[TowerTalk] 12V transient/noise filtering?

[Michael Tope]

I was considering a differential mode transient a form on conducted EMI. 
I figured one of those immunity specs would cover that, but perhaps not.

When I was hunting around I stumbled into this MFJ product which is kind 
of interesting. MFJ has plenty of downsides, but one upside is that they 
often provide detailed schematics (so you can repair it after you get it 
home and find out it doesn't work). It includes reverse polarity 
protection, a TVS, and a 4 FARAD super-capacitor filter:

https://www.dxengineering.com/parts/mfj-4403/documentation

AD5X did a pretty detailed review of the product:
http://www.ad5x.com/images/Presentations/MFJ4403Review.pdf

Although they are backordered until September at DX Engineering, it 
looks like Ham Radio Outlet has them in stock:
https://www.hamradio.com/detail.cfm?pid=H0-008765

73, Mike W4EF..................

On 5/13/2021 1:29 PM, Lux, Jim wrote:
> On 5/13/21 10:42 AM, Jim Brown wrote:
>> On 5/12/2021 7:39 PM, Michael Tope wrote:
>>> You would have to dive into the EMI/EMC specs provided in the 
>>> datasheet - in particular conducted susceptibility
>>
>> In my experience, most EMI is common mode, and is not accurately 
>> described on data sheets. 
>
>
> but here, I'm not looking at EMI - I'm concerned about differential 
> mode transients (inductive things like relay coils, etc.) blowing up 
> the other things in the circuit.  Things like having a USB interface - 
> they tend not to like big transients, and I'd rather not blow up the 
> laptop, or Raspberry Pi, etc.  Sure, they have some sort of voltage 
> regulator that brings 12V down to 3.3 or 5V, but things like the 
> venerable 7805 have a 35V absolute max so that 50V transient will kill 
> it.
>
> A DC/DC converter like those from CUI might have a wide range input, 
> but probably not 50V and they have no reverse protection.
>
>
> Something like a reverse biased 20V Zener might actually solve my 
> problems.