Input power stabilizing circuit

1. An input power stabilizing circuit, adapted to be disposed between a DC power source and a load to which DC power from said source is to be supplied through an input power supply line and a current line, said input power stabilizing circuit comprising:

a voltage storing unit which stores voltage supplied from the DC power source, supplies the stored voltage to the load when a trouble has occurred, and stabilizes the voltage input to the load;

a current detecting unit which detects a reverse current from said voltage storing unit in the input power supply line; and

a current interrupting unit, responsive to detection of the reverse current, to interrupt the current line.

2. An input power stabilizing circuit in accordance with claim 1 , wherein said current detecting unit comprises:

a current transformer having its primary side connected in the input power supply line; and

a first transistor having a gate connected to receive a voltage generated at the secondary side of said current transformer.

3. An input power stabilizing circuit in accordance with claim 2 , wherein said current detecting unit further comprises:

a diode which rectifies the voltage generated at said secondary side of said current transformer;

a capacitor which smoothes the voltage rectified by said diode; and

a first voltage divider which divides the voltage smoothed by said capacitor and takes out a first designated voltage, wherein:

said gate of said first transistor switches said first transistor “on” when the voltage taken out from said first voltage divider is applied to said gate of said first transistor, and the “on” state of said first transistor activates said current interrupting unit.

4. An input power stabilizing circuit in accordance with claim 3 , wherein said current interrupting unit comprises:

a second voltage divider which divides the voltage inputted from the DC power source and takes out a second designated voltage; and

a second transistor which is disposed in the current line, said second transistor having a gate connected to receive the voltage taken out from said second voltage divider, wherein:

said second transistor is switched “off” when said second voltage divider applies substantially no voltage to said gate of said second transistor, interrupting the current line.

5. An input power stabilizing circuit in accordance with claim 4 , wherein:

said second voltage divider comprises two serially-connected resistors, and in the “on” state, said first transistor provides a short circuit across the ends of one of said resistors, interrupting the voltage from said second voltage divider to said gate of said second transistor.

6. An input power stabilizing circuit in accordance with claim 5 , wherein said voltage storing unit is responsive to a short circuit across output terminals of the DC power source, to discharge said voltage storing unit, causing reverse current to flow in the input power supply line.

7. An input power stabilizing circuit in accordance with claim 2 , wherein said current detecting unit comprises plural current transformers in the input power supply line in parallel.

8. An input power stabilizing circuit in accordance with claim 7 , wherein said current detecting unit further comprises:

a diode which rectifies the voltage generated at the secondary sides of said current transformers;

a capacitor which smoothes the voltage rectified by said diode; and

a first voltage divider which divides the voltage smoothed by said capacitor and takes out a first designated voltage, wherein:

said gate of said first transistor switches said first transistor “on” when the voltage taken out from said first voltage divider is applied to said gate of said first transistor, and the “on” state of said first transistor activates said current interrupting unit.

9. An input power stabilizing circuit in accordance with claim 8 , wherein said current interrupting unit comprises:

a second voltage divider which divides the voltage inputted from the DC power source and takes out a second designated voltage; and

a second transistor which is disposed in the current line, said second transistor having a gate connected to receive the voltage taken out from said second voltage divider, wherein:

said second transistor is switched “off” when said second voltage divider applies substantially no voltage to said gate of said second transistor, interrupting the current line.

10. An input power stabilizing circuit in accordance with claim 9 , wherein:

said second voltage divider comprises two serially-connected resistors, and

in the “on” state, said first transistor provides a short circuit across the ends of one of said resistors, interrupting the voltage from said second voltage divider to said gate of said second transistor.

11. An input power stabilizing circuit in accordance with claim 7 , wherein said voltage storing unit is responsive to a short circuit across output terminals of the DC power source, to discharge said voltage storing unit, causing reverse current to flow in the input power supply line.

12. An input power stabilizing circuit in accordance with claim 2 , wherein said voltage storing unit is responsive to a short circuit across output terminals of the DC power source, to discharge said voltage storing unit, causing reverse current to flow in the input power supply line.

13. An input power stabilizing circuit in accordance with claim 2 , wherein said current detecting unit comprises plural current transformers in the input power supply line in series.

14. An input power stabilizing circuit in accordance with claim 13 , wherein said current detecting unit further comprises:

a diode which rectifies the voltage generated at said secondary sides of said current transformers;

a capacitor which smoothes the voltage rectified by said diode; and

a first voltage divider which divides the voltage smoothed by said capacitor and takes out a first designated voltage, wherein:

said gate of said first transistor switches said first transistor “on” when the voltage taken out from said first voltage divider is applied to said gate of said first transistor, and the “on” state of said first transistor activates said current interrupting unit.

15. An input power stabilizing circuit in accordance with claim 14 , wherein said current interrupting unit comprises:

a second voltage divider which divides the voltage inputted from the DC power source and takes out a second designated voltage; and

a second transistor which is disposed in the current line, said second transistor having a gate connected to receive the voltage taken out from said second voltage divider, wherein:

said second transistor is switched “off” when said second voltage divider applies substantially no voltage to said gate of said second transistor, interrupting the current line.

16. An input power stabilizing circuit in accordance with claim 15 , wherein:

said second voltage divider comprises two serially-connected resistors, and

in the “on” state, said first transistor provides a short circuit across the ends of one of said resistors, interrupting the voltage from said second voltage divider to said gate of said second transistor.

17. An input power stabilizing circuit in accordance to claim 13 , wherein said voltage storing unit is responsive to a short circuit across output terminals of the DC power source, to discharge said voltage storing unit, causing reverse current to flow in the input power supply line.

18. An input power stabilizing circuit in accordance with claim 1 , further comprising:

an inductor which delays the reverse current, in said input power supply line, from said voltage storing unit.

19. An input power stabilizing circuit in accordance with claim 1 , wherein said voltage storing unit is responsive to a short circuit across output terminals of the DC power source, to discharge said voltage storing unit, causing reverse current to flow in the input power supply line.

20. An input power stabilizing circuit in accordance with claim 1 , wherein said current interrupting unit comprises:

a voltage divider which divides the voltage inputted from the DC power source and takes out a designated voltage; and

a transistor which is disposed in the current line, said transistor having a gate connected to receive the voltage taken out from said voltage divider, wherein:

said transistor is switched “off” when said voltage divider applies substantially no voltage to said gate of said transistor, interrupting the current line.

21. An input power stabilizing circuit in accordance with claim 20 , wherein:

said voltage divider comprises two serially-connected resistors, and

said current detecting unit is responsive to detection of the reverse current to cause a short circuit across the ends of one of said resistors, interrupting the voltage from said voltage divider to said gate of said transistor.

22. A method of stabilizing input power between a DC power source and a load to which DC power from the source is to be supplied through an input power supply line and a current line, said method comprising:

storing voltage supplied from the DC power source, for supplying to the load when a trouble has occurred;

detecting a reverse current from the voltage storing unit in the input power supply line; and

in response to detection of the reverse current, interrupting the current line.