Will the TVS diode protect the DC line from AC power?

Thread Starter

Glebiys

Joined Mar 11, 2019
14
Hi,

I have a line with a voltage of 5V DC. It is possible to supply high voltage AC (230 V) to this line.

Will the TVS diode protect the DC line from AC?

My TVS: LittleFuse SMBJ5.0A

Thank you!
 

DickCappels

Joined Aug 21, 2008
5,882
Not a lot of information to go on here, but a TVS diode will limit the voltage across it. If you just want, for example, to prevent +5V from being driven negative, then an appropriate rectifier would prevent that.

If you can describe what you want to do in a little more detail, you can get a more specific answer.
 

Thread Starter

Glebiys

Joined Mar 11, 2019
14
@DickCappels ,

Thanks for the answer!

Schematic:


Description:
Using the Arduino output, I supply 5V to the control pin of the solid state relay (AQH1213), after which the solid state relay supplies high voltage to the load.

R1 is a current limiting resistor.
R2 - pull-up resistor

Purpose: to protect the low voltage circuit from high AC voltage.
 

AlbertHall

Joined Jun 4, 2014
8,358
The SSR provides 5kV isolation but if you want to add the TVS then then it should connect directly to the SSR pin 2.
 

Thread Starter

Glebiys

Joined Mar 11, 2019
14
@AlbertHall ,

There is a 330 Ohm resistor between the SSR and TVS to limit the breakdown current. As far as I understand, if you connect the TVS directly, then it can explode at high current. The power of my TV is 600 watts. It is important to minimize the risk of fire / explosion.
 

AlbertHall

Joined Jun 4, 2014
8,358
The idea is that the breakdown of the TVS blows the fuse and provides the ultimate protection. The resistor prevents that happening.
 

Alec_t

Joined Sep 17, 2013
10,362
If you're worried about the SSR breaking down then you could put a 1N4007 or other high-voltage diode in series with R1.
 

DickCappels

Joined Aug 21, 2008
5,882
upload_2019-10-13_20-4-35.png

I doubt you have to worry much at all, with 50 G Ohms isolation resistance. If you are worried about signals capacitively coupling because of unfortunate choices of wire routing, electrostatic discharge, or similar hard-to-anticipate events, you can, as indicated above use ordinary Zener is you don't have a TVS on hand. Make sure the TVS diode's voltage is the same as the power supply voltage for your Arduino so the Arduino is not driving the diode with much current yet the voltage is low enough to clamp the I/O pin voltage below the voltage at which dangerous currents might be drawn through the input protection diodes. (from memory of AVR devices this is about 20 ma).

I doubt the thing will ever be needed.
 

Thread Starter

Glebiys

Joined Mar 11, 2019
14
@DickCappels , @AlbertHall , @Alec_t ,

Thanks for the answers!

I'm sorry for the late reply.

What I've done:

1) Made an insulating slot for the relay between HV and LV.

2) On the control line of the relay, I set a current-limiting resistor, a fast-acting fuse and a TVS diode.
The resistor must limit the current for the TVS, when the voltage rises, the TVS will close to ground and the fuse will break the circuit.

The option with a diode and an optocoupler is also good, I will use them on another board.
 

dendad

Joined Feb 20, 2016
3,002
The SSR is already isolated so I think you would be quite unlucky to have a fail to send 240V to the Arduino. Cutting slots between the low and high volts parts is good design practice, (often omitted in the cheap Chinese power supplies) .
Adding another opto in line would require another isolated power supply to take the opto output and drive the SSR.
Just use a good quality SSR I think, with slots as you mentioned. Your first circuit is just how I would do it.
 

MisterBill2

Joined Jan 23, 2018
3,869
The danger of higher voltage AC getting into the arduino comes more from the possibility of some mechanical problem involving the connections to that SSR. A fuse on the AC side along with diodes on the DC side can reduce the damage done by such a failure. But the shunting diodes need to be rated for enough current to clear the fuse.
And what has happened to the forum? It looks totally different from what it was a few hours ago, and I see the change as NOT AN IMPROVEMENT!!!
 
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