Auxiliary Supplies: Top Switch or small transformer?

[EnvisionAudio]

I am working on an offline, full bridge power supply that requires an auxillary standby supply. I am happy with using a small transformer, but have recently been introduced to the Power Integrations Top Switch line of integrated switching controllers.

My gut feeling is that the PI parts offer lightweight, lower loss advantage while the transformer offers proven longevity as a passive component.

Please give your comments on the advantages or disadvantages of each. If given the choice - which would you choose.

Thank you in advance.

[Eva]

Topswitch ICs work great. Furthermore, if you only need one rail without isolation, you can avoid the transformer and use a buck derived topology with off-the-shelf axial inductors.

On the other hand, the transformer does not offer output voltage regulation, a wide input voltage range or current limiting.

[EnvisionAudio]

Originally posted by Eva
Topswitch ICs work great. Furthermore, if you only need one rail without isolation, you can avoid the transformer and use a buck derived topology with off-the-shelf axial inductors.

On the other hand, the transformer does not offer output voltage regulation, a wide input voltage range or current limiting.

Good points as usual, Eva. Thank you for your response.

[S.G. Mahbub]

Envision Audio,

You can not avoid Transformer. Top series also require a ferrite core transformer (freq. 133/66 KHZ) with sophisticated feed back/ auxiliary winding. If you decide to use Top switch, use 6 Pin GX series instead of 3 Pin ones as GX series have more useful features. If your power requirement is more, you can use HX series.

[EnvisionAudio]

Originally posted by S.G. Mahbub
Envision Audio,

You can not avoid Transformer.

I should be more clear - I do not want to avoid a transformer. I want to know if I should use a switching power supply for auxiliary or a larger 50/60Hz transformer. I am mostly concerned about reliability.

Thank you for your advise.

[Eva]

For auxiliary supplies consider TinySwitch TNY26x (TNY266). It does not require auxiliary windings and it uses "cycle-skip" (and variable on-time) control rather than duty-cycle control resulting in high efficiency at low loads and very low idle power consumption. Part count is very low too.

For buck converters consider LNK30x and LNK36x.

[S.G. Mahbub]

If your power requirement is<4 watt and current requirement is<500mA, then you can use (linear killer) LNK501 P/G which does not require feed back like Top series. Capability of Tiny and LNK is almost same. If your requirement is more, you can use Top series.
I am using LNK501 P and Top GX series. Both are very reliable. Its feedback system with TL431 and Opto -coupler is reliable. Top are
really excellent.