Power Supply Design
-an introduction
Adapted from a Presentation
By Doug Miller, SPU EE Alumnus
Power Supplies
Overview
• Linear Regulators
• Switching “DC-to-DC Converter”
Regulators
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 Regulators
A 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 Regulators
Buck Converter – V Down only
Switching Regulators
Boost Converter – V up only
Switching Regulators
Buck-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