# US 8,785,820 B2 · Resonant power supply for use with high inductive loads and method of providing same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,785,820 B2 - Document ID: US8785820B2 - Status: Granted - Kind: B2 - Application number: 12/939,392 - Filed: 2010-11-04 - Published: 2012-05-10 - Granted: 2014-07-22 - Earliest claimed: 2010-11-04 - Assignees: Leco Corporation - Applicants: Ted Casper - Inventors: Ted Casper - Web page: https://patentgrep.com/patent/US8785820B2 ## CPC - F27B 14/06: heated electrically, e.g. induction crucible furnaces with or without any other source of heat (F27B14/04 takes precedence) - F27B 14/08: Details specially adapted for crucible or pot furnaces - F27B 17/02: specially designed for laboratory use - H02M 7/5387: in a bridge configuration - H02M 7/4815: {Resonant converters (H02M7/4811 and H02M7/4826 take precedence)} - Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes - F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract A resonant power supply (900) for use with high inductive loads includes an input rectifier (903) and a switching inverter formed using a plurality of parallel connected half bridge networks for switching the voltage provided from the input rectifier (903). A transformer (927) is used whose primary is connected to the switching inverter and whose secondary is connected to load such as a crucible (931). A capacitor (929) is used in series with the primary of the transformer (927) for resonating the inductance in the secondary circuit at the frequency of the switching inverter to provide maximum power transfer to the crucible (931). ## Claims ### Claim 1 A switching power supply for heating a graphite crucible in an electrode furnace for providing maximum power to a transformer coupled load containing high inductive reactance comprising: a supply of AC voltage; a rectifier circuit converting said AC voltage to a DC voltage; an inverter having an input coupled to said rectifier to receive said DC voltage, said inverter switching said DC voltage at a switching frequency of from 25 kHz to 1 MHz, said inverter having an output; at least one transformer having a primary winding and a secondary winding; a secondary circuit directly connected to said secondary winding, said secondary circuit including an electrode connected to a graphite crucible; and wherein said primary winding is coupled to said output of said inverter by a capacitor coupled in series with said primary winding and the capacitance of said capacitor and switching frequency is selected for providing operating power to said secondary circuit at a resonant frequency of said secondary circuit. ### Claim 2 (depends on 1) The switching power supply as defined in claim 1, wherein said secondary circuit is comprised of said secondary winding, an inductance, and said crucible. ### Claim 3 (depends on 2) The switching power supply as defined in claim 2, wherein said inductance is comprised of electrical leads coupling said transformer secondary winding to said crucible. ### Claim 4 (depends on 1) The switching power supply as defined in claim 1, wherein said inverter is comprised of a plurality of switching devices used to switch said DC voltage. ### Claim 5 (depends on 1) The switching power supply as defined in claim 1, wherein said inverter is comprised of at least one half bridge network used to switch an input voltage. ### Claim 6 (depends on 5) The switching power supply as defined in claim 5, and further comprising: a switching controller operating to conduct one of said switching devices of each of the at least one half bridge at all times. ### Claim 7 (depends on 5) The switching power supply as defined in claim 5, and further comprising a switching controller for operating each of the at least one half bridge network at a substantially fifty percent (50%) duty cycle. ### Claim 8 (depends on 6) The switching power supply as defined in claim 6, wherein the switching controller is adjusted for providing a near unity power factor. ### Claim 9 (depends on 1) The switching power supply as defined in claim 1, wherein an input to the inverter is connected to a filter network for isolating said rectifier circuit from peak currents of the inverter. ### Claim 10 (depends on 1) The switching power supply as defined in claim 1, further comprising an input filter coupled to said rectifier circuit for minimizing harmonic distortion to an AC power source. ### Claim 11 (depends on 1) The switching power supply as defined in claim 1, wherein said graphite crucible has a resistance of about 5.6 milliohms. ### Claim 12 (depends on 1) The switching power supply as defined in claim 1, wherein said resonant frequency is 25 kHz and said capacitor has a capacitance of about 0.5 uF. ### Claim 13 A switching power supply for heating a graphite crucible in an electrode furnace for providing maximum power to the crucible comprising: a supply of AC voltage at a frequency of from 25 kHz to 1 MHz; at least one transformer having a primary winding coupled to said supply and a secondary winding; a secondary circuit directly connected to said secondary winding, said secondary circuit including an electrode connected to a graphite crucible; and wherein said primary winding is coupled in series with a capacitor having a capacitance selected for providing operating power to said secondary circuit at a resonant frequency of said secondary circuit. ### Claim 14 (depends on 13) The switching power supply as defined in claim 13, wherein said secondary circuit is comprised of said secondary winding, an inductance, and said crucible. ### Claim 15 (depends on 14) The switching power supply as defined in claim 14, wherein said inductance is comprised of electrical leads coupling said transformer secondary winding to said crucible. ### Claim 16 (depends on 15) The switching power supply as defined in claim 15, wherein said graphite crucible has a resistance of about 5.6 milliohms. ### Claim 17 (depends on 16) The switching power supply as defined in claim 16, wherein said resonant frequency is 25 kHz and said capacitor has a capacitance of about 0.5 uF.