Patent ID: 8773404
Filing Date: 2014-07-08
Classification: G06F

Abstract:
1. An electromagnetic pen, comprising: a reference induction and a reference capacitor, which are connected with each other in parallel in a housing of the electromagnetic pen and configured to transmit an electromagnetic signal in a handwritten frequency; and at least one control capacitor, which is connected with the reference capacitor in parallel; each of the control capacitors is respectively connected with one control switch in series, and the control switch is on or off for connection or disconnection between the control capacitor and the reference capacitor, thereby an electromagnetic signal in a control frequency can be transmitted; wherein the reference inductance and the reference capacitor, which are connected with each other in parallel, are connected with a power supply circuit, and a power control loop is connected in the power supply circuit, the power control loop comprises: a boost unit, which connects the reference inductance and the reference capacitor with the power supply circuit, is configured to carry out a boost processing for the voltage of the battery to obtain a normal working voltage of the electromagnetic pen which can drive the reference inductance and reference capacitor to transmit the electromagnetic signal when the boost function of the boost unit is enabled; a first transistor, which is connected with the boost unit and configured to generate and transmit an enable signal to the boost unit when the first transistor is turned on and the emitter of the first transistor outputs a high level to the enable signal, thereby a boost function of the boost unit is enabled; a second transistor, which is connected with the base of the first transistor and configured to turn on the first transistor when the second transistor is turned on and the collector of the second transistor output a low level to the base of the first transistor, the first transistor and second transistor are both active switching elements; and at least one charging and discharging capacitor, which is connected in the power supply circuit through any of the control switches, and configured to be charged by the power supply circuit when any of the control switches is on, and supply power to the base of the second transistor and turn on the second transistor, the charging and discharging capacitor can maintain supplying power to keep the second transistor being turned on for a maintaining time when all of the control switches are off, the maintaining time can be determined by selecting the capacitance value of the charging and discharging capacitor; if none of the control switches is turned on again during the maintaining time, as a result of the charging and discharging capacitor discharging, the second transistor can be automatically turned off and output a high level which turns off the first transistor, so the emitter of the first transistor outputs a low level to the enable signal, thereby the boost unit cannot carry out a boost processing for the voltage of the battery, and the reference inductance and reference capacitor stop transmitting the electromagnetic signal.