Build a 4-Stage Stabilised Power Supply with Short Circuit Protection

Description

A highly effective 4-stage stabilized power supply unit is presented here for evaluating electronic circuits. It delivers a precisely controlled and stable output, a crucial factor for accurate results in most electronic systems. The design incorporates an auditory-visual signal to immediately cut off power to the circuit under assessment if a short circuit is detected on the printed circuit board, thus safeguarding valuable components from potential harm.

This circuit furnishes four distinct regulated voltages – 12V, 9V, 6V, and 5V – alongside an unregulated 18V output, selectable via rotary switch S2. The chosen output level is displayed on the analog voltmeter connected to the output terminals. The circuit employs a standard 18V-0-18V, 500mA step-down transformer to generate 18V AC. A rectifier diode consisting of diodes D1 and D2 provides 18V DC, which is subsequently smoothed by capacitor C1 and supplied to the combination of regulator integrated circuits (IC1 through IC4).

These regulator ICs produce set, stabilized voltages of 12V, 9V, 6V, and 5V, respectively, which are connected to the rotary switch contacts. This power supply is suitable for loads demanding up to 200mA current. Complementary transistors T1 and T2 operate when the power to the circuit is switched on. The fully selected supply voltage is available at the collector of transistor T2, and this is utilized to power the load.

Circuit diagram:

LED3 signals the presence of output voltage. The negative terminal of piezo-buzzer PZ1 is connected to the output rail via LED2, maintaining the piezo-buzzer silent as its negative terminal is at full supply voltage (selected). Should a short circuit occur at the output, LED2 illuminates to activate the piezo-buzzer. A fuse failure indicator differentiates between short circuits at the output and input failure. It utilizes a bicolour LED (LED1) and resistors R1 and R2.

When power is accessible and the fuse is intact, the red and green segments of LED1 are effectively in parallel, producing a yellowish light. When the fuse fails, the green LED extinguishes, and the red LED illuminates to indicate a fuse breakdown. The circuit can be easily assembled on a general-purpose PCB. Incorporate small heat sinks for all ICs to manage heat dissipation. The output voltage can be read on a voltmeter. The circuit should be housed in a metal enclosure with provisions for the voltmeter, LEDs, rotary switch, and other components.