Power modulator

• US 5,905,646 A
• Filed: 02/24/1997
• Issued: 05/18/1999
• Est. Priority Date: 12/20/1996
• Status: Expired due to Term

• Current Assignee: Scandinova Systems AB
• Original Assignee: Scanditronix Medical AB
• Inventors: Crewson, Walter Frederick John, Lindholm, Mikael Rolf, Woodburn, David Kerr
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Han, Y. J.
• Application Number:
  US08/805,149
• Time in Patent Office: 813 Days
• Field of Search: 363/15, 363/16, 363/17, 363/20, 363/21, 363/24, 363/25, 363/26, 363/40, 363/41, 363/65, 363/71, 363/97, 363/98, 363/131, 363/132, 336/172, 336/178, 336/212, 327/179, 331/87
• US Class Current: 363/132
• CPC Class Codes: H02M 3/28 using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
• CPC Class Codes: H03K 3/57 the switching device being a semiconductor device

Abstract

The invention relates to a power modulator of pulse transformer type. The pulse transformer includes at least one secondary winding and a number of primary windings. The primary windings share a common ground terminal, but each "hot" terminal is independently connected to a respective dedicated pulse generating module, which includes a pulse switch, such as an IGBT-switch, connected to an energy storage capacitor. The pulse switch is electronically controllable at turn on and turn off, and eliminates the need for Pulse Forming Networks. The electronic pulse switch control is preferably used in combination with pulse voltage droop-compensating circuits that connect the switches to the primary windings. Furthermore, the transformer design is such that each primary winding only surrounds a portion of the total magnetic core cross section, giving an effect of a fractional turn primary.

Claims

1. A power modulator having a pulse generator stage for generating a first electrical pulse, and a step-up pulse transformer connected to said pulse generator stage for receiving said first electrical pulse to produce a second electrical output pulse of higher voltage, said pulse generator stage having:

a pulse generating section which comprises;

an energy storage capacitor;

a pulse switch electronically controllable at turn-on and turn-off, and connected between said energy storage capacitor and said pulse transformer; and

a passive voltage droop-compensating circuit which connects said pulse switch to said pulse transformer for compensating for a voltage droop during a discharge of said capacitor, thus controlling the shape of the second electrical output pulse,

said pulse switch being operable to turn on to start said second electrical output pulse by transferring capacitor energy via said voltage droop-compensating circuit to said step-up pulse transformer in the form of said first electrical pulse, and operable to turn off to terminate said second electrical output pulse.

2. Power modulator according to claim 1, wherein said pulse switch is an Insulated Gate Bipolar Transistor switch.

3. Power modulator according to claim 1, wherein said pulse generator stage further comprises a charging power supply connected to said energy storage capacitor for selectively charging said energy storage capacitor, said charging power supply including a series-resonant Insulated Gate Bipolar Transistor inverter.

4. Power modulator according to claim 1, wherein said pulse generator stage further comprises a trigger pulse generator for generating a trigger pulse that triggers said pulse switch.

5. Power modulator according to claim 4 further comprising means for electronically changing the length of said trigger pulse, thus changing the pulse width of said second output pulse.

6. Power modulator according to claim 1, wherein said voltage droop-compensating circuit is a parallel resistor-inductor circuit.

7. A power modulator having a pulse generator stage for generating first electrical pulses, and a step-up pulse transformer connected to said pulse generator stage for receiving said first electrical pulses to produce a second electrical output pulse of higher voltage, said pulse generator stage having:

a number of pulse generating sections, each of which comprises an energy storage capacitor, a pulse switch electronically controllable at turn-on and turn-off and connected between said energy storage capacitor and said pulse transformer, and a passive voltage droop-compensating circuit which connects said pulse switch to said pulse transformer for compensating for a voltage droop during a discharge of said capacitor,

said electronically controllable pulse switches of said pulse generating sections being operable to turn on simultaneously to start said second electrical output pulse by transferring capacitor energy via said voltage droop-compensating circuits to said step-up pulse transformer in the form of said first electrical pulses, and operable to turn off simultaneously to terminate said second electrical output pulse.

8. Power modulator according to claim 7, wherein said pulse switches are Insulated Gate Bipolar Transistor switches.

9. Power modulator according to claim 7, wherein said pulse generator stage further comprises a charging power supply connected to said energy storage capacitors for selectively charging said capacitors, said charging power supply including a series-resonant Insulated Gate Bipolar Transistor inverter.

10. Power modulator according to claim 7, wherein each one of said voltage droop-compensating circuits is in the form of a parallel resistor-inductor network.

11. Power modulator according to claim 7, further comprising:

a trigger pulse generator for generating trigger pulses that trigger said pulse switches, and

a control circuit for electronically changing the length of said trigger pulses, thus changing the pulse width of said second output pulse.

12. Power modulator according to claim 7, wherein said transformer has a number of primary windings and each one of said primary windings has an independent terminal and a common ground terminal, each one of said primary windings being separately connected through said independent terminal to a respective individual one of said pulse generating sections, thus ensuring equal current flow in said primary windings and said pulse switches.

13. Power modulator according to claim 7, wherein said transformer has a number of primary windings and each one of said primary windings surrounds only a portion of the total magnetic core cross-section of said transformer.

17. Power modulator according to claim 7, wherein said transformer has secondary windings connected to any one of a Klystron, a magnetron, a traveling wave tube and a cross field amplifier.

14. Power modulator according 7, wherein said transformer includes a secondary winding, a number of primary windings and at least two cores stacked up next to each other, each core being surrounded by a respective set of said primary windings, generally distributed equally among said cores, and said secondary winding being wound around said cores such that said primary windings are within said secondary winding, wherein each one of said primary windings surrounds only a portion of the total magnetic core cross-section of said transformer to give an effect of a fractional-turn primary winding.

15. Power modulator according to claim 14, wherein said transformer includes a further secondary winding and each one of said cores has two legs with a respective one of said secondary windings around each of the two legs.

16. Power modulator according to claim 15, wherein said transformer is of the open-frame type.

18. A power modulator provided with a step-up transformer for receiving first electrical pulses generated by a number of pulse generating sections in a pulse generator and for producing second higher voltage electrical pulses, said step-up transformer having at least one secondary winding, primary windings for receiving said first pulses and a core having at least two core sections, each core section being surrounded by a respective set of said primary windings, generally distributed equally among said core sections, and said secondary winding being wound around said core sections such that said primary windings are within said secondary winding, wherein:

each one of said primary windings surrounds only a portion of the total magnetic core cross-section of said transformer to give an effect of a fractional-turn primary winding; and

each one of said primary windings is separately connected to a respective individual one of said pulse generating sections,

in operation, at least one primary winding, on each one of the core sections, is driven such that each core section contains flux to induce a correct voltage in said secondary winding.

19. Power modulator according to claim 18, wherein said transformer includes two secondary windings, and each one of said core sections has two legs with a respective one of said secondary windings around each of the two legs.

20. Power modulator according to claim 18, wherein said step-up transformer is of the non-enclosed type, and said core comprises two identical core sections, half of said primary windings being wound around the first of said core sections and the remaining primary windings being wound around the other core section.

21. A power modulator having a pulse generator stage for generating first electrical pulses, and a step-up pulse transformer connected to said pulse generator stage for receiving said first electrical pulses to produce a second electrical output pulse of higher voltage, said pulse generator stage having a number of pulse generating sections, wherein:

each one of said pulse generating sections comprises an energy storage capacitor, an Insulated Gate Bipolar Transistor (IGBT) pulse switch electronically controllable at turn-on and turn-off and connected between said energy storage capacitor and said pulse transformer,

said pulse transformer has a number of primary windings, each of which is separately connected to a respective individual one of said pulse generating sections, and

said electronically controllable IGBT pulse switches of said pulse generating sections are operable to turn on simultaneously to start said second electrical output pulse by transferring capacitor energy to said primary windings of said step-up pulse transformer in the form of said first electrical pulses, and operable to turn off simultaneously to terminate said second electrical output pulse.

22. Power modulator according to claim 21, wherein said pulse generator stage further comprises a charging power supply connected to said energy storage capacitors for selectively charging said capacitors, said charging power supply including a series-resonant Insulated Gate Bipolar Transistor inverter.

23. A power modulator having a pulse generator stage for generating a first electrical pulse, and a step-up pulse transformer connected to said pulse generator stage for receiving said first electrical pulse to produce a second electrical output pulse of higher voltage, said pulse generator stage having:

a pulse generating section which comprises;

an energy storage capacitor;

a charging power supply, in the form of a series-resonant Insulated Gate Bipolar Transistor inverter, connected to said energy storage capacitor for selectively charging said energy storage capacitor

an Insulated Gate Bipolar Transistor pulse switch electronically controllable at turn-on and turn-off and connected between said energy storage capacitor and said pulse transformer, said pulse switch being operable to turn on to start said second electrical output pulse by transferring capacitor energy to said pulse transformer in the form of said first electrical pulse, and operable to turn off to terminate said second electrical output pulse.