Ion nitriding power supply

• US 4,733,137 A
• Filed: 03/14/1986
• Issued: 03/22/1988
• Est. Priority Date: 03/14/1986
• Status: Expired due to Term

• Current Assignee: Warner Power, LLC (Worthington Enterprises, Inc.)
• Original Assignee: Walker Magnetics Group, Inc. (IMI Holding Corp.)
• Inventors: Dunham, Richard M.
• Primary Examiner(s): Chatmon, Saxfield
• Application Number:
  US06/839,527
• Time in Patent Office: 739 Days
• Field of Search: 315/307, 315/308, 315/224, 315/DIG. 5, 315/DIG. 7, 315/291, 315/306, 315/111.21, 315/111.81, 363/17, 363/58, 363/132
• US Class Current: 315/291
• CPC Class Codes: C23C 14/48 Ion implantation
• CPC Class Codes: C23C 8/36 using ionised gases, e.g. ionitriding
• CPC Class Codes: H01J 37/32018 Glow discharge
• CPC Class Codes: H02M 1/008 Plural converter units for generating at two or more independent and non-parallel outputs, e.g. systems with plural point of load switching regulators
• CPC Class Codes: H02M 3/1555 for the generation of a regulated current to a load whose impedance is substantially inductive
• CPC Class Codes: H02M 7/5387 in a bridge configuration

Abstract

In the ion nitriding power supply disclosed herein, power to the discharge chamber is normally current-regulated by a pulse-width modulated current switching device effectively in series with a switching inverter which energizes the chamber, instantaneous current variations being smoothed by a series inductance which, together with the chamber, is shunted by a freewheeling diode. Incipient arcing is quickly extinguished by semiconductor switching devices incorporated in the inverter which, when energized simultaneously, shunt the chamber, instantaneous current limiting being provided by the series inductance. The shunt switching devices are triggered when the voltage across the discharge drops below a level indicative of the formation of an arc.

Claims

1. Apparatus for powering a gaseous discharge device, said apparatus comprising:

a bridge of switching devices, said bridge having a pair of d.c. input terminals and a pair of a.c. output terminals;

a high frequency step-up transformer, the primary of which is connected to the a.c. output terminals of said bridge;

high voltage rectifier means for driving a gaseous discharge from the secondary of said step-up transformer;

at least one inductor;

at least one current switching means;

means connecting said current switching means, said inductor and the input terminals of said bridge in series across said d.c. supply;

at least one diode connected across said inductor and said bridge input terminals but not said current switching means for freewheeling inductive current;

means for sensing the current drawn by a discharge fed by said high voltage rectifying means;

means responsive to said current sensing means for pulse width modulating the conduction of said current switching means;

means, operative in a first state for driving the switching devices in said bridge in alternating patterns of conduction phases for converting d.c. power to a.c. power at a frequency which is substantially higher than a.c. line frequency and operative in a second state for driving all of said switching devices into conduction thereby to effectively shunt said a.c. output terminals;

means for sensing the voltage across a discharge fed by said high voltage rectifier means; and

means responsive to said voltage sensing means for switching said driving means from said first state to said second state if the discharge voltage drops below a level indicative of the forming of an arc.

2. Apparatus as set forth in claim 1 wherein the switching devices in said bridge are operated in pairs and wherein the means for driving the switching devices is an a.c. duty cycle controller which, in said first state, operates to turn off each pair of said switching devices during a preselectable portion of a corresponding half cycle of the controller cycle, both pairs of switching devices being conducting during the times between said portions.

3. Apparatus as set forth in claim 1 wherein said means for pulse width modulation comprises means for turning said current switching device off when the current through said series circuit rises above a preselected threshold and means for turning said current switching device on at preselected intervals provided the current through said series circuit has fallen below a second preselected threshold lower than the first said preselected threshold.

4. Apparatus for powering a gaseous discharge device, said apparatus comprising:

a plurality of transistors interconnected in a bridge inverter configuration having a pair of d.c. input terminals and a pair of a.c. output terminals, said transistors being operable in pairs;

a high frequency step-up transformer, the primary of which is connected to the a.c. output terminals of said bridge;

high voltage rectifier means for driving a gaseous discharge device with d.c. derived from the secondary of said step-up transformer;

a plurality of inductors;

a corresponding plurality of current switching means, one for each inductor;

means connecting each current switching means and its respective inductor in series with the input terminals of said bridge across said d.c. supply;

a corresponding plurality of diodes, each diode being connected across an inductor and said bridge input terminals but not across the respective current switching means for freewheeling inductive current when the respective current switch means is turned off;

respective means for sensing the current drawn through each inductor;

respective means for turning each switching means off when the current through the respective inductor rises above a preselected threshold;

respective means for turning each switching means on at preselected intervals provided the current through the respective inductor has fallen below a preselected threshold lower than said first;

means, operative in a first state for driving the transistors in said bridge in alternating patterns of conduction phases for converting d.c. power to a.c. power at a frequency which is substantially higher than a.c. line frequency and operative in a second state for driving all of said transistors into conduction thereby to effectively shunt said a.c. output terminals;

means for sensing the voltage across a discharge fed by said high voltage rectifier means; and

means responsive to said voltage sensing means for switching said driving means from said first state to said second state if the discharge voltage drops below a level indicative of the forming of an arc.

5. Apparatus as set forth in claim 4 wherein the means for driving the transistors is an a.c. duty cycle controller which, in said first state, operates to turn off each pair of transistors during a preselectable portion of a corresponding half cycle of the controller cycle, both pairs of transistors being conducting during the times between said portions.

6. An ion nitriding system comprising:

a high voltage supply;

chamber means defining a gaseous discharge environment;

at least one inductance;

at least one current switching means;

means connecting said current switching means, said inductance, and said chamber means effectively in series across said supply;

means for sensing the current drawn by said chamber means;

means responsive to said current sensing means for pulse width modulating the conduction of said current switching means to maintain said current at a preselectable value;

at least one diode effectively connected across said inductor and said chamber means, but not across said current switching device, for freewheeling inductive current when said switching device is turned off;

switch means for selectively shunting said chamber means;

means for sensing the voltage across a discharge in said chamber means; and

means responsive to said voltage sensing means for actuating said switch means to effectively short said chamber means if the voltage across the discharge drops below a level indicative of the forming of an arc.

7. A system as set forth in claim 6 wherein said chamber means is coupled to said series connecting means through a step-up transformer said switch means shunts said chamber means by shorting the primary winding of said transformer.

8. A system as set forth in claim 7 wherein said switch means comprises a plurality of transistors interconnected in a bridge inverter configuration for converting current obtained from said supply to a relatively high frequency a.c. for energizing the primary winding of said step-up transformer.

9. Apparatus for powering a gaseous discharge device, said apparatus comprising:

a step-up transformer;

a d.c. supply;

an inductor;

a bridge switching circuit comprising four current switching devices interconnected to provide reversing through the primary winding of said transformer of current obtained from said supply through said inductor, the current flowing through the primary in one direction when only a first pair of devices are turned on and in the opposite direction when only a second pair of devices are turned on;

cyclically operating duty cycle control means for turning off each pair of said current switching devices during a preselectable portion of a corresponding half of the operating cycle of said control means, both pairs of said switching devices being conductive during the times between said portions; and

means operative during said portions of the operating cycle of said control means for turning all of said devices on if the output voltage drops below a level indicative of arcing.

10. Apparatus as set forth in claim 9 further comprising means for sensing the current drawn by a gaseous discharge fed by said rectifier means and means controlled by said sensing means for duty cycle modulating the current provided to said transformer primary.