SMPS / Power Supply
Power
A circuit that converts power efficiently using switching regulators. Provides stable DC voltage from AC mains or other sources.
What it looks like
SMPS / Power Supply
A typical power — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Input voltage range
VRange of input voltages the supply can handle (e.g., 90-265V AC for universal input).
Output voltage
VRegulated DC voltage provided at output (e.g., 5V, 12V, 24V).
Output current
AMax current the supply can deliver at rated voltage (e.g., 3A, 10A).
Efficiency
%Power output vs. input. Higher = less waste heat (typically 70-95%).
Ripple noise
mVAC component on DC output. Lower = cleaner power (typically <1% of Vout).
Laws that govern it
- Faraday's law of electromagnetic inductionEMF = −N × dΦ/dt
Switching at tens of kilohertz means dΦ/dt is huge, so the transformer can be tiny — that is why a phone charger is not a brick of iron.
- Self-inductance formula — v = L di/dtv = L × di/dt, E = ½LI²
Energy is stored in the inductor each cycle and released to the output; duty cycle sets how much, and hence the regulated voltage.
- Lenz's lawthe minus sign in EMF = −N × dΦ/dt
The switch-off flyback is both the working principle and the hazard: the spike it makes is what stresses the MOSFET and needs a snubber.
Core loss ∝ f × Bmax^1.6 is the reason ferrite replaces silicon steel above a few kilohertz.
Each law is stated in full — with its diagram, variables and worked meaning — on the electrical laws page.
Markings
Label shows input/output specs, current rating, model number, certification marks (UL, CE). Some have +/- terminals marked.
Standard values
Common outputs: 5V, 12V, 24V, 48V DC. Common currents: 1A, 2A, 3A, 5A, 10A, 20A.
How to choose
1) Match input voltage range to source. 2) Select output voltage/current for load needs. 3) Check efficiency for thermal/energy needs. 4) Consider ripple/noise for sensitive circuits. 5) Verify certifications for safety.
Pinout & package
AC input: L, N, GND terminals. DC output: V+ and V- (often color-coded: red/black). Packages: enclosed brick, open frame, PCB mount, DIN rail.
Example circuits
- Powering microcontrollers and digital circuits
- Industrial motor drives
- Battery charging circuits
- LED lighting systems
- Telecom equipment
Common failures
Output voltage drops or fluctuates (bad caps), no output (dead switching element), overheating (poor ventilation), increased ripple (aging caps). Bulging capacitors are a common visual sign.
How to test
1) Check input voltage present. 2) Measure output voltage at rated load. 3) Check for excessive ripple with oscilloscope. 4) Monitor temperature under load. 5) Test with dummy load if possible.
Substitutes
Use same voltage/current rating. Linear regulators (less efficient, simpler) for low-power apps. Batteries for portability. Different topology (buck vs boost) if voltage conversion needed.