Regulator 15V input, 15V output - Page 1
Forum section: electronics / projects

author: Halban
author_rank: Contributor
timestamp: February 25, 2021, 10:20:56 am
content: Hello guys!I have a new project where the OLED display needs to be supply with a stable 15V-150mA (minimum voltage allowed is 14.5V)My board is supplied with a Meanwell desktop PSU delivering 15V, but I don't want to use this "unsecured" supply to directly power my OLED screen.Do you know a nice "low-cost" solution, like linear regulators or non-isolated DC/DC converters 15V to 15V ?Thanks a lot for your advices!

author: wraper
author_rank: Unknown
timestamp: February 25, 2021, 10:33:05 am
content: By desktop you mean power brick? There is no such thing as linear regulator which can input and output same voltage, there is a voltage drop required. Actually the same input and output voltage is the worst condition for regulator. You cannot use neither buck, linear or boost regulator. You need either a more complicated buck-boost converter or boost converter + linear regulator. However what's wrong with powering directly? That PSU already should be SMPS with stabilized output voltage. What "unsecured" even means?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 25, 2021, 10:35:59 am
content: Maybe unsecure means it just has a plug and user can replace it with a different supply? That could happen easily when the supplied brick is lost or mixed up with some other brick which happens to have the same connector.If this is the case and you don't want to go for a specialized plug, change your design for input voltageover15V and buck it down (or use a linear regulator) to 15V for the display. For example, go with a 18V laptop supply brick, or even a 24V input, with that you have a lot of supplies available for more convenience.

author: Psi
author_rank: Super Contributor
timestamp: February 25, 2021, 10:39:58 am
content: How cheap is cheap.15v to 15v direct is pretty uncommon.A cheap 5V reg on your 15V rail powering one of these is probably the cheapest option you're going to find.https://www.digikey.com/en/products/detail/gaptec-electronic-gmbh-co-kg/3S7B-0515S3U/13692172Sadly they don't seem to have stock atm

author: Halban
author_rank: Contributor
timestamp: February 25, 2021, 12:35:56 pm
content: Thanks a lot for all your quick replies! I understand it's uncommon, I had no idea about it, so thanks for that!- indeed, I mean I use a power brick of 15V (and I can't really change it, it's a standard in electronic musical instruments)- and yes, the connector is also standard and people can plug like +18V if they want, that's why it can be dangerous to power the screen with the 15V power brick- @Psi the 3S7B_0515S3U seems a good solution but not really distributed and a little bit too much expensive... I'm looking for something around $3If I power the OLED screen with its minimal supply rating (14.5V) do you think that the 0.5V drop can allow a linear regulator or a converter to work?I've tested the linear regulator 15V to 14.5V solution (with a LM2941SX), it seems work perfectly but it makes the regulator whistle (a high frequency noise). I'm not enough experienced to understand on the datasheet what is the minimal voltage drop allowed. Maybe an other linear regulator allows that kind of small voltage drop?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 25, 2021, 01:12:10 pm
content: Those small black isolated DC/DC modules are typically unregulated or poorly regulated, you can see if this is the case from the narrow input voltage range. This is because passing regulation feedback through isolation barrier costs money. They are extremely cheap parts to get functional isolation. OP doesn't need isolation, OP needs regulation, so this component type is the polar opposite of what they need.So what I gathered:* Musical instrument, expect some abuse* 15V nominal supply will be used, but there is a possibility a 18V supply gets plugged in insteadNow if you supply 15V nominal from a Meanwell brick, there's no way you are going to regulate it down to 14.5V guaranteed with any regulator solution. The reason is, 14.5V is likely within the possible range of that 15V brick already! On a bad day, you are out of luck even if you find a 0.00V dropout regulator!So youneedto convert the voltage from, say, 14.0V. There is no way to avoid boosting.Then, design the upper limit so that slight overvoltage ("Oh, this says use 15V supply, 18V can't be too much can it? let's try!") is acceptable.So we are looking at Vin=14 - 20V converter. If at all possible, I'd say go for 14 - 26V. And once we are boosting anyway, maybe you can accept as low as 11V to allow very common 12V bricks to be used, right?The easiest way out might be to look for a display unit that does not require such high voltage. If this is not the possibility, some SEPIC or maybe buck-boost if the load is floating (such as display backlight) supply seems the only way out.What is the display module part#? Looking for the actual specs. You told us the minimum voltage is 14.5V, but what would be the maximum?

author: magic
author_rank: Super Contributor
timestamp: February 25, 2021, 07:02:48 pm
content: Assuming that the power brick is guaranteed to provide at least 14.5V, ...A high voltage, high current CMOS LDO could provide almost negligible dropout at 150mA, but I'm not sure if such chips exist. The best high power bipolar LDOs might do 100~200mV.If you are into cheap and crazy, I think LM317L could be used with ADJ grounded, OUT serving as a current feedback input and IN driving the gate of a P channel MOSFET. Some arrangement would be necessary to provide for a few mA of class A bias through the LM317L and compensation. Alternatively, there are opamps with integrated 2.5V references too.

author: ajb
author_rank: Super Contributor
timestamp: February 25, 2021, 07:41:19 pm
content: What other rails do you already have in your device? Since you only need a couple of watts, a reasonable solution would be to provide a boost converter from a lower voltage rail you already have, especially if that rail is supplied by a buck converter. You could easily have one converter providing something like a 5V output to supply your general circuitry from a 12-24V input, and simply boost the 5V to 15V with a second small dedicated converter for the display. This would give you a great deal of flexibility in input voltage range with no concerns about the display's input voltage being violated.

author: Pawelr98
author_rank: Regular Contributor
timestamp: February 25, 2021, 10:02:39 pm
content: How about just non-isolated flyback ?It will be able to obtain both higher and lower output voltages from the supply, and lack of isolation means direct measurement of output voltage.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2021, 08:02:43 am
content: Multiple buck (or boost, if necessary) supplies done using modern integrated regulator ICs end up order of magnitude cheaper and (smaller) than multi-output transformer, and you get regulation on all rails.No need to complicate a simple matter.

author: sleemanj
author_rank: Super Contributor
timestamp: February 26, 2021, 08:27:39 am
content: Buck-Boost/SEPIC modules are available in your price target from the usual places and will handle your current requirements without issue.Search for "LM2577 Solar" you'll find them, identifiable by 2 inductors on board.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2021, 09:49:25 am
content: And post all your required voltage rails (voltages and current requirements) for more specific advice.

author: Distinctly Average
author_rank: Contributor
timestamp: February 26, 2021, 04:00:55 pm
content: Could you not just change the connectors to a more secure one? By that I mean one that is very unlikely to be on any other common power brick.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2021, 04:04:35 pm
content: Quote from: Distinctly Average on February 26, 2021, 04:00:55 pmAudio folks will hate the product as a result. As we already saw, people want to use some "standard" 15V supply, so clearly swap the supplies between devices.Even if it costs a bit more, it's often a good idea to support widely used voltage ranges so that people can succesfully use other than the official brick. You can still print the requirement to only use the official brick in the manual so customer does it on their own risk, but practically it works and everybody wins.Low cost integrated regulator IC market is wide up to about +26V maximum input which would do the job up to 24V bricks.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 26, 2021, 04:46:14 pm
content: Do you have e.g. a 5V rail in your product that is derived from the 15V input (and is powerful enough)?Then just install a smallish step-up converter from 5V to 15V for the OLED supply only. It's not so uncommon to do so, I've seen such solutions before.

author: drussell
author_rank: Super Contributor
timestamp: February 26, 2021, 05:06:04 pm
content: What is theactualoutput voltage in normally-loaded, typical operation of the types of supplies that might ever get plugged into your device that you want it to be able to operate properly on?If they are always at least 15.0V and you're happy with it only working at 15.0V or higher and just want to protect against someone plugging some supply in that provides more than a regulated 15.0V output, you could just use an LDO style regulator since the voltage seen by the display will still be above 14.5V, while protecting and regulating it if someone plugs in an 18 or 19 volt plug pack or something. Most sloppily-regulated or unregulated "15V" supplies will be more like 16-17+ volts when unloaded or lightly loaded relative to their rated output current.If some supplies you want it to still work properly with might ever output less than about 14.7-14.8V then you will need to boost-buck or buck-boost, double convert somehow. Then someone could probably even use, say a 12V input to your device just fine as long as the rest of your circuitry was happy with that.

author: Psi
author_rank: Super Contributor
timestamp: February 27, 2021, 11:06:17 pm
content: You can get little boost models on aliexpress that would probably do what you want for $1-$3but really, quality wise, you'd probably be safer to just use the 15V you have from the meanwell psu direct rather than trying to use a dirt cheap china boost module.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 28, 2021, 08:22:20 am
content: I think "my board" refers to a PCB designed by the OP. No need to use Alibay modules; just pick a simplest and cheapest modern boost IC and incorporate the reference design on your own PCB.

author: Halban
author_rank: Contributor
timestamp: March 05, 2021, 10:07:05 am
content: Thank a lot for all your ideas!The best solution for my application seems to be a step-up converter to generate a 15V from my on-board 5V. I will try it soon!

author: Jan Audio
author_rank: Frequent Contributor
timestamp: March 05, 2021, 02:50:38 pm
content: Cant you just secure the voltage is correct ?If they use 18 volt, should it work ?, maybe you can make it not work on 18 volt, i dont know how.2 regulators sound like not clean technology.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 05, 2021, 03:36:12 pm
content: There is nothing "unclean" or wrong in cascading two regulators.Do proper engineering; run the numbers. Cost, size, efficiency are the typical parameters. Simplicity of design, too.Especially if input has wide range and protection needs, having one regulator directly off the input for the most convenient rail, then other regulators out of that rail, is very typical.For example, market is full of very small, cheap and well performing regulators with absolute maximum input voltage somewhere 6-7V. They are great for all those digital rails, but can't accept a 12V input.That is why if you want, to give you an example, a universal 10 - 30V input and outputs of 1.2V, 2.5V, 3.3V, 5V and 15V at lower current, you'd often buck down 10-30V to 5V, and do all the others from this 5V rail: buck to 1.2V, 2.5V, 3.3V, and boost to 15V. Depending on the current requirements, some of these rails may use just linear regulators.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: March 05, 2021, 04:12:08 pm
content: Do you have the model number? I feel like its 15V maximum input, you can probably supply it from +12VDC by using LM7812 and it should be fine.

author: Halban
author_rank: Contributor
timestamp: March 10, 2021, 09:04:23 am
content: The display is thehttps://www.wisechip.com.tw/en/product-380065/2-70%E2%80%9D-OLED-Display.htmlBut I can't share the datasheet as it is confidential. The minimum input voltage is 14.5V (I can try to lower the voltage to see if it is still working but I think it's dangerous to go out of the specs)---For my interest, how can I know what is the minimal voltage drop of my regulator LM2941SX on the datasheet ?https://www.ti.com/lit/ds/symlink/lm2941.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&DCM=yes&ref_url=https%3A%2F%2Fwww.mouser.fr%2F&distId=26

author: drussell
author_rank: Super Contributor
timestamp: March 16, 2021, 05:07:43 pm
content: Quote from: Halban on March 10, 2021, 09:04:23 amYou read the datasheet.The third line under the first section, "1 Features" on page 1 says "Dropout Voltage Typically 0.5 V at IOUT= 1 A"The first sentence of the first paragraph of the device "3 Description" section, also on page 1 says "The LM2941 positive voltage regulator features the ability to source 1 A of output current with a typical dropout voltage of 0.5 V and a maximum of 1 V over the entire temperature range."Section "6.6 Electrical Characteristics" also includes the following specifications for typical and maximum:Furthermore, the first two graphs under section "6.7 Typical Characteristics" are typical examples of the dropout characteristics:I'm curious as to which of these parts you don't understand....

author: drussell
author_rank: Super Contributor
timestamp: March 16, 2021, 07:51:41 pm
content: Quote from: Halban on March 05, 2021, 10:07:05 amWhy would that be the best solution?Does your device need to support correct operation with a "15V" input of less than 14.7V?If you want to to be able to operate, for example, from a mobile vehicle "12V" supply, (11-15V real-world actual) then sure, that does make sense, but you still haven't mentioned whether operating with a 14.7V minimum input voltage to your device (to always keep above 14.5V at the screen) is adequate, in which case something simple like your proposed LM2941 would work fine.