TIME-AT-TEMPERATURE A-C REFLOW SOLDERING POWER SUPPLY

• US 3,778,581 A
• Filed: 08/03/1972
• Issued: 12/11/1973
• Est. Priority Date: 08/03/1972
• Status: Expired due to Term

• Current Assignee: Bradley J. Denny
• Original Assignee: Bradley J. Denny
• Inventors: Denny, Bradley J.
• Primary Examiner(s): Albritton, C. L.
• Application Number:
  US05/277,849
• Time in Patent Office: 495 Days
• Field of Search: 219/85,110,111 317/40
• US Class Current: 219/85.18
• CPC Class Codes: B23K 3/0478 comprising means for controlling or selecting the temperature or power
• CPC Class Codes: G05D 23/22 the sensing element being a thermocouple

Abstract

An improved a-c power supply for use in a reflow soldering system is disclosed. The output from a thermocouple attached to the heater bar is amplified and compared to a preset reference voltage. This controls the rate at which a-c current is fed to the heater and thus controls the heater temperature. A timing circuit synchronized to the line frequency is activated when the heater temperature reaches its preset value. A fail-safe shutdown circuit is provided to disable the output should one of the thermocouple leads break. Furthermore, should the heater not reach the desired temperature within a reasonable time, the power is turned off, thereby protecting the circuit elements in the event of a shorted heater or cabling to the heater.

Claims

1. In a reflow soldering system, the combination comprising:

a heater bar;

a thermocouple attached to said heater bar;

reference means for providing a reference output corresponding to a desired heater bar temperature;

comparison means for comparing the output from said thermocouple with said reference ouput;

regulating means responsive to said comparison means for controlling the rate at which current is supplied to the heater bar;

timing means responsive to said comparison means for controlling the length of time during which current is supplied to said heater bar;

detection means for detecting a failure in said thermocouple; and

disabling means responsive to said detection means for disabling the supply of current to said heater bar upon detection of a thermocouple failure.

2. In a reflow soldering system, the combination comprising:

a heater bar;

a thermocouple attached to said heater bar;

reference means for providing a reference output corresponding to a desired heater bar temperature;

comparison means for comparing the output from said thermocouple with said reference output;

regulating means responsive to said comparison means for controlling the rate at which current is supplied to said heater bar;

timing means responsive to said comparison means for controlling the length of time during which current is supplied to said heater bar; and

disabling means for disabling the supply of current to said heater bar in response to the failure of said thermocouple output to attain a preset value within a preset period of time.

3. In an a-c power supply for use in a reflow soldering system having a heater bar maintained at a potential close to ground, a thermocouple mechanically and electrically connected to said heater bar, and a welding head:

means for preselecting heater bar temperature;

means for preselecting '"'"''"'"''"'"''"'"'time-at-temperature;

'"'"''"'"''"'"''"'"' means for preselecting a power range appropriate to the size of the heater bar in use; and

means for indicating normal and abnormal operation of said system including means for detecting a failure in said connection between said thermocouple and said heater bar evidenced by the output of said thermocouple assuming a potential essentially equal to that of a bias potential connected to said thermocouple output via a bias resistor.