# Boost converter with 2A load

I'm trying to put together a boost converter to take a 11-14.4v input and boost it to ~17v with a max current of 2A.

Most of my designs (made either by calculations done by me or a calculator tool from the web, all of which have actually given me different values) work fine at low loads (~100-150 mA), but the voltage drops off quite quickly as I increase the load and I just get a small ripple followed by a flat voltage somewhere below 12v after about 300mA upwards.

I've made the circuit physically once, but now I am using LTspice to simulate it.

I'll be using a 100KHz switching frequency (LM2585T-ADJ) and the online calculators I've used have said to use: Min 64uH inductor with 38% duty cycle (http://www.coilcraft.com/apps/selector/selector_2.cfm) Min 6.28uH inductor with 15-35% duty cycle(https://learn.adafruit.com/diy-boost-calc/the-calculator)

EDIT: Good point about the schematics, don't know why I didn't include them straight away.

• schematic & LTspice-schematic would be helpful. does it fail under heavier load both in sim & on the bench? or only one - if so, which one? Jun 25, 2015 at 3:07
• There's no magic to a 2A boost converter, so if yours isn't working there's something wrong with your design or implementation. Remember your switch current limit has to be higher than the 2A since the switch is switching the input current (which is around Vout/(Vin*efficiency). As @Techydude said a schematic would be very helpful. Jun 26, 2015 at 3:02
• Yeah, fails under heavier load on both. Real circuit worked exactly as expected under very light load, the sim doesn't level out at the desire voltage, but I assume that's because there is no feedback circuitry to control the output. Good point about the switch current limit, but in my simulation there shouldn't be any current limit on the switch, should there? I am pretty new to LTspice though so I may be wrong. I assume I have misunderstood something about boost converters because they do seem fairly simple in operation.
– Eddy
Jun 26, 2015 at 4:53