Filter help (circuit protection, automotive environment)

[Rajinder1268]

Hi all,
I have some electronics powered from a car battery going from a PTC fuse (trip current of 5A). I do not have much space on the PCB
I am looking a adding some over voltage and EMI filtering.
I have selected a TPSMC30A TVS diode.
Any advice on what I could add for EMI filtering? Could It use ESD capacitors?
I am limited to adding around 2 components, must be SMD.
Any help would be appreciated.

 

[barry]

EMI and ESD are two totally different things. And your question is so vague, it’s meaningless.
If your only design requirement is “two components”, I’d use a ferrite bead and a cap.

 

[Rajinder1268]

EMI and ESD are two totally different things. And your question is so vague, it’s meaningless.
If your only design requirement is “two components”, I’d use a ferrite bead and a cap.

Hi
Sorry for the vague question. The car battery voltage is destroying an IC that is rated at 40V. Not sure if it is overvoltage inductive spikes or overcurrent. The PTC fuse is still intact.
Hence I wanted to put in some protection but not sure what?
That is why I was looking into a TVS diode for over voltage and perhaps EMI filtering. As mentioned I am really restricted for PCB area and probably can only fit two components maximum, which need to be SMD.
Are you suggesting an LC filter?
Ferrite bead + cap? This idea did occur to me, however I was unsure due to their physical size and if they are likely to get damaged i.e. due to their current and voltage ratings.

 

[barry]

How do you know it’s the battery voltage that’s destroying the IC and not some input or output condition?

 

[KlausST]

Hi,

You say destroying an IC.
Can you give us
* a photo of the circuit
* the schematic
* a more detailed failure description
* the exact type of IC

There are different tyoe of pulses.
* low energy, high voltage. Like ESD. They may be suppressed by capacitors
* high energy ones. With these you have to limit the current with one device, while limiting the voltage with another device.
Bot devices need to react very fast, thus a PTC is not suitable.

It depends a lot on your applications what protection circuit to use.

Klaus

 

[Rajinder1268]

Hi,

You say destroying an IC.
Can you give us
* a photo of the circuit
* the schematic
* a more detailed failure description
* the exact type of IC

There are different tyoe of pulses.
* low energy, high voltage. Like ESD. They may be suppressed by capacitors
* high energy ones. With these you have to limit the current with one device, while limiting the voltage with another device.
Bot devices need to react very fast, thus a PTC is not suitable.

It depends a lot on your applications what protection circuit to use.

Klaus

Hiyes I will give you a schematic and the info you have requested.

The device is a AQY412S (60V 500mA). The battery voltage is going through a PTC fuse, then switched by this relay to provide power to other circuitry. This device fails but not sure why.

 

[KlausST]

Hi,

this is a photoMOS relay. It has an nput side and an output side.
Does the input side fail (still meet the specifications)?
Or does the output side fail? Fail-open, or fail-closed?

Klaus

Added:
Did you read the datasheet? especially section "PhotoMOS Cautions for use".. and operating conditions.

 

[Rajinder1268]

Hi,

this is a photoMOS relay. It has an nput side and an output side.
Does the input side fail (still meet the specifications)?
Or does the output side fail? Fail-open, or fail-closed?

Klaus

Added:
Did you read the datasheet? especially section "PhotoMOS Cautions for use".. and operating conditions.

I have seen that it is not recommended for automotive use, this was not my decision to use this device. I replaced it with a omron g3vm61 but still get the fault. I was not aware of the input and output pins, as I thought for the omron device you can use pin 3 or 4 as the either with pin 2 as and.

 

[barry]

What’s the load? Is there a short?

you should be able to measure the input LED and verify if that is still ok.

 

[Rajinder1268]

What’s the load? Is there a short?

you should be able to measure the input LED and verify if that is still ok.

The load current is around 250mA when other circuits are working but this isn't the case usually, so it is around 100mA.
The relay does not work as 12V is not being switched.

--- Updated Mar 8, 2022 ---

I am looking for a preventative measures based on goodprinciples i.e. TVs diode (for over voltage transients) and filtering such as common mode choke or EMI.

 

[barry]

Maybe the LED is being stressed by too much current. Maybe the output is being overloaded. Maybe there's an overvoltage on the input. Maybe invisible space worms are inside your circuit. You insist upon not giving us any useful information. There's no way we can help you.

 

[Rajinder1268]

Maybe the LED is being stressed by too much current. Maybe the output is being overloaded. Maybe there's an overvoltage on the input. Maybe invisible space worms are inside your circuit. You insist upon not giving us any useful information. There's no way we can help you.

The LED is not being overstressed, it is operating at 5mA. I think there is either overvoltage due to inductive transients or over current. I am giving you as much as info that I have. Unfortunately I can't replicate any of the issues that are seen in the field.

I will send you the schematic and my suggestion for preventative measures.