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Two Isolated Power Design on the same Electronics Circuit

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Farooq Muzammil

Newbie level 1
Jun 2, 2011
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I am designing a mixed (analog and digital) electronic circuit. The system is composed of 5 different modules. One module is dedicated for conversion (28 V to 5 and 3.3 V) and distribution to other modules. One of the module consists of a microprocessor and related interfacing components.
Now, the requirement is to provide two isolated power supplies to this module. One of the supply (5 V) will be used for running all the main circuit modules and another supply (also 5 V) will be used to activate a series of buffers only in special cases.
The design should be such that I could use any buffer any time i.e. activate and deactivate the buffer whenever i require.
Kindly provide some solution or approach guidelines.

You can separate the analog and digital supplies of your circuit by connecting the analog and digital supply pins to separate nodes, and then joining these nodes at the point closest to your power supply. You can join the supplies with the use of inductors, which will block noise traveling between the nodes. This will reduce noise caused by digital circuitry being injected into analog circuitry. You can also insert capacitors between power and ground to reduce noise further.
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