Linear vs switched mode power supplies
Here’s a clear, practical comparison, with an emphasis on noise-sensitive and technical uses.
Linear Power Supply (LPS)
How it works
Mains → transformer → rectifier → smoothing capacitors → linear regulator.
Advantages
- Very low electrical noise
No high-frequency switching; excellent for sensitive analog and RF work. - Clean output spectrum
Minimal EMI and ripple when well designed. - Simple and predictable behavior
Easy to troubleshoot and modify. - Good transient response
Stable under varying loads.
Disadvantages
- Inefficient
Excess voltage is burned off as heat. - Bulky and heavy
Large transformer and heatsinking required. - Limited input range
Usually fixed to a specific mains voltage.
Typical uses
- Audio equipment
- RF receivers, preamps, oscillators
- Laboratory bench supplies
- Precision measurement systems
Switched-Mode Power Supply (SMPS)
How it works
Mains → rectifier → high-frequency switching → small transformer/inductor → regulation.
Advantages
- High efficiency (often 80–95%)
- Compact and lightweight
- Wide input voltage range
- Less heat generation
Disadvantages
- High-frequency noise and EMI
Switching creates broadband interference. - More complex design
- Can inject noise into ground and supply rails
- Poor choice for sensitive RF without heavy filtering
Typical uses
- Computers and servers
- Consumer electronics
- Embedded systems
- Battery chargers and adapters
Side-by-Side Summary
| Feature | Linear PSU | SMPS |
|---|---|---|
| Efficiency | Low | High |
| Size/Weight | Large/heavy | Small/light |
| Output noise | Very low | Higher (HF noise) |
| EMI | Minimal | Significant without filtering |
| Complexity | Simple | Complex |
| Best for | Precision, RF, audio | Digital, power-hungry systems |
Practical Guidance
- Noise-critical applications → Linear PSU
- High-power or space-limited designs → SMPS
- Best of both worlds → SMPS followed by linear post-regulation or LC filtering
In RF and measurement setups, many people use an SMPS to get close to the voltage, then clean it up with a linear regulator at the point of load.