This was a common way LM317 was used to get a stable power for small devices. It is still useful for learning and some blocks of the circuit are still used today in modern industrial systems.
Before the SMPS took over as the default DC source in most systems; designers would use switchers to reduce thermal losses in Linear Supplies.
Power Electronic Circuits
Linear Supplies have practically no noise or EMI_RFI (generation) issues . It is clean but not green. The efficiency is low. Transformer loss, heat loss in devices.
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