ELECTRIC BLANKET CONTROL

• US 3,597,590 A
• Filed: 02/12/1969
• Issued: 08/03/1971
• Est. Priority Date: 02/12/1969
• Status: Expired due to Term

• Current Assignee: Bobby R. Fleming
• Original Assignee: Bobby R. Fleming
• Inventors: Fleming, Bobby R.
• Application Number:
  US04/798,722
• Time in Patent Office: 902 Days
• US Class Current: 219/501
• CPC Class Codes: G05D 23/1909 whose output amplitude can only take two discrete values
• CPC Class Codes: G05D 23/2401 using a heating element as a sensing element
• CPC Class Codes: H05B 1/0272 For heating of fabrics
• CPC Class Codes: H05B 3/34 flexible, e.g. heating nets or webs

Abstract

An electronic control for an electric blanket or other heated device in which the heating element of the blanket senses the ambient temperature and the other elements of the control are separated from the heating element so that the components of the control are less susceptible to sensing change in ambient temperature near the blanket. The electronic control circuit controls current to the heating element of the blanket by gating an SCR at the zero crossings of the applied voltage so as to prevent radiofrequency interference which would occur if the SCR were switched at other than the zero crossings. Unidirectional current means is connected in a bridge circuit which controls the gating of the SCR so that the temperature coefficients of the components in the two legs of the bridge circuit are balanced enhancing temperature compensation.

Claims

1. A control circuit for an electrical heating element comprising a. switching means connected in series with the heating element for connection of a source of AC voltage, b. means for biasing said switching means to provide current conduction through the heating element including 1. circuit means for supplying a biasing voltage including means for advancing the phase of the biasing voltage with respect to the phase of the source of AC voltage, 2. a gating switch circuit connected between a point in said circuit means and said switching means, 3. electrical means comprising a bridge including temperaturesetting means in a leg of said bridge for detecting a temperature change of the heating element and connected to said gating switch for actuation thereof in response to the temperature of the heating element, and 4. means connected in circuit with said electrical detecting means for compensating said detecting means for ambient temperature variations said compensating means comprising a pair of diodes located in series in a leg of said detecting bridge on either side of said temperature-setting means and said diodes being temperature-responsive in compensating mode with respect to each other such that variations in temperature do not affect the temperature setting.

2. a gating switch circuit connected between a point in said circuit means and said switching means,

3. A control circuit according to claim 1 wherein said phase-advancing means includes a capacitor.

4. means connected in circuit with said electrical detecting means for compensating said detecting means for ambient temperature variations said compensating means comprising a pair of diodes located in series in a leg of said detecting bridge on either side of said temperature-setting means and said diodes being temperature-responsive in compensating mode with respect to each other such that variations in temperature do not affect the temperature setting.

5. A control circuit according to claim 4 wherein said gating switch circuit includes a second transistor coacting with the first transistor.

6. A control circuit according to claim 1 including current-limiting means connected in series with the heating element and the source of AC voltage, and a protective diode connected in parallel with the heating element for protecting said load.