Dual voltage adjustable regulated power supply circuit

The dual-voltage adjustable regulated power supply circuit shown can be used as a power supply frequently used in circuit experiments. The current does not exceed
1A, but the two voltages are adjustable separately and do not affect each other.
    Nl and N2 are 78 series three-terminal voltage stabilizing
integrated circuits. Since their output voltage is equal to the sum of
the nominal voltage stabilizing value and the common ground terminal voltage
, as long as an
adjustable positive and negative voltage is added to the common terminal, the The output
voltage is adjustable. The lines N1 and N2
share a set of rectified power supplies.
Another set of outputs of transformer T , after VD rectification, C4
filtering, current limiting, and VS voltage stabilization, specially
provides a common ground reference negative voltage. The polarity
of
the voltage , and then adjust RP1 or RP2 to
adjust the two output voltages respectively. According to
the data shown in the figure, the two output voltages can
continuously change within the range of 1. 5-25V, and the voltage stability also meets the usage requirements. When the voltage is lowered, the input/output voltage difference of the integrated circuit
is very large, and the power consumption increases accordingly, so a heat sink must be installed.
    In addition, when selecting a positive reference voltage, the closer the sliding arm of the potentiometer is to the ground, the higher the output voltage will be. When selecting a negative reference voltage, the
closer the sliding arm of the potentiometer is to the ground, the lower the output voltage will be.
    The selection principle of RP1 and RP2 is to make the voltage regulation value slightly higher than the nominal value of the integrated circuit. The maximum input/output voltage difference of the voltage stabilizing circuit
generally does not exceed 35V. Therefore, the secondary side voltage of the transformer should not be higher than 25V to avoid damage to the integrated circuit.