Quote: Originally Posted by
drutort 
i understand the issue with the 12v but i fail to see the reason for the 5v? why does a simple 5v voltage regulator isnt sufficient? i have seen some range from 1-5A i believe.
There are many reasons for choosing a switching regulator, including higher input noise immunity, more accurate regulation, but main reason is efficiency. Because of the significantly improved performance of switchers, they produce far less heat, and they make better use of the battery while the engine isn't running.
As a simple exercise we'll run through a simple 5V@1A linear Vs. experimental data from my device.
Primer:
A linear regulator works by passing the required current to the load while wasting the excess voltage between the input and output. It acts kind of like a large automatic variable resistor. The regulator also uses some current itself to operate. The system follows this equation: Iout + Iregulator = Iin.
A switching regulator uses a transistor as a switch to connect the input to the output for very short periods of time. An inductor is used to maintain the electron momentum at the output and steady the pulses of power coming from the switch. While the switch is off the circuit is consuming no power, even though the output is still providing power.
Linear:
This assessment will neglect the power used to operate the linear regulator, the actual efficiency will be lower than this prediction.
Pin = 12 * 1A = 12W
Pout = 5V * 1A = 5W
Efficiency = Pout/Pin = 5W/12W = 41.67%
With a linear regulator, 7Watts is wasted as heat while 5Watts are being used.
Switcher:
Experimental (measured) data from the ACPPS v1:
Pin = Vin * Iin = 12V * 2.112A = 5.68W
Pout = Vout * Iout = 5V * 1A = 5W
Efficiency = Pout/Pin = 5W / 5.86 = 88%
With the ACPPS, 0.68Watts is wasted as heat while 5Watts are being used.
7W wasted Vs. 0.68W wasted. The ACPPS wastes 1/10 the power for the same load. And the ACCPS efficiency continues to improve as the output current increases. It is above 92% from 2A to 5A.
At 1A output the linear wastes 7watts. All that heat is generated from one component that will require a heat sink to keep from overheating. At 5A the linear regulator would be wasting 35W of power as heat, requiring a large heat sink and fan. Just think about how hot a 35W soldering iron gets.
At 8A output the ACPPS is ~90% efficient, wasting only 4.44W as heat spread across 5 separate components, none of witch requires a heat sink. The copper on the PCB is enough to cool everything.
Quote: Originally Posted by
drutort 
and for the 12v why not step it up and then use a regular linear regulator? 12v is used for the LCD's and at max need 2A
In order to step it up, requires a switching regulator.
Quote: Originally Posted by
drutort 
That chip would be WAY nice to use, unfortunately I don’t have the equipment to solder it. It only comes in a BGA (ball grid array) package. Way too small for my comfort.
Also the ACPPS v2 (5&12) uses a very similar type of circuit; it just requires a few more parts.