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| Switch mode PSU with linear output stage |
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| DrGeoff:
This was usually done in SMPS that had a primary rail and several auxilliary rails. Back in the 80's we had SMPS that had a beefy 100A 5V rail and a couple of 1A +/-12V rails. The SMPS regulation was performed using feedback from the 5V rail and the transformer windings for +/-12V did not have the same load regulation as the 5V rail so were fed through a the 7812/7912 regulators to maintain good regulation. Linear regulators won't help you with noise, it passes straight through them as the frequencies are usually very high (>100kHz). Usually good ferrites and chokes were used to keep the noise down. |
| tridac:
There were several of that type, even decades ago. Some even used a thyristor as a preregulator. The key thing is that the pre and post regulators track, or are in sync. Maintaining a constant voltage drop across the linear part to minimise power dissipation and improve efficiency. The main reasons for such a design approach, while providing a low noise at the output... |
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