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January 13, 2011
News - Enginursday: A new and im…
about 10 months ago
Look at Vishay SMF15A-E3-08, standoff voltage of 15V and breakdown of 16.7V. Max clamping voltage of 24.4V @ 8.2A. Even though the clamping voltage at 8.2A is above your 20V max doesn’t mean this TVS wouldn’t work. This is where the engineering comes in, how much energy does your transient carry with it? Will the diode clamp below 20V can then be determined through simulation and testing. I mean props to you guys for verifying your work but did you try using a TVS diode instead of dismissing a readily available solution?
Side-note: I would also be worried about ESD blowing the gate-source junction of your FET. There’s nothing to limit the voltage across the junction during a large voltage transient and since your cap is after your suppression circuit it might not help enough to save the transistor.
The other thing that you might want to consider is using a battery to power your circuit, something that can deliver some actual current. The voltage of your transient is going to depend on how much current is available to charge those input caps. If you get above 20V on your gate-source junction then the MOSFET is going to be damaged.
Another solution entirely is to use a soft start circuit for your cable length problem.
Why not use a TVS diode for the voltage clamping? That’s what they’re designed for. Just make sure the standoff voltage is above your max intended DC voltage and the clamping voltage is below the max input voltage of your regulator. They come in all sorts of power ratings. If the clamping voltage is above what your regulator can handle then get another regulator, there are plenty to choose from with higher max input voltages.
News - According to Pete Episode…
about 2 years ago
Nice work Pete, the lighting looks great. I also recently installed some LED lights under my cabinet but ended up using those waterproof LED strips.
News - According to Pete: Curren…
about 3 years ago
Applications of the basic current mirror circuit that I have used it for:
1) Very simple voltage controlled current source (this has been the most handy for myself)
2) Change a sinking current into a sourcing current or the other way around
3) Active loads on an amplifier (okay… not something I usually do)
4) Setting bias currents that are identical or multiples of the mirrored current
5) I’ve used it to maintain consistent LED brightness over a bunch (10ish) LEDs
News - The Geekiest Wedding Invi…
about 4 years ago
Congrats to Bill and Mara and great job with the cards! I just hope you didn’t have to send out too many of these, weddings are expensive enough as it is.
News - Introduction to Robotic M…
about 4 years ago
Jeff, you got some real talent at lecturing! You do a great job at getting your message across, keep up the awesome work.
about 4 years ago
It’s a Samsung monitor with 170 degree horizontal and 160 degree vertical viewing angle. This isn’t a POS monitor. The fact is computer monitors have dropped in price significantly over the last few years. I bought my Acer 24" LCD for $180 bucks two years ago and I loved it when I bought it and still love it now.
I agree this monitor seems a bit over-priced. I can purchase a 22", 1920x1080 with HDMI and VGA inputs, LED backlight for $139.99 at TigerDirect. I recognize that this display runs on 12V which is definitely a convenience factor but still…
News - According to Pete: March …
about 5 years ago
I enjoy these videos a lot and they offer some good information but you mentioned something about the body diode I would like to re-clarify. The body terminal in the majority of discrete MOSFETs is tied to the source terminal because that is the most common usage. The body terminal must be connected to something otherwise you have a BJT structure with the NPN but the base terminal would be floating causing random behavior. However, tying the body diode to the source terminal creates a parasitic diode from the body P-doped structure to the N-doped drain terminal. The body diode doesn’t have any usefulness for ESD. The whole ESD issue for MOSFETs is the electric field created between the Gate and Body terminals. The oxide layer is so thin that you get enormous electric fields (electric field is Volts/meter) across the oxide layer. Some discrete MOSFETs do include ESD protection but it is a added TVS-type diode from Gate to Source.
Thanks for the video, keep them coming!
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