1
Beginners / Re: The old "Replace blue LEDs with red LEDs" 7 segment question (74HC595)
« Last post by pcprogrammer on Today at 11:20:17 am »I have some doubts though, as I can see on the layout that it appears that the IR supply is just a 3V3 Zener diode dropping the 5V line.
How much current can a small SMD Zener usually handle?
>1A?
It is not so much as to what the zener can handle, it is about the series resistor dissipating the remainder of the voltage. The zener is biased to some current and can keep the voltage in check as long as the current drawn stays within limits. To be able to use the 3V3 made this way to drive up to 300mA the resistor needs to be 5.6 Ohms and the zener must be able to dissipate about 1 Watt of energy when no current is flowing into the displays.
Most likely it will not be designed for this, so not a good idea to start using this supply for driving the displays.
A series diode or two in the common connection of the 7 segment displays, like SeanB suggested, might be an easier solution.