INRUSH-CURRENT LIMITING DEVICE

• US 3,781,637 A
• Filed: 01/02/1973
• Issued: 12/25/1973
• Est. Priority Date: 01/02/1973
• Status: Expired due to Term

• Current Assignee: Geoffrey Potter
• Original Assignee: Geoffrey Potter
• Inventors: Potter, Geoffrey
• Primary Examiner(s): Shoop, Jr., William M.
• Application Number:
  US05/320,038
• Time in Patent Office: 357 Days
• Field of Search: 321/11,45S
• US Class Current: 363/27
• CPC Class Codes: H02M 7/517 with special starting equipment
• CPC Class Codes: Y10S 323/908 Inrush current limiters

Abstract

Apparatus, associated with an inverter circuit, for limiting inrush-current into a storage capacitor during an initial charging period, while minimizing the power dissipation of the limiting device during normal inverter operation. A resistive element provides a limiting device for the initial charging period of the storage capacitor. A silicon-controlled rectifier with associated apparatus, placed in a conducting state by the operation of the inverter circuit, provides an alternate low impedance path in parallel with the resistive element following the initial charging period.

Claims

1. An electrical power supply comprising:

a current limiting resistor coupled to a first power supply input terminal;

a first storage capacitor coupled between said current limiting resistor and a second power supply input terminal;

a second storage capacitor coupled to said first storage capacitor;

means for charging said second storage capacitor comprising a first inductive impedance and a first electronic switch coupled in series with said first inductive impedance, said charging means coupled between said current limiting resistor and said second capacitor, said charging means operating in response to a first control signal;

means for discharging said second storage capacitor comprising a second inductive impedance and, a second electronic switch coupled in series, said discharge means coupled between said second capacitor and a second power supply input terminal, said discharge means operating in response to a second control signal;

means for controlling said charging means and said discharging means, said control means producing alternately said first control signal and said second control signal;

means for producing a rectified and filtered output signal, said output means coupled to at least one of said first and said second inductive impedance; and

a third electronic switch coupled in parallel with said current limiting resistors said third electronic switch coupled to said second storage capacitor, said third electronic switch being conductive during a charging of said second storage capacitor.

2. The power supply of claim 1 further comprising:

means for maintaining said third electronic switch in a conducting state for a preselected time after a charging of said storage capacitor.

3. The power supply of claim 2 wherein said third electronic switch includes a silicon-controlled rectifier and wherein a gate terminal of said silicon-controlled rectifier is coupled to said second storage capacitor.

4. The power supply of claim 3 further including:

a third storage capacitor coupled to said first storage capacitor and said second storage capacitor, said third storage capacitor being alternately charged and discharged out of phase with said second capacitor.

5. The power supply of claim 4 wherein said conducting state maintenance means is a third capacitor coupled between said gate terminal and a cathode terminal of said silicon-controlled rectifier.

6. The power supply of claim 5 wherein a first resistor is coupled between said gate terminal and said cathode terminal, and wherein a second resistor connected in series with a diode is coupled between said gate terminal of said silicon-controlled rectifier and said second storage capacitor.

7. The power supply of claim 6, wherein said control means monitors said output signal, an interval of time between said first and said second control signals determined by said output signal.

8. A electrical power supply comprising:

a first resistor having one terminal coupled to a first power supply input terminal;

a first capacitor coupled to said first resistor and coupled to a second power supply input terminal;

a First silicon-controlled rectifier (SCR), an anode terminal of said first SCR coupled to said first resistance, a first inductive impedance coupled to a cathode of said first SCR;

a second SCR coupled to said second input terminal;

a second inductive impedance coupled between said first inductive impedance and second SCR;

a second capacitor coupled between said first and said second inductive impedance, and coupled to said second input terminal;

a third SCR, an anode terminal of said third SCR coupled to said first input terminal, a cathode element of said third SCR coupled to a said anode terminal of said first SCR, a gate terminal of said third SCR coupled to said cathode terminal of said third SCR through a second resistor and a third capacitor connected in parallel, said gate terminal of said third SCR further coupled to said second capacitor through a third resistor and a diode connected in series;

means for controlling said first and said second SCR, said first SCR becoming conductive during a first portion of a cycle for said control means, whereby said second capacitor becomes charged, said control means causing said second SCR to become conductive during a second portion of said control means cycle, whereby said second capacitor is discharged; and

means for producing an output signal one of said first and said second SCR coupled to at least one inductive impedance, said output signal produced in response to signal changes across said inductive impedance.

9. The power supply of claim 8 wherein control means is coupled to said output signal, said output signal determining an interval for said control means cycle.

10. A power supply comprising:

means for producing a rectified output signal from a time-varying secondary signal;

means for producing a time-varying primary signal, said primary signal means coupled to said output signal means for producing said secondary signal;

an input impedance for limiting current into said power supply, said input impedance coupled to said primary signal means; and

means for by-passing said input impedance, said by-pass means directly coupled to said primary signal means, wherein said by-pass means is activated by primary signal.

11. The power supply of claim 10, wherein said primary signal means comprises at least one inductive impedance and at least one electronic switch connected in series, wherein charging of conductive and non-conductive states of said electronic switch causes said time-varying primary signal.

12. The power supply of claim 11 further comprising a capacitor coupled to said primary signal means, wherein charging and discharging of said capacitor is produced by changing of said state of conduction of said silicon-controlled rectifier.

13. The power supply of claim 12 further including means for controlling said electronic switch, said control means coupled to said output signal, wherein said output signal controls a rate of change of said states of conductivity of said electronic switch.

14. An improved circuit of the type having a resistor which limits current flowing into a first capacitor, and having a second capacitor, said second capacitor being alternately charged through a first inductive impedance and discharged through a second inductive impedance, wherein the improvement comprises:

a switching device coupled in parallel with said resistor, wherein a control terminal of said switching device is coupled to said second capacitor, wherein a charging of said second capacitor causes said switching device to assume a conducting state.

15. The improved circuit of claim 14 wherein the improvement further comprises:

means for maintaining said switching device in a conducting state for at least a preselected time after charging of said second capacitor.

16. The improved circuit of claim 15 wherein said switching device is a silicon-controlled rectifier and wherein said control terminal is a gate terminal oF said silicon-controlled rectifier.

17. The improved circuit of claim 16 wherein said means for maintaining said silicon-controlled rectifier in said conducting state comprises a capacitor coupled between said gate terminal and a cathode terminal of said silicon-controlled rectifier.

18. The improved circuit of claim 17 wherein said gate element is coupled through a first control resistor to said cathode terminal and is further coupled through a second control resistor to said second capacitor, said first and second control resistor forming a resistance dividing network for protection of said silicon-controlled rectifier.

19. The improved circuit of claim 18 wherein said silicon-controlled rectifier gate is coupled through a diode to said second capacitor, said second diode preventing a reverse current from flowing from said gate terminal.

20. In a circuit in which a state of at least one electronic switch is rendered alternatively conducting and non-conducting, wherein changed in said electronic switch state cause a varying current in an inductive element, said current composed of charge extracted from a storage capacitor, said current applied to an output circuit, wherein said output circuit provides a steady output voltage in response to said varying current, an input device comprising:

a resistor coupled between said storage capacitor and an input power source, said resistor limiting current flowing from said power source to said capacitor, and a silicon-controlled rectifier (SCR) coupled in parallel with said resistor, a gate of said SCR coupled to said inductive element, wherein said varying current causes said SCR to assume a conducting state.

21. The circuit of claim 20 wherein said gate is coupled to said inductive element through a first control resistor and a diode and wherein said gate is coupled to a cathode of said SCR through a capacitor and a second control resistor, said capacitor and said second control resistor connected in parallel, wherein said capacitor causes said SCR to remain in a conducting state for a preselected time after an alternation in said state of said electronic switch, and wherein said first and second control resistors prevent excessive voltage between said gate and said cathode.

22. A circuit comprising:

a storage capacitor;

a limiting resistor coupled to said storage capacitor for limiting current flowing into said storage capacitor;

a switch element coupled in parallel with said limiting resistor, wherein activation of said switch element causes said switch element to be in a conducting state, said conducting state of said switch element providing an electrical path for by-passing said limiting resistor; and

an inverter circuit for changing a DC signal to an AC signal, said inverter circuit coupled to said storage capacitor, wherein said storage capacitor provides said DC signal to said inverter circuit, said inverter circuit coupled to said switch element, wherein operation of said inverter circuit causes said switch element to be in said conducting state.

23. The circuit of claim 22 wherein said switch element includes a silicon-controlled rectifier, wherein a gate terminal of said SCR is coupled to said inverter circuit.

24. The circuit of claim 23 wherein said switch element further comprises a capacitor coupled between said gate terminal and a cathode terminal of said silicon-controlled rectifier, said capacitor providing biasing means for maintaining said switch element in a conducting state for a preselected period of time after an operation of said inverter circuit.

25. The circuit of claim 24 wherein said switch element further comprises a first resistor coupled between said gate terminal and said cathode terminal and wherein said switch element further comprise a second resistor and a diode couple between said gate terminal and said inverter circuit.