dvd power supply - Page 1
Forum section: electronics / beginners

author: carrierspace
author_rank: Newbie
timestamp: July 29, 2012, 03:26:06 am
content: hello my name is Justin and i'm new to this forum and pretty new to electronics. I tore apart a broken dvd player and found that it had a separate board for the power supply and was hoping i could use it for powering my micro controller projects safely. I know that the ic on it (tea1521p) is an ic for switch mode power supplys and aside from the ic it pretty much has all the basic components that are in dave's video on linear/switch mode power supply. i attaced some pictures of it and one does any one know why one of the boards for mounting holes has a metal sleeve around it and above it says GP1?

author: amyk
author_rank: Super Contributor
timestamp: July 29, 2012, 07:20:56 am
content: GP1 looks like it's for grounding.You'll have to trace the outputs from the transformer to the diodes and look up their part numbers to get an idea of the power output it's capable of. It's probably good for 10-20W.

author: SeanB
author_rank: Super Contributor
timestamp: July 29, 2012, 07:49:50 am
content: Well, this supplies 12V, probably at around 300mA, -12V at around the same and 5V at about 1A. Perfect for powering microcontrollers, provided you remember only the 5V rail is regulated, the other 2 rails can vary from 8-16V depending on load on them and the 5V rail. The connector marked GP1 is the connection from the class Y capacitors in the power supply to the case, to ideally be connected to mains earth in the case you place it in. remember that almost 3/4 of this board is connected directly to the mains and is dangerous to touch when plugged in, even if not turned on, and will hold lethal voltages for around 10 minutes after the power cord is removed. When mounting in the case use spacers of non conducting plastic ( the 3 plastic ones and the steel one that came from where it was mounted will do) for the other holes, and either use a plastic case or a grounded metal one, with a grounded cord. Take the output to either 4 sockets or 4 terminal screws to attach the load.

author: mariush
author_rank: Super Contributor
timestamp: July 29, 2012, 01:37:56 pm
content: As you say you're a beginner, I would suggest to NOT use this as a power supply for your projects because it's too risky to have the mains voltage so close to you on the bench.I would suggest getting an old AC adapter from a switch or a hub or a scanner ( might find these at recycling centers or stores selling used parts) which outputs 7.5-12v DC and then use a simple linear regulator to generate the desired output voltage.It's a very simple project for a beginner.For example, this is how I power my pic controllers with 5v :I'm using an AC adapter I got from an old 4 port switch, it's 7.5v 1A rated, but since it's not regulated it outputs up to 11v when there's no load. The LT1085 linear regulator doesn't care, it just needs the voltage you need at output + 1 volt so as long as the AC adapter gives it at least 6v, this board will output 5v like I designed it to.The circuit is basically exactly the one in the datasheet:The resistors are just different than what's in datasheet because I used what I had around ... the formula is simple : output voltage you want = 1.25v ( 1 + r2 / r1) - with the resistors in the picture above i get about 5.1v output which is close enough to 5vThe capacitors also don't matter much as long as they're there, I've used what I had around, I believe it's a 47uF 16v and a 220uF 35v at output. Very over the top since the output is 5v, but that's what I had around.For the current a PIC controller needs plus a lcd screen, the chip doesn't need a heatsink. It will need one only if you plan to use a lot of power, let's say more than 0.2A. With a good heatsink it can output up to 3A

author: Monkeh
author_rank: Super Contributor
timestamp: July 29, 2012, 02:52:15 pm
content: Can I just say that that's really ugly?

author: carrierspace
author_rank: Newbie
timestamp: July 29, 2012, 06:00:03 pm
content: I took my multimeter and carefully tested the headers and it was like you said, 10.2 on the 12 volt lines , 5.1 on the 5. I'm not sure how to connect it to mains earth because the cable that goes from it to the wall only has the two connectors on it , the left and the right ones not the bottom middle one. so if i mount that screw hole directly to the bottom of a case will it be sufficient?