Over-voltage protection

[Demon]

its a different animal , ... those others are buck only ie 7.2v-35v in 5v out

That's ok. I haven't used weaker wall-adapters than required at output yet. I'm always using exact ratings, like a 5V wall-adapter for a 5V circuit, or a stronger wall-adapter and using voltage regulators to bring it down.

I ordered 10 and I'll see what the railure rate is. Some comments say they suck, but you never know how they treated the units.

Found the Alice design is on Amazon (same IC), but they're advertising it as boost only:
https://www.amazon.com/Eiechip-Volta.../dp/B07RNBJK5F

[Demon]

Just a note to the next guy, you don't absolutely have to have 5V to operate a lot of these PICs.

For example, on a 16F628, check the DC Characteristics in section 17.1 of the datasheet and look at VDD supply voltage.
- it runs fine from 3.0 - 5.5 V, just keep an eye out on Brown-out Detect Voltage if you're using that feature.

Just don't fixate on the Absolute Maximum Ratings in section 17.0 (like I was doing).
- 6.5 V max on VDD.
- 14V max on MCLR.

If you run a bit lower than the "normal" 5 volts, you might have to adjust the resistors a bit for things like LEDs.

Robert

[amgen]

why aren't you just using a simple LM7805 regulator which will take any input of say 6 to 32 volts and protect the micro ? That could take the place of all the other circuitry, plus input voltage fluxuation.

[Demon]

why aren't you just using a simple LM7805 regulator which will take any input of say 6 to 32 volts and protect the micro ? That could take the place of all the other circuitry, plus input voltage fluxuation.

That was my first idea, but I don't know just how far a 7805 can take abuse, compared to the TVS, NTC and MOV?

And then I'd still like to pop a fuse if things get out of hand. Been playing some more with it, added some caps up front, took off the red LED (fuse will tell me something went wrong), added direction diode and simplified the green LED.



What happens with a 7805 if a user plugs in the wrong wall adapter? I have dozens myself of all powers, accumulated over the ages.

Robert

[amgen]

well, the 7805 takes up to I think 32 volts at the input so you could use any adapter that is under that voltage with only exception that the input has a minimum of about 1 volt over the regulated 5 volts. Those TVS and MOV's are generally used for possible heavy surges of power and lightening type events, and even then, the electronics can be damaged due to "instantaneous power/voltages" that strike. The NTC, when used in power circuits, are also called "inrush current limiters" are generally used for limiting "initial" current inrush if there are large capacitors to charge or motor or transformer windings that may take large startup current. The resistance for NTC's goes down as the device heats up reaching the 'steady-state' current. Lastly, there are 3 terminal linear voltage regulators with a higher input voltage ratings, if that is a worry.
ps: that is a pretty circuit you drew !

[richard]

That was my first idea, but I don't know just how far a 7805 can take abuse, compared to the TVS, NTC and MOV?

they are pretty tough, i don't go much for linear regs due to their low efficiency and heatsink requirements [ for batt powered stuff].
for low power mains powered roles they served well for years and still can

absolute vin max is 35v but dropping 20v or so across the reg @250mA makes a lot of heat whereas for a switching reg , no heat

[Ioannis]

Maybe I missed the scope but, why are you so worried?

If you have a low current circuit, a 7805 is just fine for up to 35 or so voiltages.

If you have higher currents, then a smps like the expensive Recom that Richard uses or the cheaper https://gr.mouser.com/ProductDetail/490-VXO7805-1000 I use is good enough.

And last but not least, the circuit that you posted for reverse polarity protection with the p-mosfet in post #14 is the best protection with no voltage drop.

Ioannis

[Demon]

Maybe I missed the scope but, why are you so worried?

If you have a low current circuit, a 7805 is just fine for up to 35 or so voiltages.

If you have higher currents, then a smps like the expensive Recom that Richard uses or the cheaper https://gr.mouser.com/ProductDetail/490-VXO7805-1000 I use is good enough.

And last but not least, the circuit that you posted for reverse polarity protection with the p-mosfet in post #14 is the best protection with no voltage drop.

Ioannis

I get crazy power surges and spikes here in thunderstorms, lots of trees messing with lines and transformers.

I might end up using a combination of devices.

Yeah, that diode was costing me .7V and was bugging me like crazy, but with that boost circuit, that's not really a problem. That boost circuit also gives me the choice of splitting my power source: 5V for PIC and other ICs, and what ever I need for more power-hungry circuits.

I have only one major concern, whatever I chose, I have to be able to provide at least 100 within a year, hopefully 1000 over the next few years (gotta have goals in life ).

Robert