Start up circuit and current-foldback protection for voltage regulators
First Claim
1. A circuit, connectable to a pass transistor for starting-up and limiting pass current in the pass transistor, having an output terminal with an output voltage, the circuit comprising:
- a start-up circuit to provide a start-up signal and a foldback signal, wherein the start-up signal and the foldback signal are responsive to a start-up control signal;
an output stage circuit, having an input terminal with an input voltage, responsive to the start-up signal, to control the pass current in response to the input voltage when the pass transistor is coupled to the output stage circuit;
a signal generator circuit, coupled to the output voltage terminal, to provide a current limit signal and the start-up control signal, wherein the current limit signal and the start-up control signal are responsive to the output voltage; and
a current limit amplifier responsive to a current sense signal and a limit signal, and coupled to the input terminal of the output stage to limit the pass current from exceeding a current limit threshold, where the current sense signal is indicative of the pass current and the limit signal is responsive to the foldback signal and the current limit signal.
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Accused Products
Abstract
A circuit providing start-up capability and foldback protection to a voltage regulator. A start-up circuit provides a start-up signal to initiate current flow to a load and also provides a foldback signal to set a current limit threshold under an over-load or short-circuit condition. A signal generator circuit operating on the regulated output voltage of the voltage regulator provides a current limit signal and a start-up control signal. The start-up circuit provides the start-up signal in response to the start-up control signal. The current limit signal sets the current limit threshold under normal operating conditions after start-up.
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Citations
24 Claims
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1. A circuit, connectable to a pass transistor for starting-up and limiting pass current in the pass transistor, having an output terminal with an output voltage, the circuit comprising:
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a start-up circuit to provide a start-up signal and a foldback signal, wherein the start-up signal and the foldback signal are responsive to a start-up control signal; an output stage circuit, having an input terminal with an input voltage, responsive to the start-up signal, to control the pass current in response to the input voltage when the pass transistor is coupled to the output stage circuit; a signal generator circuit, coupled to the output voltage terminal, to provide a current limit signal and the start-up control signal, wherein the current limit signal and the start-up control signal are responsive to the output voltage; and a current limit amplifier responsive to a current sense signal and a limit signal, and coupled to the input terminal of the output stage to limit the pass current from exceeding a current limit threshold, where the current sense signal is indicative of the pass current and the limit signal is responsive to the foldback signal and the current limit signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A voltage regulator, having an output terminal with an output voltage, for regulating the output voltage, the voltage regulator comprising:
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a pass transistor to provide a pass current to a load; a start-up circuit to provide a start-up signal to start the pass current in the pass transistor when the output voltage is less than a lower limit, and to provide a foldback signal, wherein the start-up signal and the foldback signal are responsive to a start-up control signal; an output stage circuit, having an input terminal with an input voltage, responsive to the start-up signal, coupled to the pass transistor to control in response to the input voltage the pass current; a signal generator circuit, responsive to the output voltage terminal, to provide a current limit signal, a first reference voltage, and the start-up control signal; a signal combiner circuit connected to receive the foldback signal and the current limit signal so as to provide a limit signal responsive to the foldback signal and the current limit signal; a difference amplifier, the difference amplifier being responsive to the first reference voltage and the output voltage, the difference amplifier having an output terminal coupled to the input terminal of the output stage circuit, wherein a control voltage at the output terminal of the difference amplifier is responsive to the difference between the first reference voltage and a difference input voltage, wherein the difference input voltage is a function of the output voltage; a current sense circuit, responsive to the pass current, to provide to the current limit amplifier a current sense signal indicative of the pass current; and a current limit amplifier responsive to the current sense signal and the limit signal, and coupled to the input terminal of the output stage to limit the pass current from exceeding a current limit threshold, where the current sense signal is indicative of the pass current. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. An integrated circuit with a substrate and an output voltage terminal for regulating an output voltage between the output voltage terminal and the substrate, and for starting-up and limiting pass current in a pass transistor having a base, a collector, and an emitter, the integrated circuit comprising:
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an input voltage terminal having an input voltage with respect to the substrate; a current source, having a first terminal coupled to the input voltage terminal and having a second terminal, for providing at the second terminal a source current responsive to the input voltage and for providing on a first line coupled to the second terminal a start-up signal responsive to the source current and responsive to a first current shunted from the second terminal of the current source to the substrate; output stage means, having a first terminal with a voltage with respect to the substrate, and having second, third, and fourth terminals, for controlling the pass current in the pass transistor in response to the voltage at the first terminal of the output stage means when the collector, emitter, and base of the pass transistor are respectively coupled to the second, third, and fourth terminals of the output stage means, the first terminal of the output stage means coupled to the second terminal of the current source via the first line, the second terminal of the output stage means coupled to the input voltage terminal, and the third terminal of the output stage means coupled to the output voltage terminal; voltage reference means, coupled to the output voltage terminal, having first, second, third, and fourth terminals, for providing at the first terminal a first reference voltage with respect to the substrate, a current limit signal at the second terminal, a bias current at the third terminal, and a start-up control signal at the fourth terminal, so that the first reference voltage, the current limit signal, the bias current, and the start-up control signal are regulated by the output voltage at the output voltage terminal; a difference amplifier, having a first input coupled to the first terminal of the voltage reference means, and a second input with a voltage with respect to the substrate and coupled to the output voltage terminal, the difference amplifier including a matched pair of transistors coupled to the first and second inputs and having emitters coupled to the third terminal of the voltage reference means so that current flow in the emitters of the matched pair of transistors is regulated by the bias current, the difference amplifier having an output terminal with a control voltage coupled to the first terminal of the output stage means for regulating the output voltage at the output voltage terminal, wherein the control voltage is responsive to the difference between the first reference voltage and the voltage at the second input of the difference amplifier; current shunt means, having a first terminal coupled to the fourth terminal of the voltage reference means and a second terminal coupled to the second terminal of the current source, for shunting the first current from the second terminal of the current source to the substrate in response to the start-up control signal; first signal means, responsive to the pass current flowing in the pass transistor, for providing at a first node a first signal indicative of the pass current; second signal means, coupled to the second terminal of the voltage reference means, for providing at a second node a second signal responsive to the current limit signal; and current limit means, coupled to the first and second nodes, for shunting a second current from the first terminal of the output stage means to the substrate in response to the first and second signals. - View Dependent Claims (20, 21)
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22. An integrated circuit with a substrate and an output voltage terminal for regulating an output voltage between the output voltage terminal and the substrate, and for starting-up and limiting pass current in a pass transistor having a base, a collector, and an emitter, the integrated circuit comprising:
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an input voltage terminal having an input voltage with respect to the substrate; a current source, having a first terminal coupled to the input voltage terminal and a second terminal coupled to a first line, for providing at the second terminal a source current responsive to the input voltage and for providing at the first line a start-up current responsive to the source current and responsive to a first current shunted from the second terminal of the current source to the substrate; output stage means, having a first terminal with a voltage with respect to the substrate, and having second, third, and fourth terminals, for controlling the pass current in the pass transistor in response to the voltage at the first terminal of the output stage means, the collector, emitter, and base of the pass transistor respectively coupled to the second, third, and fourth terminals of the output stage means, the first terminal of the output stage means coupled to the second terminal of the current source via the first line, the second terminal of the output stage means coupled to the input voltage terminal, and the third terminal of the output stage means coupled to the output voltage terminal; a voltage reference circuit coupled to the output voltage terminal and the substrate, having first and second terminals, for providing on the first terminal a first reference voltage and for providing on the second terminal a second reference voltage where the first and second reference voltages are regulated by the output voltage; a voltage-controlled current sink coupled to the second terminal of the voltage reference circuit, the voltage-controlled current sink having a terminal for sinking at the terminal a reference current responsive to the second reference voltage; a first current mirror coupled to the output voltage terminal and the terminal of the voltage-controlled current sink, the first current mirror having a bias current terminal, a start-up control current terminal, and an output terminal, for sourcing at the bias current terminal, the start-up control current terminal, and the output terminal a bias current, a start-up control current, and a second reference current, respectively, responsive to the first reference current; a second current mirror coupled to the output terminal of the first current mirror, coupled to a second line, for sinking on the second line a limit current responsive to the second reference current; a difference amplifier, having a first input coupled to the first terminal of the voltage reference circuit, and a second input with a voltage with respect to the substrate and coupled to the output voltage terminal, the difference amplifier including a matched pair of transistors coupled to the first and second inputs and having emitters coupled to the bias current terminal of the first current mirror so that current flow in the emitters of the matched pair of transistors is regulated by the bias current, the difference amplifier having an output terminal coupled to the first terminal of the output stage means for regulating the output voltage at the output voltage terminal; current shunt means, having a first terminal coupled to the start-up control current terminal of the first current mirror and a second terminal coupled to the second terminal of the current source, for shunting the first current responsive to the start-up control current; first signal means, responsive to the pass current flowing in the pass transistor, for providing at a first node a first signal indicative of the pass current; second signal means, coupled to the second line, for providing at a second node a second signal responsive to the limit current; and current limit means, coupled to the first and second nodes, for shunting a second current from the first terminal of the output stage means to the substrate in response to the first and second signals. - View Dependent Claims (23, 24)
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Specification