ROAD VEHICLE REAR WINDOW HEATER CIRCUITS

• US 3,858,027 A
• Filed: 03/05/1973
• Issued: 12/31/1974
• Est. Priority Date: 04/07/1972
• Status: Expired due to Term

• Current Assignee: Edward Graham Phillips
• Original Assignee: Edward Graham Phillips
• Inventors: Phillips, Edward Graham
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Shaw, Clifford C.
• Application Number:
  US05/338,221
• Time in Patent Office: 666 Days
• Field of Search: 219/490,507,501,203,492,522 307/293
• US Class Current: 219/203
• CPC Class Codes: H05B 1/0236 for vehicles
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 3/84 Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields

Abstract

A road vehicle rear window heater circuit is operated by a manually operable switch urged to an open position. Closure of the switch charges a capacitor, which controls a bi-stable trigger circuit determining the length of time for which the heater remains on.

Claims

1. A road vehicle rear window heater circuit, which comprises:

a rear window of a road vehicle having rear window heating means associated therewith;

a battery connected to said rear window heating means for supplying electrical energy thereto;

a first switch connected in series between said battery and said rear window heating means; and

timing circuit means connected between said battery and said rear window heating means for selectively actuating said rear window heating means for a predetermined time interval after the closure of said first switch, said timing circuit means comprising;

a second switch which is resiliently urged to an open position;

a capacitor connected to said battery through said second switch and said first switch, said capacitor being charged upon momentary closure of said second switch;

a bistable trigger circuit comprising first and second transistors connected in a Schmitt trigger configuration, the base of said first transistor connected to receive the charge from said capacitor to initially be rendered conductive while said second transistor is rendered non-conductive;

a third transistor connected across said second transistor, said third transistor being initially driven into conduction by a connection through said first switch to said battery;

a relay having a coil, and a pair of contacts connected between said first switch and said heating means, said coil and contacts being actuated by the output from said third transistor for energizing said rear window heating means;

said first transistor being rendered non-conductive after the discharge of said capacitor to thereby render said second transistor conductive and said third transistor non-conductive to thereby deactivate said relay and disconnect said rear window heating means from said battery.