• Frequent contributor R. • Jayapal recently shared an interesting Design Idea (DI) for power supply control and sequencing in MCU-based applications that combine analog and digital circuitry: " Short push, long push for sequential operation of multiple power supplies ." The application becomes challenging when there’s a requirement to have the digital side powered up and stable for a programmable interval (typically approximately a second or two) before the analog comes online. • Wow the engineering world with your unique design: Design Ideas Submission Guide Since Jayapal had already published a fine digital solution to the problem, I’ve taken the liberty of attempting an (almost painfully) simple analog version using an SPDT switch for ON/OFF control and RC time constants, and Schmidt triggers for sequencing. • Figure 1 shows how it works. • Figure 1 Simple analog supply sequencing accomplished using an SPDT switch for ON/OFF control and RC time constants, and Schmidt triggers for sequencing. • Switching action begins with S1 in the OFF position and both C1 and C2 timing caps discharged.
Article Summaries:
- R. Jayapal’s recent Design Idea (DI) proposes a simple analog method for sequencing power supplies in MCU‑based systems that combine digital and analog circuitry. The scheme uses an SPDT switch to toggle a 15‑V rail, RC time constants to delay activation, and Schmitt triggers to control PFET and NFET switches. When the switch is turned on, the 5‑V rail powers up within ~1 ms, while the 15‑V rail is delayed by a programmable interval (≈2.2 s with the shown values). Turning the switch off reverses the sequence, ensuring orderly shutdown. The design includes protection diodes and notes that MOSFETs need adequate current handling.
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