Sizing Decoupling Capacitors for 240AC to 5VDC Conversion

Thread starter Pagedown
Start date Feb 18, 2011

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SUMMARY

This discussion focuses on sizing decoupling capacitors for a 240VAC to 5VDC conversion using a 20:1 step-down transformer, a full-wave bridge rectifier, and a 7805 voltage regulator. Key recommendations include using a minimum of 2000uF electrolytic capacitor rated at 25V for C2 and a 0.1uF to 0.22uF capacitor for high-frequency transients. The MDA3551 bridge rectifier is deemed inappropriate for 1A applications, and a 1N400x diode is suggested to prevent reverse biasing of the 7805. Proper grounding and load considerations are emphasized to ensure reliable operation.

PREREQUISITES

Understanding of AC to DC conversion principles
Familiarity with capacitor sizing and filtering techniques
Knowledge of voltage regulator operation, specifically the 7805
Basic circuit simulation skills, preferably using LTSpice or similar tools

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USEFUL FOR

Electronics engineers, hobbyists designing power supply circuits, and anyone involved in the development of low-voltage DC power systems.

Mar 3, 2011

Pagedown

Attached is the simulation, full load is 0.2A. and the current drawan from rectifier is 900mA.

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Mar 14, 2011

Pagedown

Latest update : Without the PI-filter, the inrush current is less. Simulated using multisim, using just a RC capacitor input filter, I can use a lower VA transformer to supply the same amount of current.