US 5,632,039 A · Circuit that automatically switches between supplying a microprocessor with a first voltage and a second voltage

Abstract

A circuit that automatically switches the power supply voltage PVDD provided to a CPU between 3.3 volts and 5 volts. The circuit detects whether the CPU installed in a socket is a 3.3-volt part or a 5-volt part by determining the state of a voltage detect sense pin provided by the socket. If the voltage detect sense pin is driven low, that indicates a 3.3-volt CPU is being used. If a 5-volt CPU is installed, the voltage detect sense pin is left floating by the CPU, which allows a pullup resistor to pull the voltage detect sense pin high. The power supply voltage provided to the CPU is regulated through a power field effect transistor (FET). The gate of the power FET is connected to the output of a voltage reference source and is coupled to a 12-volt supply signal. If the voltage detect sense pin is pulled high, the voltage reference source is turned off, allowing the 12-volt supply signal to drive the gate of the power FET. This in turn allows the power FET to pass a 5-volt supply signal to the CPU supply signal PVDD. If the voltage detect sense pin is pulled low, the voltage reference source is turned on to drive the gate of the power FET to approximately one threshold voltage above 3.3 volts. In response, the power FET passes only 3.3 volts to the CPU supply signal PVDD.

Claims18

Dependent claims

A circuit for automatically switching a power supply voltage provided to a microprocessor used in a computer system between a first voltage and a second voltage, said first voltage being greater than said second voltage, wherein the computer system includes a power supply having a first power supply output providing the first voltage, and wherein the microprocessor provides a voltage detect sense signal pin for indicating whether the microprocessor requires the power supply voltage at the first voltage or the second voltage, the voltage detect sense signal being at a first state to indicate the first voltage, and the voltage detect sense signal being at a second state to indicate the second voltage, the circuit comprising:

a feedback circuit responsive to the voltage detect sense signal and providing an output signal, said output signal being driven to a third voltage if the voltage detect sense signal is at the first state, and said output signal being driven to a fourth voltage if the voltage detect sense signal is at the second state;
and
a field effect transistor having a gate driven by said output signal, a drain connected to the first power supply output, and a source coupled to a microprocessor power supply voltage pin wherein the field effect transistor drives the microprocessor power supply voltage to the first voltage if said output signal is at said third voltage and to the second voltage if said output signal is at said fourth voltage.

A computer system, comprising:

a socket having a voltage detect sense pin and a power supply pin;
a microprocessor having a plurality of pins for insertion into said socket, one of said microprocessor pins being connected to said voltage detect sense pin and-another of said microprocessor pins being connected to said power supply pin, wherein said microprocessor drives said voltage detect sense pin to a first state if said microprocessor requires said power supply pin to be driven to a first voltage, and wherein said microprocessor drives said voltage detect sense pin to a second state if said microprocessor requires said power supply pin to be driven to a second voltage, said first voltage being greater than said second voltage;
a power supply having a first power supply output for providing said first voltage;
and
a circuit coupled to said power supply and said socket for automatically switching said power supply pin between said first voltage and said second voltage, including:
a feedback circuit coupled to said voltage detect sense pin for providing an output signal, said output signal being driven to a third voltage if said voltage detect sense pin is at said first state, and said output signal being driven to a fourth voltage if said voltage detect sense pin is at said second state;
and
a field effect transistor having a gate driven by said output signal, a drain connected to said first power supply output, and a source coupled to said power supply pin, wherein said field effect transistor drives said power supply pin to said first voltage if said output signal is at said third voltage and to said second voltage if said output signal is at said fourth voltage.

5 more elements

Dependencies are inferred from the claim text.

Circuit that automatically switches between supplying a microprocessor with a first voltage and a second voltage

Life of this patent

Circuit that automatically switches between supplying a microprocessor with a first voltage and a second voltage

Life of this patent

Abstract

Claims18