Most stabilizers in Pakistani homes are the relay type or the servo type. But there are four kinds, and the difference matters for your appliances. Here it is in plain words.
Relay (AVR) — the budget stabilizer
This is what most shops sell by default. It switches between transformer taps with relays, so the output jumps in steps (±5–10%). You hear a click every time it corrects. It is the cheapest to buy, and the relay contacts wear a little with every click. Fine for one appliance on a budget.
Servo (SVC) — the motor type
A small motor drags a carbon brush along a winding to correct voltage smoothly (±1%). It is proven and good value, especially for large and motor loads. But it is slow — about 25–30 volts per second — and the motor and brush wear out over time and need service. It makes a faint hum.
SCR (thyristor) — solid-state at a sensible price
Like a relay stabilizer, it picks between transformer taps — but with silicon switches (thyristors) instead of metal contacts. No spark, no click, nothing to wear. It corrects in about 20 ms and holds 220V ±5%. Good for laser machines, clinic devices, electronics and homes where you want nothing to service. How an SCR stabilizer works.
Inverter (IGBT) — the top of the range
This works like an inverter AC. It builds the correct voltage electronically with no moving parts, rated 0 ms. It holds 220V ±2% from a 90–310V input, gives a clean pure sine output and runs silent. It costs more up front, and it is the best fit for inverter ACs, sensitive machines and very-low-voltage areas. How an IGBT stabilizer works.
Relay and servo fix voltage by moving something. SCR and IGBT do it with silicon. That is why we think solid-state is the future.
Compare them head to head: SCR vs servo · IGBT vs servo · SCR vs IGBT. Or read the full guide to solid-state stabilizers.