- Joined Oct 19, 2013
Is it possible to modify a 12V SMPS adapter based around a Viper22A and TL431AA to output 5V instead?
Thanks for the link. It's more about learning than just being able to buy a 5V one. Although, if it's not just a few components that need to be changed and the transformer will need rewinding I won't bother!Why bother? Wall-Warts and similar are prolific, and available everywhere.
But it DOES need the auxiliary winding to supply it, because it only has a "startup" current source.It will only be necessary if the viper uses the winding to self power itself when it's kicked up, like in the example if the output drops too low the viper won't work.
If it's easier to rewind it do it.
Moving the voltage from 12 to 5 is a long way. There is a 240 ohm resistor that limits the current into the LED opto isolator. At 5V there is likely not enough current to send feedback to the IC.Yes it can be done,
This drawing is an example i cut from the internet, we don't know his psu design!Moving the voltage from 12 to 5 is a long way. There is a 240 ohm resistor that limits the current into the LED opto isolator. At 5V there is likely not enough current to send feedback to the IC.
The top lead of the TL431 cannot drop below 2V. It really needs 1mA of current to work. The top of the TL431 if often designed to work at 1/2 supply or 6V. Now that the output is 5V we only have 2V to 5.5V to work in. (I forgot the LED needs 1.5V) Really we have a very small window of voltage to work in. The 240 will need to be adjusted to the LED current is the same as back at 12V.
View attachment 279539
and the AUX winding will be wrong. Thanks Lan0.
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by Jeff Child
by Jeff Child