Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
1998-10-09
2001-03-20
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C327S378000, C327S538000, C323S907000
Reexamination Certificate
active
06204720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a circuit for controlling load current from multiple power supplies connected to drive a single load.
2. Description of the Related Art
FIG. 1
shows a block diagram of a power supply circuit wherein multiple power supply units
100
1
-
100
N
drive a common load
102
. The power supply units
100
1
-
100
N
may each include a power metal oxide semiconductor field effect transistor (MOSFET) having a source to drain connecting V
DD
to the load
102
. As an alternative to MOSFETS, the power supply units
100
1
-
100
N
may also include some other suitable power or switching elements. Current provided to the load
102
in each of the power supply units
100
1
-
100
N
is controlled using a voltage bias circuit driving the gate of each of the power MOSFET transistors in the power supply units
100
1
-
100
N
. Typically, the bias circuitry is controlled so that the load current is equally shared between the MOSFETs of the power supply units
100
1
-
100
N
.
By equally distributing the load current between the power MOSFETs of the power supply units
100
1
-
100
N
, the difficulty a particular unit may have in achieving a desired current level is not taken into account. For example, suppose two power supply units share a 10 amp load. A typical current sharing scheme would force each power supply unit to provide
5
amps of load current. Now assume that a MOSFET in a first power supply unit has a drain to source resistance (Rds) that is 25% higher than the second power supply unit. The power dissipated by the first power supply unit would then be 25% higher than power dissipated by the second unit. The first unit could then run significantly hotter than the second unit, potentially causing reliability problems.
SUMMARY OF THE INVENTION
The present invention allows multiple power supply units to drive a single load with each power supply unit contributing equally from the perspective of power dissipation so that a uniform temperature can be achieved among all power supply units.
The present invention senses power dissipated in each power supply unit by measuring the temperature of the integrated circuit power supply unit, and then controls the current provided from each power supply unit to equalize the temperatures.
The present invention includes current control circuitry with a first bipolar diode placed in close thermal proximity to the MOSFET in each power supply unit. By being placed in close thermal proximity to a MOSFET, each first diode provides a voltage varying inversely proportional to temperature changes caused by power dissipated from the respective MOSFET.
The control circuitry further includes a second diode and amplifier provided in each power supply unit to apply the voltage from the first diode with the lowest voltage (or highest temperature) on a bus external to the power supply units. The amplifier and second diode of each power supply unit then function so that if the voltage across the first diode in a unit is equal to the bus voltage, the bias voltage applied to the gate of the MOSFET in that unit is not increased since it has the highest temperature. However, if the unit has a first diode voltage greater than the bus voltage, bias voltage applied to the gate of the MOSFET in the unit is increased so that the unit supplies a greater share of the load current. Lower temperature units will then heat up and higher temperature units will cool down until an equilibrium is reached.
REFERENCES:
patent: 5939872 (1999-08-01), Dubos et al.
patent: 5973542 (1999-10-01), Okayasu et al.
Callahan Timothy P.
Elantec Semiconductor Inc.
Fliesler Dubb Meyer & Lovejoy LLP
Nguyen Minh
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