XL6009 5 V → 12 V Boost Converter
Step a USB pack up to 12 V with one chip, one inductor, and a feedback divider you can dial.
Difficulty: Breadboard. Estimated build time: about 45 minutes. Estimated parts cost: about US$5.00. 6-line bill of materials. Compare supplier offers when available. A bench boost converter built around the XL6009, a $0.50 monolithic step-up regulator that takes any input between 3.3 V and 28 V and produces a regulated output up to 60 V at up to 4 A switching current.
Read the datasheet topology and identify the four external parts
The XL6009 datasheet shows the same boost topology any textbook draws: an inductor from Vin to the SW pin (an internal MOSFET pulls SW to ground at 400 kHz), a Schottky diode from SW to Vout, and a big electrolytic capacitor from Vout to GND. The fourth external part is the feedback divider that scales Vout down to 1.25 V at the FB pin. The breakout you ordered uses a 22 µH inductor, an SS34 Schottky, a 220 µF / 25 V output cap, and a 10 kΩ + multi-turn trimpot divider. Find each one on the board so you can tell at a glance what each part is doing.
Wire 5 V in and confirm switching at SW
Feed 5 V from a bench supply (or USB through a header) into the VIN and GND pads. Probe the SW pad with your scope: you should see a square wave around 400 kHz that swings between 0 V and roughly Vin + Vf (about 5.7 V here), with sharp edges and ringing at the switch transitions. If you see no switching, the chip is shut down — check that EN (or the enable header on your specific board) is tied high and that you don't have an output short.
Measure the unregulated output with the trimpot at its initial position
These breakouts ship with the trimpot wherever the factory left it, anywhere from 5 V to 35 V. Measure VOUT with a multimeter and write the value down — this tells you which direction to turn the pot. Turn the screw SLOWLY (these are 25-turn pots — most of the motion does very little) while watching the multimeter.
Dial in 12.0 V and check ripple
Once the output reads 12.0 V, leave the pot alone and switch the scope to AC-coupling on Vout to see the ripple. You should see a 400 kHz sawtooth with peak-to-peak ripple of 50–150 mV at no load. If the ripple is much worse (over 300 mV), the output cap has been abused or replaced with something undersized. The ripple is mainly the inductor current sweeping in and out of the output cap, so the cap's ESR sets the ripple amplitude — this is why every datasheet stresses low-ESR caps on the output.
Replace the trimpot with a fixed divider (optional)
For a permanent 12 V supply, lift one end of the trimpot and replace it with fixed resistors that hit Vout = 12 V. The XL6009's FB reference is 1.25 V, so the divider ratio is Vout/Vfb = 12/1.25 = 9.6. A 27 kΩ top resistor and 3.3 kΩ bottom resistor gives 1.25 × (27 + 3.3) / 3.3 = 11.48 V — close. 30 kΩ and 3.3 kΩ gives 12.6 V. Pick the closest pair you have, measure, and move on. A fixed divider is more vibration-tolerant and removes the temptation to bump the screw with a screwdriver and accidentally fry whatever you plugged in.
Drive a real load and watch thermal behaviour
Connect a 100 Ω resistor across Vout (120 mA load at 12 V) and feel the XL6009's tab — it should be barely warm. Step up to a 33 Ω load (360 mA) and the tab gets noticeably warm; this is normal. Above about 600 mA you will need to either heatsink the XL6009 or step up to a beefier chip (LM2587, XL6019). The module is rated for 4 A switch current, but real continuous output is closer to 800 mA without external cooling. This is the universal lesson of switchers: datasheet ratings are best-case-everything, and real boards run cooler when you respect them.