Current Limiting Bench PSU Schematic – 3V to 24V

Description

This is a 1-amp adjustable-voltage power supply. It adjusts from approximately 3 volts to 24 volts, and incorporates a feature enabling the maximum output current to be restricted. This functionality is particularly valuable when initializing a project for the first time or performing endurance testing on a piece of equipment.

Schematic Diagram

SW3 functions as the power switch. It also provides selection between the output with current limiting and the one without. SW2 offers a selection of three distinct current limits. The values can be increased or decreased as needed. These limits are determined by resistors R4, R5, and R6, which are set at 10mA, 25mA, and 65mA, respectively. However, users can select whichever limits are preferred. If an attempt is made to draw current exceeding the chosen limit, the output voltage will decrease. Consequently, a voltmeter will indicate when the load placed on the output is excessive.

Veroboard Layout

Adequate ventilation of the enclosure is essential. The heatsink is a folded aluminum strip measuring approximately 2mm in thickness, 18cm in length, and 6cm in height. SW1 facilitates the selection between (3V to 12V) and (3V to 24V) outputs. This reduction minimizes the heat dissipation required by the heatsink when operating at lower voltage levels.

Rear Of Front Panel

The front panel drawing primarily serves as a wiring guide, allowing for customized layouts. The pin spacing of the L200C is not compatible with stripboard, but it can be adapted with sufficient effort. Given that the limiting resistors may have relatively low values, even a small current flowing between the contacts of the wafer-switch can exert a noticeable influence. If, over time, the limits appear to have fallen, a spray-cleaner can be used to restore the switch’s functionality.