15-step digital power supply

Description

The 15-step digital power supply is a simple circuit to obtain variable DC voltage from 1.25V to 15.19V in reasonably small steps. The input voltage may lie anywhere between 20V and 35V. The first section of the circuit comprises a digital up-down counter built around IC a quad 2-input NAND Schmitt trigger (4093), a binary up-down counter (4029). Two gates of IC 4093 are used to generate up-down logic using pushbuttons S1 and S2, respectively, while the other two gates form an oscillator to provide clock pulses to IC (4029). The frequency of oscillations can be varied by changing the value of the capacitor or preset.

The 15-step digital power supply is more durable. When the power is switched on, resets itself, and hence the output at pins 6, 11, 14, and 12 is equivalent to binary zero, i.e. ‘0000’. The corresponding DC output of the circuit is minimum (1.25V). As count-up switch S1 is pressed, the binary count of IC increases and the output starts increasing too. At the highest count output of 1111, the output voltage is 15.19V (assuming the in-circuit resistance of preset as zero).

• Can be used for trimming the output voltage as desired.
• The input voltage may lie anywhere between 20V and 35V.
• To decrease the output voltage within the range of 1.25V to 15.2V, count-down switch S2 is to be depressed.