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Diodes in place of 3.3V LDR?
Posted: Thu Nov 06, 2008 8:24 am
by morrog
On the homepage for AVR USB, the schematic shows two diodes in place of a 5V to 3.3V regulator. Would that really work? I can't image how two diodes are supposed to drop the voltage down from 5V to 3.3V.
Thank you.
Re: Diodes in place of 3.3V LDR?
Posted: Thu Nov 06, 2008 11:54 am
by henni
morrog wrote:...two diodes in place of a 5V to 3.3V regulator. I can't image how two diodes are supposed to drop the voltage down from 5V to 3.3V.
A silicon diode has a forward voltage (Flussspannung) of about 0.7 V. Two diodes will drop the 5V down to 5V - (2* 0.7V) = 3.6V, which is sufficient low voltage for the USB lines. An extra advantage is that diodes have no quiescent current, therefore, standard conform USB sleep mode (less than 500 µA current) is easiest with these two diodes.
Posted: Thu Nov 06, 2008 7:41 pm
by morrog
I'm still pretty new to electronics, so I had not known about the forward voltage on diodes. Thank you for the explanation. Very helpful
