overvoltage protection

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ken roper

Joined Dec 6, 2014
19
Am I missing something here or what, as far as I can see the only component blocking the input voltage to the output connections is the resistor R1, as far as I understand power takes the path of least resistance, so the power would flow throught R1 straight to the output connection, the other side is ground or negative so what are the other components for, you could take them out and it would make no difference to the output voltage.
I also know that resistances can go short ( unlikely as they would burn out and go open circuit) nevertheless for a brief moment if R1 were to go short it would allow more of the voltage from the power source to go to the output connection than it was designed to drop so destroying the device. So where does the overvoltage protection come from, I am trying to protect a device costing £200 from getting fried by an overvoltage.
I have been in touch with the manufacturer (they recommend a battery backup but it is only for brief periods) so as far as I am concerned placing a battery backup of 2 AA cells across the memory and clock circuits is no good why? because the device can be left for long periods switched off ( the battery backup is there so settings are maintained) and the battery backup would only last aprox 9 days.
This device can be left for months without being switched on.
I am after a power source supplied from 240A/h 12 volt batteries that are constantly being charged using solar power that will step the power down to 3 volts with some sort of overvoltage protection that is fast and would cause no damage to the load at the output terminals. Also as I understand it a device will only take as much current as it needs, you can feed it say 1amp if it requires 0.1 amps thats all it would take provided it was working as designed.
 

Alec_t

Joined Sep 17, 2013
14,280
Am I missing something here?
Perhaps the fact that if the overvoltage protection device itself fails (e.g. due to a lightning strike)? As I said, you can't guarantee 100% protection. All you can hope for is minimal chance of failure.
In the circuits I posted the TL431 clamps the voltage at ~3V. You could add a second one in parallel, in case the first fails. You could also add a second 'R1' in series with the first.

Edit: Another option would be a 3V rechargeable battery permanently trickle charged from the main 12V battery.
 
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