Ideal circuit that reduces 24 volts to 5 volts

[ertansuluagac]

Is there an ideal power circuit for PIC that reduces 24 volts to 5 volts and is not affected by interference?
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Es

[temtronic]

Yes, but how much current do you need ?

I used simple 7805 series regulators for 3+ decades to convert 24 VDC into 5 V, 1 amp using reasonably well laid out PCB, some caps for high frequency filtering, the +5v is noise free even in industrial enviroments like welding shops, foundries, etc. supplying power up to 1500 feet away on shielded copper wire.

The 'trick' is to KNOW what the 'interference' is. 'scope or SA will show, then properly filter the EMI 'nose' or 'interference'. Done right it's a combination of 1/2 math, 1/2 luck and 1/2 black magic.

Jay

[ertansuluagac]

thanks 2 Amper
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Es

[temtronic]

OK, 2 amps, 7805 won't work, LM338K (?) should, it's a 5 Amp unit...if my memory is good.
Best to design for 3 amps.....
There are switching PSUs that could work, if 'high efficiency' is needed...
24-5=19V x 2A = 38W ....that'd be a lot of power to waste....

Jay

[newguy]

Search for "TI simple switcher". Web-based tool. You enter your parameters, and the tool gives you options in terms of switching power supplies.

Once you choose a design, make sure you read the data sheet for the regulator IC very thoroughly. It will have layout tips. Follow them.

[elcrcp]

I don't know how much interference you are talking about but I did use 2596 modules in factory environment without problem. Their output is variable so just set the required output and fix the pot with glue if you don't want to change it again. It is very cheap so I suggest using it as a module if you are not going to use it on a mass product project.
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There is nothing you can't do if you try

[Ttelmah]

Is this 'peak' or actual 'rated' current? There is a huge difference. For example
a typical SD card has a specified maximum current of 100mA, but the supply
has to be able to deliver momentary spikes of up to about 500mA. However
these only last for nSec, so can be delivered by good decoupling. It makes
an enormous difference to the actual ratings required.
2A seems a lot of current. Typical PIC projects usually only need a few mA.

[ertansuluagac]

I am using 320x240 lcd already it draws 450 mA. I use the jz863, the room draws 100 mA. So it pulls about 1000 mA with other materials. I say 2A so I don't have to worry.
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Es

[Ttelmah]

OK.
The simple switchers can do this easily enouigh (there are version that
support up to 5A). The same comments made in this thread apply:

<http://www.ccsinfo.com/forum/viewtopic.php?t=58278>

Careful PCB design, part selection, and correct component selection.

I've used these on circuits with mixed power and analog, and have
the basic supply, then and extra filter feeding the analog Vdd, and
a proper Vref. The make sure the board layoout does not have power
running 'across' board areas involving the analog, and merrily get
repeatable readings down to uV levels without problems.

[temtronic]

That 'jz863' is an RF transceiver so be sure to read the specs for power needed during transmit. Some take well over 1 amp. While it may be a short perod of time, the power supply MUST have ample capacity, so that VDD does NOT go below 'brownout' level. Even then , if it drops say 5%, that's .25 volts, could affect operation of PIC or peripherals.
I'd design for a solid 5 amp PSU. Cost is same for 2A or 5A.

I got curious... found these
https://www.banggood.com/RIDEN-DC-12V-24V-To-DC-5V-5A12V-5A-Step-Down-Buck-Module-p-1187550.html?rmmds=search&ID=49552&cur_warehouse=CN

About $10 CDN, 95% efficient ! I KNOW I can't buy 1/2 the parts to make one for $10, let alone design a PCB, install, test, rework, test again.....

I have ordered lots from them and never had a problem. Today it's better to buy a module than design/build.


Jay

[dluu13]

There's also a consideration for efficiency.

Some voltage regulators (linear type) are less efficient. They will dump all the excess voltage and load current = supply current. That means in your case, going from 24V to 5V you are dumping pretty much 80% of your power as heat. They are very easy to use though.

Other types like switching regulators will be much more efficient but you also need to probably have a couple more auxiliary components and you have to be more careful in filtering because there will be some noise from the switching action.

[benoitstjean]

Or just do a quick search on DigiKey for DC-DC converters and use parameteric search to eliminate products...

Note here I haven't done much research on this device but searching for a device that can take 24VDC input with a 5VDC output rated for 2A gave me the following part: 1589-1465-ND for 7.47$ (CAD) which is a bit more than 5$ USD.

It says it's a Linear Regulator Replacement. Linear regulators are like the 78xx series. I stopped using them because they are big and get hot and so on.

It all depends on your goal. Does it have to be part of your circuit or does it just need to power the circuit externally (like a laptop power supply vs the internal supply on a tower PC... one is external and connects with a small barrel connector, the other is internal with a big power cord).

On my device, I use an LT8610 switching regulator IC which can go up to 42VDC. It is set to output 3.5VDC and runs a crap-load of parts (PIC24, accelerometer, SD card, altimeter, modem etc).

Good luck.

Ben

[Ttelmah]

The only caveat, which I warned about on the other recent thread talking
about supplies, is to be very careful about your choice of output capacitors.
Most of these have _maximum_ specifications for the capacitor for
stability. They suggest a 2.2uF input capacitor, and 10uF output capacitor.
Don't be tempted to put a much larger output capacitor than this.

[ertansuluagac]

to all of you very thank.
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Es