Voltage regulation circuit 12V to 5V in 5A range

[Demon]

EDIT: Figured I'd concentrate my power supply circuit here instead of my MSFS thread.

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Figures that I would hit a roadblock after wiring an ammeter to be able to see current and voltage in real-time. That DC-DC converter under the meters has too much noise on VDD and VSS for stable ADC readings.




I made a 7805 circuit for testing, but it's only rated for 1.5A.




I wish I had seen the LM1084 before; it can handle 5V up to 5A, more than enough for my design. At least it's a piece of cake wiring a through-hole LM1084 with some caps instead of the DC-DC converter.

[tumbleweed]

I wish I had seen the LM1084 before; it can handle 5V up to 5A

Just be aware that if you're starting with 12V VIN then the regulator is going to dissipate roughly 5W with 700mA out (from your other thread).
Pd = (12V-5V) x 0.7 = 4.9W

That's going to get quite hot... over 100degC rise depending on the package type.

[Ioannis]

Well, the SMPS you used are crap and although they say it is a LM25xx in fact they are just bad copies. Also the caps and inductors are crap too.

I would design my own SMPS and make sure to follow the manufacturer advices (either TI or Microchips). Having a goal of 20mV p-p is totally acceptable and doable.

Linear regulators will get too hot and while DC output, if well designed, may be clear enough, it is wasting too much power. You will need a big (and expensive) heat sink also, with ventilation holes on the final product.

Ioannis

[Demon]

I had 2 options originally:

- stay under 500mA and use USB power
- use a wall adapter and add a voltage regulator component.


USB power is no longer an option with the 4 LCDs. I don't have any "simple" design for a SMPS that would have noisy power.

The LM1084 "should" be as clean as the 7805 (I hope).

I can use the TO-220 package with cooling fins, and even add a tiny cooling fan. Tests will confirm how much heat I will generate with everything.

[Demon]

I bought a bunch of these a while back; aluminium heatsink with double-sided tape.

It fits just right on the back of a IRFZ44N (TO-220). I don't seem to have to bother with a screw/nut (unless you highly recommend a model with a fastener).




Aliexpress:

8.8 x 8.8 x 5, I tried removing the fin once attached, and it doesn't come off unless I usetools.

https://www.aliexpress.com/item/1005004079109702.html


My alternative was this screw/nut model with thermal paste for maximum efficiency:

https://www.aliexpress.com/item/32882672963.html

I'd just prefer in bare aluminium; I don't like paint on a cooling surface, seems counter productive to me.

[Ioannis]

Paint on heatsinks is not for cosmetic reasons. Black heatsinks radiate more IR energy than bare aluminum ones.

As for the power loss on the regulator (either 7805 or 1084 or 317, it does not matter which), it depends on the Vin and the current you will need on the load.

Example:
Vin 12 volts
Vout 5 volts
Max current 1A

The power loss on the regulator will be (12-5)*1A=7 Watts.

According to datasheet Power dissipation diagram, at about 35 degrees celsius ambient temp, you will need better than 10°C/W heatsink. So if you opt for 50°C ambient temp, then around 5°C/W maybe just enough.

How this 5°C/W translates to a physical heatsink part? something like this https://www.mouser.ca/ProductDetail/...jU4NS4xNi4wLjA.

Just tested a 7805 with 1A load and 12 volt input, roughly 7 watts of heat and the 7°C/W I used, is over 80°C with just 24°C ambient !!!

So, you will need a large and expensive piece of aluminum heat sink...

Better use a SMPS, I insist on this.

Ioannis

[Demon]

Option 1:

Do you have a schematic for a reliable SMPS that can do 12V to 5V somewhere under 5A?

I don't have a final current consumption cause I haven't built a complete unit.

And most importantly, will it generate a noise-free VDD/VSS?

[Demon]

Option 2:

How about these with a fan?

25mm x 34mm x 12mm
https://www.amazon.ca/Easycargo-Insu...7H5GQVTD/?th=1


25mm x 7mm 12V brushless fan

https://www.amazon.ca/GDSTIME-25x7mm...8CMMB6VJ/?th=1

[Demon]

Option 3:

Would it be easier to have 3 LM1084 with that regular black heatsink:

- one to power all PICs and ICs.
- one to power the 3 LED strips.
- one to power the 4 LCDs.

That way I'd get minimal noise on VDD/VSS, and limit heat loss to more manageable levels.

A sort of distributed power management system.

[amgen]

2 cents....... the LCD and LED's stuff aren't that badly affected by slight power supply fluctuations ... slight. The PIC's and IC's need good stable power 7805 or similar on their own circuit.

[Ioannis]

Are you sure you need 5Amps at 5 volts? That is 25 Watts of power.

And about 35 Watts of power loss on the Linear regulator. This means that you will need a monster heatsink like intel CPU with a fast spinning fan. Not anything close of what you posted.

Better use seperate linear regulator as amgen said for the PIC and a switcher for the power hungry LED and Displays.

Or check these:

Vin 4.5-24, Iout 3A: https://www.ti.com/product/TPS56339

Vin 4.5-17, Iout 5A: https://www.ti.com/product/TPS565208

Following the design examples you may have less or equal to 20mV noise. For me good enough even for PIC using ADC.

Ioannis

[Demon]

2 cents....... the LCD and LED's stuff aren't that badly affected by slight power supply fluctuations ... slight. The PIC's and IC's need good stable power 7805 or similar on their own circuit.

Yup, I'm thinking of running a dual system.

Are you sure you need 5Amps at 5 volts? That is 25 Watts of power. ...

Yeah, I'm waiting for a 9V 2A wall adapter to help reduce the waste heat. I'm getting 7V 2A wall adapter tomorrow to reduce that even more.


I'll probably need 2A, but I hate running stuff at peak power, hence why I said 5A.

A component running near max is generating more heat than another running at 50% power; that's not good for long life.

[Demon]

I did encounter a problem with the LM1084-5. Voltage drops when I add load.

I expected a specialized IC like the LM1084 to remain at a stable 5V throughout its workable current range.

I used the bottom of figure 7.2.8 with 2 electrolytic capacitors:

[Ioannis]

That 50 ohm resitor will worsen the regulating output. It forces the upper IC to have higher than 5V output but regulation depends now on the resistor.

Have you had a look at TPS565208? It is a chip with low noise and ripple, easy to use SOT-563 package, very small footprint and cheap. I would not mess with any Linear, heatsinks, wall adapters etc.

Only downside (maybe) is that it accepts only up to 17 volts DC. But if your source is upt to 12volts your are more than good to go.

Ioannis

[Demon]

I only used the bottom regulator on that schematic.

I have 9v 2a wall adapter coming in today, and a 7v 2a coming in tomorrow.

That should reduce wasted heat a lot.

[amgen]

I know you already ordered some things, I have used few of these things..... no other regulator needed. The output voltage is pretty stable.

[Ioannis]

Camparing the various chinese power supplies I ended up with Sunny brand, that is represented in Europe by a reputable firm. https://en.sunny-group.com

Opening one of them reveals that the design is in pretty good level.

Please be very carefull with all these cheap SMPS that are sold at low prices. They can have really catastrophic failures (I was almost hurt by this), with very bad "protection" circuits that fail after the big-bang...!

The idea of having a 5V wall adapter may seem good but there is a risk that the user may by mistake connect a 12V adapter at the 5V entry...

Ioannis

[amgen]

.

The idea of having a 5V wall adapter may seem good but there is a risk that the user may by mistake connect a 12V adapter at the 5V entry...

Very true. I wouldn't use that for product for resale, only for building and testing some circuits or maybe a simple small product. But I always hardwire power supply in to avoid exactly what you said....... That was interesting what you said about some dangerous failures, those SMPS's 'should' have the input separated from the output with some kind of high frequency transformer for 'galvanic isolation' meaning no actual electrical connection from in to out.

[Ioannis]

Yes, all of these SMPS do have that high frequency transformer and do isolate the secondary. Few have poor isolation.

Many have bad fuses in the line input and they blow after the explosion of low quality capacitor/bridge/MosFet. And had cases of pcb traces that were melted also.

These two images show WellMax LED panel drivers that drop my three phase protection fuse on the wall distribution box! The pcb fuse was the last to blow after burning pcb traces!

Had other similar case of 12V/5A power supplies that were poor made. I do understand that inrush currents are high enough and the fuse should be relatively slow, but they should add a thermistor then to lower that current and have a faster fuse.

Ioannis

[Demon]

I just noticed the LM1084-ADJ is claimed to "provide 5 A at high efficiencies and very low drop-out." I just ordered a few from Digikey.

Ioannis, will the TPS565208 or TPS56339 voltage drop when I add load?

Current consumption so far:
- 800mA, ICs and 4 LCDs
- 510mA LED strip 1
- 510mA LED strip 2
- 510mA LED strip 3

I'm at 2.330A and I have a few other ICs to add, hence why I target a power supply that can manage 5A.

The thing with the LED strips is that they can be dimmed from 0 to 100%, that's a respectable load change.

(I'll be limiting the LED strips to 350mA or so, but still, I want to be safe if they get stuck "full ON").

[Demon]

Piece of crap 7V wall adapter worked 10 minutes...

https://www.amazon.ca/dp/B091YHX8RY

[amgen]

Yes, all of these SMPS do have that high frequency transformer and do isolate the secondary. Few have poor isolation.

....
....
wow, looks like you were trying to take 100 amps from that little power supply..... (just kidding)
.
adding..... should probably never try to use a power supply at it's full rating, maybe 1/2 of rating is safer.







9

[richard]

chinese amps are quite a bit smaller than normal ones. 0.75 seems close

[tumbleweed]

I just noticed the LM1084-ADJ is claimed to "provide 5 A at high efficiencies and very low drop-out." I just ordered a few from Digikey.

The only difference between the LM1084-ADJ and the fixed output LM1084-5 is the latter already has the resistors to set the output voltage built inside it. You will only get 5A out of it if you have the input > the Vdo drop out voltage spec, and stay within the max power dissipation. With no heatsink you're not going to get anywhere near 5A out, not with 12V in.

You said the output voltage of the LM1084-5 dropped when you added a load. That shouldn't happen as long as you're within the datasheet specs.

If you're trying to get 2.5A out, with your 12V adapter that gives a Pd = (12v-5v) x 2.5 = 17.5W !!

Yeah, I'm waiting for a 9V 2A wall adapter to help reduce the waste heat. I'm getting 7V 2A wall adapter tomorrow to reduce that even more.

You'll need an adapter with more than 2A out if you want 2.5 or 5A out of the linear regulator.

[Ioannis]

Not so tumbelweed.

With Linear regulators, your Input current is the same with the output current! Beware of that! Plus the current of the regulator of course, though this is small enough.

The opposite happens with SMPS. In that case wattage is the same plus the losses in the regulator itself.

The voltage drop with increased load is called Load Regulation and is there in the specs. And of course it is different for every regulator, either linear or SMPS. Besides that spec, which is typically small enough (less that 1% for the TPS565208), the voltage will drop for many other reasons, like design of PCB, part selection, thickness of wires and the point where output voltage sample is taken for the regulator to compensate for. the drop.

More output current, more copper on PCB and thicker wires are needed. After all, the regulator will have the nominal voltage on the output but if your wire is 10 meters long, you will have voltage drop on the cable, right?

I think TPS565208 is one of the easiest to handle and very good in terms of cost, pcb estate, output noise and efficiency.

Ioannis

[Ioannis]

Piece of crap 7V wall adapter worked 10 minutes...

https://www.amazon.ca/dp/B091YHX8RY

Noname chinese rubbish... They don't even have the proper distances or creapage on the PCB...

Prefer good brands like Mean Well or Sunny.

Ioannis

[tumbleweed]

That's what I said in the second part about getting more than 2A out.

You can't get 5A out if the adapter can only supply 2A

[Demon]

That's what I said in the second part about getting more than 2A out.

You can't get 5A out if the adapter can only supply 2A

The 2A wall adapter was a quick fix to be able to continue testing.

The 9V 2A is holding up for now.

[Demon]

Received the LM1084-ADJ, still waiting on the recommended caps (to properly test ripples), but it's already running nicely with what I have on hand.

Also got a thermal imager to help identify hotspots. Looks like I fried 2 PICs with those 12V and 7V bursts (lesson learned).

LM1084-5V on right, supplies PICs, ICs and LCDs, essentially everything that is "always ON", with a slight tweak on ADJ pin to get it slightly above 5V to compensate for voltage drop.

LM1084-ADJ on left, supplies LED strips, cooling fans (to be determined) and anything else that doesn't care about ripples.

(HIKmicro E02)



No thermal compound yet, this was a temporary setup to help prevent forest fires.



I'm sure there's better ways to skin a cat, but this was the simplest technique I could come up with. It remains to be seen if the ripples are "manageable" for the ADC on the PIC circuit.

[Demon]

Wasted so much time trying to figure out why I STILL had a lot of ripples with the LM1084.

I checked directly on the wall adapter:



GIGO; can't expect the LM1084 to do miracles with that.


So I pulled out a 12V-5A Fqcmogu AL-1250 adapter (no idea what it's for):



Definite improvement.


This is the LM1084-5V running at 5.0V (LED strips and whatnot):




This is the LM1084-ADJ running at 5.2V (PIC, LCDs and other ICs), note that is had less ripples as stated in the specs:

[Aussie Barry]

chinese amps are quite a bit smaller than normal ones. 0.75 seems close

ROFL...
Good one, Richard!

[amgen]

if you didn't already........ put your probe lead on 'ground/negative' at a distance from the negative/ground probe connection..... and probe to various ground/neg locations. Sometimes noise is 'introduced' into circuits from other sources called common mode noise.....
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Key Takeaways

Noise appears in two forms in an electrical interconnect: as differential mode and common mode noise.
Differential mode noise is measured between two sections of an interconnect with equal and opposite polarity, while common mode noise applies to interconnects with the same phase and polarity.
Both forms of noise are induced in an interconnect via Faraday’s law from external radiation.

[Demon]

if you didn't already........ put your probe lead on 'ground/negative' at a distance from the negative/ground probe connection..... and probe to various ground/neg locations. Sometimes noise is 'introduced' into circuits from other sources called common mode noise.....
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Nope, haven't done that. Good idea.

I'm also redoing my prototype board to have a somewhat "star pattern" for VDD and VSS. Right now the 2 rails run all over the place.

Right now I'm just basking in the glory of having found the root cause of most of that noise on the lines, and started looking for a source of affordable "good" 9V 5A power adapters.

[amgen]

Right now I'm just basking in the glory of having found the root cause of most of that noise on the lines, and started looking for a source of affordable "good" 9V 5A power adapters.

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not trying to 'rain on your parade'..... it is possible that isn't where your noise is coming from...... if you haven't already, put a 10 or 100 microfarad electrolytical and a couple of .1 or .01 microfarad caps at the output of the power supply..... and I didn't look to see but you would want to put the same capacitor duo on each separate circuit board..... that SHOULD squash the noise. Plus..... a bunch of interconnected grounds running here and there are often culprits for noise. And keep in mind that often serious engineers and engineering is involved with noise and interference

[Ioannis]

Also breadboards are the worse for low noise circuits!

Ioannis