The gsm shield required is 1.5A.
Here a NPN setup
The GSM shield can often require up to 2A of current in short bursts - especially when turned on, reset, or initiating a call. However your Arduino board can only supply up to just under 1A. It is highly recommended that you use an external 5V power supply capable of delivering 2A of current - from an AC adaptor, large battery with power regulator, etc. Otherwise there is a very strong probability of damaging your shield and Arduino. Ignore this at your own risk. When connecting this supply DO NOT use the DC socket on the Arduino. Instead, connect the 5V (positive) from the supply to the 5V pin on the GSM shield, and the negative to the GND pin.
I'm using linear regulator because it is easy to make and it is only a school project. So i will only use it once. I already have a big heatsink and thermal paste so generating heat is not a problem.
You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.I would do this use a PNP to get you more current
thank god we don't live in a simulator.
Here's a circuit
Quote from: dhenry on Jan 04, 2013, 01:29 pmthank god we don't live in a simulator.You don't really know that. (Sorry, off topic, but couldn't resist. )
Quote from: eloso on Jan 05, 2013, 12:47 amI'm using linear regulator because it is easy to make and it is only a school project. So i will only use it once. I already have a big heatsink and thermal paste so generating heat is not a problem.I think you under-estimate how hot a regulator will get passing 1.5A of current. I'm too lazy to do the math, but if it's dropping any voltage whatsoever, it may be impractical to keep the die temperature cool enough to survive. I built a 28v-to-15v regulator to supply 100mA or so of current, and the little 1"x2"x0.5" heatsinks got hot enough that I couldn't touch them comfortably. You're asking for a lot more current than that. Trust me -- that "1.5A" spec on the regulator is nothing short of wishful thinking. There's no way you'll keep the case cool enough that the die won't damage itself at that kind of load.That is unless the 1.5A spec is for a very brief, worst-case, transient load... and average current is really *significantly* less.