How about these power supply boards from Aliexpress? And how to start designing them?

Hello,


I was searching on Aliexpress for dual power supply for my electronics collection. And I ran by these boards.

They actually receive AC input at lower voltages, which I think not very easy to use because I need AC source at low voltage, which means I need another stage to lower the mains voltage for this module.

The following two links are for power supplies that receive AC input and provide +/- dual variable voltages which are very nice except they need AC input at low range.

https://www.aliexpress.com/item/New-Assembled-LM317-LM337-Dual-Power-Adjustable-Regulated-Power-Supply-Board/32346362104.html?spm=2114.10010108.1000014.2.165565467WuaLO&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.112237.000000000000000&scm_id=1007.13338.112237.000000000000000&scm-url=1007.13338.112237.000000000000000&pvid=0f0928e5-df87-431d-a8a5-42318eeaa9dd

https://www.aliexpress.com/item/LM317-LM337-1-5V-37V-Adjustable-Dual-Voltage-Regulator-Power-Supply-Module/32515637290.html?spm=2114.search0104.3.8.29222e4bSYuXlH&ws_ab_test=searchweb0_0,searchweb201602_8_10065_10870_10068_319_10867_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536_10902,searchweb201603_6,ppcSwitch_0&algo_expid=8557a30c-fde5-4cec-af74-26a9c89e9cb4-1&algo_pvid=8557a30c-fde5-4cec-af74-26a9c89e9cb4&transAbTest=ae803_3


These two are much better in my opinion, because they are DC/DC converters which means I just need to plug a DC power adapter and then I get +/- voltages:

This one has 1A output.

https://www.aliexpress.com/item/LM317-LM337-negative-dual-power-adjustable-power-supply-board-Electronic-Component/32863878979.html?spm=2114.10010108.1000014.3.4e3e3bbfJadd6f&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.112237.000000000000000&scm_id=1007.13338.112237.000000000000000&scm-url=1007.13338.112237.000000000000000&pvid=3b94f08d-354c-4b8f-b1d4-8dc24aad4972


I also like this one, it has much power 3A for +ve rail and 2A for -ve rail.

**broken link removed**



What do you think guys about these boards? Are there better options?

What do I need if I want to start designing similar boards to serve my bench applications?

Since ac input for the first link power supply supposed to be from the secondary of the transformer , if you have a suitable transformer then you can consider.

The third link ($4) board does not seem to have a heat sink . Avoid it.

Fourth one also good.

But all the power supplies are not continuosly variable.
You can set a fixed + and - voltage with the preset.

You have indicated that you have a DC adapter. What is the voltage and current rating ?

It is not difficult to make a + and - supply , if you have the PCBavailable.

What is the required + and - supply voltage for your use?
fixed one or a variable? What is the estimated current requirement?

srizbf said:

Since ac input for the first link power supply supposed to be from the secondary of the transformer , if you have a suitable transformer then you can consider.

Click to expand...

After considering this again, with all the 4 boards whether they have AC or DC input, I need an extra power source. But DC power adapters are much more easier.

Fourth one also good.

Click to expand...

I also liked the forth one,

But all the power supplies are not continuosly variable.
You can set a fixed + and - voltage with the preset.

Click to expand...

How ? they have a pot to adjust the output voltage. They also mention at the title of the page that these boards are adjustable.

So I didn't get your point ..

You have indicated that you have a DC adapter. What is the voltage and current rating ?

Click to expand...

These are the adapters I have right now.

It is not difficult to make a + and - supply , if you have the PCBavailable.

Click to expand...

I usually don't need -ve source, but currently I'm working on an op amp circuit, so I needed a -ve source that where I thought to have something in case one day I need it.

Now I solved the problem by getting two voltage regulators, L7905 and Lm7805 to get the proper voltages for the 741 op amp.

What is the required + and - supply voltage for your use?

Click to expand...

For now I'm using +/- 5V for the op amp. But the boards I listed provide much voltages and enough current.

fixed one or a variable? What is the estimated current requirement?

Click to expand...

The ones I listed are variable, but I don't have current requirements. I just need to amplify a signal coming from a current sensor.

eagle1109, If you wish I can provide you with pricing information about items you mentioned in your first post. You will be able to buy at the lowest prices on Aliexpress.

OK, but I already bought the last one for $8.

It just for in case I needed +/- voltages in my projects.

if you can find a computer power supply that has rail like the old ones it is very usefull for the projects it has +5v output and +12v output.

also designing usb chargers or directly from transformer with pcb is very usefull with lmXX series

Yes, how about this design:
**broken link removed**

So this basic for the main purpose of the voltage regulating stage that takes a DC voltage and convert it to an adjustable voltage output.

But what about the other considerations of designing a voltage regulation system? Like protection for overcurrent and short circuit, I think these two points are the most important for a power supply at the output stage. Are there other protection circuits for the output stage?

This is all for the low DC voltage stage.

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But what if I want to design a SMPS board, that has the following:
1. AC/DC conversion circuit
2. AC input protection components and how to connect them
3. I also want to learn the principles of AC protection and filtering, their components and how to connect them
4. Auxiliary components, what are they? and how much necessary they are?
5. HIGH voltage stage, also with its protection strategies and how to deliver that voltage to the chopping circuit with the power transistor.


But maybe I can start by buying SMPS power supply and learn from them. Then learn some principles about SMPS. Then I start designing my own SMPS.

Hi,

But maybe I can start by buying SMPS power supply and learn from them.

Click to expand...

There are many application notes around from reliable sources like the semiconductor manufacturers.
They are much more detailed than a forum thread can be.
And they are straight forward.
In a forum there are many people - each of them may have good skills - but they may have different styles to design a SMPS.

I don´t think it´s a good idea to buy an SMPS and try to learn how they built them.

I rather recommend to go through onlie tutorials with design examples.
They show you step by step what to do and show with the examples how this looks like.

***
When you open a SMPS you may see the parts, but you don´t see the specification of the parts.
Some examples:
* Often SMPS use low ohmic resistors for current sense. Maybe a simple 0.47 Ohms resistor ... but usually you don´t recognize that this needs to be a "low inductive" one (no wire wound).
--> use a wire wound 0.47 Ohms resistor and it won´t work.
And maybe you don´t recognize the kelvin wiring.
--> Witout kelvin wiring you get wrong current limits.

* SMPS use electrolytics. You don´t recognize that these are "low ESR" types designed for high frequuency and high ripple current.
--> but a standard electrolytics capacitor and your output voltage will look "noisy" and maybe the capacitor heats up and explodes.

***
Don´t be afraid of looking into application notes. The semiconductor manufacturer have a good reason why the provide them. They have the experience that designers come back and claim the SMPS IC is not working properly. But in 98% (my estimation) there are design mistakes. Thus they assist the designers with information to build reliably running SMPS.

Klaus

****
Added:
Your LM317 circuit:
Don´t rely on random internet schematics. --> read the datasheet, go to the manufacturer´s internet site and look for additional information. They are most reliable.

****
You ask about current limit:
Why don´t you look for a IC with built in current limit? Like the L200...
--> Be sure for most of the ideas you have there already is a solution. Others had the same problems before. No need for breaking your head, no need for your own pitfalls and no need to reinvent the wheel.

Take it easy and straight forward.

30 years ago we had no internet. There were only a couple of really good application eniginers that are able to teach you. And there were books - but maybe you didn´t know that these books exist.
Nowadays you have the internet with a huge ammount of informations. Lucky you. Use it.
..and learn to find the reliable sources.

hi again,
i dont advise you to adjust the gnd.cause many applications use the 2.pin as gnd not adj.
i advise you to build a voltage divider
try to use these systems with voltage dividers at the end of the circuit

buying a smps can also be a cure but you wont see many appliences as you try to observe