crenyen,
LDO (Low Drop Out voltage) regulators are linear series regulators that are designed to operate at small input-output voltage differentials. They share the advantages of other linear regulators:
~ Low Noise
~ Good frequency response
~ Excellent line and load regulation.
By applying an unregulated input that is just above the (Output voltage + Dropout Voltage) spec , you can keep the dissipation of the regulator reasonably low. However, you must be very careful to design the power supply so that under worst case (low line voltage, low filter capacitance, low input frequency) that the dropout voltage spec is met. If you do this, then the dissipation under worst case high unregulated voltage conditions, the dissipation may be excessive.
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Switching regulators, as a rule have:
~ Worse Regulation
~ Higher Noise
~ Lower dissipation
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Regards,
Kral