Micro-Cap Tutorial: MOSFET Reverse Polarity Protection (RPP) Highside PMOS
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- Опубликовано: 7 ноя 2024
- We explore in this video how reverse polarity protection (RPP) works using a passive highside P-Channel MOSFET. Simulation steps show idealization and then realization with actual parts. Part selection though Digikey is performed and as a bonus, some engineering career advice.
Very helpful explanation of this application, which is exactly what I was looking to understand.
Of course! Glad you found it helpful are there any other topics you think I should cover?
@@pauljstar With the RPP, I have a circuit example where a .01uF cap is recommended across Drain/Gate for ESD protection. Maybe you could speak to that in your tutorial?
Otherwise, I don't have anything specific. You could continue deeper into a circuit design by covering voltage regulators for 5V0 and 3V3, for example. The only reason I suggest that is because I'm working on a design, and the RPP is the first module, followed by those two voltage regulators in series. You could discuss trade-offs in placing those regulators in series vs parallel. In my case, I'm using very low drop-out regulators, and to save some cost, the 3V3 I chose has a maximum input of 5V, so it has to be downstream of the 5V reg.
@@andygeppertok good input thanks!
@@andygeppert for you particular case, LDO regulators are fine generally to stack in series. I would recommend:
1. determining load usage; common surface mount implementations can provide 50.0 mA, maybe up to 100.0 mA
2. determining rate of usage (to determine what output capacitors to select)
3. accounting for likely disturbances so that noise doesn't propagate through the low voltage power channels.
Selection of regulator type typically has to do with intended efficiency of power usage for the rated input. So, often designers will prefer switched-mode for when they're going from higher voltages to lower levels...linear regulators waste current and produce heat. Switching-mode regulators sample, store, and regulate charge...essentially taking enough cost-co/sams club food samples to make lunch. However, that comes at the price of introducing electromagnetic noise into your system which if you want to pass EMC/EMI testing you'll have to manage somehow.
@@andygeppert Parallel usage would likely be problematic/unpredictable if the outputs are tied together. The reason is basically in answering the question, "which regulator actually gets to regulate the line?" or "how many cooks are in the kitchen?" They will all likely try to usurp current control at some point and generally the best manufactured one (impossible to determine) ends up doing more work than it should... until the situation changes. Maybe this system of regulators converges to a homeostatic place, but perturbations could reset system. Note: If you aren't trying to regulate the same line then having multiple 5V sources would be fine so long as they don't interface in ways that create weird looping (i.e., stay isolated).
Can you make video on basic and. Power full things to know in micro cap software for beginners
Anything in particular?
@@pauljstar
How to probe multiple points in
Schematic and view it on graph at same time
Very good video!
Thanks!
Current flows from Source to drain in PMOS so how you can connect it''s drain to Vin and source to Vout ....
Typically, that's how it goes. Most applications will follow the theory-pattern you mentioned. However, current can flow either way through a MOSFET once the junction is conductive.
This specialized reverse polarity protection (RPP) application uses a little trick with the MOSFET that is different than most standard applications.
PRINCIPLES:
A MOSFET can be understood more easily as a high impedance device when OFF and a low impedance device when ON. You'll see this tend to act like a mega-ohms resistor switching to a micro-ohms resistor. So, P-Channel and N-Channel compositions dictate the voltage arrangement by which they are switched.
NEEDS:
1. The load needs a path to the supply/battery charge to operate.
2. The P-Channel MOSFET needs to activate to provide that path from the supply/battery to the load.
3. The P-Channel MOSFET needs a difference of charge concentration between the gate and source to provide the path between supply/battery and the load.
PROCESS:
At first, the supply/battery charge has to make it's way through the body diode to reach the source terminal of the P-Channel device. Once the charges on the gate and source terminals reach the difference threshold, the source-drain junction becomes conductive. At that point in time, the charge doesn't need to go through the body diode as much anymore.
If you're curious amd want to test in the lab, you can measure OFF-state source-drain resistance directly with multimeter (regular resistance setting). You can then measure ON-state source-drain resistance indirectly with multimeter (low voltage measurement setting). Using voltage data to calculate with the known current (RDS = VGS / I). Note: The current (I) could be known by measuring it a from sense resistor, by cable clamp, or by knowing the power dissipation of a load that the MOSFET is providing access to.
Also make video on how to use
Crystal in micro cap
Crystal oscillator you mean right?
@@pauljstar
Passive crystals piezoelectric crystal which are used in Microcontroller
Thanks ❤️🙏
Can you provide the calculation for resistor used for zener protection
I'll try on a new video if possible. It's a bit more than what can be conveyed easily for inline on comments
wow, just what i need now😘
Great!