FAQ
TL;DR: DC‑DC buck/boost converters can hit about 95% efficiency; “None of these devices amplify.” They trade voltage for current, so power out ≈ power in minus losses. This FAQ explains how bucks, boosts, inverters, and transformers differ, with clear examples. [Elektroda, Anonymous, post #21684727]
Why it matters: If you’re sizing power gear or troubleshooting sagging voltage, knowing that converters don’t create power prevents burnt parts and dead batteries.
Quick Facts
- Boost = higher DC output than input; active electronics; typical peak ≈95% efficiency. [Elektroda, Anonymous, post #21684727]
- Buck = lower DC output than input; active electronics; efficiency similar to boost stages. [Elektroda, Anonymous, post #21684727]
- Inverter example: 100 W at 220 V ≈ 0.55 A; same 100 W from 12 V draws ≈10–12 A. [Elektroda, Anonymous, post #21684732]
- Transformers are passive AC–AC devices; good units run well above 90% efficient. [Elektroda, Anonymous, post #21684732]
- Universal rule: Power out = Power in × efficiency (use RMS for AC). [Elektroda, Anonymous, post #21684734]
What’s the difference between a buck, a boost, an inverter, and a transformer?
A boost raises DC voltage; a buck lowers DC voltage. Both are active switch-mode stages. An inverter converts DC to AC, often using similar switch-mode blocks plus a transformer. A transformer passively shifts AC voltage using two windings on a common core. None of them create power. [Elektroda, Anonymous, post #21684727]
Do any of these devices amplify power?
No. They convert voltage and current while conserving power minus losses. “None of these devices amplify.” Amplifiers increase signal power by drawing extra energy from a supply, which is different from conversion. [Elektroda, Anonymous, post #21684727]
How can a 12 V inverter run a 220 V appliance without increasing power?
It raises voltage but draws more current from the 12 V source. Example: 100 W at 220 V is about 0.55 A, but at 12 V that same 100 W needs around 10 A, or about 12 A including losses. The inverter doesn’t create power; it trades current for voltage. [Elektroda, Anonymous, post #21684732]
What efficiency should I expect from buck/boost converters?
Expect high efficiency, with good designs reaching about 95%. Actual efficiency depends on components, switching frequency, magnetics, and load. Plan thermal and input current for real, not ideal, efficiency. [Elektroda, Anonymous, post #21684727]
How efficient are transformers?
Quality transformers are highly efficient. The thread cites “well above 90%” for good units. Core material, frequency, and loading affect losses. Ferrite cores suit higher frequencies; laminated iron cores suit mains frequencies. [Elektroda, Anonymous, post #21684732]
Do buck/boost controllers use transformers?
Typical buck and boost regulators use inductors, not transformers. Some topologies add transformers for isolation or large ratios, but the common non‑isolated buck/boost stages are inductor‑based. [Elektroda, Anonymous, post #21684727]
What does RMS mean for AC power calculations?
Use RMS (root mean square) voltage and current when calculating AC power. The basic relation is Power = Volts × Amps, using RMS values. Good meters report RMS, which makes comparisons to DC straightforward. [Elektroda, Anonymous, post #21684734]
What’s inside an inverter?
A typical design includes switching electronics to generate AC from DC and a transformer to step voltage as needed. Simple units output a square wave. Pure sine wave models add more sophisticated control to shape the output. [Elektroda, Anonymous, post #21684732]
Quick calc: How many amps from 12 V for a 100 W load?
About 10 A at ideal efficiency, and around 12 A allowing for losses. As voltage increases at the output, input current rises to conserve power. This is why cabling and fusing on the 12 V side must handle high current. [Elektroda, Anonymous, post #21684732]
Can I power an inverter from any DC source?
Use the specified input voltage range. Car inverters target about 12 V. Solar inverters may accept a wider DC range and must synchronize phase and voltage when grid‑tied. Without proper phase and voltage offset, they won’t feed the grid. [Elektroda, Anonymous, post #21684734]
Is a buck‑boost “transformer” the same as a buck‑boost converter?
Terminology varies. Some switch‑mode literature calls push‑pull or forward‑converter transformer stages “buck‑boost” applications. They’re magnetic stages within DC‑DC or inverter systems, not the simple non‑isolated buck‑boost regulator. Context matters. [Elektroda, Anonymous, post #21684735]
What is a forward converter in plain terms?
It’s a switched‑mode power supply topology that uses a transformer and pulse‑width modulation to produce a regulated DC output. An output inductor reduces ripple. Designers may refer to related stages with terms like inverter, DC converter, or buck. [Elektroda, Anonymous, post #21684735]
How do I calculate inverter input current from a known AC load?
- Compute load power: P_load = V_out × I_out (use RMS if AC).
- Estimate input power: P_in ≈ P_load ÷ efficiency.
- Compute input current: I_in ≈ P_in ÷ V_in.
Example: 100 W ÷ 0.85 ≈ 118 W; at 12 V, I_in ≈ 9.8 A. [Elektroda, Anonymous, post #21684734]
Why do people think converters “amplify”?
Voltage may rise dramatically, which looks like amplification. But current falls so power stays similar minus losses. True amplifiers use an external supply to increase signal power. Converters only trade voltage and current. [Elektroda, Anonymous, post #21684727]
What happens if my inverter isn’t a pure sine wave?
Functionally, simpler designs can output a square wave, while pure sine models use more complex electronics. Choice affects compatibility and performance, but both still obey power conservation. “It’s easy enough to make a square wave inverter.” [Elektroda, Anonymous, post #21684732]
https://www.powerelectronicsnews.com/special/power-design-notes/
