bench power supply

finally I'm back! looking a little bit around i found that the lm317 is not the best IC to use in parallel: LM317 in parallel - Answered -> LM2596 circuit question  so i will just be happy with its <1.5A

i draw again the circuit with your precious suggestions:

now i have the input of 12V filtered by a 1000uF electrolityc and a 0.1uF ceramic capacitators with:

-"high" current output with the lm317 (i think that now it is correctly wired)

-low current output where i could choose between 12/5/3.3 volts

the ammeter/voltmater that i am using is this: https://it.aliexpress.com/item/1pcs-DC-100V-10A-Voltmeter-Ammeter-Blue-Red-LED-Amp-Dual-Digital-Volt-Meter-Gauge-Voltage… as i said before it's the same that jw0752 is using

i think that i could start to draw the board, anyone have any suggestion?

about the power supply from the 220V I was undecided between: https://it.aliexpress.com/item/Free-shipping-2pcs-lot-Power-adapter-EU-UK-AU-US-AC110-220V-to-DC12V-2A-led/1806497704.ht…  and https://it.aliexpress.com/item/New-24W-Regulated-Switching-Power-Supply-LED-Driver-Lighting-Transformer-For-LED-Strip-Li…

the second one is far away better, isn't it?

EDIT: i was thinking that maybe the ams1117 would stay in a safer position if i use the Vout from the lm7805, correct?

EDIT2: instead of all these output caps (3,4,5,6,7,8) wouldn't be better if a just put a 100nF ceramic cap before every output? or do you think i will need more filtering?

As COMPACT said the regulators need some voltage above their output.

A good rule of thumb is 2v.

Rather than go ot the 24v supply, many of the power bricks for laptops are 15v and have more than 2A capability.

That assumes you want to have the adjustable voltage got from zero to 12v.

Also a minor difference but if you can the voltmeter input should be on the Output of the ammeter.

Most ammeters use a small resistance in series and measure the voltage across it to derive the current figure, some are negliglble but others are higher.

You will need to be very disciplined when using the fixed output switch. You really don't want to have 5v (or worse) into a 3v3 device

Otherwise it looks like it will work.

Mark

Maybe just a 0.1uF ceramic in the input and one identical at both outputs will be ok

The 0.1uF is a must, and it should be as close to the output terminals as possible.

You can always add another one across the terminals when you build it, and place the other closer to the regulator.

The 0.1 removes high frequency ripple and spikes, while the larger capacitors tend to smooth out the voltage fluctuations.

You need both to do proper filtering.

A good rule of thumb is 1,000uF per amp as the absolute minimum, so if we assume that C2, 4, 6, 8 electrolytics then 2,200 - 4,700 uF is a good size and you can stick with 25v versions to cover any location.

Much bigger and you have to leave a little more room (which you can).

Over the years the sizing has gotten smaller despite the capacity and voltage rising, so you're winning already.

Mark

Actually all of the capacitors are not mandatory.

If you're feeding you circuit with a regulated DC power supply it'll already have its own filtering.

A low impedance (ceramic or otherwise) capacitor at the input leads may only be required for situations where longer leads are used.

The only way to determine whether capacitors are required is from testing.

I will use the suggestion of Mark for the size and position of the caps, but i completely agree with compact that testing would be the best solution

I wanted to say that i m not doing it not because I am lazy and i don t want to build and test the circuit on a breadboard but because with my 3 dollars voltmeter i don t think that i will feel any difference between a smooth or a disturbed line  

COMPACT Not trying to start a war here ...  but I wonder if we can't elaborate for those with 'less technical experience' here.

If you're feeding you circuit with a regulated DC power supply it'll already have its own filtering.

Correct ... but introducing regulators into the line between the existing regulated supply and the output sort of negates the ones in the source ...

It should be recognised that the plan was to use a cheap asian sourced supply, which is probably closer to the minimal, rather than over engineered.

The only way to determine whether capacitors are required is from testing.

I agree but the reality is most builders will not have access to the type of equipment that would allow the testing.

For the few cents a 0.1 cap costs, surely it is better to add it, than have issues further down the track.

We're not making 1000 units where the 50c we saved is more profit, it's a single unit.

IMO bench type supplies tend to get used for various purposes, and one day it may be a resistive load, and the next a circuit that has lots of switching noise.

Cheers

Mark

The easiest is just to get a 3 pin Linear Regulator and a heatsink as a starting point.

In this day and age almost all Wall warts and power supplies are already regulated so it is likely that the necessary capacitors are already present.

The learner will then understand that larger voltage In can be output as an lower voltage with the unwanted power dissipated as heat.

This was the technology of the of the late 20th century until recently.

If a learner wants to know more then they can attach an oscilloscope and observe the waveforms of their power supply and see how the addition of capacitors may or may not affect it.

21st century Switch Mode Power Supplies (SMPS) are much more efficient at the cost of electrical noise, complexity and material usage.

Here the usage of capacitors is critical to obtain the desired performance.

To highly excite learners one might deliberately have polarised capacitors attached back to front or use capacitors beyond their rated working voltage to see what happens.

If the learner just wants a power supply just get them to use a couple of modern wall warts.

USB adapters provide at least 1A @ 5VDC and 12VDC adapters are readily available.

To get the 3V3 just use a DC:DC Converter Module.

In this day and age an Oscilloscope is a mandatory piece of electronics hobbyist equipment.

With it one can visualise the power!

NEVER BREADBOARD a power supply design

(Unless you have the means to limit the power.)

The resistance and power handling characteristics of a breadboard are not necessary suitable

Always ensure that you used appropriately sized conductors and insulation.

In this day and age an Oscilloscope is a mandatory piece of electronics hobbyist equipment

You're right, BUT they aren't always cheap unless you aim for an older 2nd hand one with limited bandwidth ...

Many newbies struggle to see the value in purchasing good meters, and it takes either good advice or experience to see why they should apy for better quality.

I think jw0752 power supply blogs are a good example of an easy to implement supply.

The results also show they work well.

deliberately have polarised capacitors attached back to front or use capacitors beyond their rated working voltage

That used to be a demonstration when we were venturing into electronics.

With the newer case nowdays, the result is less than spectacular.

Mark

Here is an example of what I mean.

8V in from a regulated power supply being output as 5VDC using an LM7805 Linear Regulator.

(The current limit has been set to 50mA on the bench power supply as not to risk melting the breadboard or voltage regulator without a heatsink.)

The most important point here is that the circuit works!

The test apparatus on the left is a TENMA bench power supply; it is a beauty of a unit and can be remotely controlled by a computer.

The test apparatus on the right is a DC Electronic Load; it provides a test load for the regulator output whilst acting voltmeter and ammeter.

If you look at the numbers on the apparatus; you'll notice that the input power used is greater than the power being output; the missing power is expelled as heat!

"Wherever I lay my cap, that's my home". - Paul Young

"You can keep your cap on" - Joe Cocker

As for PCB layouts of Linear regulators search for "S100 boards" on the Internet.

There you will find lots of examples.

As for PCB layouts of Linear regulators search for "S100 boards" on the Internet.

There you will find lots of examples.