Traditional dual power supplies (symmetrical positive and negative power supplies) lack continuous adjustability, making them less convenient for practical use. In this article, we connect two three-terminal regulators, the 7815 and 7915, symmetrically to create a set of positive and negative symmetrical regulated power supplies. This setup allows individual adjustments or simultaneous adjustments of the output voltages.
As illustrated in the diagram, the AC voltage output from the transformer (dual 18V) is rectified by diodes D1 through D4. Capacitors C1 and C2 filter the DC voltage. The center tap of the transformer serves as the common ground terminal. The DC voltage is then connected positively and negatively to pins 1 and 3 of the 7815 and 7915 regulators, respectively. Pin 3 of the 7815 is connected to the sliding contact "d" of potentiometer W2, while pin 1 of the 7915 is connected to the sliding contact "C" of potentiometer W1. Sliding contact "C" to the "0" terminal grounds it, and adjusting W2 yields a positive variable voltage ranging from "+6V to +15V" at the "a" end. Conversely, sliding contact "d" to the "0" terminal grounds it, and adjusting W1 provides a negative variable voltage ranging from "-6V to -15V" at the "b" end. Replacing W1 and W2 with a coaxial potentiometer creates a symmetrical adjustable power supply, allowing continuous adjustment of the output voltage from ±6V to ±15V, achieving synchronous adjustment capabilities.
The circuit's 7815 and 7915 three-terminal voltage regulator blocks require heat sinks. The transformer's power rating depends on the load requirements of the application.
It’s worth noting that this design offers significant advantages over traditional fixed dual power supplies. The ability to adjust both positive and negative outputs independently or together provides flexibility that is highly beneficial in various applications, such as audio amplifiers, laboratory equipment, and educational tools. Additionally, the use of high-quality components like the Murata capacitors ensures reliability and performance stability.
In real-world scenarios, the design also considers safety features, such as overcurrent protection, which prevents damage to the circuitry under abnormal conditions. Furthermore, the coaxial potentiometer simplifies user interaction by allowing simultaneous adjustments of both channels with a single control knob.
Overall, this symmetrical adjustable power supply is a practical solution for anyone needing a versatile and reliable power source. Its design balances simplicity with functionality, making it an excellent choice for hobbyists, engineers, and educators alike.
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