Charging method and circuit

Abstract

In this charging method, a charge of Q = CV is charged by applying a voltage to a capacitor of a capacitance C while gradually changing the voltage. In each stage, charging of the next stage starts after completion of charging. By applying the voltage while gradually changing the voltage, when the number of stages is 2, the energy loss is 1 / 2 compared to a case of charging at one time by applying a voltage V from the beginning.

Description

Charging Method and Circuit

[0001] The present invention relates to a charging method and a circuit.

[0002] Conventionally, when charging a capacitor from a battery, a method of connecting the capacitor and the battery via a switch is common. The energy stored in the capacitor is Q 2 / 2C, but it is known that an equivalent amount of energy is consumed as a loss (see Non-Patent Document 1 and Non-Patent Document 2). This is a fundamental energy loss that occurs regardless of the presence or absence of resistance.

[0003] Jan M. Rabaey and Massoud Pedram, "Low Power Design Methodologies", The Springer International Series in Engineering and Computer Science , pp. 65-100, 1996. By Tomoya Noro, "Evaluation of Capacitor Charge-Discharge Characteristics".

[0004] In a circuit, various stray capacitors exist in wiring and the like. Since the aforementioned energy loss occurs in various stray capacitors, it becomes a problem in high-efficiency circuit design.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to reduce energy loss when charging a capacitor.

[0006] A charging method according to the present invention charges a charge of Q=CV by applying a stepwise changing voltage to a capacitor of capacitance C.

[0007] Further, a circuit according to the present invention comprises N batteries connected in series with each battery having a voltage of V / N (N is a natural number of 2 or greater), a capacitor connected in parallel with the series-connected batteries, and N switches for switching connection between each of the batteries and the capacitor.

[0008] As explained above, according to the present invention, a capacitor of capacitance C is charged with a charge of Q = CV by applying a voltage that is changed in steps, so that energy loss when charging the capacitor can be reduced.

[0009] Figure 1 is an explanatory diagram illustrating a charging method according to an embodiment. Figure 2 is a circuit diagram showing a circuit for implementing the charging method according to an embodiment. Figure 3 is a circuit diagram showing another circuit for implementing the charging method according to an embodiment.

[0010] The following describes a charging method according to an embodiment of the present invention.

[0011] This charging method charges a capacitor of capacity C by applying a voltage that is changed in stages to charge it to a charge of Q = CV. At each stage, charging is completed before starting the next stage. The voltage is changed in N stages (where N is a natural number greater than or equal to 2), and at the nth stage (a natural number between 1 and N), a voltage of V / (N+1-n) is applied to the capacitor to charge it.

[0012] Using Figure 1 to explain the conventional configuration, first, a battery 103 with voltage V is connected to a capacitor 101 (including wiring, etc.) with capacity C via a switch 102. When the switch 102 is turned on, a charge Q = CV is accumulated in the capacitor 101 when charging is complete. At this time, the capacitor 101 has Q 2 Energy equal to 2C is stored, but the same amount of energy is lost. This is an energy loss that would occur even without resistance.

[0013] In contrast, first, when the voltage of battery 103 is halved to V / 2 (first stage), the capacitor will have a charge of Q = CV / 2 when charging is complete. At this time, the energy stored in the capacitor and the energy lost are (Q / 2). 2 This results in a charge of 2C. After this, when the voltage of battery 103 is set to V (second stage), an additional charge of Q = CV / 2 is added to capacitor 101, and when charging is complete, the charge stored in capacitor 101 will be Q = CV. The loss in this second charge is (Q / 2). 2 It becomes / 2C.

[0014] Therefore, the total loss from the first and second stage of charging is (Q / 2) 2 / 2C + (Q / 2) 2 / 2C = Q 2 This results in a voltage of 4C. By applying the voltage in stages in this way, the energy loss is halved compared to charging in one step by applying the voltage V from the beginning. It is important to change the voltage in each stage once the capacitor has finished charging.

[0015] By simply varying the voltage of the battery in stages during charging, energy loss can be reduced. For example, if the number of stages is N (where N is an integer greater than or equal to 2), and the voltage is varied in N stages, the first stage charges the capacitor by applying a voltage of V / (N+1-1), the second stage charges it by applying a voltage of V / (N+1-2), and the Nth stage charges it by applying a voltage of V / (N+1-N). In this way, if the number of stages in which the applied voltage is varied is N, the energy loss becomes 1 / N. Using this method, it is possible to reduce losses in the capacitors and wiring of the circuit, or in batteries that use capacitors.

[0016] Figure 2 shows a circuit according to an embodiment. This circuit comprises N batteries (where N is a natural number of 2 or more) connected in series, each with a voltage of V / N, a capacitor connected in parallel with the series-connected batteries, and N switches for switching (turning on / off) the connection between each battery and the capacitor. In this example, first, there are first batteries 103-1, 2, and so on, the Nth battery 103-N, each with a voltage of V / N, connected in series. Capacitor 101 is connected in parallel with the series-connected first batteries 103-1, 2, and so on, the Nth battery 103-N. There are also first switches 102-1, 2, and so on, the Nth switch 102-N, for switching (turning on / off) the connection between each of the first batteries 103-1, 2, and so on, the Nth battery 103-N and the capacitor 101.

[0017] By turning on the switches one by one, starting with the first switch 102-1, the voltage can be changed by V / N. Although energy consumption occurs due to the switches, if the capacitance C of capacitor 101 and the voltage V are large, the energy loss due to the switches becomes relatively small, thus achieving an energy loss suppression effect. The same function can be obtained with a ladder resistor circuit such as a digital-to-analog conversion circuit, but energy loss occurs in the steady state.

[0018] Furthermore, as shown in Figure 3, a charge pump circuit 104 can be used as the power source. For example, charge pump circuits are used for boosting voltage in battery-less circuits and low-voltage drive circuits (reference). Energy loss can be suppressed by charging the capacitor during the voltage change process using the charge pump.

[0019] As described above, according to the embodiment, a capacitor of capacity C is charged with a charge of Q = CV by applying a voltage that is changed in steps, thereby reducing energy loss when charging the capacitor. The embodiment is applicable to electronic circuits in general and is particularly useful in the following fields: for example, high-efficiency power supply circuits, low-power IoT devices, energy management for electric vehicles, battery-less circuits, and power supply circuits for semiconductor memory and processors. According to the embodiment, energy loss can be suppressed and the efficiency of the circuit can be improved.

[0020] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art.

[0021] [References] Kazuma Akabane, "The Mechanism of Charge Pumps and Convenient ICs for Low-Voltage Operation," Transistor Technology, June issue, pp. 151-152, 2008.

[0022] 101...Capacitor, 102-1...First switch, 102-2...Second switch, 102-N...Nth switch, 103-1...First battery, 103-2...Second battery, 103-N...Nth battery.

Claims

1. A charging method in which a capacitor of capacitance C is charged to a charge Q = CV by applying a voltage that is changed in stages.

2. The charging method according to claim 1, wherein the charging of the next stage is started only after the charging of the previous stage is completed in each stage.

3. The charging method according to claim 2, wherein the voltage is changed in N steps (where N is a natural number of 2 or more), and the nth step (1 ≤ n ≤ N) is charged by applying V / (N+1-n) to the capacitor.

4. A circuit comprising N batteries (where N is a natural number of 2 or more) connected in series, each with a voltage of V / N, a capacitor connected in parallel with the series-connected batteries, and N switches for switching the connection between each of the batteries and the capacitor.

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