An efficient way to limit current of a cheap DC-DC buck/boost converter - Page 1
Forum section: electronics / beginners

author: shamooooot
author_rank: Regular Contributor
timestamp: February 09, 2024, 03:58:14 pm
content: HelloI am looking for a simple -yet efficient way to limit the current consumption/output for an XL-6009 based DC-DC buck boost converter:https://www.amazon.com/Adjustable-Converter-Automatic-Voltage-Regulator/dp/B07NTXSJHB

author: Andy Chee
author_rank: Super Contributor
timestamp: February 09, 2024, 04:05:15 pm
content: What is your load? This may influence the type of current limiting circuit topology implemented.

author: shamooooot
author_rank: Regular Contributor
timestamp: February 09, 2024, 04:25:43 pm
content: I want to use a battery as a load..

author: djacobow
author_rank: Super Contributor
timestamp: February 09, 2024, 04:45:04 pm
content: If you're fine using a cheap Amazon board, then get one with current limiting:https://www.amazon.com/dp/B01EQT63SS/I actually don't know how well it works. There is a XL4015 buck converter on there and I suspect that the current limiting is handled by having the LM358 adjust the feedback.

author: shamooooot
author_rank: Regular Contributor
timestamp: February 09, 2024, 05:06:54 pm
content: thank you..The thing is the input is varying between 4-10V and the output need to be 8.4V constant. This converter is unfortunately a buck converter only..

author: Smokey
author_rank: Super Contributor
timestamp: February 09, 2024, 07:24:56 pm
content: Fuse?

author: djacobow
author_rank: Super Contributor
timestamp: February 09, 2024, 08:56:25 pm
content: The OP didn't say, but given that the load is a battery, I suspect the goal is to charge it. So this means starting a low battery in CC mode and then getting to CV mode when it gets nearly charged. Crapping out when connected to a low battery is probably not what he had in mind, but who knows?

author: ejeffrey
author_rank: Super Contributor
timestamp: February 10, 2024, 02:49:00 am
content: The no design approach is to use a boost module to get 12 V and use the current limitable buck converter.Another option is put a constant current load between the battery and ground. Search around there are tons of threads and a few eevblog videos about this. Use a MOSFET so that when you enter the constant voltage charging range the drop across the load drops to near zero.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 10, 2024, 04:15:29 am
content: The input source voltage is 4-10V which I'm guessing might be a small solar panel? Could the OP tell us what the input power source is?The output voltage is current limited 8.4V which I'm guessing is for charging a two cell Li-ion battery? Could the OP confirm this?

author: Jwillis
author_rank: Super Contributor
timestamp: February 10, 2024, 09:03:46 am
content: Quote from: djacobow on February 09, 2024, 04:45:04 pmNot a very good one for low voltage and low current. They oscillate so bad you can make a strobe light with a 12V power LED.Quote from: shamooooot on February 09, 2024, 03:58:14 pmThis won't be elegant but it could be done one of two ways. Power BJT in series on the positive output. Collector on the converter side and emitter as the output positive. A 1K resistor from collector to a 10K to 20K potentiometer set up as a rheostat. Between wiper and base add another 1K resistor. This will limit current but will also change the output voltage some. You will probably have to experiment with the resistor values.Second way is with a Mosfet with drain at the converter side positive and source as output. Add an adjustable voltage divider before the Mosfet between positive and negative rails. Resistor values will be in the range of 1M from negative to a 100K potentiometer then a 100K to positive rail. From wiper add 10 ohm to the gate. Depending on the mosfet used, you'll have to experiment with resistor values. A change in output voltage will occur with current adjustment.Not a great way to current limit but it does work.Very few of those cheap buck converters have very good current control a low power.. Most just have current limit, which is to say when the amount of current drawn reaches set limit the voltage drops out.Battery charging can be even more problematic because the Battery will want to draw as much as it can. Sometimes just a power resistor in series works the best.