Actually, I have repeatedly said "why" throughout this entire thread. To repeat...
There are some designs that provide only an open-collector output (a switchable ground) which may or may not be used to control an external relay. In the case where an external relay is attached (i.e., not...
MacGyverS2000, thank you for sharing your thoughts. Most people don't read product documentation, and while that is technically not the fault of a product manufacturer, it is prudent to give due consideration to that reality in a given design. And as to "wanting guarantees for everything under...
zeusfaber, thank you for the tip (and for not charging me $150k). More specifically, you are referring to this document from Dec. 1991:
http://www.sre.org/pubs/Mil-Hdbk-217F.pdf
Since we are specifically speaking about Zener diode reliability, the only mention of a Zener in that entire PDF is...
If the non-repetitive limit is indeed 5x the working current, and if one argues that 2.1x the working current is "death by a thousand cuts," then how many cuts will result in death for say 1.5x the working current? What about 1.2x? Does even a teensy but above 1x working current spell death...
Understood, but when reviewing my two previous posts, please ignore EMI considerations and let me know your thoughts regarding (a) your interpretation of "non-repetitive peak reverse current" on zener diode datasheets and (b) whether a 1N4749A zener would suffice in light of the current-pulse...
sreid,
Furthermore...
Earlier in this thread I posted (14 Jun 17 02:22) a scope measurement and the following current-peak calculations:
At that CH2=26.0V, the other probe (CH1) consistently measured 25.2V. So the voltage drop across Rtest is:
26.0V - 25.2V = 0.8V
Therefore:
i ("current...
190mA surge "once forever more" on the 1N4749A 24V Zener? At this stage, we need to define datasheet terminology and review multiple datasheets.
Consider this Vishay datasheet which says nothing other than 190mA for Tp=10ms:
http://www.vishay.com/docs/85816/1n4728a.pdf
Based on that...
Skogsgurra, thank you for the clarifications and for the schematic. Curious as to why you prefer the resistor there instead of a Zener (with cathode facing the transistor's Collector)?
Regardless, you are putting the suppression across the relay coil. As I've been saying, there are designs...
Skogsgurra, I appreciate your input. Thank you for performing a practical test and posting the results.
Firstly, I should explain that my citing of that one thread on StackExchange was not a matter of me saying "this thread is when all the chatter started." I primarily linked to it because it...
SparWeb,
I'd actually seen that PDF (or something similar) before. Interestingly, your PDF is date stamped Nov. 1998. But despite that good advice from 19 years ago, many engineers continue to use a 1N400x across the relay coils, unconcerned about possible tack-welding implications. I...
SparWeb, thank you for the SPICE simulation.
GroovyGuy (and everyone else), although the 300V may appear on the simulation, the actual benchtop circuit measurements I provided earlier in this thread were the peak voltages detected on a scope in my testing over the course of 1 hour. In other...
A LittleFuse 1.5KE27A 27V TVS diode costs 6x more than a 1N4749A 1W 24V Zener at in quantities ranging from 1000pcs to 20,000pcs. It makes absolutely no sense to use a part costing 600% more when the suppression result and protection of the BJT and relay is the same. And while a 1N4007 across...
analogkid2digitalman, a TVS diodes would be more expensive than a single Zener, and as mentioned in my opening post, the aim here is good long-term suppression at the lowest possible cost.
GroovyGuy, btrueblood already posted an answer for you, but I wish to further answer it by repeating what...
I've actually put a Fluke 8845A benchtop multi-meter in series with the battery on select Japanese (made and sold in Japan) models about a year ago (all 2015 or 2016 model cars). On all the cars the lowest standby current draw was measured to be 10mA to 12mA. But it takes a while to see the...
In terms of relay coil voltage spike suppression, the following thread focuses on using a 1N4007 diode in series with a Zener across the relay coil:
thread248-291225
But there are times when you need to suppress coil spikes but cannot put components across the relay coil. In this case, a...
