This is my first post on this forum, so if I'm doing something wrong don't hesitate to tell me.
Now to my question; I need 2aa batteries or an LiPo battery(3v-3v7) to be boosted to 5v(Done), boosted to 13.6v and inverted boosted to -15v. As you can see in the schematic below, I've got 2 boost converters to make the 5v and 13.6v. But since the current consumption on the 13.6v and -15v 5mA is. It's an waste of money to get an Buck boost converter for the 13.6v.
But this doesn't include the solution for the -15v. So what would be best, cheapest and most efficient way(can be 3 different methods ;) ) to make large negative voltage out of an small positive voltage?
These are some simulations I ran (The load resistor is currently simulating an 10times bigger load then needed. But changing it didn't effect the outcome, it did speed up the simulation..) all voltages dropped below the input voltage:13.6v. I got tired of waiting, so don't look at the output voltages
I was planning on using the charge pump method on the SW pin on the 13.6v regulator. But after some wishfull thinking I figured out that you can't get an higher voltage then the input voltage on the charge pump method.(to be honest, it took me to long to figure out..)
The least efficient method I could figure out myself would be to get an Boost converter to generate, lets say, 20v. Inverting that voltage to -15v, stepping it down using an level shifter or zener diode to 13.6v and using an regulator to make 5v out of it. Ow and last but not least, it has to fit on an 17mm*20mm PCB(components single sided)