I'm planning the next Amp4 to build. I'll be running it on a 12.8V 3400mAh LiFePO4 pack from Batteryspace.com. I'll probably build a voltage doubler to get short-run high-power from the battery pack and more power in car usage.
About power saving and flexibility in the Amp4 ...
* I'll omit the relay, as it'd take some manouevering to get it to close on lower voltages. Might put it back in later, or perhaps have a bypass switch. Saves power, too.
* I may replace the diode bridge with a Schottky diode bridge to lower the voltage drop there.
* I'll replace the preregulator with a PS4, so we eat less idle current.
* I'll replace the 5V regulator with a low-dropout one. The LiFePO4 pack cuts out at 10V, and the PS4 must perform a minimum 40% voltage drop. I'll have reverse-polarity protection in, perhaps another 0.5-1V. This means the preregulator will at worst put out just under 6V. To squeeze the last drop of juice out of the batteries, an LDO regulator ought to put out a stable 5V until the last moment the battery cuts out. Also the LDO regulators have lower output impedance, which is never bad, eh?
Research questions (for me - though answers / ideas are ofcz most welcome):
- Is the PS4 a drop-in replacement for the TO-220 regulator in the Amp4?
- Do we gain anything by going to a Schottky bridge?
- Does it make sense to add an override/bypass switch for the relay? (The simplest form of this wouldn't make sense here - the relay drivers etc. still eat power even if the relay is bypassed. I'd need to take the transistors off-board or cut traces and disable power to them to really have a *full* relay bypass switch.)
- Does the preregulator only feed the 5V regulator, or is it used elsewhere? Will it bring any noise into any circuits?
- If there's any significant noise from the PS4, how well does the 5V regulator clean it up? Does the LDO perform differently in this regard?
- What changes does using an LDO regulator bring about? Is the max current the same? Is the noise spec the same? Does the lower output impedance have any effect? Do I need to take extra precaution at low supply rails to not disturb the 5V line? Does the LDO save any power over a normal one?