I need 3.3 volts @250 mA and 5 volts supply for a board. What would be the issues if I use 3 diodes to derive 3.3 volts from 5 volts? Considering .6 to 0.63 volts drop at 250 mA for 1N4001, I should be getting the required voltage. Please comment on the following points

1. If I use 7805, there could be a possibility of the output voltage being 4.9 volts instead of 5. If I use 3 diodes, and if diode drop is 0.63 volts, then my Vcc is going to be 2.9 volts instead of 3.3 volts, and this is a bit dangerous. But then at 250 mA, diode drop will be less then 0.63, and this should bring the voltage to 3 volts.

2. It is better to use LM317, to produce 5.1 volts with an extra tuning resistor. In this case, I can hope to get Vcc of 3 volts plus instead of 2.9 or 2.95 volts.

3. The above methods are better than using a 1 watt zener, considering long term reliability.

3. It is better to invest in 3.3 volts regulator like 7833/LM2937/LM3940.

Please guide.

Raj Nambiar