Hi guys,
what's the recommended method for adding a snubber across the secondary of a transformer if it's centre tapped and being used with a 2 diode full wave rectification?
Do you only need a single snubber across the 2 outer wires, ignoring the centre tap or is it better to have 2 lots of snubbers going to the centre tap like this?
I did a bit of searching around but couldn't find a definitive answer.
thanks,
James
what's the recommended method for adding a snubber across the secondary of a transformer if it's centre tapped and being used with a 2 diode full wave rectification?
Do you only need a single snubber across the 2 outer wires, ignoring the centre tap or is it better to have 2 lots of snubbers going to the centre tap like this?
I did a bit of searching around but couldn't find a definitive answer.
thanks,
James
Although a single snubber may well suffice, the aim of the snubber is to continue to circulate the diode current at the diode turn-off transition - that current is flowing through just half the winding (ie. back o the CT) and so the snubber should ideally be tested for each half winding and applied to each half winding.
Semantics, possibly, but the goal is to continue to circulate transformer winding current, not diode current. If a well chosen diode is selected, diode snubbing creates more problems than it solves. This is transformer snubbing.
With one snubber, you rely on the unused winding's DCR to provide a path for this transient current. Any reasonably or properly sized snubber will have a transformer DCR that does not significantly affect operation of the snubbing action. And this action occurs equally on both winding halves, so if a R value is chosen, it is based on the contribution from the transformer DCR. As an example, if the ideal R value is 100 but the half-winding DCR is 10, you may find the ideal R selected is 90 ohms. It all needs to be selected by test with a scope.
I have checked operation with a scope on multiple designs, and without exception it works. Get closely zoomed into the transient, and a clean smooth waveform is verified. Installation on the primary works just fine too.
With one snubber, you rely on the unused winding's DCR to provide a path for this transient current. Any reasonably or properly sized snubber will have a transformer DCR that does not significantly affect operation of the snubbing action. And this action occurs equally on both winding halves, so if a R value is chosen, it is based on the contribution from the transformer DCR. As an example, if the ideal R value is 100 but the half-winding DCR is 10, you may find the ideal R selected is 90 ohms. It all needs to be selected by test with a scope.
I have checked operation with a scope on multiple designs, and without exception it works. Get closely zoomed into the transient, and a clean smooth waveform is verified. Installation on the primary works just fine too.
The importance of snubber position is likely dependant on leakage inductance levels in the windings, as that is the driver of the disturbance being snubbed, and also a hurdle to jump when trying to divert or couple current through other windings. If leakage inductance is low, then yes the diode loop current will easily pass around or couple to any other winding you choose.
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