Maybe it is a silly question but I want to ask. What is the easiest and cheapest method to get 5 volts for the logic gates from a 12 volts supply?

 

I thought 5v regulators were cheap enough. How about a zener and a resistor.

 

Is this for an automotive application?

A 7805 Voltage regulator and 2 capacitors are all you need. It'll give you a 5 supply with plenty of current.

might be alittle more expensive than a Zener shunt regulator, but it's much easier to implement.

__________________
Jeff
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

Use a voltage divider employing 2 resistors only, that their R2/(R1+R2) gives you 0.42 ratio (5/12). Take a look:

http://hyperphysics.phy-astr.gsu.edu...ic/voldiv.html

 

but the Vout will change if the input voltage or output load changes.
If it's for a in a car, the battery voltage is at 12V with the car off, and 13.5 with the car on.

and depending on how many logic IC's he's using, The load could change alot.

__________________
Jeff
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

also if you use a voltage divider to generate the 5V line you then have source impedance and thus are straight away limited to how much current to can draw (based upon top resistor).

use a 5V reg, simple and very good

 

and i remember someone said that if you want a regulated voltage from such a voltage divider you have to supply 5 times the load current to the voltage divider. thats alot of wastage of power. so a linear regulator like the 7805 would be more efficient.

 

:wink:

I think you must use an IC voltage regulator, If I know a car battery will give you a 12 v and then your IC will regulate it into 5volts so 7805 will be more effective. In using a divider i think its not that good in terms like this and Im not positive regarding this I never tried to do this.

thanks anyway

 

Technically, he asked for voltage to logic gates and not Vdd. If that is really what he meant, then a regulator would be extreme over kill. Either a voltage divider, or if the gates have protection diodes then a simple resistor of about 10k to the pin would be fine (if its CMOS). A cap to ground would be good too, in conjuction with the resistor or divider of course.

__________________
A rectangular bear is just a polar bear after a coordinate transform. -- I dunno who.
A recent study shows that research causes cancer in rats. -- I dunno who said that one either.