Switched-mode power supply startup circuit, method, and system incorporating same
First Claim
1. A startup circuit for a switched-mode power supply, said startup circuit comprising:
- a voltage input node;
an output current node;
a disable input node;
a startup current circuit configured to provide a startup current from the voltage input node to the output current node when enabled, and to block the startup current when disabled, said startup current being substantially constant in magnitude irrespective of a voltage difference between the voltage input node and the output current node; and
a control circuit configured to enable the startup current circuit when a voltage is first applied to the voltage input node, and to disable the startup current circuit in response to one or more voltage excursions on the disable input node which exceed by a first offset a voltage of the output current node;
wherein said control circuit comprises;
a first power supply node coupled to a first node of the startup current circuit;
a reference power supply node coupled to the output current node;
an input circuit having an input coupled to the disable input node, said input circuit configured to generate on an output node thereof a signal having different voltage and time characteristics relative to a signal coupled to its input node; and
a comparator circuit having a first input coupled to the input circuit output node, having a second input coupled to the output current node, and having an output coupled to an enable input for the startup current circuit, said comparator circuit configured to disable the startup current circuit when a voltage of the first input exceeds a voltage of the second input by a second offset.
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Abstract
A startup circuit delivers regulated startup current to a control IC in a switched-mode power supply (SMPS) system, and automatically disconnects the startup current when the SMPS Control IC starts switching the transformer or inductor used as the energy storage element in the SMPS system. Disconnection of the startup current may be triggered by detecting a time-varying voltage waveform on an accessible node in the SMPS system, or by detecting an increased current consumption by the SMPS Control IC, without requiring any ground reference to the SMPS Control IC, nor without requiring any logic signals generated by the SMPS Control IC. This provides for rapid and predictable startup of an SMPS Control IC and reduced power loss once the SMPS Control IC is operational, and is independent of the operating voltages of the SMPS control IC, and independent of the particular control scheme and switch topology of the SMPS system.
115 Citations
30 Claims
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1. A startup circuit for a switched-mode power supply, said startup circuit comprising:
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a voltage input node; an output current node; a disable input node; a startup current circuit configured to provide a startup current from the voltage input node to the output current node when enabled, and to block the startup current when disabled, said startup current being substantially constant in magnitude irrespective of a voltage difference between the voltage input node and the output current node; and a control circuit configured to enable the startup current circuit when a voltage is first applied to the voltage input node, and to disable the startup current circuit in response to one or more voltage excursions on the disable input node which exceed by a first offset a voltage of the output current node; wherein said control circuit comprises; a first power supply node coupled to a first node of the startup current circuit; a reference power supply node coupled to the output current node; an input circuit having an input coupled to the disable input node, said input circuit configured to generate on an output node thereof a signal having different voltage and time characteristics relative to a signal coupled to its input node; and a comparator circuit having a first input coupled to the input circuit output node, having a second input coupled to the output current node, and having an output coupled to an enable input for the startup current circuit, said comparator circuit configured to disable the startup current circuit when a voltage of the first input exceeds a voltage of the second input by a second offset. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A switched-mode power supply (SMPS) circuit comprising:
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a startup circuit having a voltage input node, an output current node, and a disable input node, said startup circuit comprising; a startup current circuit configured to provide a startup current from the voltage input node to the output current node when enabled, and to block the startup current when disabled, said startup current being substantially constant in magnitude irrespective of a voltage difference between the voltage input node and the output current node; and a control circuit configured to enable the startup current circuit when a voltage is first applied to the voltage input node, and to disable the startup current circuit in response to one or more voltage excursions on the disable input node which exceed by a first offset a voltage of the output current node; wherein said control circuit comprises; a first power supply node coupled to a first node of the startup current circuit; a reference power supply node coupled to the output current node; an input circuit having an input coupled to the disable input node, said input circuit configured to generate on an output node thereof a signal having different voltage and time characteristics relative to a signal coupled to its input node; and a comparator circuit having a first input coupled to the input circuit output node, having a second input coupled to the output current node, and having an output coupled to an enable input for the startup current circuit, said comparator circuit configured to disable the startup current circuit when a voltage of the first input exceeds a voltage of the second input by a second offset; said SMPS circuit further comprising; a switched-mode control circuit having a power supply terminal coupled to the output current node, having a ground terminal, and being configured when operational to pulse current through a coil of an energy storage transformer or inductor of the SMPS circuit; and means for generating voltage excursions on the disable input node in response to said current pulses through said coil. - View Dependent Claims (20, 21, 22)
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23. A method for starting up a switched-mode power supply (SMPS) circuit, said method comprising:
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providing a startup current to a power supply terminal of a switched-mode control circuit to thereby develop an increasing voltage on the power supply terminal, said startup current being substantially constant in magnitude irrespective of the magnitude of an input voltage provided to the SMPS circuit; generating on a disable node a voltage excursion exceeding by a first offset the voltage of the power supply terminal when the switched-mode control circuit begins to operate; and disabling the startup current provided to the power supply terminal in response to the voltage excursion on the disable node, said disabling comprising; generating an output signal on an input circuit output node, said input circuit having an input node coupled to the disable node, said output signal having different voltage and time characteristics relative to a signal coupled to its input node; generating an output signal on an output of a comparator circuit, said comparator circuit having a first input coupled to the input circuit output node, having a second input coupled to the power supply terminal, and having said output coupled to an enable input for a startup current circuit, said output signal being suitable to disable the startup current circuit when a voltage of the first comparator input exceeds a voltage of the second comparator input by a second offset. - View Dependent Claims (24, 25, 26, 27)
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28. A method for making a startup circuit product for a switched-mode power supply, said method comprising:
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providing a voltage input node; providing an output current node; providing a disable input node; providing a startup current circuit configured to provide a startup current from the voltage input node to the output current node when enabled, and to block the startup current when disabled, said startup current being substantially constant in magnitude irrespective of the voltage difference between the voltage input node and the output current node; and providing a control circuit configured to enable the startup current circuit when a voltage is first applied to the voltage input node, and to disable the startup current circuit after a voltage conveyed to the disable input node exceeds by a first offset a voltage of the output current node; wherein said control circuit comprises; a first power supply node coupled to a first node of the startup current circuit; a reference power supply node coupled to the output current node; an input circuit having an input coupled to the disable input node, said input circuit configured to generate on an output node thereof a signal having different voltage and time characteristics relative to a signal coupled to its input node; and a comparator circuit having a first input coupled to the input circuit output node, having a second input coupled to the output current node, and having an output coupled to an enable input for the startup current circuit, said comparator circuit configured to disable the startup current circuit when a voltage of the first input exceeds a voltage of the second input by a second offset. - View Dependent Claims (29, 30)
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Specification