using 24v and using unkown brand chips

[TimB]

Hi all

First of I want to say so many thanks for the help get here. I worry people will get fed up with my posts..

My never ending project (coming to and end soon yay!!!!) is an industrial controller for automatically monitoring steam quality. I have a patent for the process, but I hasten to add that a patent does not mean it works 

Anyway It runs on 12v raw and regulated to 5v and then to 3,3v where needed. I decided on 12v for various legacy reasons. But now I'm thinking I should use 24v as it seems to be standard in low voltage industrial panels.

The issue is whats the best method to get from 24v to 5v for my board. Switch mode and or linear?

The next question is unknown chip suppliers. I have 4 DACs 0-5v by Mchip. They work well. But my many proto boards has revealed I need more connector space and hence a bigger case. That led me to thinking I can use the extra space to swap out the dacs for4-24ma chips. Searching I could not find a nice i2c to 4-24ma device. Until I came across this board

https://wiki.dfrobot.com/SKU_DFR0972_I2C_4_20mA_DAC_Module#target_0

Its using a GL14P04-8 that it seems I can get only from LCSC from a company called Guestgood. It does all I need but worried that if I design it in, I  may be scuppered with availability in future.

Whats peoples thoughts on using not so well known parts? Yay or Na?

Thanks

Tim

[John Lawton]

Tim,
you will need to tell us your current requirements at 5V and 3.3V as that will determine the choice of regulation from 24V.

[trastikata]

Searching I could not find a nice i2c to 4-24ma device.

Hi Tim,take a look here:

https://www.analog.com/en/parametricsearch/11818#/

I know they are expensive, but for a single prototype board you can get 2 or 4 samples.

[TimB]

John

Current for 3.3v max 10ma. 5v with lcd back light and all the i2c devices max estimated at max 200ma

I started looking at it seems its pretty simple with a DC-DC converter. The Maxcomp MP-K7805-500R3 looks ideal and not expensive.

[John Lawton]

Yes that looks a good solution as long as you can accept a small amount of noise on the 5V line. A 3.3V linear regulator should make the 3.3V line clean for the PIC.

[TimB]

Yes that looks a good solution as long as you can accept a small amount of noise on the 5V line. A 3.3V linear regulator should make the 3.3V line clean for the PIC.

The 3.3v is for the PT100 converter Max31685 all 4 of the pics connected run off the 5v rail.

[John Lawton]

When I've used DC-DC converters like this, I've added some chunky MLCC caps like 10uF 16V on the output to reduce noise, plus some distributed 100nF XR7 MLCC caps on the power pins of devices run on that power line.

[TimB]

Thanks John

I have 220uf electrolytes on the input and output of my current reg. Every ic has it's own 100uf cap. So looks like it should be fine as a drop in replacement to my current regulator.

[John Lawton]

Electrolytics don't have low ESR values, high value MLCC caps are much better here.

[TimB]

Electrolytics don't have low ESR values, high value MLCC caps are much better here.

Right. I had a bucket load of Low ESR Electrolytics from a SM power supply project and been using them, no idea if Low ESR Elec's are a valid replacement. But thanks for informing me on cap types. I have a lot to learn. Really appreciated.

Tim

[kcsl]

Every ic has it's own 100uf cap.

When you say 100uf did you mean 100nf ?
If you do use linear regulators, be wary of high capacitances on the output as you can damage them if the regulator input voltage drops below the output. Depending on the regulator of course.

Joe

[TimB]

[/quote]

When you say 100uf did you mean 100nf ?
If you do use linear regulators, be wary of high capacitances on the output as you can damage them if the regulator input voltage drops below the output. Depending on the regulator of course.

Joe

[/quote]


Oops Yes I meant 100nf. I have a lot to learn about analogue