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Bench PSU for PC Schematic Circuit Diagram


Essential Equipment for Engineers: Bench Power Supply

A bench power supply is a fundamental tool found on the workbenches of electrical engineers and circuit designers. It serves as a crucial piece of test and measurement equipment, providing direct current (DC) voltage to devices under test, including circuit boards and other products undergoing validation.

Utilizing PC Power for Variable Supply

Considering that every personal computer (PC) is equipped with a robust, well-regulated Power Supply Unit (PSU) delivering various outputs, including a 12 V rail, why not harness it to create a variable power supply ranging from 1.25 to 10 V? This innovative approach is precisely what we’re suggesting here. This power supply design can also serve as an excellent addition to a traditional bench supply, especially if the latter has only one output, allowing simulation of an analog voltage when needed.

Bench PSU for PC Schematic Circuit Diagram

Efficient DC-DC Conversion with MC34063

For the conversion process, the cost-effective and widely used MC34063 DC-DC converter takes charge, configured as a step-down converter. Employing a switching solution enables the minimization of losses attributed to the Joule effect. The MC34063 interfaces with a microcontroller, complemented by an LCD display (1×16 characters), providing the capability to showcase both the output voltage and the current supplied by the Power Supply Unit (PSU) (connect K3 to pins 4 and 5 of K4). Under optimal conditions, the circuit can deliver a current of up to 700 mA; however, the IC incorporates a built-in current limiter that activates once the specified limit is exceeded.

Microcontroller Programming and Calibration

To operate the microcontroller, utilize the software accessible from [1], and adjust P2 to align the displayed output voltage with the actual value. It’s important to note that specific single-line 16-character displays function similarly to displays with two lines of eight characters. The downloadable package comprises two HEX files tailored for both display scenarios.

Convenient Installation and Precision Adjustment

Upon assembling the PSU, it can be conveniently accommodated within one of the available slots in your computer, designed for a 5¼-inch floppy disk drive. A noteworthy detail to enhance the precision of output voltage adjustment involves the incorporation of a second 1 kΩ potentiometer in series with P1, allowing for more accurate voltage setting.


A Bench power supply is a tool that converts Alternating Current (AC) to Direct Current (DC). It is typically used to test equipment on lab benches. It has a much more controlled voltage, thus protecting circuits under test.

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