This guy gives a pretty good tutorial on working with transistors. He is using it to switch but he also gives the info needed to regulate output. Transistors in TO3 packages are the highest output transistors. NPN transistors are the easiest to figure out. Not that any are easy.
http://www.youtube.com/watch?v=8DMZSxS-xVc&feature=related
This is the closest I could quickly find of a amperage boosting circuit using a 2n3055 transistor. You'd have to gang several to get the amperage you wanted. Just substitute your voltage regulator for the LM317. Eliminate P1 and R2. I think P2 determines the base/emitter amperage which is about at least 1/20th of the output amperage of the transistors. Each base/emitter is a branch so the trigger amperage will be equally divided among the bases of the 3055's. It sets the amperage limit on the output for the transistors. The reasons for all the diodes and capacitors is to shunt and filter voltage spikes that could damage the transistors.
http://electronics-diy.com/schematics/654/6amp_reg_powersupply.gif
This is another example but a different approach. Using power transistors like a 2n3055 will boost output.
http://www.extremecircuits.net/2009/08/ampere-or-current-booster-circuit.html
As you can see its not all that easy.
I looked up ganging voltage regulators but they interfere with one another outputs so I guess that isn't possible.
Steve
On 3/16/2012 7:12 AM, S_Wilson wrote:
Use the regulator to drive a power transistor that can handle that load. The problem there is coming up with a design that works. I was never very good at figuring out transistors myself. I used to be involved in remote controlled gas airplanes. I needed a similar design for using a car battery on the glow plugs for the motors. I got lucky and had a guy at an electronics store show me a voltage follower transistor circuit that was easy and it worked. Any power transistor that is driven at that amperage will need a good heat sink. I think all it took was using the regulator to drive the base of the transistor. You may have to use a couple of transistors for 20 amps. There are also some other devices called MOSFETS that are good for handling larger loads. My experience working with either is very limited.
Good luck
Steve
On 3/16/2012 6:24 AM, Edward Hughes wrote:I need to regulate a 12v source with a load of up to 20 amps. I don’t think a small 3 leg regulator will handle that load, so how can I achieve this?
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