Power Supply Design-an introduction

Adapted from a PresentationBy Doug Miller, SPU EE Alumnus

• Linear Regulators• Switching “DC-to-DC Converter”

Regulators

Power SuppliesOverview

Linear Regulators

+ Simple, inexpensive+ Electrically “quiet” pure DC output- Vout < Vin- Poor Efficiency

e.g., if Vin = 6V, Vout = 3V, Efficiency near 50%

- Can be physically large

Switching Regulators

• Also known as “DC-DC Converters” or “Switchmode Regulators”

+Wide range of input voltages+Multiple output voltages possible+High Efficiency (often > 90% )+Compact- Complex, more expensive- Electrically “noisy” (not pure DC)

Switching RegulatorsA few types…

• Buck (step-down)• Boost (step-up)• Flyback (supports multiple outputs;

transformer needed)• Buck-boost (step-up or –down)• Charge Pump (no inductor)

Switching RegulatorsBuck Converter – V Down only

Switching RegulatorsBoost Converter – V up only

Switching RegulatorsBuck-Boost – V Up or Down

• What the source power fluctuates up/down past the desired output voltage?

• A Buck-Boost regulator can go either way as needed

• More complicated, but often worth it

Design Considerations• Use linear regulators only if:

– Energy conservation is not a concern – Wasted power is insignificant (less than 1

Watt)– Low noise is critical

• Switching regulators are finicky– Use only the specified parts (by brand if

possible)– Read and follow app note precisely

• Make regulators “isolatable” with jumpers and/or fuses that can be removed