Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-01-28
2001-06-26
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S901000
Reexamination Certificate
active
06252385
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control and regulation circuits for a power supply, and more particularly, to an integrated circuit, on a chip, for controlling and regulating a power stage external to the chip.
BACKGROUND OF THE INVENTION
In general, a power supply for a video device such as a camera includes a power stage, for example, having a power transistor and a decoupling and filter capacitor connected in series on a transistor emitter collector path. This power stage is composed of discrete components due to the high value (on the order of 10 &mgr;F) of the decoupling and filter capacitor, and power transistor cooling needs. A control input to the power stage, for example, the base of the power transistor, is connected to a control and regulation circuit. This circuit is preferably integrated on a chip. This circuit includes a regulation loop that receives a signal (for example a voltage) on an input, representing the value of the regulated power supply output voltage, and with an output coupled to the control input to the power stage. In a known manner, this loop reacts in order to minimize a difference between the real value of the output voltage and a theoretical voltage which is the required nominal value of the power supply output voltage.
Apart from its regulation function, this integrated control and regulation circuit also protects the power supply and powered circuits in the case of a short circuit, and limits the value of the current to a value acceptable by all elements in the circuit when the power supply is switched on. Protection against short circuits may be provided in a known manner by adding a resistor in the output circuit and by measuring the value of the voltage at the terminals of this resistor. An excessively high voltage would switch the power supply off via known circuits.
There are at least two disadvantages with this known manner of limiting the value of the current and therefore providing protection against short circuits and/or current limitations. Firstly, the voltage actually available for powered circuits is reduced by the value of the voltage drop in the resistor. This reduction varies as the value of the current output by the power supply, which causes fluctuations in the voltage actually available for circuits on the load side. Furthermore, picking up the value of the real voltage at the resistor terminals requires an additional external connection to this circuit, and it is known that the total number of connections in an integrated circuit is limited.
Another known manner of avoiding short circuits is to use a voltage comparator. The problem is to ensure that the comparison is not carried out until after the start up and stabilization phase, in order to avoid switching the power supply off immediately after it was switched on.
Furthermore, a control and regulation circuit, particularly for a camera with a port for communication with a universal standard bus (USB), includes constraints on the power supply. Thus, the current must never exceed a limiting value, for example 500 mA, particularly during start up. However, normal use may require current values of up to 300 mA. Therefore, this is a power supply in which the authorized current range is very close to the prohibited current range. The power supply must also have the normal protections against short circuits while enabling the power supply to be switched on, which (as explained above) involves two contradictory requirements.
SUMMARY OF THE INVENTION
An object of this invention is to provide a control circuit on a chip with only two connections being necessary between this circuit and elements of the power stage external to the circuit contained on the chip.
For this and other purposes, the invention is directed to a control and regulation circuit for a regulated DC power supply. The circuit is for a power stage with one control input, one input for an unregulated power supply DC voltage, one output to carry the regulated DC voltage, a decoupling capacitor connected between a constant potential source and the output from the power stage enabling a gradually regulated increase in voltage. The control and regulation circuit includes a regulation loop with an input coupled to the output from the power stage and an output coupled to the control input to this stage. Furthermore, the circuit includes a first controllable switch and a current generator connected through the first switch to the input of the control and regulation circuit connectable between the output from the power stage and the decoupling capacitor. The first controllable switch is controlled by the value of an output signal from a logic circuit with a first input for receiving a first threshold voltage value, a second input for receiving a signal representing a difference between a nominal value of the output voltage from the power stage and a real value of this output voltage. The logic circuit carries a first value of the output signal on one output corresponding to a first position of the first switch in which the first switch is closed such that the decoupling capacitor is charged by the current generator. This first value is present as long as the value of the signal representing a difference between a nominal value of the output voltage from the power stage and a real value of this output voltage received on the second input of the logic circuit is less than the value of the first threshold voltage received on the first input to the logic circuit. The logic circuit switches over to a second output value when the value of the signal representing a difference between a nominal value of the output voltage from the power stage and a real value of this output voltage becomes greater than the value of the first threshold voltage. This second value corresponds to an open position of the first switch.
In the preferred embodiment, the control and regulation circuit also comprises a second switch controllable by the logic circuit connected in the regulation loop. This second switch is open as long as the value present at the output from the logic circuit is equal to the first value, such that the regulation loop is open and the power stage does not output. This second switch is closed when the value at the output from the logic circuit is equal to the second value.
For protection against short circuits, a second value of the threshold voltage is applied to a third input on the logic circuit, and a signal representing the value of the regulated output voltage is applied on a fourth input. The output from the logic circuit is set equal to the first value and the two switches representing the position corresponding to this first value if the value of the signal present on the fourth input becomes less than the second threshold voltage applied to the third input.
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“Power Supplies”, Machine Design, Jun. 1991, No. 13, Cleveland Ohio, pp. 490-509.
Holter et al., “High Temperature Integrated Voltage Regulator System Design”, IEEE, Mar. 8, 1997, pp. 465-468.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Berhane Adolf Deneke
Galanthay Theodore E.
STMicroelectronics S.A.
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