US2979669A - Circuit arrangement for a high frequency furnace - Google Patents

Circuit arrangement for a high frequency furnace Download PDF

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Publication number
US2979669A
US2979669A US588899A US58889956A US2979669A US 2979669 A US2979669 A US 2979669A US 588899 A US588899 A US 588899A US 58889956 A US58889956 A US 58889956A US 2979669 A US2979669 A US 2979669A
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Prior art keywords
circuit
coil
voltage
anode
resonant
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US588899A
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English (en)
Inventor
Blok Lourens
Ruiter Jacob Willem De
Sytsma Sijtze Johanne Cornelis
Zwanenburg Gooitzen
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/04—Sources of current
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
    • H03B5/08—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance
    • H03B5/10—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being vacuum tube

Definitions

  • the present invention relates to high frequency furnace circuit arrangements. More particularly, the invention relates to high-frequency furnaces of high power, for example of l kilowatt or more, which are provided with a grid-controlled output tube having a resonant circuit connected in the anode circuit, the coil of the resonant circuit being coupled to a coupling coil connected in the load circuit.
  • the anode voltage of the output tube is taken from an anode voltage supply source one end of which is connected to ground.
  • High-frequency furnaces of this kind are used in practice both for dielectric and for inductive heating.
  • the resonant circuit in a high-frequency fur nace of the kind described in the preamble, is provided with a tapping point connected to ground.
  • the anode and cathode of the tube are connected each to one of two points of the resonant circuit situated on either side of the tapping point; said points being each at approximately one half of the circuit alternating voltage.
  • both the anode and the cathode are connected to the anode voltage supply source through a high-frequency choke coil.
  • the alternating voltage produced at the circuit ends with respect to ground is approximately halved; hence, the output transformers have to satisfy reduced requirements only with respect to insulation and this permits not only the use of a cheaper construction, but also of a smaller spacing between the resonant-circuit coil and the coupling coil, which enables the leakage losses to be materially reduced in practice.
  • the grounded tapping point on the resonant circuit is the grounded tapping point on a capacitive voltage divider connected between the circuit ends.
  • Fig. 1 is a schematic diagram of an embodiment of circuit arrangement of a known high-frequency furnace
  • Fig. 2 is a schematic diagram of an embodiment of a circuit arrangement of a high-frequency furnace in accordance with the invention
  • Fig. 3 is a modification of the circuit arrangement of Fig. 2;
  • Fig. 4 is a schematic diagram of a preferred embodiment" of a circuit arrangement of a high frequency furnace of the present invention.
  • the high-frequency heating energy is taken from an electron-tube oscillator comprising a triode 1.
  • the tuned anode circuit of the oscillator which is connected in a Colpitts circuit, is provided with a resonant circuit 2 which determines the oscillator frequency and comprises a coil 3 and a circuit capacity constituted by a capacitive voltage divider comprising a capacitor 4 and a three-electrode capacItor 5 connected in series therewith.
  • the anode of the triode 1 is coupled through a blocking capacitor 6 to that end of the capacitor 4 which is connected to the resonant-circuit coil 3 and also, through a high-frequency choke 7, to an anode-voltage supply source 8, one end of which is connected to ground and which is shunted by a smoothing capacitor 9.
  • a grid capacitor 10 and a leakage resistor 11 the control grid of the triode 1 is connected to a tapping point on the capacitor 5, which tapping point is constituted by the middle one of the three electrodes.
  • the grounded tube cathode is connected to a junction of the capacitors 4 and 5, which junct'on is approximately the electrical middle of the resonant circuit 2.
  • FIG. 2 A high-frequency furnace in accordance with the invention will now be described in detail with reference to Fig. 2.
  • Fig. 2 parts similar to those in Fig. l are designated by like reference numerals.
  • the high-frequency furnace shown in Fig. 2 contains a directly heated triode 1 which is supplied from an anode voltage source 8 which is shunted by a smoothing capacitor 9.
  • the cathode-filament current for the tube is taken from an alternating voltage supply source (not shown) and supplied to the tube filament through input terminals 17, 17' and a filament current transformer 18.
  • the triode 1 is again connected as a Colpitts oscillator; the anode circuit contains an anode resonant circuit 19 having a coil 20 which is shunted by a capacitive voltage divider comprising capacitors 21 and 22 which form part of the circuit capacitance.
  • the voltage produced across the capacitor 22 is supplied as a feedback voltage, through a grid capacitor 10, to the control-grid of the tube.
  • the anode circuit is inductively coupled to a load circuit 13, through a coupling coil 12, .which, together with the resonant-circuit coil 20, constitutes an output transformer.
  • the resonant circuit in order to reduce to a minimum the requirements to be satisfied by the output transformer 20, 13' with respect to insulation, and consequently the leakage losses, is provided with a tapping point connected to ground.
  • the anode and cathode of the tube areconnected each to one of two points of the resonant circuit situated on either side of the grounded tapping point, which points are each at about one half of the circuit alternating voltage.
  • both the anode and the cathode of the oscillator tube are connected to the anode voltage I supply source through a high-frequency choke coil.
  • the coil 20 is provided with a grounded center tapping point 23.
  • the anode of the triode 1 is coupled, through a blocking capacitor 6, to the junction of the capacitor 21 and the coil 20 and also, through the high-frequency choke 7, to the anode voltage Supply source 8.
  • the cathode of the triode 1 is connected to the tapping point on the voltage divTder 21, 22 and also, through filament-current leads 24, 24' having chokes 25 and 25 connected in them, to the secondary winding 26 of the filament current transformer 18.
  • the transformer 18 is shunted by two series-connected capacitors 27, 27, the junction of which is connected to ground.
  • the grounded connecting terminal of the anode voltage supply source 8 is connected to the middle, of the secondary'winding 26 of the filament current transformer 18.
  • the triode 1 has an anode direct voltage of about 12 kilovolts suppliedto it, with an alternating voltage of, for example, 1 kilovolt set up across the capacitor 22, the total circuit voltage may be about 13 kilovolts.
  • the alternating voltage at the circuit ends, however, in this case is only about 6 /2 kilovolts with respect to ground,
  • the voltage between the circuit-coil and the coupling coil is about halved as compared with the known circuit arrangements, so that a corresponding reduction of the insulation requirements is achieved.
  • the circuit-coil to coupling-coil spacing can be made considerably smaller in order to reduce the leakage losses of the output transformer.
  • the high-frequency furnace shown in Fig. 2 is provided with a startstop switch 28 connected in the control-grid circuit.
  • the switch 28 connects the conrolgrid of the triode 1, through the series combination of a, high-frequency choke coil 29 and a grid resistor ll, to ground, so that oscillating is produced.
  • the grid resistor 11 is shunted by a bypassing capacitor 30 in order to bypass it with respect to high-frequency voltages.
  • the control-grid circuit is connected to a negative grid-bias source 31, so that the triode 1 is cut ofi.
  • Fig. 3 is an alternative embodiment of the high-frequency furnace of Fig. 2. Similar elements are again designated by like reference numerals.
  • the embodiment shown in Fig. 3 contains a directly heated triode 1 connected as an oscillator.
  • the anode circuit of the triode 1 is provided with a resonant circuit 32 comprising a coil 33 which, together with thecoupling coil 12 connected in the load circuit 13, constitutes an output transformer which is made variable for load matching.
  • the resonant circuit 32 is again provided with a grounded tapping point.
  • the grounded tap ping point on the anode circuit is constituted by the grounded tapping point on a capacitive voltage divider which is connected between the circuit-ends and comprises the series-combination of capacitors 34, 35 and 22.
  • the voltage-divider capacitors 34 and 35 are con-f nected-between the anode and the cathode to replace-the voltage-divider capacitor 21 of Fig. 2.
  • the junction of the capacitors 34 and 35 is, connected to ground. This manner of connecting the resonant circuit to ground is constructionally attractive and also has the advantage that the variable output'transformer can be designed as is described in United States Patent No. 2,662,162, issued December 8, 1953 to Blok, whereby the circuit-coil is axially movablein the coupling coil.
  • the cathode filament is directly connected to the secondary 26 of the filament-current transformer 18, the cathode-end which is connected to the resonant circuit being connected, through a high-frequency choke 36, to the grounded terminal of the anode voltage supply source.
  • the primary winding 37 of the filament-current transformer 18 is, connected, through chokes 38, 38, to the input terminals 17, 17' which are also connected to an alt mating voltage supply source (not shown).
  • the primary transformer circuit is symmetrically grounded through the coupling capacitors 39, 39' connected to input terminals 17 and 17', respectively.
  • the transformer windings 26, 37 are inter-connected through two capacitors 40, 40', through which the ends of the primary 37 and the secondary 26-. respectively, are inter-connected.
  • the chokes 38, 38 carry the primary current of the filament-current transformer, which current is much smaller than the filamerit-current itself. This provides the advantage that the chokes 38, 38 may be proportioned comparatively small in spite of the large filament currents (about 100 I amperes) used for high power tubes.
  • the circuit arrangement operates in a manner which is substantially similar to that described with reference to Fig. 2; in addition, it may be observed that a suitable choice of the capacitors of the voltage divider 34, 35, 22 connected between the circuit ends permits a symmetrical voltage loading of the circuit with respect to ground.
  • Fig. 4 is a modification of the embodiment of 3 which has proved of advantage in practice. Similar elements are again designated by like reference numerals.
  • the resonant circuit 41 which is connected in the anode circuit of the triode 1 and isturrd to the operating frequency, similarly to the circuit arrangement shown in Fig. 3, is grounded through the grounded tapping point on a capacitive voltage divider connected between the circuit ends.
  • the capacitive voltage divider comprises the series combination of four capacitors 42, 43, 44 and 22.
  • Voltage-divider capacitors 43 and 44 have equal capacitance values and are connected between the anode and cathode of the triode 1. The junction of these capacitors is connected to ground.
  • the capacitor 42 is connected betweenthe anode and the adjacent circuit end and its capacitance value is equal to that of the voltage-divider capacitor 22 which is connected between the cathode and the circuit end adjacent the cathode.
  • the grounded tapping point on the voltage divider 42, 43, 44, 22 is the electrical center of the circuit, so that not only the alternating voltages produced at the anode and the cathode but also those set up at the circuit ends are symmetrical with respect to ground.
  • alternating voltage of 12 kilovolts is produced, the alternating voltages appearing at the anode and the cathode are each 6 kilovolts with respect to ground and balanced with respect to one another; the alternating voltages produced at the circuit-ends, in this event, are, for example, 7 kilovolts with respect to ground.
  • a 'Th'efilament-current supply circuit is distinguished from that used in the embodiments described hereinbefore by field produced by the high-frequency voltages set up across the secondary 46 is limited substantially entirely by the screening cylinder 48 and the fianges47, so that the primary 49 and the iron core of the filament-current transformer 45 are efliciently screened.
  • the primary 49 is directly connected, without the interposition of choke .coils, to the alternating voltage supply source (not shown) from which the filament-current supply is derived.
  • the cathode-lead choke similarly to the embodiment of Fig. 3, is connected to one of the cathode ends.
  • the invention is not restricted to the use of the oscillator provided with capacitive feedback which is shown in the various embodiments, but that obviously the invention can also be used, when the triode 1 is provided with inductive feedback or when the triode 1 is excited by a preceding tube.
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and at least one grid, an output circuit connected in the anode circuit of said tube, said output circuit comprising a resonant circuit having a resonant coil and a shunt circuit connected across said resonant coil, a capacitor, means connecting said anode through said capacitor to a first point in said output circuit, means connecting said cathode to a second point in said output circuit, means connecting said grid to a third point in said output circuit thereby to control the grid excitation voltage, a tapping point in said output circuit interposed between said first and second points, said tapping point being connected to a point at ground potential and being connected substantially symmetrically with respect to the ends of said resonant coil and being so positioned that the voltage between each of said first and second points and, said tapping point is substantially half the voltage produced by said circuit arrangement, a load circuit including a coupling coil inductively coupled to said resonant coil whereby a
  • a circuit arrangement for a high frequency fur nace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit con? nected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, a capacitor, means conmeeting said anode through said capacitor to a first point in said shunt circuit, means connecting said cathode to a second point in said shunt circuit, a tapping point on said resonant coil interposed between said first and second points substantially symmetrically with respect to the ends of said resonant coil, said tapping point being connected to a point at ground potential and being so positioned that the voltage between each of said first and second points and said tapping point is substantially half the voltage produced by said circuit arrangement, a load circuit including a coupling coil inductively coupled to said resonant coil whereby a substantially reduced voltage appears between said resonant coil and said coup
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit connected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, a capacitor, means connecting said anode through said capacitor to a first point in said shunt circuit, means connecting said cathode to a second point in said shunt circuit, a tapping point on said resonant coil interposed between said first and second points substantially symmetrically with respect to the ends of said resonant coil, said tapping point being connected to a point at ground potential and being so positioned that the voltage between each of said first and second points and said tapping point is substantially half the voltage produced by said circuit arrangement, a load circuit including a coupling coil inductively coupled to said resonant coil whereby a substantially reduced voltage appears between said resonant coil and said coupling coil, means connecting said grid to a third
  • a load circuit including a coupling coil variably inductively coupled to said resonant coil whereby a substantially reduced voltage appears between said resonant coil and said coupling coil, a source of voltage supply having a pair of terminals, one of the terminals of said supply source being connected to a point at ground potential, at first high frequency choke coil, means connecting said anode to one terminal of said supply source through said first high frequency choke coil, a second high frequency choke coil, and means connecting saidcathode to the other terminal of said supply source through said second high frequency choke coil.
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit connected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, said shunt circuit comprising at capacitive voltage divider, said voltage divider'comprising at least two capacitors connected in series circuit arrangement, means connecting said anode to a first point in said shunt circuit on one side of two of said capacitors, means connecting said cathode to a second point in said shunt circuit on the other side'of said two capacitors, a tapping point on said voltage divider between said two capacitors, said tapping point being connected to a point atground potential and being so positioned that the voltagefbetween each of said first and second points and said tapping point is substantially half the voltage produced by said circuit arrangement, a load circuit including a coupling coil variably inductively coupled to said resonant
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit connected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, said shunt circuit comprising a capacitive voltage divider, said voltage divider comprising a plurality of capacitors connected in series circuit arrangement, means connecting said anode to a first point in said shunt circuit on one side of two of said capacitors, means connecting said cathode to, a second point in said shunt circuit on the other side of said two capacitors, a tapping point on said voltage divider between said two capacitors, said tapping point being connected to a point at ground potential and being so positioned that the voltagebetween each of said first and second points and said tapping point is substantially half the voltage producedby said circuit arrangement, a load circuit including at coupling coil variably inductivelycoupled to said resonapt;
  • a source of voltage supply having a pair of terminals, one of the terminals of said supply source being connected to a point at ground potential, means for applying a control voltage to said grid comprising athird capacitor connected in said shunt circuit between said cathode and the said grid, current supply means for said cathode comprising a current transformer having a primary winding, a secondary winding, a pair of choke coils, means for applying an alternating voltage to said primary winding, said choke coils being connected between the terminals of said primary winding and said means for applying an alternating voltage, and means directly connecting the terminals of said cathode to the terminals of said secondary winding, a first high frequency choke coil, means connecting said anode to one terminal of said supply source through said first high frequency choke coil, a second high frequency choke coil and means connecting said cathode to the other terminal of said supply source through said second high frequency choke coil.
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit connected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, said shunt circuit comprising a capacitive voltage divider, said voltage divider comprising a plurality of capacitors connected in series circuit arrangement, at least two of said capacitors having equal capacitance values, means connecting said anode to a first point in said shunt circuit between a third of said capacitors and said two capacitors, means connecting said cathode to, a point in said shunt circuit between a fourth of said capacitors and said two capacitors, said third and fourth capacitors having equal capacitance values, a tapping point on said voltage divider between said two capacitors, said tapping point being connected to a point at ground potential and being so positioned that the voltage between each of said first and second points and said tapping point
  • a circuit arrangement for a high frequency furnace comprising an electron discharge tube having an anode, a cathode and a grid, a resonant circuit connected in the anode circuit of said tube, said resonant circuit comprising a resonant coil, a shunt circuit connected across said resonant coil, said shunt circuit comprising a capacitive voltage divider, said voltage divider comprising a plurality of capacitors connected in series circuit arrangement, two of said capacitors having equal capacitance values, means connecting said anode to a first point in said shunt circuit between a third of said capacitors and said two capacitors, means connecting said cathode to a second point in said shunt circuit between a fourth of said'capacitors and said two capacitors, said third and fourth capacitors having equal capacitance values, a tapping point on said voltage divider between said two capacitors, said tapping point being connected to a point at; ground potential and being so positioned that the voltagebetween eachvoft said first and second point:
  • a load circuit including a coupling coil variably inductively coupled to said resonant coil whereby a substantially reduced voltage appears between said resonant coil and said coupling coil, a source of voltage supply having a pair of terminals, one of the terminals of said supply source being connected to a point at ground potential, means for applying a control voltage to said grid comprising said fourth capacitor connected between said cathode and the said grid, current supply means for said cathode comprising a current transformer having a primary winding, a metal shield connected to a point at ground potential and having a substantially cylindrical configuration and protruding flange arms thereon, a secondary winding positioned in said shield, means for applying an alternating voltage to said primary winding and means directly connecting the terminals of said cathode to the terminals of said secondary winding, a first high frequency choke coil, means connecting said anode to one terminal of said supply source through said first high frequency choke coil, a second high frequency choke coil,

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  • General Induction Heating (AREA)
US588899A 1955-06-03 1956-06-01 Circuit arrangement for a high frequency furnace Expired - Lifetime US2979669A (en)

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NL340922X 1955-06-03
NL2979669X 1955-06-03

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190089412A1 (en) * 2017-09-21 2019-03-21 Enphase Energy, Inc. Apparatus for communicating across an isolation barrier

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1739299A (en) * 1927-03-18 1929-12-10 Lorenz C Ag High-frequency oscillator
US1755386A (en) * 1925-08-10 1930-04-22 Chireix Henri Vacuum-tube generator system
US2145124A (en) * 1935-06-29 1939-01-24 Gen Electric Therapeutic apparatus
US2446032A (en) * 1944-12-09 1948-07-27 Gen Electric High-frequency generating apparatus
US2579525A (en) * 1942-06-19 1951-12-25 Arthur A Varela Rectangular and saw-tooth impulse generator

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1755386A (en) * 1925-08-10 1930-04-22 Chireix Henri Vacuum-tube generator system
US1739299A (en) * 1927-03-18 1929-12-10 Lorenz C Ag High-frequency oscillator
US2145124A (en) * 1935-06-29 1939-01-24 Gen Electric Therapeutic apparatus
US2579525A (en) * 1942-06-19 1951-12-25 Arthur A Varela Rectangular and saw-tooth impulse generator
US2446032A (en) * 1944-12-09 1948-07-27 Gen Electric High-frequency generating apparatus

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190089412A1 (en) * 2017-09-21 2019-03-21 Enphase Energy, Inc. Apparatus for communicating across an isolation barrier
US11206060B2 (en) * 2017-09-21 2021-12-21 Enphase Energy, Inc. Apparatus for communicating across an isolation barrier

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