08-02-2025, 12:05 PM
I think the photos answered your question!
The trouble is, the forward voltage has a negative temperature coefficient... if one of the three runs slightly hotter, it's forward voltage drops a bit, it takes more than its 1/3 share of current, and gets hotter still, till that rectifier is carrying nearly all the current.
The reduction in power dissipated due to the voltage drop decreasing, isn't enough to cancel out the increase in power due to it hogging more current.
The only safe way to parallel rectifiers is to have current-sharing resistors. If transformer-fed, winding resistances can do this - but you need a separate secondary winding for each rectifier.
The trouble is, the forward voltage has a negative temperature coefficient... if one of the three runs slightly hotter, it's forward voltage drops a bit, it takes more than its 1/3 share of current, and gets hotter still, till that rectifier is carrying nearly all the current.
The reduction in power dissipated due to the voltage drop decreasing, isn't enough to cancel out the increase in power due to it hogging more current.
The only safe way to parallel rectifiers is to have current-sharing resistors. If transformer-fed, winding resistances can do this - but you need a separate secondary winding for each rectifier.
