5V Power Supply Design

flux

3:29

Evaluating power supply components.

Parsing design intents.

Checking LM2678 specifications.

Calculating inductor ripple.

Calculating ripple and checking components.

Accessing knowledge base.

Looking for "switching frequency" in lm2678.pdf

Looking for "oscillator frequency typical" in lm2678.pdf

Looking for "maximum output current" in lm2678.pdf

Looking for "inductor selection guidelines" in lm2678.pdf

Looking for "output capacitor ESR requirement" in lm2678.pdf

Looking for "design example 5 V output inductor value" in lm2678.pdf

Calculating.

Planning calculations and tool usage.

Here’s a quick reasonableness check for 3 A at 5 V using LM2678SD-5.0/NOPB and a 100uH Inductor, assuming the LM2678’s fixed fSW from the datasheet.

Datasheet facts (LM2678)

Fixed switching frequency: 260 kHz typical (225–280 kHz over temp).
Capable of driving up to 5 A loads.
Inductor selection guidance targets about 30% ripple of IOUT(max). Source: TI LM2678 datasheet.

Ripple with L = 100 µH, Vout = 5 V, Iout = 3 A

At Vin = 30 V:
- ΔIL = 0.1603 A pk–pk
- Ripple = 5.34% of 3 A
- Inductor peak current = 3.080 A
- Recommended Isat (≥1.2 × Ipeak, per best practice) ≈ 3.70 A
At Vin = 10 V:
- ΔIL = 0.0962 A pk–pk
- Ripple = 3.21% of 3 A

Interpretation

LM2678-5.0: Suitable for 3 A (datasheet up to 5 A).
100 µH inductor: Electrically “safe” with very low ripple (3–5%), but this is well below the datasheet’s ~30% ripple design target. That usually means:
- Slower transient response and physically larger inductor.
- Ensure Isat ≥ 3.70 A and check DCR for I²R loss and thermal rise.
If you want closer to the datasheet’s ripple target (20–40% rule-of-thumb), a smaller L is typically used. With 100 µH you’ll have low ripple and gentle dynamics; acceptable if the choke meets Isat/DCR and transient response is okay for your load.

If you’d like, I can propose concrete inductor options (Isat ≥ 3.7 A, low DCR) and verify output-cap ESR per the LM2678 stability guidance.

State input range

Request inductor options

Check losses and heating

Verify output capacitor needs

Prefer smaller inductor

81 days

SW_3

NC_2

NC_3

VIN

ON/~OFF

SW_2

NC_4

VIN_2

BOOST

NC_5

GND

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