Stupid question but i am totally out of experience and training: How do i do this?
I need to power a SD Card with my PICO which doesnt have a 3v3 line...
So how do i make this happen? G
With a voltage divider:
+5v ---////--- + ---////--- Gnd
R1 | R2
|
+3.3V
The voltage drops to Vin * (R1/(R1 + R2)).
Use any values of R1 and R2 that add up to about 10K.
Ahh thanks, i knew it was something like that but didnt think of an voltage divider anymore :0)
Problem with a potential divider for powering a circuit is that you need about 10 times more current down the divider than you are going to use as power. It is also a very high impedance so you need plenty of capacitors. The simple solution is to use one of the many 3v3 three terminal regulators.
that or a resistor + 3.3v Zener diode, which many do not have on hand
How about a 3-terminal 3.3V regulator? They're not quite as common as 7805s, but they're not that hard to find. LM1117 is popular...
It depends on the current, I found this:-
Upon initial insertion, SDIO and combo cards shall draw a maximum of 15mA, averaged over a 1 second
interval. Note that a memory or combo card built to meet the SD Physical specification version 1.0 may not
meet this initial current requirement. Any card built to meet a specification later than 1.01 shall meet this
requirement.
Once the card receives the CMD5 or ACMD41 initialization commands, the average current shall be:
? 50 mA or less, averaged over a 400 [ch956]S period for SDIO only cards
? 100 mA or less, averaged over a 1 second period for combo cards
This current limit will continue until the card exits the initialization procedure (Disabled for SD and in_idle_state
for SPI).
Which practically rules out a potential divider.
The MCP1700 (3v3 version) will do this nicely.
Need more numbers?
LT1086CT
LM3940IT3.3
LF33CV -- low cost!
LM2937ET3.3 --0.5A only