Overvoltage protection for boost converter?

[LooseJunkHater]

I have [this](https://www.aliexpress.com/item/32909813839.html) boost converter which has CC & CV that I'll be using to boost 19v to 40v to charge a 36v battery (42v fully charged) @2A. I want to only charge the battery to 80% capacity, hence only boosting to 40v. I'd like the overvoltage to "trigger" at 42v (and actually hope that it'll never trigger). I don't really trust the cheap boost converter, hence why I want to add the extra protection.

I have two questions;

1. Will the noise of the boost converter cause OVP to trip? Will this lead to the battery frequent cycling between charging --> not charging --> charging?
2. Which design of OVP should I go with? I've attached two designs I've found online but don't really know the benefits/downsides of each, but if you have a better design please link it.


[Source of image 1]()
[Source of image 2](https://www.wellpcb.com/overvoltage-protection-circuit.html)

[MathWizard]

What if at the output, u added some RLC filter, to smooth the OP, and feed to a comparator/op-amp peak detect circuit ? Most of these little SMPS I've seen, that use a controller chip, it's pretty easy to tie on a shutoff, that just takes some pin low, like their internal op-amp OP, which usually has a pin for compensation, and as the external shutoff, when pulled low. And it could be isolated, just use a cheap opto-coupler, if there's a primary hot side, and secondary side.

I guess it would have to be done right, to avoid oscillations, but really if it was a custom built charger, they would just be sensing off the battery too, and adjusting the switching to be at the desired voltage or current.

Like over current in a basic DIY analog powersupply, yeah what is it supposed to do long term, you could just make it shut down for good, with some 555 timer , 1 shot circuit added.

[David Hess]

1. Will the noise of the boost converter cause OVP to trip?

It might.  Overvoltage protection circuits usually include a little bit of RC filtering in the trigger so they ignore transients and high frequency interference.

[LooseJunkHater]

What if at the output, u added some RLC filter, to smooth the OP, and feed to a comparator/op-amp peak detect circuit ? Most of these little SMPS I've seen, that use a controller chip, it's pretty easy to tie on a shutoff, that just takes some pin low, like their internal op-amp OP, which usually has a pin for compensation, and as the external shutoff, when pulled low. And it could be isolated, just use a cheap opto-coupler, if there's a primary hot side, and secondary side.

I guess it would have to be done right, to avoid oscillations, but really if it was a custom built charger, they would just be sensing off the battery too, and adjusting the switching to be at the desired voltage or current.

Like over current in a basic DIY analog powersupply, yeah what is it supposed to do long term, you could just make it shut down for good, with some 555 timer , 1 shot circuit added.

I'd rather not go this route as it'll likely be more complex plus I want a completely separate module as a fail-safe.

[LooseJunkHater]

I've also recently stumbled upon "Supervisor IC's" which appear to do what I want, but much of the ones that I find that can support input voltages of 50v+ are like $10/piece... Maybe someone knows of one that's cheaper? Maybe even one with a built-in MOSFET driver?

Edit: Here's the IC I was referencing with my comment: MAX6495 https://datasheets.maximintegrated.com/en/ds/MAX6495-MAX6499.pdf

[LooseJunkHater]

Update: Attached is a crude schematic of my current OVP. It should function similarly to the MAX6495, except it uses parts I already have available (including the mosfet driver, PNP transistor) making it cheaper.

Datasheet for fet driver: https://www.ti.com/lit/ds/symlink/ucc27324-q1.pdf

Two questions;

1. Will this schematic theoretically work for OVP? I know there will be tolerances for the 42v zener diode; I plan to replace it with an adjustable zener diode.

2. I don't understand what the max INA (input signal A) voltage is. Is it 3.3v? 15v? 2v? The datasheet is unclear, however I plan to use a resistor divider to drop the voltage to the correct amount. I also don't know how the resistor divider would work either, considering the "input current" for INA/INB is between -10 to +10 μA?

Edit:

3: Should I add a resistor to ground for the PNP mos gate just to unsure it's normally pulled low, so that it stays on? Then once the fet driver turns on, the PNP mosfet will turn off (no longer conduct)?

[LooseJunkHater]

Another question regarding the variable zener; since there appears to be no high voltage TL431's, I stumbled upon [this thread](https://www.eevblog.com/forum/projects/tl431-common-base-amplifier-stability) on using the TL431 above its rated voltage. It requires a lot of components however; is there a way to decrease the component count?

I also thought of using a comparator instead, but again, there appears to be no high voltage (above 36v) voltage references, so I can't go that route either...

[David Hess]

If you consider that to be too many parts, then you are going to have problems.

[LooseJunkHater]

If you consider that to be too many parts, then you are going to have problems.

Do you have any feedback/suggestions on my other questions?