AC/DC chopper for power tool

A corded/cordless system for power tools, comprising:

• a low-voltage DC power tool operable in a preselected voltage range, said power tool including;
• an exterior, an interior, and a pre-defined interface for mechanically and electrically mating with a power module;
• a motor of a preselected rating having a predetermined minimum inductance and an operating speed;
• and
• a tool module to control the operating speed of the motor;
• and
• a corded chopper power module to convert line power from a source of electric power to a series of voltage pulses having an average DC voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said corded chopper power module mechanically and electrically configured to connect to the source of electric power and to mate with the low-voltage DC power tool, said corded chopper power module including a chopper circuit operable at a predetermined switching frequency, in response to said tool module, to convert the line power to said series of voltage pulses having a duty cycle, said voltage pulses being averaged across the motor predetermined minimum inductance, thereby applying the average DC voltage to the motor.

A corded/cordless system for power tools, comprising:

• a low-voltage DC power tool operable in a preselected voltage range, said power tool including;
• an exterior, an interior, a pre-defined interface for mechanically and electrically mating interchangeably with a power module;
• a motor of a predetermined rating having a predetermined minimum inductance;
• and
• a tool control to control the operating speed of the motor;
• and
• a source power module to convert electric power from a source of electric power to a series of voltage pulses having an average DC motor voltage in the preselected voltage range suitable for powering the low-voltage DC power tool, said source power module mechanically and electrically configured to connect to the source of electric power and to mate with the low-voltage DC power tool, said source power module including a filterless chopper circuit operable at a predetermined switching frequency, in response to said tool control, to convert the electric power to the series of voltage pulses having a pulse width, said voltage pulses being averaged across the motor predetermined minimum inductance, thereby applying the average DC motor voltage to the motor.

A method of supplying power to a DC power tool operable in a preselected voltage range, said power tool including exposed surfaces and a DC motor having a winding inductance, the method comprising the steps of:

• determining the winding inductance of the motor;
• providing electrical power from a source of power;
• converting the electrical power to a series of voltage pulses having a duty cycle, an average voltage, and a predetermined operating frequency;
• selecting the operating frequency of the voltage pulses to correspond with the winding inductance of the motor;
• setting the duty cycle of the voltage pulses such that the average voltage is within the preselected range suitable for powering the DC motor;
• coupling the series of voltage pulses to the DC motor, whereby the motor is powered from the source of electric power.