Temperature control for resistance heating element

• US 4,243,875 A
• Filed: 11/13/1978
• Issued: 01/06/1981
• Est. Priority Date: 11/13/1978
• Status: Expired due to Term

• Current Assignee: Daniel C. Chang
• Original Assignee: Daniel C. Chang
• Inventors: Chang, Daniel C.
• Primary Examiner(s): Reynolds, B. A.
• Assistant Examiner(s): Paschal, M.
• Application Number:
  US05/959,809
• Time in Patent Office: 785 Days
• Field of Search: 219/518, 219/497, 219/494, 219/492, 219/501, 219/505, 219/240, 219/241, 219/242, 219/247, 219/257
• US Class Current: 219/497
• CPC Class Codes: B23K 3/033 comprising means for controlling or selecting the temperature or power
• CPC Class Codes: G05D 23/1913 delivering a series of pulses

Abstract

A temperature control system for a resistance element which is heated by a power supply connected to it by a switching member, the switching member being controlled by an electronic circuit which is operative to produce alternate ON-cycles and OFF-cycles whose durations are controlled by separate time constants. The durations of these alternate cycles respectively set the higher and lower temperature limits within which the heating element temperature remains. The electronic circuitry further provides a single initial ON-cycle of greater duration which occurs only when the circuit is newly turned ON and operates to bring the resistance element up to operating temperature from ambient temperature, an indicator being provided to glow during each ON-cycle interval. The control system is illustrated for use with a soldering iron which is supportable in a cradle connected with a switch to turn OFF the system when the iron rests in the cradle.

Claims

1. A control circuit for controlling the temperature of an electric soldering iron including a cradle-operated switch for connecting a power supply to the circuit when the iron is raised from the cradle and disconnecting the supply when the iron rests on the cradle, the control circuit comprising:

(a) an ON/OFF switching member connecting the power supply to the soldering iron and enabling the flow of current thereto when conductive;

(b) a first monostable means having a stable state and a non-stable state and connected to render said ON/OFF switching member conductive when in said non-stable state, said first monostable means having two separate time constants each energizable separately from the other to determine when energized a longer and a shorter duration of said non-stable state;

(c) a second monostable means having a stable state and a non-stable state of constant duration, the first and second monostable means being mutually interconnected and operative so that as each returns to its stable state it triggers the other to begin its non-stable state;

(d) a bistable flip-flop having two stable states and having two output terminals respectively connected to said two separate time constants of the first monostable means, and the flip-flop having separate input terminals for triggering the flip-flop into one or the other of its stable states, one of said inputs being operative upon raising of the iron from the cradle and closing of said switch connecting the power supply to the circuit to energize the longer duration time constant, and the other input being coupled to the first monostable means to be triggered by the return thereof to stable state to trigger the flip-flop to energize the shorter duration time constant as long as the iron remains raised from the cradle, brief manual depressing of the cradle and release thereof actuating said one input to trigger the flip-flop to re-energize the longer time constant and raise the operating temperature of the iron.

2. A control circuit as claimed in claim 1, wherein at least one of said time constants is adjustable to set its duration.