cupoftea
Advanced Member level 5
Hi,
Would you agree, that for the ultimate in product longevity of ~25W offline SMPS,
one should use a large value NTC (eg 50R) and have it upstream of the mains rectifier
bridge? The NTC should also be upstream of the mains input X2 capacitor.
-Because even though X2 capacitors self heal after transient damage, they will
last even longer if say a 50 ohm NTC is upstream of it. So this way both
electro HVDC primary bus cap, and the X2 cap have long life.
The HVDC primary bus Electro cap will be about 47uF and with the NTC upstream of it, thats a nice RC filter to filter out those transients.
-Specially in light load times when the NTC will be cold and high resistance.
I am speaking here of offline SMPS's which are plugged in 24/7 for decades here.
For much of the time they may be on only very light load.
...Having the NTC upstream of the X2 cap is so good for longevity of SMPS....So much so, that in one case, due to enclosure tightness/restrictions, we had to put the
primary HV electro just after the diode bridge, and then the NTC had to go
"after" that (ie "after" as in nearer the control section)….but we still elected (due to desired longevity)
to connect the NTC to the incoming mains line (the mains line bit thats just upstream of the X2 capacitor)….so what happened, was that
we had to route the incoming mains line (the bit just after the fuse) right up to the control section
so that we could connect it up to the NTC there....as you know, this isn't desirable for noise reasons....
...but due to desired longevity, we still elected to do it in that case.
(N.B. We dont like MOVs as they eventually die and crowbar the fuse.)
Would you agree, that for the ultimate in product longevity of ~25W offline SMPS,
one should use a large value NTC (eg 50R) and have it upstream of the mains rectifier
bridge? The NTC should also be upstream of the mains input X2 capacitor.
-Because even though X2 capacitors self heal after transient damage, they will
last even longer if say a 50 ohm NTC is upstream of it. So this way both
electro HVDC primary bus cap, and the X2 cap have long life.
The HVDC primary bus Electro cap will be about 47uF and with the NTC upstream of it, thats a nice RC filter to filter out those transients.
-Specially in light load times when the NTC will be cold and high resistance.
I am speaking here of offline SMPS's which are plugged in 24/7 for decades here.
For much of the time they may be on only very light load.
...Having the NTC upstream of the X2 cap is so good for longevity of SMPS....So much so, that in one case, due to enclosure tightness/restrictions, we had to put the
primary HV electro just after the diode bridge, and then the NTC had to go
"after" that (ie "after" as in nearer the control section)….but we still elected (due to desired longevity)
to connect the NTC to the incoming mains line (the mains line bit thats just upstream of the X2 capacitor)….so what happened, was that
we had to route the incoming mains line (the bit just after the fuse) right up to the control section
so that we could connect it up to the NTC there....as you know, this isn't desirable for noise reasons....
...but due to desired longevity, we still elected to do it in that case.
(N.B. We dont like MOVs as they eventually die and crowbar the fuse.)
Last edited:
