Anyone know a good 5 amp adjustable or -12v ic? I can only seem to find 3amp online
While the LM337 is the negative voltage equivalent of the LM317, I have not seen a negative equivalent to the LM338.
You may need to consider adding a high power pass transistor to your negative supply circuit using the lm337.
You can use an external pass transistor to increase the current capability
Or you can use two linear regulators in parallel with some precautions to keep them from fighting each other.
Option 1: Set them to slightly different voltages so one regulates the voltage until the current reaches it's current limit. At that point the voltage starts to drop and the second regulator starts supplying current. The advantage of this is simplicity, but you end up with one device operating at maximum power all the time.
Option 2: Put a small resistance in each output line so the regulators don't fight each other. The advantage is that the power is shared between the two devices (if everything is balanced). The disadvantage is that you have additional resistance with some voltage drop and power dissipation.
I guess that design wont work with a mosfet to keep the heat down?downloading
a mosfet to keep the heat down
No ....... FETs only keep the heat down in switching circuits because the volts drop across them is smaller. In this application the point of the semiconductor is to have the voltage dropped across it. The heat generated is the same with a FET or bi-polar transistor.
That makes sense,
unfortunetly I don't have. 56 ohm resistors, would 1 ohm resistors work instead? I don't have enough to put in parrallel and also have 4 ohm ones instead of 5.6?
from the last hour of googling they don't make anymore than 3 amp negative regulator
I think it may be easier to use a positve used
know any good links for that?
would 1 ohm resistors work instead?
Depends on what you mean by work.
Those resistors are over current protection, so by making them higher then you make the over current protection kick in sooner. That is you don't get so much current out of the supply.
Are those resistors and that first transistor necessary if I want to do without overcurrent protection? I was planning on having a current limit resistor of like 2.5 ohms on the output as protection, all I need is to ensure its not over 12 volts I don't mind if it drops as I approach 5 amps, that's a max so I don't plan on going that high but I want to design to be able to handle it if the times come
Yes, the 0.56 Ohm resistors and lower transistor are for current limiting. If there is a big voltage difference between the supply and output (-12V), I'd want some resistance in the supply to burn up some of the power at high current and limit the max current in the event of a short.
4 Ohms in place of the 5.6 will be ok, but I'd be inclined to put 2 in series to reduce the current into the regulator. When the output is drawing 5 amps, the base current of the external transistor will be 100-200mA. There will be between 0.5 and 1V across the Base-Emitter, so the 4 Ohm resistor will see 125-250mA. The regulator will have to sink up to 450mA, so a 1A regulator will be fine.