Power control for appliance using high inrush current element

• US 4,334,147 A
• Filed: 02/01/1979
• Issued: 06/08/1982
• Est. Priority Date: 02/01/1979
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Payne, Thomas R.
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): PASCHALL, MARK H
• Application Number:
  US06/008,376
• Time in Patent Office: 1,223 Days
• Field of Search: 219/492, 219/490, 219/485, 219/497, 219/483, 219/501, 219/486, 323/18, 323/24, 323/22, 323/235, 323/238, 307/252 VA, 307/38-41, 363/37, 340/337, 340/146.3 Z
• US Class Current: 219/497
• CPC Class Codes: G05D 23/1913 delivering a series of pulses

Abstract

A power control arrangement for controlling the power output of a resistive heating element of the type having a fast thermal response time and a highly variable resistance with temperature. The power control arrangement includes a plurality of operator selectable power settings and an electronic switching system responsive to operator selection of these settings to rapidly couple and decouple a power supply to the element. The switching action is selected to permit rapid heat up of the element without causing an unacceptable current to flow and to prevent excessive cooling of the element after it reaches operating temperatures during steady state operation.

Claims

1. A power control system for controlling power delivered to a heating element in response to selection of one of a plurality of power control settings including an OFF setting, said settings corresponding to different levels of power applied to said heating element, said element exhibiting a relatively high resistance at high temperatures and a relatively low resistance at low temperatures, at least one of said power level settings operative to deliver power to said element, when at said relatively low temperature, which results in a current level which exceeds an acceptable limit, said power control system including transition detection means operating independently of current and voltage in said element for detecting a transition from said OFF setting to said one power setting, transient control means responsive to said detection means for delivering power to said element for a preselected time at a level lower than that associated with said one power setting, when said transition is detected, said lower power level being sufficiently low that current in the element does not exceed said acceptable limits, and steady state control means for controlling power to said element in accordance with said one setting after expiration of said preselected time.

2. The system recited in claim 1 wherein said preselected time is of sufficient duration to allow the temperature of the heating element energized at said lower level to rise to a temperature at which the current in the element does not exceed said acceptable current limit when said element is energized in accordance with said one selected power setting.

3. The system recited in claim 2 wherein said one setting is operative to apply a first duty cycle power signal to said element, and said transient control means includes means for applying a preselected second duty cycle power signal to said element, said second duty cycle being lower than said first.

4. The combination recited in claim 1 wherein said transition detecting means comprises means for generating a digital control signal representative of selected power settings, memory means for storing said control signals, and means for monitoring the contents of said memory and detecting a change from a control signal representing an OFF setting to a control signal representing said one setting.

5. A power control arrangement for controlling the output power of a resistive heating apparatus energized by a pulsating power supply, in response to a power setting selected by an operator from a plurality of available discrete power settings including an OFF power setting comprising:

a resistive heating element exhibiting a relatively high resistance at relatively high temperatures, which decreases with temperature to a relatively low resistance near room temperature,

means for generating a digital control signal representative of said operator selected power setting,

memory means for storing said digital signal,

electronic switch means for serially connecting said heating element with said power supply,

means responsive to said control signal stored in said memory for generating a signal which switches said switch means between a conductive and a non-conductive mode in a pattern determined by said control signal,

said power settings including at least one power setting operative to apply power to said element at room temperature which would result in current to element which exceeds an acceptable current limit for said electronic switch means,

means operating independently of electrical conditions in said element for detecting the transition to one of said plurality of power control settings from an OFF setting,

and means responsive to the detection of said transition for limiting the power to said element for a preselected time to a level sufficiently low to limit current below said acceptable limit in said element, said low power level being applied independently of said selected power level.

6. The system recited in claim 5 wherein said preselected time is of sufficient duration to allow the temperature of the heating element energized at said lower level to rise to a temperature at which the current in the element does not exceed said desired maximum current limit when said element is energized in accordance with said one selected power setting.

7. In a system employing a heating element and operator selectable power control settings including an OFF power setting, said system adapted in normal operation for coupling to a protective means for disconnecting power to said system in response to the occurrence of a preselected threshold electrical condition and wherein said element exhibits a relatively high resistance at high temperatures and a relatively low resistance at room temperature, an improved power control arrangement for preventing the occurrence of said threshold condition comprising means for detecting a transition to one of said plurality of power control settings from an OFF setting independently of electrical conditions in said element, and means responsive to the detection of said transition for energizing said element for a preselected time at a power level independent of said selected power control setting to prevent the occurrence of said threshold condition.

8. The combination recited in claim 7 wherein said means for detecting said transition comprises:

means for generating a digital control signal representative of said operator selected power settings,

memory means for storing said control signal,

means for monitoring the contents of said memory, detecting a change from a control signal representing an OFF power setting to a control signal representing some other power setting, and generating a signal indicative of the detection of such occurrence.

9. The combination recited in claim 8 wherein said means for energizing said element comprises:

means for applying power to said heating element at a predetermined level independent of said control signal for a predetermined period of time in response to a signal from said monitoring means, and at a level determined by said control signal in the absence of a signal from said monitoring means, whereby a predetermined power level is temporarily substituted for the power level associated with the actual power setting during the brief period immediately following a change from OFF to some other setting.

10. A power control arrangement for controlling the duty cycle of a resistive heating element in response to a power setting selected by an operator from a plurality of available discrete power settings including an OFF power setting comprising:

means for generating a digital control signal representative of said operator selected power setting,

memory means for storing said digital control signal,

a pulsating power supply coupled to said heating element for providing a power signal for energizing said heating element,

electronic switch means serially connected to said heating element and said power supply,

means responsive to the control signal stored in said memory for generating a signal which switches said switch means between a conductive and a non-conductive mode in a pattern determined by said control signal,

test means for monitoring the contents of said memory and generating a signal when said contents represent an OFF power setting;

first latch means responsive to said test means, said first latch means switching to a set state in the presence of said test signal,

second latch means responsive to said first latch means and said memory, said second latch means switching to a set state upon the concurrence of said first latch means being in a set state and the control signal stored in said memory representing a non-OFF power setting,

said triggering means being adapted to trigger said switch means in a predetermined pattern independently of said control signal when said second latch means is in said set state, and

timing means enabled by the set state of said second latch means, and responsive to said trigger means, arranged to count a predetermined number of said trigger signals and reset,

said second latch means being arranged to switch to a reset state upon the completion of said predetermined count by said timing means, whereby a predetermined duty cycle is temporarily substituted for the duty cycle associated with the actual power setting when the power setting is changed from an OFF power setting to some other power setting.

11. An electric cooking appliance comprising an operator control arrangement including a plurality of manually selectable power level settings including an OFF setting, a heating element adapted for connection to a household power supply, means operative in response to selection of said settings to apply different steady state levels of power to said element, said element having a resistance which varies greatly with temperature, the resistance of said element at room temperature being such that the application of power to said room temperature element in accordance with at least one of said settings would result in current to the heating element in excess of an acceptable current threshold condition;

and a power control arrangement responsive to the selection of said one setting subsequent to the OFF setting independently of sensed electrical conditions in said element for applying a preselected average power level to said element lower than the power associated with said one setting for a preselected time to permit the gradual increase in the temperature and resistance thereof without exceeding said threshold condition, whereby after passage of said preselected time power may be applied to said element in accordance with said one setting.

12. The combination recited in claim 11 wherein said power control means rapidly couples and decouples said power supply to said element.

13. The combination recited in claim 12 wherein said supply is a pulsating supply, and said power control means operates to repetitively segment said pulsations into control periods having a preselected number of said pulsations therein, and to apply a preselected number of said pulsations to said element during each control period.