Circuit for controlling the maximum current in a MOS power transistor used for driving a load connected to earth
First Claim
1. A circuit for controlling the current in a MOS power transistor, having a source and drain, used for driving a load connected to ground, including:
- a direct-current voltage supply to which said drain of the MOS transistor is connected,a resistor in series with the drain-source path of the MOS transistor, a charge pump circuit for enabling the gate capacitance of the MOS transistor to be charged to a voltage higher than the voltage of said voltage supply, anda transconductance operational amplifier which is connected to be powered from a supply terminals and which has an output connected to the gate of the MOS transistor and differential inputs connected to the resistor in a relationship which limits the current through the power transistor to a maximum value proportional to a reference voltage;
said charge pump circuit having an output which is connected to supply current to said supply terminal of said transconductance operational amplifier.
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Accused Products
Abstract
An improved circuit for controlling the maximum current in a MOS power transistor, in which resistor is in series with the drain-source path of the MOS power transistor. The supply terminal of a transconductance operational amplifier is connected to the output of a voltage-raising or charge pump circuit which can output a voltage higher than that of the voltage supply to which the drain of the MOS transistor is connected. The inputs of the amplifier are connected to the resistor and its output is connected to the gate of the MOS transistor so that, in operation, the maximum current flowing through the power transistor is limited to a value proportional to a reference voltage.
39 Citations
26 Claims
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1. A circuit for controlling the current in a MOS power transistor, having a source and drain, used for driving a load connected to ground, including:
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a direct-current voltage supply to which said drain of the MOS transistor is connected, a resistor in series with the drain-source path of the MOS transistor, a charge pump circuit for enabling the gate capacitance of the MOS transistor to be charged to a voltage higher than the voltage of said voltage supply, and a transconductance operational amplifier which is connected to be powered from a supply terminals and which has an output connected to the gate of the MOS transistor and differential inputs connected to the resistor in a relationship which limits the current through the power transistor to a maximum value proportional to a reference voltage; said charge pump circuit having an output which is connected to supply current to said supply terminal of said transconductance operational amplifier. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A circuit for controlling the maximum current in a field-effect power transistor connected to drive a load with a sensing resistor in series therewith, comprising:
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connections for receiving first and second power supply voltages;
a charge pump connected to receive said power supply voltages, and therefrom to generate a boosted output at a more extreme voltage than said first power supply voltage; anda transconductance operational amplifier connected to receive the voltage across the sensing resistor as a differential input thereto, and connected to receive a supply current from said boosted output, and connected and configured to drive the gate of the power transistor either toward said boosted output, or else toward said second supply voltage, in accordance with said differential input; whereby the current through said power transistor is prevented from exceeding a predetermined maximum value. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A circuit for controlling the maximum current in a field-effect power transistor connected to drive a load with a sensing resistor in series therewith, comprising:
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connections for receiving first and second power supply voltages;
a charge pump connected to receive said power supply voltages, and therefrom to generate a boosted output at a more extreme voltage than said first power supply voltage; anda transconductance operational amplifier connected to receive the voltage across the sensing resistor as a differential input thereto, and connected to receive a supply current from said boosted output, and connected to provide an output current therefrom to the gate of the power transistor in accordance with said differential input; wherein said amplifier includes at least a first transistor pair with unequal current densities, connected to define a voltage offset for said differential input. - View Dependent Claims (15, 16, 17, 18)
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19. A circuit for controlling the maximum current in a field-effect power transistor connected to drive a load with a sensing resistor in series therewith, comprising:
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connections for receiving first and second power supply voltages;
a charge pump connected to receive said power supply voltages, and therefrom to generate a boosted output at a more extreme voltage than said first power supply voltage; anda transconductance operational amplifier connected to receive the voltage across the sensing resistor as a differential input thereto, and comprising a first branch, including a first transistor of a first majority-carrier conductivity type, and a first transistor of a second majority-carrier conductivity type, said first transistors being connected in series between said boosted output and a first terminal of said resistor, and an intermediate node between said first transistors being connected to a control terminal of the power transistor; and a second branch, including a second transistor of said first majority-carrier conductivity type, and a second transistor of said second majority-carrier conductivity type, said second transistors being connected in series between said boosted output and a second terminal of said resistor, with said first transistors being connected in a current mirror relationship from said first branch to said second branch, and said second transistors being connected in a current mirror relationship from said second branch to said first branch. - View Dependent Claims (20)
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21. A method for controlling the maximum current in a power field-effect transistor connected to drive a load, comprising the steps of:
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generating a boosted voltage in a charge pump which is connected to receive first and second supply voltages; providing a differential signal, which indicates the current passed by said power transistor, to the differential inputs of a differential amplifier which is exclusively supplied by said charge pump, and not directly connected to at least one said supply voltage, said differential amplifier being configured to provide a current output; connecting said current output of said differential amplifier to drive a gate terminal of the power transistor. - View Dependent Claims (22, 23, 24, 25, 26)
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Specification