Single power source, multiple devices, how to stabilize?

Thread Starter

nardev

Joined Feb 26, 2018
26
I'm having an issue with power on PCB, don't know how to stabilize it.

I have single 12V DC source and i need to power:

1. 12V Device (static current around 80mA, don't know during the max. Might be up to 150-200mA )
2. 5V buck converted
3. From those 5V i power Relay (typical from 70mA up to max 150)
4. From those 5 V i power linear voltage regulator for 3.3V lm1117
5. From 3.3V i power up MCU (draw around 120 up to absolute max 500mA)
6. Another 12V device which also have a coil (up to 200mA when it kicks)

Is there a way to stabilize powering device under, especially under 6.? Everything is on PCB so, might make some problems.
Or i would be enough to have proper main source with 2-3A adapter?
 

MrChips

Joined Oct 2, 2009
21,090
Everything looks ok.

Make sure the voltage regulators have recommended input and output capacitors.
For #6, put a 1000μV/25V aluminum electrolytic capacitor across the power supply input of the 12V device.
 

BobaMosfet

Joined Jul 1, 2009
1,110
You say you're having an issue, but you don't tell us exactly what the issue is. You didn't tell us how much current for #2, or #4. You're only accounting for 1.05A Max, because of this. Do you account for inrush? Have your inductors got diodes to localize current spikes? Do you know that your adapter is actually providing 12V and can support up at 2-3A? What MCU are you using, it has a limit on how much current it can handle across all pins (per the datasheet)? If you draw too much, it could shut down if it has circuitry to protect itself.
 

Thread Starter

nardev

Joined Feb 26, 2018
26
You say you're having an issue, but you don't tell us exactly what the issue is. You didn't tell us how much current for #2, or #4. You're only accounting for 1.05A Max, because of this. Do you account for inrush? Have your inductors got diodes to localize current spikes? Do you know that your adapter is actually providing 12V and can support up at 2-3A?
Ah, you are right, i didn't say much about the issue. When 1., relay at 3. and 6. spikes at once, the 5V buck converter simply resets and goes off.

Everything pretty much works fine until that spike when 1. relay at 3. and 6. start at once.

The 1. and 2. devices are not under my control. The thing is that the 6. one is magnetic coil like magnetic lock.

Pretty much all the devices are isolated properly with input and output caps. I followed the guide for all converters, but i didn't try that one with stabilizing the 1. and 6. with additional caps. Will try that now.
 
Top