Re: Overvoltage protection design ideas
The simplest thing I can see doing is to connect a suitably sized power transformer across the AC input before the UPS transformer, and connect the output of the power transformer in series, anti-phased, with the UPS transformer primary winding. This will reduce the input voltage that the UPS transformer sees, thus reducing it's output voltage.
(Note that connecting the output of the power transformer in-phase with the AC will INCREASE the voltage the UPS transformer sees.)
Of course, this might cause more voltage drop during high loads, but it will give you headroom so that if the mains input is higher, you won't violate the DC-DC regulator input voltage ratings.
As for other solutions, there are ICs made by some manufacturers that can drive FETS, used as electronic fuses, or surge stoppers.
Check the LTC4366 as an example.
-Ben
P.S. In the case of the LTC4366, you'll need to make sure the FET can handle the power dissipation if/when there is a surge. So pick a FET that has a large SOA (Safe Operating Area). You'll need to make sure you set the overvoltage timer, so that the transistor is kept under it's SOA. (SOA varies, depending on time and power dissipation.)
P.S.2. The LTC4366 is a small chip, dunno if you would be able to solder it! Linear Technology has some other similar chips, possibly in a larger package, so you should check out their site.
The simplest thing I can see doing is to connect a suitably sized power transformer across the AC input before the UPS transformer, and connect the output of the power transformer in series, anti-phased, with the UPS transformer primary winding. This will reduce the input voltage that the UPS transformer sees, thus reducing it's output voltage.
(Note that connecting the output of the power transformer in-phase with the AC will INCREASE the voltage the UPS transformer sees.)
Of course, this might cause more voltage drop during high loads, but it will give you headroom so that if the mains input is higher, you won't violate the DC-DC regulator input voltage ratings.
As for other solutions, there are ICs made by some manufacturers that can drive FETS, used as electronic fuses, or surge stoppers.
Check the LTC4366 as an example.
-Ben
P.S. In the case of the LTC4366, you'll need to make sure the FET can handle the power dissipation if/when there is a surge. So pick a FET that has a large SOA (Safe Operating Area). You'll need to make sure you set the overvoltage timer, so that the transistor is kept under it's SOA. (SOA varies, depending on time and power dissipation.)
P.S.2. The LTC4366 is a small chip, dunno if you would be able to solder it! Linear Technology has some other similar chips, possibly in a larger package, so you should check out their site.
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