Alterable DC power supply circuit

An alterable DC power supply circuit includes a regulator, a resistor, and an adjustable load resistance. The regulator includes a voltage input pin, a voltage output pin, and an adjusting pin. The resistor is coupled between the voltage output pin and the adjusting pin. The adjustable load resistance is coupled between the adjusting pin and ground. The output voltage of the alterable DC power supply is adjustable by adjusting the adjustable load resistance. Using this alterable DC power supply to test the voltage stability of a chipset improves testing efficiency.

FIELD OF THE INVENTION

The present invention relates to power supply circuits, and particularly to an alterable DC power supply circuit.

DESCRIPTION OF RELATED ART

The power requirements of electrical systems are becoming ever more demanding. To maximize energy efficiency, power density, and system serviceability, the power system designer is required to provide increased functionality and improved performance at minimal cost.

Frequently however, an electronic component may require a somewhat lower voltage than that provided by an AC/DC converter. Therefore, a DC power supply circuit is interposed between the AC/DC converter and the electronic component. This DC power supply circuit receives a 12V supply from the AC/DC converter, and outputs a DC supply at a suitably lower voltage (typically about 3.3 volts, depending on the particular electronic component in question).

FIG. 2shows a conventional voltage regulating circuit10. The voltage regulating circuit10includes a regulator12with a voltage input pin3, a voltage output pin2, and an adjusting pin1, two resistors RF1and RF2, and two capacitors C10and C20. The resistor RF1is coupled between the voltage output pin2and the adjusting pin1of the regulator12. The resistor RF2is coupled between the adjusting pin1of the regulator12and ground. The capacitor C10is coupled between the voltage input pin3and ground. The capacitor C20is coupled between the voltage output pin2and ground.

The voltage input pin3is coupled to a voltage input port VIN. The voltage output pin2is coupled to a voltage output port VOUT. The output voltage of the output port VOUT is found using the following equation: VOUT=VREF*(1+RF2/RF1), wherein VREF is a voltage at the resistor RF1. Generally, the resistance of the resistor RF1is 125 Ohm, and the VREF is about 1.25V. The output voltage can be varied by according to the resistance of the resistor RF2selected. Therefore, to adjust the output voltage of the voltage regulating circuit10, the resistor RF2must be replaced by an operator. It is inconvenient and inefficient in voltage stability testing of a chipset to use the voltage regulating circuit10.

What is needed, therefore, is an alterable DC power supply circuit for adjusting output voltage effectively and conveniently.

SUMMARY OF THE INVENTION

An exemplary alterable DC power supply circuit includes a regulator, a resistor, and an adjustable load resistance. The regulator includes a voltage input pin, a voltage output pin, and an adjusting pin. The resistor is coupled between the voltage output pin and the adjusting pin. The adjustable load resistance is coupled between the adjusting pin and ground. The output voltage of the alterable DC power supply is adjustable by adjusting the adjustable load resistance.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, an alterable DC power supply circuit20in accordance with the present invention includes a regulator22, a resistor R1, an adjustable load resistance24, and five capacitors C1˜C5.

The regulator22includes a voltage input pin III, a voltage output pin II, and an adjusting pin I. The voltage input pin III is coupled to a voltage input port VIN. The voltage output pin II is coupled to a voltage output port VOUT. The resistor R1is coupled between the voltage output pin II and the adjusting pin I of the regulator22. The adjustable load resistance24is coupled between the adjusting pin I and ground.

The capacitor C1is coupled between the adjusting pin I and ground for regulating a voltage at the adjustable load resistance24. The capacitors C2and C3are coupled between the voltage input pin3and ground in parallel for regulating a voltage input from the voltage input port VIN. The capacitors C4and C5are coupled between the voltage output pin2and ground in parallel for regulating a voltage output from the output pin II of the regulator22.

In this embodiment, the resistance of the resistor R1is 125 Ohm, and a voltage at the resistor R1is 1.25V. Therefore, the output voltage of the output port VOUT is found using the following equation: VOUT=1.25*(1+RL/125). Wherein RL is the resistance of the adjustable load resistance24. The output voltage is selectable by adjusting the resistance of the adjustable load resistance24.

The adjustable load resistance24could be a sliding rheostat, a resistance box, or other adjustable resistor. In this embodiment of the present invention, the adjustable load resistance24includes a switch242and seven resistors R1˜R7of different pre-selected values, coupled between the switch and ground in parallel. The switch242includes a terminal connected to the adjusting pin, and another terminal selectively connected to one of the resistors R1˜R7, and other ends of the resistors R1˜R7are connected to ground. Therefore, the output voltage is adjustable by controlling the switch242to select a suitable resistance RL from the resistors R1˜R7without having to replace a resistor. It is convenient and efficient in voltage stability testing of a chipset to use the alterable DC power supply circuit20.

The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.