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Dell PA-10 ac adapter center pin
I've been looking around a lot to see if anyone had any information
about this but came up with nill...So I investigated it myself for anyone out there that may be interested in what that center pin really does. For those of you that think I don't know my butt from a hole in the ground and feel like leaving any messages against what I did I'm not asking for pointless opinions here so take them elsewhere. There was a need for it to be reverse engineered and I did it. Enough ranting lets get on to the beef of the post. I too was wondering what this third center pin is about. No voltage present to it, no resistance, no capacitance; got me wondering what kinda surprise did Dell put in the power supply that they don't want us to know about. So curiosity got the best of me and I very carefully pried the glued case apart. Standard switching power supply, but then near where the wire enters the case and is soldered to the circuit board resides a small TO-92 device. First thought was maybe a transistor that sinks a certain current upon attachment but after further inquiry, only two leads were connected. This led me to reverse engineering this small circuit. It turns out theres a 131 ohm resistor in series with the center pin wire of the DC connecter and one pin of the 'mystery device' and then there is a reverse biased diode going to ground. The other pin that is connected of said device is also connected to ground (by reverse biased I mean that the diode will only conduct if a positive voltage were applied to the ground connection of the power supply and a negative (ground) were connected to the center pin of the DC power connector. This lead me to deducing, because of the series resistor, that this diode was a zener of currently unknown breakdown voltage. The next step was to determine the true identity of the 'mystery device.' The part number read "Dallas 2501 (then a date code)." Dallas being dallas semiconductor (aka Maxim IC). A search yielded only a very incomplete datasheet refering me to the DS2502 which is a 1kbit one-wire EPROM version. The "2501" was a DS2501 of 512 bit data space. The datasheet gives specifications to a max programming voltage after EPROM write instruction of 12V. This means to protect the device from overvoltage this zener diode connected to the pins must be a 12V zener and the sereis resistor being a current limiter protecting the diode in the event that the inner barrel and center pin were to come into contact. The DS2502 and 2501 (1kbit and 512 bit respectively) use Dallas Semi. 1-Wire (R) communication protocol. It gets its power from the data line and when the data line is low a diode protected capacitor supplys power for its logic circuits, Parasite Power. This means that to communicate with the DS2502/1 one only needs two lines, a data line (logic high idle state) and ground. The power to the data/power line is supplied by the master through a 5k ohm resistor for short cable lengths. Hope anyone reading this that wants to make his/her own power converter finds this information usefull (insert disclaimer here; ie. use this information at your own risk, I am not to be held responsible if someone else's equipment gets fried b/c of poor design, I only described how it works and make no claims to it being my own design giving rights of design and operation to Dell and/or LiteOn (written on power brick) and any other engineering firm/company/manufacturer that was involved in the design of the motherboard, power brick and any other associated equipment, etc.) |
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