Change Voltage/Current Range of 250w Aliexpress Boost Converter? - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: October 14, 2024, 10:33:13 pm
content: Seemingly simple question. I havethisDC-DC Boost Converter from Aliexpress which is based around a TL494. It has constant-current control (via a 5k potentiometer, 0.2-8A output) and constant-voltage control (via a 10k potentiometer, 10-50V output).Thisappears to be a mostly-accurate schematic of the device.How can I use a potentiometer (and maybe some resistors?) to adjust the output voltage from 8v-24v, instead of the original 10-50v range? I want a more granular-control of voltage between 8-24v to adjust the brightness of some LED's.Thanks.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 14, 2024, 11:01:37 pm
content: Soldering a resistor on R4, which currently has nothing fitted to it, will allow you to achieve exactly what you require.You would have to find the TL494 datasheet, and with the output voltage formula and a little algebra you can find the correct resistor value to achieve your goal.

author: Rick Law
author_rank: Super Contributor
timestamp: October 15, 2024, 12:01:42 am
content: As you stated, "constant-voltage control (via a 10k potentiometer, 10-50V output)", so theminimum is 10V output as designed. You wanted the lower limit to be 8V -- to lower the output to below the designed minimum would be a much bigger job. If you want to say change it to a range within the designed limit, the job would be a bit easier.But since you said you are aiming to get "a more granular-control of voltage", the job could be simpler -- you could use the original 10K VR as"gross"and add a"fine"control VR.First some math here. Note that the math is approximate since the adjustment is probably not linear. The type of potential meter in thepicture looks like a 25 turn VR. So, 10V to 50V is 40 volt change (10K ohm change) in25 full turnsof the screw. 10K ohm VR so each full turn is 400ohm (4% of 10K).Now youadda 400ohm VR of the same typeas the original... You insert that 400ohm VR either in series before or after the original 10K. (Note that with the added 400ohm, short the center pin (pin2) to either pin1 or pin3 so it is a pure VR with pin1 and pin3 being real connections).Once added, you have the original one going from 0 to 10K (gross) plus the added one going from 0 to 400ohm (fine). So it takes 25 full turns of the "fine" to get the effect on one full turn of the "gross". The "gross" is (approx) 1.6V per full turn, the "fine" is (approx) 0.064V per full turn.Describing the change necessary is easy. Implementing that is much harder... Where are you going to insert the added VR? There is no space on that PCB to do it.In the past, I toy-around with some buck PCB and added stuff to it by putting the PCB on a proto-board where I can add the additional stuff. That may give you an idea of how you want to add the 400ohm VR -- not a very complex job. Here is a link to that post and pictures of how I mated the PCB to a proto-board too add stuff to it.Link to thread on adding stuff to buck PCB:https://www.eevblog.com/forum/beginners/adding-cc-to-a-cv-buck-to-make-it-cccv/Edit:Corrected typo "pint3" to "pin3"