# Creating an low current negative voltage

Good evening,

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)

• Pls Note that IC's like logic in Falstad are ideal voltage sources, so depending on Logic family add 50 Ohms for Rs out, then you will see load regulation effects. There are also many charge pump IC's for RS232 Oct 7, 2019 at 19:10
• @derekLF Why do you need -15V? Oct 7, 2019 at 19:11
• Inverting boost inductive regulator is best bet Oct 7, 2019 at 19:34
• Nice first question. Oct 7, 2019 at 20:22
• @Voltage_Spike the -15v is for an LCD. I want to recreate the Gameboy colors power board since mine died last weekend. Oct 8, 2019 at 6:03

Get a 15V buck regulator. You'll either have to drive a push-pull from the switching line, or since you don't need much current you could use a controller with no external transistors. The point of this modification is to invert the switching pattern.

Otherwise, you hook it up exactly like a 20V-15V buck controller, but connect the ground to -15V and the output (and sense) to ground. The controller will happily give you your -15V from 3.6. while happily thinking it's bucking 15V from 18.6V. Usually far cheaper than an off-the-shelf inverting switcher.

• A schematic would make this answer much more clear. Oct 7, 2019 at 20:22
• Hmm yeah, you could use the buck/boost converter with the vout and ground swapped on all pins. But using another converter for just the few mA is an waste of money and space. The_Photon he means like this: maximintegrated.com/en/design/technical-documents/app-notes/3/… Oct 8, 2019 at 6:06