Patent ID: 11964334
Assignee: MAKITA CORPORATION
Field: Machine tools (Mechanical engineering)
Classification: CPC B  H | IPC B  H

Claim 0:
1. An electric powered circular saw comprising:
a circular saw-blade;
a battery including a positive electrode and a negative electrode;
a motor configured to generate a driving force to rotate the circular saw-blade;
a power line connected to the positive electrode;
a ground line connected to a ground, the ground being connected to the negative electrode;
a trigger switch configured to be turned on or off by a user of the electric powered circular saw;
a motor driver connected to the power line, to the ground, and also to the motor, the motor driver being configured (i) to electrically connect the motor to the power line and also to the ground line in response to the trigger switch being ON and (ii) to electrically disconnect the motor from the power line and also from the ground line in response to the trigger switch being OFF;
a shunt resistor on the ground line;
a control circuit configured to output a reference voltage varying signal in response to a voltage varying condition being established, the voltage varying condition being established with the trigger switch being OFF upon an activation of the control circuit;
a reference voltage generation circuit including a PNP transistor, the PNP transistor including a base connected to the control circuit, the PNP transistor being configured (i) to turn on in response to the base receiving the reference voltage varying signal from the control circuit and (ii) to turn off in response to the base not receiving the reference voltage varying signal, the reference voltage generation circuit being configured (i) to generate a reference voltage having a first magnitude in response to the PNP transistor being ON and (ii) to generate the reference voltage having a second magnitude in response to the PNP transistor being OFF, the first magnitude and the second magnitude being larger than zero volts, and the first magnitude being larger than the second magnitude; and
an electric current measurement circuit including an operational amplifier, the electric current measurement circuit being configured (i) to receive the reference voltage and a measured voltage, (ii) to amplify the measured voltage with the operational amplifier, and (iii) to output a voltage sum from the operational amplifier, the measured voltage being generated across the shunt resistor in response to an electric current flowing through the shunt resistor, and the voltage sum corresponding to a sum of (i) the reference voltage received and (ii) the measured voltage amplified.