Reverse conduction protection method and apparatus for a dual power supply driver
AssigneeAgere Systems Inc.
InventorArvind Reddy Aemireddy
Life of this patent
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Abstract
The invention is a dual stage power supply with a protection circuit for preventing reverse conduction through the lower voltage driver of the dual stage power supply and excess power dissipation when the higher voltage driver is on. In one embodiment of the invention, the protection scheme comprises a comparator that detects when the voltage on the output pad exceeds a predetermined voltage and a protection transistor which is controlled by the comparator to block reverse conduction through the lower voltage driver when the higher voltage driver is operating.
Claims14
A protection circuit for preventing reverse conduction through a lower voltage driver that is coupled to a first node when a higher voltage driver coupled to the first node is driving the first node to a voltage higher than the maximum voltage of the lower voltage driver, wherein the lower voltage driver includes an output stage having a first transistor having a first current flow terminal coupled to a lower voltage rail and a second current flow terminal coupled to drive the first node, the circuit comprising:
- a second transistor having a first current flow terminal coupled to the second current flow terminal of the first transistor and a second current flow terminal coupled to the first node, and further having a control terminal;
- a comparator coupled to detect when a voltage on the first node exceeds the voltage of the lower voltage rail, the comparator having an output coupled to the control terminal of the second transistor and configured to turn the second transistor off if the voltage on the first node exceeds the voltage of the lower voltage rail;
- and
- a diode clamp coupled between the control terminal and the first current flow terminal of the second transistor.
An output stage for a lower voltage driver of a dual stage power supply circuit having protection from reverse conduction through the output stage when a higher voltage driver is driving a common output node of the lower voltage driver and the higher voltage driver to a voltage higher than the maximum voltage of the lower voltage driver, the output stage comprising:
- a voltage rail;
- a first transistor having a first current flow terminal coupled to the voltage rail and a second current flow terminal coupled to drive the output node;
- a second transistor having a first current flow terminal coupled to the second current flow terminal of the first transistor and a second current flow terminal coupled to the output node, and further having a control terminal;
- a comparator coupled to detect when a voltage on the output node exceeds the voltage of the voltage rail, the comparator having an output coupled to the control terminal of the second transistor and configured to turn the second transistor off if the voltage on the output node exceeds the voltage of the voltage rail;
- and
- a diode clamp coupled between the control terminal and the first current flow terminal of the second transistor, wherein the diode clamp comprises a third transistor having a first current flow terminal, a control terminal, and a tub coupled to the control terminal of the second transistor and a second current flow terminal coupled to the first current flow terminal of the second transistor.
A dual stage power supply comprising:
- a first, higher voltage power supply driver coupled to an output node;
- and
- a second, lower voltage power supply driver coupled to the output node, the second power supply driver comprising:
- an input signal source;
- a voltage rail;
- a first transistor having a first current flow terminal coupled to the voltage rail and a second current flow terminal coupled to drive the output node;
- a second transistor having a first current flow terminal coupled to the second current flow terminal of the first transistor and a second current flow terminal coupled to the output node, and further having a control terminal;
- a comparator coupled to detect when a voltage on the output node exceeds the voltage of the lower voltage rail, the comparator having an output coupled to the control terminal of the second transistor and configured to turn the second transistor off if the voltage on the output node exceeds the voltage of the voltage rail;
- and
- a diode clamp coupled between the control terminal and the first current flow terminal of the second transistor, wherein the diode clamp comprises a third transistor having a first current flow terminal, a control terminal, and a tub coupled to the control terminal of the second transistor and a second current flow coupled to the first current flow terminal of the second transistor.
Dependencies are inferred from the claim text.