present disclosure are within the scope as defined in the appended claims.