DC motor speed controller having protection
First Claim
1. A 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, said speed controller comprising:
- oscillator means for generating a pulsating DC signal of controllable duty cycle;
means for communicating said pulsating DC signal to said input control terminal of said switching device to control the average DC current of the motor;
overload protection means for turning off said switching device in response to excessive current flow in said motor, said overload protection means comprising;
current sensing means for sensing during at least the on portion of said duty cycle and for producing a signal indicative of the motor current;
comparator means responsive to the signal from said current sensing means for comparing said signal with a predetermined reference and outputting an overload signal upon occurrence of an overload;
first override circuit means communicating said overload signal to said input control terminal of said switching device, for turning off said switching device irrespective of the pulsating DC signal of said oscillator means;
wherein said comparator means comprises integration means for integrating said motor current sensing means signal;
wherein said motor current sensing means comprises resistor means for developing a voltage drop and having terminals and connected in series with said switching device;
said comparator means comprises amplifier means having inverting and non-inverting inputs, gain, and an output;
wherein each of the voltage drops at terminals of said resistor means is communicated to one of the inverting and non-inverting inputs of said comparator means; and
,wherein said amplifier means comprises one operational amplifier arranged to perform all of the functions of (a) amplification of the difference between said voltage drops at said resistor means terminals, (b) integration for achieving noise reduction and time delay of said difference, and (c) latching of the overload protection means in an overload signal condition, starting upon occurrence of the overload signal condition, until unlatched.
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Accused Products
Abstract
A controller for a battery-driven 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 changing the duty cycle of the signal, 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 compares the result with a Zener reference diode that is connected in an amplifier circuit for positive feedback. The oscillator'"'"'s pulse-width-modulated output, the undervoltage protection circuit'"'"'s output, and the overload protection circuit'"'"'s output are input to a "NOR" logic gate, whose output drives the gate of the FET.
47 Citations
5 Claims
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1. A 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, said speed controller comprising:
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oscillator means for generating a pulsating DC signal of controllable duty cycle; means for communicating said pulsating DC signal to said input control terminal of said switching device to control the average DC current of the motor; overload protection means for turning off said switching device in response to excessive current flow in said motor, said overload protection means comprising; current sensing means for sensing during at least the on portion of said duty cycle and for producing a signal indicative of the motor current; comparator means responsive to the signal from said current sensing means for comparing said signal with a predetermined reference and outputting an overload signal upon occurrence of an overload; first override circuit means communicating said overload signal to said input control terminal of said switching device, for turning off said switching device irrespective of the pulsating DC signal of said oscillator means; wherein said comparator means comprises integration means for integrating said motor current sensing means signal; wherein said motor current sensing means comprises resistor means for developing a voltage drop and having terminals and connected in series with said switching device; said comparator means comprises amplifier means having inverting and non-inverting inputs, gain, and an output; wherein each of the voltage drops at terminals of said resistor means is communicated to one of the inverting and non-inverting inputs of said comparator means; and
,wherein said amplifier means comprises one operational amplifier arranged to perform all of the functions of (a) amplification of the difference between said voltage drops at said resistor means terminals, (b) integration for achieving noise reduction and time delay of said difference, and (c) latching of the overload protection means in an overload signal condition, starting upon occurrence of the overload signal condition, until unlatched. - View Dependent Claims (2)
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3. A 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, said speed controller comprising:
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oscillator means for generating a pulsating DC signal of controllable duty cycle; means for communicating said pulsating DC signal to said input control terminal of said switching device to control the average DC current of the motor; overload protection means for turning off said switching device in response to excessive current flow in said motor, said overload protection means comprising; current sensing means for sensing during at least the on portion of said duty cycle and for producing a signal indicative of the motor current; comparator means responsive to the signal from said current sensing means for comparing said signal with a predetermined reference and outputting an overload signal upon occurrence of an overload; first override circuit means communicating said overload signal to said input control terminal of said switching device, for turning off said switching device irrespective of the pulsating DC signal of said oscillator means; latching overload protection means comprising an operational amplifier means and a Zener diode means connected from the terminal output to the non-inverting input terminal of the operational amplifier means and polarized for conduction of conventional current in a breakdown mode from said output terminal to said non-inverting input terminal; whereby said Zener diode means in conjunction with the gain of said operational amplifier means serves both (a) as an overload reference threshold, and also (b) as a latch to supply current to said non-inverting input terminal and maintain said operational amplifier means in a latched state after said threshold is exceeded. - View Dependent Claims (4)
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5. A 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, said speed controller comprising:
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(A) oscillator means for generating a pulsating DC signal having a controllable duty cycle; (B) battery undervoltage protection means for sensing the battery supply voltage and producing an undervoltage signal when it is below a threshold; (C) overload protection means for sensing the current in said switching device and producing an overload signal when the time integral of said current exceeds a predetermined threshold, and for latching said overload signal on until it is affirmatively unlatched thereafter; and (D) logic means combining said pulsating DC signal from (A), said undervoltage signal from (B), and said overload signal from (C), for providing control signals to said input control terminal of said switching device as follows; a signal of controllable duty cycle when both said undervoltage signal from (B) and said overload signal from (C) are absent; and
,a turn-off signal when either or both of said signals from (B) and (C) is present, irrespective of said pulsating DC signal from A; wherein said logic means comprises "NOR" logic circuitry for combining said signals from (A), (B) and (C); whereby the average DC current of the motor is controlled in accordance with said duty cycle when neither an undervoltage or an overload signal exists, and the motor current is turned off in response to an undervoltage or overload condition.
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Specification