JP2014071786A - Electronic pen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic pen that can charge an electric double-layer capacitor in a short time and with high efficiency in a range not exceeding above an electric current maximum value of a charging electric power.SOLUTION: An electronic pen having position display means for position information according to the present invention is configured to comprise: capacitor voltage monitor means that detects voltages of a step-up or step-down converter supplying power to the position display means, the electric double-layer capacitor accumulating supply power for the position display means and the electric double-layer capacitor; a step-down type chopper circuit that controls a charging electric current of the electric double-layer capacitor; and switch control means that controls an ON/OFF duty of the step-down type chopper circuit on the basis of voltage information detected by the capacitor voltage monitor means. The switch control means controls such that the ON duty of the step-down type chopper circuit gets greater as the voltage information detected by the capacitor voltage monitor means gets greater.

Description

  The present invention relates to charge control of an electric double layer capacitor.

  In recent years, with the spread of computerization in the paperless and educational fields, electronic capture and display of handwritten information is required. Some electronic pens used in electronic blackboards and large tablets that meet these requirements have a built-in power supply to detect pen position coordinates and pen depressions on the board surface, and the control device displays pen position information and Some communicate operation information. The electronic pen has a built-in battery as a power source, but weight reduction is required so that the pen does not feel uncomfortable.

  It is conceivable to use an electric double layer capacitor as another power source of the electronic pen. Electric double layer capacitors are characterized by being lighter and longer in life than batteries using chemical reactions. Patent Document 1 discloses an example of a digital pen using an electric double layer capacitor.

Utility Model Registration No. 3162788

  The electric double layer capacitor is characterized in that since ionic molecules store electric charges, there is little deterioration due to charging / discharging, and the voltage changes linearly during charging / discharging. In addition, since the electric double layer capacitor has a small internal resistance, it can be discharged with a large current and can be charged with a large current, and can be charged in a short time.

  This simultaneously involves the following problem. In other words, if no special current limitation is performed during charging, an excessive load is imposed on the power supply side. For example, when power is supplied via the USB interface, the supply power is limited to 0.5A in USB 2.0.

  In Patent Document 1, a charging current value is limited by a current limiting resistor. However, this method has a problem that a loss due to the current limiting resistor occurs and a charging time until full charging is extended.

  An object of the present invention is to provide an electronic pen capable of charging an electric double layer capacitor in a short time and with high efficiency within a range not exceeding the maximum current value of a charging power source.

  In order to solve the above-described problems, an electronic pen having position information position display means according to the present invention includes a step-up or step-down converter for supplying power to the position display means, and an electric double layer for storing the power of the position display means. Based on the voltage information detected by the capacitor, the capacitor voltage monitor means for detecting the voltage of the electric double layer capacitor, the step-down chopper circuit for controlling the charging current of the electric double layer capacitor, and the voltage information detected by the capacitor voltage monitor means Switch control means for controlling the ON / OFF duty of the step-down chopper circuit.

  The switch control means controls the ON duty of the step-down chopper circuit to be larger as the voltage information detected by the capacitor voltage monitoring means is larger, and the ON duty of the step-down chopper circuit is the capacitor The voltage monitoring means is proportional to the change in voltage information detected.

  In the present invention, charging of the electric double layer capacitor is configured to transmit power by switching, and the input current on the supply side is controlled by chopper control according to the voltage level of the electric double layer capacitor. Thus, the electric double layer capacitor of the electronic pen can be charged in a short time and with high efficiency without applying an excessive load on the power supply side.

It is a figure which shows the circuit structure of an Example. It is a figure which shows the capacitor voltage of an Example, and the relationship between the on-duty of a chopper. It is a figure which shows the time change of the chopper control signal and capacitor voltage of an Example. It is a figure which shows the other circuit structure of an Example. It is a figure which shows the other circuit structure of an Example.

  In the present invention, the voltage difference between the output voltage of the power supply and the electric double layer capacitor determines the charging current value. From the electric double layer capacitor voltage at a certain time, the current value of the power supply becomes the maximum current value. The chopper circuit is switching controlled so as not to exceed. A specific configuration will be described below.

  FIG. 1 is a diagram illustrating an internal configuration of an electronic pen according to an embodiment of the present invention. The position display means 3 of the electronic pen is supplied with electric power after the electric power accumulated in the electric double layer capacitor 10 is converted into a voltage by a step-up / step-down converter 8 that steps up or down according to the operating voltage of the position display means 3. . The electric double layer capacitor 10 is charged by a step-down chopper circuit composed of a switch 6, an inductor 7, and a diode 11 controlled by the switch control means 1.

  The operation of this step-down chopper circuit will be described later. The voltage of the electric double layer capacitor 10 is detected by the capacitor voltage monitoring means 2, and the detected voltage information of the electric double layer capacitor 10 is notified to the switch control means 1, so that the step-down type The ON / OFF duty of the switch 6 of the chopper circuit is controlled. The ON / OFF duty of the switch 6 determined by the switch control means 1 is obtained in advance so as not to exceed the current allowable amount of the power source.

  Further, an inductor 5 and a capacitor 9 are provided on the power supply side of the switch 6 in FIG. 1 for smoothing the input voltage of the step-down chopper circuit. The voltage converter 4 supplies power from the power source to the switch control means 1 and the capacitor voltage monitor means 2 when no electric charge is stored in the electric double layer capacitor 10. When electric charge is stored in the electric double layer capacitor 10, the output of the voltage conversion 4 and the step-up / step-down converter 8 is diode-ORed so that power can be supplied also from the step-up / step-down converter 8. Connected to capacitor voltage monitoring means 2.

  Here, the same effect can be obtained by replacing the diode 11 of the step-down chopper circuit with a second switch and configuring the step-down chopper circuit as a synchronous rectification type chopper circuit.

  In addition, the electronic pen position display means 3, switch control means 1, and capacitor voltage monitoring means 2 can be implemented as separate ICs or partly as the same IC. It does not matter.

  FIG. 2 is a diagram showing the relationship between the terminal voltage of the electric double layer capacitor 10 and the ON duty of the switch 6. The switch control means 1 holds the voltage information and the ON duty control value of the switch 6 in a table so as to satisfy the relationship of FIG. 2, and controls the switch 6 according to the input voltage information.

  As shown in FIG. 2, when the terminal voltage of the electric double layer capacitor 10 is low, the ON duty of the switch 6 is reduced. As a result, the output voltage of the step-down chopper circuit supplied to the electric double layer capacitor 10 is lowered, and the input current of the step-down chopper circuit is also limited, so that the current value of the power supply may exceed the maximum current value. Absent.

  Further, as the voltage of the electric double layer capacitor 10 increases, the ON duty of the switch 6 increases with a certain slope, and when the voltage of the electric double layer capacitor 11 exceeds a certain value, Also increase with a steep slope.

  FIG. 3 is a diagram showing the time change of the terminal voltage of the electric double layer capacitor 10 and the ON duty of the switch 6. Charging is performed by sequentially switching the ON duty control values of the four switches 6 according to the terminal voltage of the electric double layer capacitor 10. When the terminal voltage of the electric double layer capacitor 10 reaches a predetermined voltage value, the driving of the switch 6 is stopped and the charging operation is ended.

  FIG. 4 is obtained by adding connection detection means 12 for detecting that an external power source is connected to the configuration of the electronic pen of FIG. With this configuration, charging of the electric double layer capacitor 10 is started when the electronic pen is connected to an external power supply device such as a PC USB port.

  Specifically, the connection detection unit 12 detects the voltage of the power supply line, and when detecting a predetermined value of voltage, determines that the power source is connected and notifies the switch control unit 1 of a detection signal. The switch control means 1 notified of the detection signal acquires the start duty of the ON duty charging operation of the switch 6 according to the voltage level of the electric double layer capacitor 10 at this time, and starts the above charging operation.

  5 is obtained by adding voltage detection means 14 for detecting the voltage value of the external power supply to the configuration of the electronic pen of FIG. 1, and the switch control means 1 of FIG. The switch control means 13 changes the ON duty control value table of the switch 6 for each of a plurality of voltage conditions in accordance with the voltage information notified from the voltage detection means 14. For example, when an external power supply having a high voltage level is connected, the switch 6 is controlled by changing the ON duty of the switch 6 from a smaller value to an ON duty control value table for starting charging.

  With the above configuration, it is possible to connect to a plurality of external power supply apparatuses having different voltage levels.

  1 ... switch control means, 2 ... capacitor voltage monitoring means, 6 ... switch, 7 ... inductor, 10 ... electrical double layer capacitor, 11 ... diode

Claims (5)

In an electronic pen having position display means for position information,
A step-up or step-down converter for supplying power to the position display means;
An electric double layer capacitor for accumulating power supplied by the position display means;
Capacitor voltage monitoring means for detecting the voltage of the electric double layer capacitor;
A step-down chopper circuit for controlling the charging current of the electric double layer capacitor supplied from the outside;
Switch control means for controlling ON / OFF duty of the step-down chopper circuit based on voltage information detected by the capacitor voltage monitoring means;
An electronic pen comprising: The electronic pen according to claim 1,
The electronic switch according to claim 1, wherein the switch control means controls the ON duty of the step-down chopper circuit to increase as the voltage information detected by the capacitor voltage monitoring means increases. The electronic pen according to claim 1 or 2,
The electronic pen according to claim 1, wherein the switch control unit stops the operation of the step-down chopper circuit when voltage information detected by the capacitor voltage monitoring unit is a predetermined value. The electronic pen according to claim 1,
Furthermore, it has connection detection means for detecting that an external power supply is connected,
The electronic pen characterized in that when the connection detecting means detects that a power source is connected, the switch control means controls the step-down chopper circuit to charge the electric double layer capacitor. The electronic pen according to claim 1,
Furthermore, it has voltage detection means for detecting the voltage value of the external power supply,
The electronic pen according to claim 1, wherein the switch control means changes ON duty control of the step-down chopper circuit for each of a plurality of voltage conditions in accordance with voltage information notified from the voltage detection means.

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