Timer circuit

• US 4,555,743 A
• Filed: 07/22/1983
• Issued: 11/26/1985
• Est. Priority Date: 07/27/1982
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Tokai RIKA Denki Seisakusho
• Original Assignee: Kabushiki Kaisha Tokai RIKA Denki Seisakusho
• Inventors: Kokubu, Sadao, Sakakibara, Takao, Hirano, Masatoshi
• Primary Examiner(s): EISENZOPF, REINHARD
• Application Number:
  US06/516,363
• Time in Patent Office: 858 Days
• Field of Search: 361/196, 219/203, 219/492, 219/493, 307/600, 307/605, 307/590, 307/592
• US Class Current: 361/196
• CPC Class Codes: H01H 47/18 for introducing delay in the operation of the relay short-circuited conducting sleeves, bands or discs H01H50/46

Abstract

A timer circuit suitable for operating, for a required period of time, the windshield defrosting heater in an automobile, comprises a switch operative only in one direction, such as a momentary unidirection switch, a timer which starts timing operation after a lapse of a predetermined time, and a flip-flop circuit or the like. The switch allows setting and cancelling for timing operation, whereby the operative characteristics are improved and the mechanical design is simplified. Moreover, the use of a flip-flop circuit reduces the occurrence of chattering.

Claims

1. A rear window heater control circuit for an automobile, comprising:

a power source switch;

a first transistor connected to said power source switch so as to become conductive when said power source switch is turned on;

a timer circuit provided between said power source switch and said first transistor, said timer circuit including a capacitor and a resistor, said first transistor having a base connected to said timer circuit;

a second transistor arranged to become conductive when said first transistor becomes conductive;

a bistable circuit including a third transistor and a fourth transistor, said third transistor having a base receiving a bias current from said second transistor;

a normally open momentary switch having a first terminal which is grounded, and a second terminal connected to said power source switch;

a first diode connected between said power source switch and said normally open momentary switch, said first diode having an anode connected to said connection between the base of said first transistor and said time circuit;

a second diode having a cathode connected to said connection between said normally open momentary switch and said first diode and an anode connected to said power source switch;

a relay having a first end connected to said power source switch, and a second end connected to a collector of said fourth transistor,

whereby conductivity of said third transistor and said fourth transistor is reversed to energize said relay upon closing of said normally open switch while said timer circuit starts discharging.