2 linear regulators

I have a lot of 5 volt devices Xbee,arduinos,compass,accelerometer, ping,PIR, any many others. I have heard that using 2 external linear regulators in parallel can cause problems because the regulator's output voltage is slightly different. So I am thinking of using 2 linear regulators and power half the devices with other and the other half with the other. can this cause signal problems between the 2 half's?

I know some people will say that I should use a switching regulator and I have a question about them. Can I use a switching regulator using 12 volts on [u]ANY[/u] 5 volt device? could it hurt my xbee or Arduino or one of my sensors? also what is the chance one of these will break and surge 12 volts through my 100's of dollars in sensors and Arduinos?

using 2 linear regulators and power half the devices with other and the other half with the other.

This should work just fine.

also what is the chance one of these will break and surge 12 volts through my 100's of dollars in sensors and Arduinos?

They usually break because the load (current) is more than they can source (check the datasheet). From what I reckon, a broken regulator would not provide any voltage (rather than allow the input voltage to go through). You can get a 5V/3A switching mode regulator on ebay for \$5 or less.

also what is the chance one of these will break and surge 12 volts through my 100's of dollars in sensors and Arduinos?

The same as if you used one regulator, except that you may only blow up half your circuit.

As to whether they fail open or closed circuit I have no idea.

Rob

"I have a lot of 5 volt devices Xbee,arduinos,compass,accelerometer, ping,PIR" Some of those are 3.3V devices as far as I know, like the Xbee.

Is your source 12V? Then a 5V switching regulator would be great if you have lots of current needs. For example: 5V, 3.5V http://www.pololu.com/catalog/product/2110 5V, 600mA http://www.pololu.com/catalog/product/2104 3.3V, use a small linear regulator from the 5V to make 3.3V like the current Arduino's do.

Otherwise, use walwarts, here are 2 that I use: 5V, 2A: http://www.dipmicro.com/store/DCA-0520 5V, 4A http://www.mpja.com/5VDC-4A-Regulated-Plug-Supply-Openpeak/productinfo/18520+PS/

12V, 1A for powering strings of LEDs http://www.dipmicro.com/store/DCA-1210

also what is the chance one of these will break and surge 12 volts through my 100's of dollars in sensors and Arduinos?

The same as if you used one regulator, except that you may only blow up half your circuit.

As to whether they fail open or closed circuit I have no idea.

Rob

They will shutdown on over-current or over-heat - never have seen a regulator fail myself BTW - the usual issue is a short circuit so the over-current shutdown covers that eventuality.

Try to ensure that the parts of the circuit that are powered separately cannot try to power each other via signal lines should one regulator shutdown - adding series resistors can help (for logic lines 10k in series usually works, perhaps with 100pF across it if a fast logic signal).

The only weird sorta fail would be a 7805 I got off ebay that put out 4.73 volts but never seen one fail and short, I've hadthem overheat and shutdown, but that's alliance

The reason I ask this is because I am making a large robot with a ton of sensors (50 pound robot) it will have a 12 volt lead acid battery at 12 A/hr and I will need something of 5 volts at .8 amps idle and 3-4 amps max (the 5 volt line is for sensors,leds,servos ,ect) I was going to use a 9 volt linear regulator and then a 5 volt linear regulator to distribute heat between 2 regulators. I know people will recommend switching regulators but I don't know if this will mess with any sensitive systems.

Use the switchers if you possible can at all. use two and separate the loads according to function. A linear regulator can be thought of as a "Voltage Variable Resistor"... Heat in a regulator is wasted power... Much better to deliver that Power to the load than to warm the environment... The Environment won't turn your wheels... If you are really paranoid about regulator failure... something that never happened to me in production and use of Both buck and boost mode devices, a simple "crowbar" (SCR and a Zener diode) device can be used to "Blow" a fuse and I recommend "Polyfuses" in the 12V supply to the switchers... I used Tranzorbs... 1.5KE18's for the 12V stuff and 1.5KE 6.8's for the 5V stuff as they also provide spike clipping, should it happen... it never did for me But any protection at all is good. Easy to find power issues... the higher current's drawn by "defects" cause the fuses to get hot... Use Your 10 "digital wattmeters" or fingers.... to find a "hot" polyfuse Linear regulators are easy to use but mostly really inappropriate for power control as they convert unwanted voltage... to heat, Wasted heat unless your "robot" is also your "coffee warmer"...

Doc