DC motor speed controller having protection

• US 4,873,453 A
• Filed: 10/19/1988
• Issued: 10/10/1989
• Est. Priority Date: 10/27/1987
• Status: Expired due to Fees

• Current Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Hansen, James E., Schmerda, Richard F.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/238,447
• Time in Patent Office: 356 Days
• Field of Search: 307/112, 307/116, 307/130, 388/819, 388/821, 388/822, 388/824, 388/831, 388/833, 388/903, 318/434, 318/599, 320/9, 320/13, 320/39, 320/48
• US Class Current: 307/130
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements
• CPC Class Codes: H02J 7/0063 with circuits adapted for supplying loads from the battery
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02P 7/288 using variable impedance
• CPC Class Codes: Y10S 388/903 Protective, e.g. voltage or current limit

Abstract

A controller for a batter-drive DC motor controls the average motor current by switching a series-connected FET on and off with a pulse-width-modulated gate signal. Motor speed is changed by chaning the duty cycle of the signl, which is generated by an oscillator. An undervoltage protection circuit senses the battery voltage and compares it with a reference system that has hysteresis. An overload protection circuit senses the motor current, integrates the sensed signal, and comprares the result with a Zener reference diode that is connected in an amplifier circuit for positive feedback. The oscillators'"'"'s pulse-width-modulated output, the undervoltage protection circuits'"'"'s output, and the overload protection circuit'"'"'s output are input to a "NOR" Logic gate, whose output drives the gate of the FET.

Claims

1. Speed controller for a DC motor connected in series with a switching device that controls the average DC current of the motor by controlling the switching duty cycle, said switching device having an input control terminal, comprising:

oscillator means for generating an AC signal having controllable duty cycle;

means for communicating said AC signal to said input control terminal of said switching device;

undervoltage protection means for producing an under voltage signal upon occurrence of a low-battery condition below a predetermined threshold voltage level;

override circuit means communicating said undervoltage signal to said input control terminal of said switching device, for turning off said switching device irrespective of the AC signal of said oscillator means upon an undervoltage condition;

and wherein said undervoltage protection means comprises one operational amplifier circuit having;

means for establishing a first battery voltage threshold corresponding to said predetermined threshold voltage level and a second battery voltage threshold which is higher than said first threshold;

means for providing said undervoltage signal when battery voltage is below said first threshold and withholding said undervoltage signal when battery voltage exceeds said second threshold; and

,

means for providing or withholding said undervoltage signal when the batter voltage is between said first and second thresholds, depending upon whether the battery voltage entered between said thresholds when said undervoltage signal was already being provided on already being withheld, respectively;

whereby said operational amplifier circuit performs both (a) a threshold comparator function and (b) a hysteresis function.

2. A speed controller as in claim 1 and wherein said operational amplifier circuit has an inverting input terminal, a non-inverting input terminal, and an output terminal;

and,

said undervoltage protection means comprises battery undervoltage sensing means as follows;

Zener diode means for offsetting the battery voltage, connected from a first terminal having the battery voltage of a first polarity to a first resistance whose other end is connected with a second terminal having the battery voltage of the other polarity;

resistor means connected with the junction between said Zener diode and said first resistance for conducting current to the inverting input of said operational amplifier circuit;

diode means connected for conventional current conduction from said inverting input terminal to said non-inverting input terminal;

resistive bias means connected with said non-inverting input terminal for threshold biasing of said non-inverting input terminal; and

resistive feedback means connected from said output terminal to said non-inverting input terminal for feeding back hysteresis offset from said output terminal to affect the threshold voltage level of said undervoltage protection means.