Power supply with thermistor precharge and protection circuit

• US 6,153,851 A
• Filed: 07/02/1997
• Issued: 11/28/2000
• Est. Priority Date: 01/16/1996
• Status: Expired due to Term

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Illinois Tool Works Inc.
• Inventors: Schneider, Joe
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US08/886,801
• Time in Patent Office: 1,245 Days
• Field of Search: 219/121.54, 219/121.53, 219/121.57, 219/121.39, 219/121.45, 361/102-109, 361/6-12
• US Class Current: 219/121.54
• CPC Class Codes: B23K 10/006 Control circuits therefor circuits for plasma torches H05H1/36
• CPC Class Codes: B23K 9/1043 characterised by the electric circuit B23K9/1012 takes precedence
• CPC Class Codes: H02M 3/155 using semiconductor devices only
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel

Abstract

A power supply with an input protection circuit is disclosed. The protection circuit includes a thermistor that heats up if the power supply is mistakenly connected to an excessive input voltage. When the thermistor gets hot, its resistance increases, and isolates the down stream portion of the power supply from the input voltage. A relay in parallel with the thermistor is closed, thus shorting the thermistor, after a preset time if the input voltage had a proper magnitude.

Claims

1. A plasma cutting power supply that receives an input voltage and provides an arc output having an input protection circuit that comprises a thermistor in series with the input voltage, wherein the protection circuit is in electrical communication with the input voltage and wherein in the event an excess input voltage is applied the thermistor increases in resistance and electrically isolates the input voltage from a portion of the power supply downstream from the protection circuit, wherein the protection circuit includes a relay in parallel with the thermistor, wherein the relay is closed after a predetermined period of time after the application of power in the event the thermistor does not electrically isolate the input voltage.

2. The apparatus of claim 1 wherein the protection circuit is part of a precharge circuit.

3. A plasma power cutting supply that provides an arc output and includes an input protection means for disconnecting the input voltage from the power supply in the event that excess voltage is applied, wherein the protection means includes means for increasing in resistance in response to excess input voltage, wherein the thermistor means includes a relay in parallel with the thermistor, wherein the relay is closed after a predetermined period of time after the application of power in the event the thermistor does not disconnect the input voltage.

4. A arc welding power supply that receives an input voltage and provides an arc output having an input protection circuit comprising a thermistor in series with the input voltage, wherein the protection circuit is in electrical communication with the input voltage and wherein in the event an excess input voltage is applied the thermistor increases in resistance and electrically isolates the input voltage from a portion of the power supply downstream from the protection circuit, wherein the protection circuit includes a relay in parallel with the thermistor, wherein the relay is closed after a predetermined period of time after the application of power in the event the thermistor does not electrically isolate the input voltage.

5. The apparatus of claim 4 wherein the protection circuit is part of a precharge circuit.

6. A welding power supply that provides an arc output and includes an input protection means for disconnecting the input voltage from the power supply in the event that excess voltage is applied, wherein the protection means includes means for increasing in resistance in response to excess input voltage, wherein the thermistor means includes a relay in parallel with the thermistor, wherein the relay is closed after a predetermined period of time after the application of power in the event the thermistor does not disconnect the input voltage.