ESD/Transient Supression

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dknguyen

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I'm confused...

**broken link removed**

"Optimal placement of ESD suppressors begins at the location of ESD penetration into the system. This tactic reduces the ESD voltage and current initially experienced by the circuit and attenuates the ESD pulse that propagates past the ESD suppressor. Design as much practical space as possible between the ESD suppressor and the protected chip.


Placing an ESD suppressor too far away from the line it's protecting can reduce its effectiveness. The board trace inductance can cause an additional amount of voltage, or "overshoot," on the chip. To avoid this, install the ESD suppressor as close to the protected line as possible
"

Don't these statements conflict? Or am I misinterpreting the wording?
 
It is worded kinda funky, but in both cases it is saying the suppressor should be at point of entry.
Placing an ESD suppressor too far away from the line it's protecting can reduce its effectiveness.
In this case it is saying to far from line it is protecting, not IC. For example: Transient line enters card connector, this is the line you want to protect because down the line is your sensitive component.
 
The wording is a little bit confusing. The idea is to suppress the transient as soon as possible so you want to connect the suppressors with as short a lead/trace as possible where the transient enters the system. The ideal way is to use a surface mount suppressor with the two traces being protected running through the suppressor's respective mounting pad. That reduces the inductance between the suppressor and the lines to the bare minimum.

After that you want to place the protected circuit some distance away with a capacitor across the line near the protected device (with traces going through the pads as with the suppressor). This allows the inductance of the traces along with the capacitor to nip the high frequency portion of the transient.

Does that make sense?
 
So it's saying have it close to the IC with as direct connections to the line it's protecting and not to make some weird maze of traces from the protected line to the TVS diode?
 
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No, I'm say that you want some distance from the suppressor and the IC it's protecting.

You want the suppressor to be close to the input line (source of transient).

The idea, of course, is to provide as much isolation as possible between the transient and the IC.
 
Check out this guys website. He is like the Yoda of signal integrity. His books are the best.
**broken link removed**
I think he has some articles on ESD and EMI on his website.
And no affiliation
 
THis isn't exactly for ESD (I'm not too worried about ESD). THis is more for additional flyback protection of some MOSFETs, so the transient voltage isn't due to ESD but due to inductive spikes in the wire- I was a trying to extrapolate what to do from this ESD article but didn't quite understand it.

So for inductive spikes I'm going to place it as close as possible to the component since decaying current in the wire between the FET and TVS diode. The reason being that, unlike ESD, the wire inductance between FET and TVS diode will not filter out the spike, but just becomes a unsupressed source for the spike.
 
Okay. If it's an inductive spike, than you do want the suppressor as close to the FET as possible.

In switching regulators they often use a small capacitor in series with a small resistor (to damp resonant oscillations) for suppressing the inductive spike.
 

Yeah, I have those too. I might not be able to use the TVS diodes after all because I can't seem to find any place that carries 30,000W TVS diodes. I was going to solder them directly across these MOSFET modules I got so that they would "do the avalanche breakdown" for the FETs instead of the FET itself. I'm having a hard time guessing how much I will need because I don't know the inductance of the motor windings. I can estimate it for the wires, but I have no idea for the windings.

Look like I may have to do destructive testing at some point. All the MOSFETs are off-PCB now on screw modules. $30 a FET so expensive to blow, but much easier to replace than a PCB and easy to test without a PCB.

Does anyone happen to know the ballpark inductance of a 3500W-4200W brushless motor with a voltage constant of about 500-600krpm/V and weighs 400-500 grams 8-wind motor? Because I sure don't.
 
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Does anyone happen to know the ballpark inductance of a 3500W-4200W brushless motor with a voltage constant of about 500-600krpm/V and weighs 400-500 grams 8-wind motor? Because I sure don't.
Click to expand...
Not to ask the obvious, but why not call the motor manufacturer. I am sure the apps engineers can give you layout guidelines as well.
 
Mikebits said:
Not to ask the obvious, but why not call the motor manufacturer. I am sure the apps engineers can give you layout guidelines as well.
Click to expand...

I guess I could. I guess I never expected them to know it either. RC motors seems to be a "build it first, test it out second" kind of deal.
 
Wait, sort these out for us please:

3500-4200W? Watts?
400-500 grams? Motor total mass?
500-600krpm/V? You mean 2V gives a million rpm?
$30 FETs?
30,000W TVS diodes?
 
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Generic Motor specs:
3500-4200 watts
400-500 grams
500-600rpm/V
8-wind, 14 pole, 12 stator

Since the laws of physics and technology are bounded, someone who has encountered a similar motor might have some idea of the inductance.


$30 FETs- modules so they're expensive
30,000W TVS diodes (peak rating since they're TVS diodes)
 
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reversing? I regularly deal with 3HP DC motors and for unidirectional drive by far the easiest thing to diode is to just put a fast diode across it.
 
dknguen

A 4kW motor.. must.. surely.. weight - more than half a kg..

I do find your smart postings not being the true match to the supplied picture. Some things just do not happen like that..

I do enclose some files you might be interested in. The bottom line in the protection is the distance, make it employed as close as you can to the device you're trying to protect. Make it your habit and think of it - no more.

Regards,
xnadunow
 

Attachments

  • 15KP17 Protek Protector.pdf
    65.6 KB · Views: 242
  • 15KP series Protec Protectors.pdf
    45.1 KB · Views: 220
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