How to make 3.3V from 5V and vice versa???

3.3V and 5V

how can i make 3.3V from 5V and vice versa???

how can i have this circuit interface with an FPGA....

thanks alot,
Salma

3.3V and 5V

probably the simplest way with CD4049 or 4050

Re: 3.3V and 5V

You should first say that if wether you need to make a 3.3V supply off a 5V one or do you need to connect I/I signals of a 5V system to a 3.3V system.

I assume you are into the need of the second one,
you could connect your 3.3V outputs to the 5V system but as for your inputs to the 3.3V system from a 5V powered IC you will need a level convertion.
There are multiple ways of Level convertion :
1- Using the Level Convertors such as :
74VHC244 , https://www.fairchildsemi.com/ds/74/74VHC244.pdf

2- Using a resistor division network in a way that you multiply your 5 volts system's output by 2/3. This would translate your 5V to a ~3.3V signal.

3- You can use 5V-Tolerant chips. These chips can tolerate when feeded by a 5V signal where they are being supplied by a 3.3V supply.

4- Using an open-collector output in the 5V section you could pull-up your outputs to 3.3V to solve the problem.

Farshid

Re: 3.3V and 5V

if the i/o pins are 3.3V and tolerrent to 5V , u can use a simple pull up resistor to shift 3V to 5v . other wise u can use CMOS buffer ICs for level shifting .

Re: 3.3V and 5V

hi
go to TI WEB SITE
there are alot of power regulators specially made for FPGA of xilinx and altera
and in single chip you can set 3 diffrent voltages (1.8v,2.5v,3.3v..........)
you can choose the one that suite you.


regards.

Re: 3.3V and 5V

I agree with bmwcoupe, TI has low dropout voltage regulators (LDO) with different options like low-noise, various packages, etc. I've used REG104.

3.3V and 5V

Why aren't simple voltage dividers used to do that?

Re: 3.3V and 5V

ya thats much better if u just need to convert voltage, then simply use voltage divider.

Re: 3.3V and 5V

It is 3.3 volts

Re: 3.3V and 5V

the simplest way to do it :
voltage divider (using resisters just like the mentioed above)
then take the output of the divder as an input to the buffer
and the output of the buffer to the fpga...

a simple buffer:
u can use LM741 (OPAmp).. input at the non-inverting input .. and connect its negative input to its output

Re: 3.3V and 5V

good question from cmosbabe, why or when use regulators or voltage divisors ?

Re: 3.3V and 5V

ok here's the thing .. the chip has an input resistance that acts parrallel to one of the dividers resistor and messes up the divider ratio!!

case1:
if the supplied chip draws a constant current from the supply, hence it has a constant input resistance.
in this case, u CAN use ONLY a voltage divider BUT!!!. if u dont know the input resistance u can not determine the values of the 2 resistors that makes up the divider.
what u can do in this case is to fix one resistor say(a 10KΩ) and then have the othe resistor as variable resistor which you could change inorder to get the output u need from it .. this calibration is done WITH the chip connected to the divider.

case2:
if the supplied chip draw a variable current. then u have to add either a regulator or a buffer between the divider and the chip.
again thats is needed becuse the chip has an input resistance that acts parrallel to one of the dividers resistor and messes up the divider ratio!!