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Comment by acrefoot | Hacker News Reader

> AC power enters the charger and is converted to DC. The PFC circuit (Power Factor Correction) improves efficiency by ensuring the load on the AC line is steady. The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer. Finally, the secondary receives low-voltage power from the transformer and outputs smooth DC to the laptop.

I had a hard time reading this. It sounds like the transformer is getting DC power? Do transformers even work with DC power?

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The drive transistors turn on and off at high speed to chop up the DC. You can think of these pulses as AC; they provide the changing magnetic field the transformer needs. Since this charger is a resonant converter, it's a bit more complex than most; the inductor-capacitor circuit resonates and the pulses turn into sinusoids.

> The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer.

It chops it up to AC for the transformer.

Ah, this makes sense. Do you know how the "chopping it up into AC"works?

This transformer would be a flyback transformer therefore doesn't need to be driven by anything so hard-to-generate as a sine wave. It can be driven by a "switch" (MOSFET) at it's primary which is connected to DC.

https://en.wikipedia.org/wiki/Flyback_transformer#Operation_...

All switching power supplies (hence the name) are driven by either full-on or full-off ("switching") transistors. A "flyback" topology is only one of many possible ways to build a switching power supply, but as it's the simplest, it's the most common in low power supplies.

See the Switch−Mode Power Supply Reference Manual from ON Semiconductor for info on all the other possible ways to build a switching power supply.

I'm no expert so may be corrected, but I assume just an inverter https://en.wikipedia.org/wiki/Power_inverter

I was wondering this too, I've never heard of a DC transformer. I thought AC-DC conversion circuits stepped down the voltage with a transformer prior to sending them through the full wave rectifier?

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