Hi Kevin,
On Mon, May 09, 2011 at 07:26:58PM +0200, Kevin Redon wrote:
here v0.8 : https://gsm.tsaitgaist.info/SIMtrace/v0.8/ Compared to v0.7+, I added 2 1n4148 after the parallel voltage regulator outputs. I wanted to avoid the regulators to fuzz each other, but I don't know if it's right. Maybe an additional zener diode is also required.
I understand the intention, but I doubt it's a good idea. First, the 1N4148 is quite low-power/low-current, i.e. it will be the weakest element in the chain. Second, it's a silicium diode and thus causes a voltage drop of 0.7V, i.e. we will have 3.3-0.7= 2.6V only, which is really bad.
I think you should just leave them out. You could simplify the design by removing the DC/DC converter (SC120) and simply attach the battery connector to the +5V input. The TPS73633 is a ultra-low-drop regulator, i.e. from voltages >= 3.375V on it will provide a stable 3.3V output.
This means a battery pack with 3 or 4 1.2V cells should do just fine.
What do you think? We can save the step-up regulator and loose the design risk of leaking power from the USB into the step-up regulator at the same time...
Regards, Harald