Operation of the charger
You may have noticed that when you plug the connector into a Macbook, it takes a second or two for the LED to light up. During this time, there are complex interactions between the Macbook, the charger, and the Magsafe connector.
When the charger is disconnected from the laptop, the output transistor discussed earlier blocks the output power.[15]
When the Magsafe connector is plugged into a Macbook, the laptop
pulls the power line low.[16]
The microcontroller in the charger detects this and after exactly one second enables the power output.
The laptop then loads the charger information from the Magsafe connector chip.
If all is well, the laptop
starts pulling power from the charger and sends a command through the data pin to light the appropriate connector LED.
When the Magsafe connector is unplugged from the laptop, the microcontroller detects the loss of current flow and shuts off the power, which also extinguishes the LEDs.
You might wonder why the Apple charger has all this complexity. Other laptop chargers simply provide 16 volts and when you plug it in, the computer uses the power. The main reason is for safety, to ensure that power isn’t flowing until the connector is firmly attached to the laptop.
This minimizes the risk of sparks or arcing while the Magsafe connector is being put into position.
Why you shouldn’t get a cheap charger
The Macbook 85W charger costs $79 from Apple, but for $14 you can get a charger on eBay that looks identical. Do you get anything for the extra $65?
I opened up an imitation Macbook charger to see how it compares with the genuine charger. From the outside, the charger looks just like an 85W Apple charger except it lacks the Apple name and logo.
But looking inside reveals big differences.
The photos below show the genuine Apple charger on the left and the imitation on the right.
Inside the Apple 85W Macbook charger (left) vs an imitation charger (right). The genuine charger is crammed full of components, while the imitation has fewer parts.
The imitation charger has about half the components of the genuine charger and a lot of blank space on the circuit board.
While the genuine Apple charger is crammed full of components, the imitation leaves out a lot of filtering and regulation as well as the entire PFC circuit. The transformer in the imitation charger (big yellow rectangle) is much bulkier than in Apple’s charger; the higher frequency of Apple’s more advanced resonant converter allows a smaller transformer to be used.
The circuit board of the Apple 85W Macbook charger (left) compared with an imitation charger (right). The genuine charger has many more components.
Flipping the chargers over and looking at the circuit boards shows the much more complex circuitry of the Apple charger.
The imitation charger has just one control IC (in the upper left).[17]
since the PFC circuit is omitted entirely. In addition, the control circuits are much less complex and the imitation leaves out the ground connection.
The imitation charger is actually better quality than I expected, compared to the awful
counterfeit iPad charger and iPhone charger that I examined.
The imitation Macbook charger didn’t cut every corner possible and uses a moderately complex circuit.
The imitation charger pays attention to safety, using insulating tape and keeping low and high voltages widely separated, except for one dangerous assembly error that can be seen below.
The Y capacitor (blue) was installed crooked, so its connection lead from the low-voltage side ended up dangerously close to a pin on the high-voltage side of the optoisolator (black), creating a risk of shock.
Safety hazard inside an imitation Macbook charger. The lead of the Y capacitor is too close to the pin of the optoisolator, causing a risk of shock.
