Using 18V Zener Diode to Drop 36V Input Before 7809 Regulator for Micro Circuit

The discussion addresses the feasibility and practicality of using an 18V Zener diode to drop a 36V input before a 7809 linear voltage regulator to power a microcontroller circuit while reducing heat dissipation. It is clarified that using a Zener diode for voltage dropping does not reduce overall heat dissipation but shifts it between components, as the power loss remains the same. A series dropping resistor is necessary with the Zener, which will dissipate significant heat. Alternatives suggested include using a switching regulator to improve efficiency or cascading multiple 78xx series regulators (e.g., 7824 followed by 7812 or 7815) to handle large voltage drops more effectively. Another approach involves using a series pass transistor with the Zener to reduce voltage before the 78xx regulator, though this still results in heat dissipation. The 7809 regulator requires a suitable input voltage margin (typically 3V above 9V output) for proper regulation. The discussion also questions the use of 9V for modern microcontrollers, noting that some boards like the Arduino Nano accept 9V at the VIN pin. The original poster emphasizes the need for stable 9V and 18V supplies from a 36-50V input for powering a Nano board and a MOSFET driver gate, with heat management and long-term reliability as key concerns.
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