SMPS topologies
The inner structure of switch-mode power supplies. For each topology, follow the current's path on the schematic, see the waveforms at the measuring points and learn how to recognise it on a board.
Flyback
One MOSFET, one transformer; energy is transferred when the MOSFET turns off.
Where: Phone chargers, laptop adapters, TV and monitor standby supplies, supplies up to ~100 W
🔒 repair packHalf-bridge (LLC)
Two stacked MOSFETs and a resonant circuit; efficient medium-to-high power.
Where: LED TV power boards (main supply), 150–500 W supplies, server power supplies
🔒 repair packPFC (power factor correction)
A boost after the bridge: draws a sine-shaped current from the mains and makes 390 V.
Where: Supplies above 75 W: TVs, PC power supplies, LED drivers, air conditioners
🔒 repair packForward
Energy is transferred while the MOSFET is on; the secondary has an output inductor like a buck.
Where: Computer (ATX) power supplies, 100–400 W industrial supplies
🔒 repair packBuck (step-down)
Lowers voltage efficiently; no transformer, input and output share ground.
Where: Motherboard VRMs, graphics cards, 12 V → 5 V / 3.3 V converters, car chargers
🔒 repair packBoost (step-up)
Raises voltage; inductor at the input, diode towards the output.
Where: TV LED backlight drivers, power banks, PFC circuits
🔒 repair packFull bridge (H-bridge) and SPWM
Makes a 230 V AC sine from DC with four switches and pulses whose width follows a sine.
Where: Hybrid and off-grid solar inverters, UPSs, motor drives, welding machines
🔒 repair packPush-pull
A centre-tapped transformer and two MOSFETs taking turns; makes high voltage from a battery.
Where: Car inverters (12 V → 230 V), the battery → DC bus stage of UPSs and hybrid inverters, 12/24/48 V DC-DC boosters
🔒 repair packMPPT solar charge controller
A synchronous buck between panel and battery; keeps the panel at the voltage where it gives the most power.
Where: Solar charge controllers, the PV input of hybrid and off-grid inverters, caravan/boat solar systems