Resistive heating control system and method that is functional over a wide supply voltage range

• US 5,483,149 A
• Filed: 10/28/1993
• Issued: 01/09/1996
• Est. Priority Date: 10/28/1993
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Barrett, Tony
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/144,597
• Time in Patent Office: 803 Days
• Field of Search: 323/299, 323/300, 323/235, 323/236, 323/237, 323/239, 323/241, 323/319, 323/320, 323/322, 323/324, 363/142, 363/143
• US Class Current: 323/300
• CPC Class Codes: G05D 23/1913 delivering a series of pulses

Abstract

This present invention takes advantage of the understanding that the voltage rating associated with resistive heating element can be ignored over the common line voltage range, provided the power dissipation is controlled. This is accomplished by applying a fractional amount of power to a heating element from the power source. The method consists basically of determining, or estimating, a ratio of the amount to be applied to the amount of power available. A control signal is generated with a duty cycle approximately equal to that ratio. A zero crossing switch, under control of the control signal switches half cycles to the heating element. Thus, by applying a portion of the available half cycles to the heating element, the average power dissipation by the heating element can be controlled.

Claims

1. An apparatus for regulating an amount of power a heating element consumes, said heating element being designed to operate at a first RMS voltage, said apparatus comprising of:

a main power supply generating an output voltage, said output voltage having an RMS value between said first RMS voltage and a second RMS voltage, said first RMS voltage being less than said second RMS voltage, said output voltage from said main power supply being periodically varying;

zero crossing detector for detecting a zero crossing of said output voltage where said zero crossing occurs between positive and negative half cycles of said output voltage;

signal generator means for generating a control signal, said control signal having a first state and a second state, a ratio of said first state and said second state being a function of said first RMS voltage and said output voltage, said signal generator means changing said control signal between said first state and said second state only when said zero crossing detector detects said zero crossing; and

switch arranged to receive said control signal from said signal generator means, said switch connecting said output voltage from said main power supply to said heating element when said control signal is in said first state.

2. An apparatus as claimed in claim 1 wherein said signal generator means further comprising voltage sensing means for sensing said output voltage and generating a voltage level signal that is proportional to said output voltage, said generator means using said voltage level signal to determine said ratio.

3. An apparatus as claimed in claim 2 wherein said signal generator means is a microcomputer arranged to receive said voltage level signal, as a function of said voltage level signal, said microcomputer determines said ratio and based on said ratio, said microcomputer generates said control signal with said ratio.

4. A method for regulating a first amount of power consumed by a heating element said method comprising the steps of:

receiving output power from a main power supply, said output power being between said first amount of power and a second amount of power, said second amount of power being greater than said first amount of power, said main power supply generating an output voltage, said output voltage from said main power supply being periodically varying;

determining a ratio of said first amount of power to said output power;

generating a control signal, said control signal having a first state and a second state, a duty cycle of said first state and said second state being a function of said ratio;

detecting a zero crossing of said output voltage of said main power supply where said zero crossing occurs between positive and negative half cycles of said output voltage; and

allowing said output power to flow from said main power supply to said heating element when said control signal is in said first state and said step of detecting detects said zero crossing, said step of allowing interrupts said output power flow from said main power supply to said heating element when said control signal is in said second state and said step of detecting detects said zero crossing.

5. A method for regulating power consumed by a heating element, said method comprising the steps of:

receiving an output voltage from a main power supply, said output voltage having an RMS value between a first RMS voltage and a second RMS voltage, said second RMS voltage being greater than said first RMS voltage, said output voltage from said main power supply being periodically varying;

determining a ratio of said first RMS voltage to said output voltage;

generating a control signal having a first state and a second state, a duty cycle of said first state and said second state being a function of said ratio;

detecting a zero crossing of said output voltage where said zero crossing occurs between positive and negative half cycles of said output voltages; and

connecting said main power supply to said heating element when said control signal is in said first state and said step of detecting detects said zero crossing, said step of connecting disconnects said main power supply from said heating element when said control signal is in said second state and said step of detecting detects said zero crossing.