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Soft-start switch with voltage regulation and current limiting
| Details |
Inventors: Goerke, Ulrich B.; Pieper, Mark S.;
Assignee: Data General Corporation (Westborough, MA)
Primary Examiner: Hecker; Stuart N.
Assistant Examiner:
Attorney, Agent or Firm: Bromberg & Sunstein LLP
A MOSFET, an op-amp, a comparator circuit, and voltage dividers with capacitors are employed in combination to effectuate a soft-start switch with current limiting. The transconductance of the MOSFET is employed so that no sense resistor is required. The MOSFET and op-amp are configured as a closed-loop feedback circuit in which the output of the op-amp is coupled to the gate of the MOSFET and the inverting input of the op-amp is coupled to the output of the soft-start switch via a voltage divider. A first RC circuit provides a voltage to the non-inverting input of the op-amp which can be triggered to gradually rise from a value close to zero to some reference voltage so as to soft-start a load. Current limiting means are effectuated by a comparator circuit and voltage dividers with capacitors. The current limiting means brings the MOSFET to an OFF state and the non-inverting input of the op-amp close to zero volts if the op-amp charges a second RC circuit so that the voltage drop across its capacitor exceeds a pre-determined limit-reference, and also, once the current limiting means brings the MOSFET to the OFF state, the current limiting means allows the soft-start switch to begin a soft-start power-up after a pre-determined time dependent upon the time constant of the second RC circuit. |
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DETAILED DESCRIPTION An advantage of the present invention is a soft-start switch with regulation of voltage drop across the soft-start switch, i.
e.
, V.
sub.
0 -V.
sub.
out, so that load sharing among a plurality of power supplies coupled to the same soft-start switch is facilitated.
Another advantage of the present invention is a soft-start switch in which a load may be hot-plugged to the soft-start switch without causing a current surge.
Another advantage of the present invention is a soft-start switch that automatically soft-starts a hot-plugged load.
Yet another advantage of the present invention is a soft-start switch with current limiting without the need for a sense resistor.
In the preferred embodiment of the invention to be disclosed, a MOSFET, an op-amp, a comparator circuit, diodes, and voltage dividers with capacitors are employed in combination to effectuate a soft-start switch.
The MOSFET and op-amp are configured as a closed-loop feedback circuit in which the output of the op-amp is coupled to the gate of the MOSFET and the inverting input of the op-amp is coupled to the output of the soft-start switch via a voltage divider.
A first RC circuit provides a voltage to the non-inverting input of the op-amp which can be triggered to gradually rise from a value close to zero (typically one diode voltage drop above ground) to some reference voltage.
The combination of the first RC circuit and closed-loop feedback circuit controls the current through the MOSFET such that the output voltage of the soft-start switch rises gradually from a value close to zero to the reference voltage when the MOSFET is initially turned ON.
Current limiting means are effectuated by a comparator circuit and voltage dividers with capacitors.
The current limiting means brings the MOSFET to an OFF state and the non-inverting input of the op-amp close to zero volts if the op-amp charges a diode-capacitor circuit so that the voltage drop across its capacitor exceeds a pre-determined reference, and also, once the current limiting means brings the MOSFET to the OFF state, the current limiting means allows the soft-start switch to begin a soft-start power-up after a pre-determined time dependent upon the time constant of a second RC circuit
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Metal Working 
