Here’s a
circuit for linear workbench desktop power supply
circuit converts a high input voltage (12V) from the SMPS of a PC into low
output voltage (1.25 to 9 volts). An adjustable three-pin voltage regulator
chip LM317T (IC1) is used here to provide the required voltages. The LM317T
regulator, in TO-220 pack, can handle current of up to 1 amp in practice. This
is the figure of the design circuit;
This figure shows the circuit of the desktop power supply.
Regulator IC LM317T is arranged in its standard application. Diode D1 guards
against polarity reversal and capacitor C1 is an additional buffer. The green
LED (LED1) indicates the status of the power input. Diode D2 prevents the
output voltage from rising above the input voltage when a capacitive or
inductive load is connected at the output. Similarly, capacitor C3 suppresses
any residual ripple. The circuit can be wired on a common PCB. After
fabrication, enclose the circuit in a metallic cover. Then open the cabinet of
your PC and connect the input line of the gadget to a free (hanging) four-pin
drive power connector of the SMPS carefully. Connect a standard digital
voltmeter in parallel with the output leads to accurately set the desired
voltage with the help of variable resistor VR1. You can also use your digital
multi meter if the digital voltmeter is not available. Switch on S1 and set the
required voltage through preset VR1 and read it on the digital voltmeter. Now
the power supply is ready for use.
