Short circuit protection for network of IoT sensors

Thread Starter

CostasGr

Joined Apr 8, 2022
4
Hello all,

I have a network of IoT sensors that all get power from a PSU. Let’s assume that the PSU is providing 14V.

I have two requirements. First, I want to provide different voltage to each sensor. As you can see below one of the sensors requires 12V as input voltage, the other 12,5V and the third 10V.

Second, I need short circuit protection on the sensor level. That means that if for some reason the power is short circuited at the sensor circuit, this short circuit must be isolated from the rest of the network. In other words, the rest of the sensors should still have power.

I am providing you the diagram below to make things clear.
1649455557144.png
In order to solve this, I have used three DFR0205 buck DC to DC Power Modules but I failed big time. Of course I provided to each sensor the correct voltage but when I short circuited one of the IoT sensors all of them lost power. So, although the DFR0205 protects the circuit from shortcut, it somehow propagates this back to the PSU and the PSU shuts down.

So my questions is simple. Which module should I use for each of the three blue boxes? Any suggestions?

Thank you.
 

ronsimpson

Joined Oct 7, 2019
2,067
I have used a "poly fuse" or resettable fuse. If you unplug the short and wait a little the fuse resets. Use one fuse for each sensor.
 

Thread Starter

CostasGr

Joined Apr 8, 2022
4
I have used a "poly fuse" or resettable fuse. If you unplug the short and wait a little the fuse resets. Use one fuse for each sensor.
Ronsimpson, thank you very much for your answer. Let me yet tell you, that I have indeed tried that and believe it or not it didn't work. Specifically, the short circuit is detected by the PSU short circuit protection before the poly fuse actually starts to intervine.

Actually I used the following device to split the power to each device:
AWZ579 PULSAR - Breaker: fuse block | 1A; Mounting: for building in; 44g; Inputs: 2 | TME - Electronic components (WFS)
 

Thread Starter

CostasGr

Joined Apr 8, 2022
4
I added the new circuit to your circuit, but I haven't tried it yet.

View attachment 264628
Scott, thank you very much for your effort to provide this detailed diagram, yet I would ask for a *tested* solution because I have already spent so much effort trying stuff that didn't work. So, I would appreciate if somebody could indicate to me a component that they've already tested.
 

ScottWang

Joined Aug 23, 2012
7,205
The MOSFET gate is only connected to the collector? how would it ever turn off?
I think the idea is that if the sensor voltage collapses (shot circuit) the input power would also shut down?
How would it ever start up?
Thanks.
I forgot to add the Rgs resistor.
I think the idea is that if the sensor voltage collapses (shot circuit) the input power would also shut down?
How would it ever start up?
When the sensor circuit is back to normal or cutoff and then the Switch circuit(N MOSFET and BJT) will be turned on again.
 

ScottWang

Joined Aug 23, 2012
7,205
The MOSFET gate is only connected to the collector? how would it ever turn off?
I think the idea is that if the sensor voltage collapses (shot circuit) the input power would also shut down?
How would it ever start up?
I just added the Rgs, you can check that does it has some other problems, thank you.

1649504036127.png
 

ScottWang

Joined Aug 23, 2012
7,205
Scott, thank you very much for your effort to provide this detailed diagram, yet I would ask for a *tested* solution because I have already spent so much effort trying stuff that didn't work. So, I would appreciate if somebody could indicate to me a component that they've already tested.
I just added the Rgs to the new circuit, please check post #8.

Edit:
NPN bjt -- 2N3904, 2N2222, the general bjt.

P MOSFET -- Vdc>=20V, Id>=5A, Rds<=30 mOhm.
 

Thread Starter

CostasGr

Joined Apr 8, 2022
4
What is wrong with simple fuses? That is the usual method if doing what you want.

Bob
Hi BobTPH,
please focus on the fact that the PSU has already a short cut protection that will kick-in even before the fuse will start to slightly getting warmed up. So the circuit will black out and my system will freeze until I physically restore the circuit to the faulty IoT. The idea is that I want the rest of the sensors to keep operating (as a fail safe reason).

To clearly explain, another approach is to have two or three seperate PSUs but this is not efficient.

Thank you,
Costas.
 
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