DC-DC Adjustable Step-down Module 5A 75W (CE07271)

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DC-DC Adjustable Step Down Module 5A 75W XL4015

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Can you please explain the function of the 2x pots (CC & CV) and also what the 3x LEDs indicate?

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Hi Mike,

Welcome to the forum!

They adjust the output voltage that’s provided depending on the input voltage. They should provide both fine and course control of the output voltage which you can check with a multimeter to ensure that it’s appropriate for your project. If there’s anything else that you need please let me know!

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Thanks Bryce. I was talking with Oliver who said he was planning to make a post about these. I’m also keen to understand what the different LEDs mean.

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Hi Mike,

Sorry for the delay and not keeping you updated - I saw Bryce got back to you on Thursday but didn’t notice he hadn’t answered all your questions, and I was away on Friday. I’ve got one from stock and I’m getting you an answer now.

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Ok, testing complete:

Green LED: Output Current < 0.1 times the set Current Limit
Blue LED: Output Current > 0.1 times the set Current Limit
Red LED: Current regulating mode (CC)
Red LED off: Voltage Regulating mode (CV)

Just note that if the current set point is very low, it might not trip back to the Green LED. FYI, these LEDs are very useful for LiPo battery charging with this regulator, as this load regulator when set correctly will perform (open loop) CC, CV charging (though I’d strongly recommend a using a proper LiPo charger and using batteries with circuit protection to eliminate the human factor in charging mistakes).

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Sorry to be a complete numpty but can someone explain to me in layman’s terms how to use one of these modules? I assumed they would come with some basic instructions but there were none and the info on the web site is far too technical for me!

Objective: place in between a 12v supply and a strip of LED lights to be able to adjust/dim the brightness of the LEDs.

I am told I can do that by adjusting the voltage which I presume I can do by rotating the screw on the “CV” pot. Am I right? What direction is higher and which is lower?

A previous answer talks about CC mode and CV mode. How do I switch between the two? Or more importantly, given that I don’t think I need any current control, how do I bypass it.

Finally, given that I clearly have no idea what I’m doing, can I do any serious damage if I just set up my 12v supply, LED lights and the module and just have a play?

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Hi Gordon, Welcome to the forum!

Do you have a link to the LED lights you are trying to control the brightness of so we can see what type they are?
Most modern LEDs don’t have a brightness setting in the traditional sense as you would expect from incandescent globes, the lights are either on, or off. Brightness control is often achieved by switching the LEDs on and off many times per second so that our eyes perceive them as changes in brightness. This is known as Pulse Width Modulation, I’ll link a video explaining it below.

Happy to answer your other questions as well, but might as well start with what you are trying to do and what you have on hand to build it with.

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Thank you for your response Trent.

I bought the LED strips from Jaycar. Their catalogue number is ZD0575. I plan to use 1 metre strips of these lights to illuminate various modules of a model railway. I would like to be able to vary the level of illumination depending on where my model railway is situated (at home, in an exhibition hall etc).

I have already tested the first strip using a mains powered multi-voltage DC adaptor. At 12v the LEDs were very bright but at 9v or even 7.5v, the light level was much more appropriate.

For reasons I won’t bore you with, I don’t think the use of a mains powered adaptor for all the modules of the model railway is a practical solution. So I’d like to run them off an existing 12v supply but would still like to be able to adjust the brightness. Hence I bought some of your modules.

I hope that makes sense. If not, let me know.

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Hi Gordon,

Thanks for providing that context, the LED strip from Jaycar uses 5050 chips which are a non-addressable LED strip. Addressable LEDs need data sent to them to tell them the colour and brightness they should output.

Your LEDs will have a voltage and brightness curve where supplying a higher voltage will make them a bit brighter and at some point the voltage will simply be too low and the LEDs will switch off. They can’t be damaged by undervoltage though so nothing to worry about there.
LEDs are diodes so will have a non-linear curve, you may find the difference in brightness between 11 and 12 volts is massive while the brightness barely changes between 5 and 10 volts.

If you want accurate control of the brightness you will need to drive the strip at 12 volts and use the PWM method I linked to earlier to finely tune the brightness.

To get back to your earlier question about CV and CC mode of the adjustable step down module. I’ve found this forum post explains well how you switch from CV to CC mode under certain conditions and most of the time a power supply will be running as CV mode.
https://www.eevblog.com/forum/beginners/confused-with-about-my-new-labbench-psu-c-c-c-v-is-it-working-correctly/

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Thank you again Trent for your response.

I have followed all the links you provided, read the articles and watched the videos.

The end result however is that i am none the wiser! I think it is just beyond me technically, unfortunately.

So I think what I am going to do is just hook one of your units up to my 12v supply and a strip of LEDs and have a twiddle of the adjusting screws and see what happens. Based on your comments and the fact that this unit steps down only, I don’t think I can do too much harm by doing that.

It will be next week before I can do the testing.

I will post an update with the outcome - just in case there are any other novices considering your module for a similar purpose.

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Hey Gordon,

Awesome, I’m keen to see it done! PS: once you get a brightness you’re happy with, putting a generous amount of hit glue over the adjustment screw should keep it in place so nothing accidentally bumps it while still allowing it to be removed in the future.

Keen for the results!
Liam.

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Hi guys,

I have done my testing and am providing feedback. It might be quite detailed so I may need to do it in several posts.

Before I start, in case anyone is reading this whilst considering buying the product, my conclusions are not a reflection of the product, only my electronics knowledge and ability. I’m sure its a great product for anyone who knows what to do with it!

But in summary, I have not been able to use the product to do what I hoped it would do.

Here’s what I did:

  1. I hooked up my strip of LED’s to a Multi-voltage DC adaptor as before. At 12v the LEDs were very bright and as I stepped voltage down the brightness dimmed until at 4.5v the were out completely.
  2. I then inserted the step down module between the adaptor and the LEDs and repeated the process. Changing the voltage on the DC adaptor had the same effect and a multimeter confirmed that adding the step down module made no discernable difference to the voltage.
  3. I then returned the adaptor to 12v and left it at that for the rest of the test. I tried to replicate the dimming impact by turning the adjustment screws in various directions - and various combinations of one marked CC and the one marked CV. No combination of adjustments made any difference to the multimeter voltage reading - and more importantly, none made any difference to the brightness of the LEDs.
  4. In fact, the only difference I was able to make was that turning the CC adjustment screw a long way clockwise, made the small blue LED on the module come on. Interestingly though, the green LED stayed on which surprised me given an earlier comment that the green LED was supposed to signify output current <0,1 times the set current limit and blue LED >0,1 times (which implies they are mutually exclusive).

So in summary, I have run out of ideas as to how I use this unit for stepping down voltage. If anyone has any further suggestions, I’d love to know as I’m close to giving up.

Sorry guys.

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P.S. I attached the DC power adaptor to the “In” terminals and the LEDs to the “Out” terminals. I presume that was the right way?

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Hi guys - given that I’ve been down this rabbit hole I thought I’d add what I’ve learnt, and ask a question myself. Please feel free to correct me if I am wrong.

  1. 12V LED strips are rated at 12.0V - at that point, all 3 LEDs in a group have about 2.83V across them and the resistor looks after the rest of the voltage drop.
  2. You can run them with a higher voltage - it’s called over-driving and has four consequences. They are - brighter, more heat, heaps more current draw, and shorter life. The voltage vs current (and light output) curves for LEDs are essentially exponential.
  3. You can run them with a lower voltage - under-driving. This has exactly the opposite outcome of over-driving. No great surprise there.

My preference, giving that I am looking at off grid camping lights, is to under-drive at 10V, double the amount of LEDs to counteract the drop in light intensity, and run a PWM dimmer to adjust for desired light output. This way my LED lights only produce light (NO HEAT), and my batteries last longer.

My question - where can I find a continuously variable DC-DC converter that has a fixed (regulated) output independent of input voltage. Battery output voltage does drop as the charge level decreases, and running a 12V strip directly from a 12V battery that’s sitting at 13.8V is not ideal.

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Hi Neill
Most LEDs are not terribly linear with light output vs voltage and as you are going to adjust with PWM (a very good idea) and consider your eyes response the difference between 12V and 13.8V I don’t think will be very noticeable. Particularly at the level you will get at full bright.
Your battery should not be discharged below 11V or 10.8V minimum anyway or you risk damage which will be cumulative. A low voltage shut off device is not a bad idea. It is called preserving battery quality.

Considering you intend to use PM control you don’t really need a converter. You would be lucky to find one to supply enough power at the usual hobbyist outlets. So just go with your battery and PWM control, The most critical part of this will be minimum battery discharge voltage.
Cheers Bob

PS: just looked at the start of this post. This one might do but I think a PWM device with a knob on it would be easier than a little screwdriver in the middle of the night. I am not familiar with this device but there is obviously one person who had some trouble.

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Thanks Robert, my ultimate goal is to have 100% (or near as possible) reliability, with ultra low current draw, good light and high efficiency, all combined with ease of setup and pack-down. Yes, low voltage shut off is on the list. I have also been given another project to work on for my son. If electronics was my strong suit I would design it myself, unfortunately it isn’t so I have to rely on stuff that already exists.

I just found this baby https://core-electronics.com.au/pololu-adjustable-9-30v-step-up-step-down-voltage-regulator-s18v20ahv.html, add to this a PWM controller with a switching pot and I reckon we are good to go.

thanks for the reply
Neil

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Hi Neil

Can’t have it all. Diodes and LEDs are current operated devices. Ultra low current equates to ultra low or nil light. Indeed some LED set ups are driven with constant current drivers. A good part of the power (Watts) is used up with the current limiting (note I said current limiting, NOT voltage dropping) resistors. Using a set up that utilisers constant current drivers avoids this power loss. I think it is a bit hard to control brightness though.

Just looked at some of the graphs for that regulator. In your operating range which I assume will be between 11V and 13.8V with 12V output the efficiency is about 85%. This means that for every 1Watt output you have to input 1.18W. For what result? You intend to control the brightness with PWM anyway so you are effectively burning up precious power for nothing.

A simple PWM motor speed controller will do the job. Unfortunately the selection that Core stock seem to be the H bridge reversible types or stepper controllers geared primarily for robotics etc. But there are plenty around.
Cheers Bob
Edit:
You don’t even need a motor speed control but these are convenient. An Arduino or some other source of PWM signals and a Mosfet to do the switching would do just as well. Core carry a small mosfet breakout with all the required bits on board that can be driven with Arduino or similar SKU: CE04538

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i have been looking here in aus to find these reg`s i need to be able to use 3 of them

1:5vrail 5amax for my sbc`s…etc…etc.

2:12 v rail 5a max for routers etc…any thing 12 volt in general i have some sbc`s that run 12 volt.
3 19 v rail for my monitor…
input to the supply would be around 24 volts from either battery or linear supply …or switchmode
but high enough to cover output voltage…

i just wonder how true the specs on the product page are…??

would be replacing the pots with 10 turn pots not trimmers…on voltage …

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Hi Brian,

If you need high current supply at a series of fixed voltages including 5 VDC and 12 VDC I’d start to look at a cheap low power ATX computer power supply. You are unlikely to find something with higher efficiency, in a well constructed package and with better circuit protection.

If you did want to go the path less travelled and build your own multi-rail power supply from a group of these modules that should be possible, you will need to be very careful with how you set the output voltage and current limits and keep in mind these are rated for 75 Watts.

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