Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



DVD Player Power Supply

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
I just tore apart an APEX DVD player. Just to play around. I noticed the power supply in it could be useful. It has 12 volts, 5 volts, and 3.3 volts. Unfortunately I can't measure the current because I have no meter. But I did do this. I hooked up a cheap 5 mW laser pointer from Wal-Mart to it. I figure the duty cycle on those things are pretty much forever. Well anyways I left it on for roughly 2 minutes. My point is if these little tiny cheap 5mW laser diodes can handle that 3.3 volts(at whatever current), then a DVD burner LD should sure as heck withstand it. I will post pics as soon as I get my digital camera back. So the intent of this post was to inform people that an APEX DVD player for only $29 has a nice power supply in it.
 



laserrod

New member
Joined
Aug 3, 2007
Messages
342
Points
0
Use a current limit resistor or the diode with fail.

Cheers [smiley=beer.gif]
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
Well here is my rigged up little circuit I was talking about. In the picture, The switch at the bottom activates the laser. Like I said I do not know the current of the power supply but I have had this laser on for a FULL 3 minutes with no problem and it is from Wal-Mart. The cheap 5 mW $2.99 laser pointers. I was wondering about the GB LDs. If this Power supply could power it. That is without Daedal's circuit. I will post a close up of the DVD power supply. I know without knowing the current of this power supply there is no safe way of saying about the GB LDs.
 

Attachments

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
Is there a driver board in the cheap laser...what kind of battery(s) did it take. 3.3 volts to the GB diode will kill it. You will want to use a resistor, or a silicon diode in series.
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
Ahh yes you are right there is a driver board in the cheap laser. But you say 3.3 volts will kill the GB LD? Well that is without any resistor or anything right? Meaning its not a good idea to hook my power supply of 3.3 volts directly to the LD? Unless maybe I check the current that the power supply is putting out. What would be safe? 200-250 mA? Oh and sorry for so many question but what is the difference between mA and mAh?? If I end up getting a multimeter and I check the current from the 3.3 volts and it is only 200 mA, would that be safe to hook DIRECTLY to the GB LD?
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
A meter would be very helpful. But you can't check the current without a load across the power supply, and there is no way to check the current capacity of the power supply without blowing the fuse. The power supply you have appears to be well filtered, so I think you can get buy with just a resistor in series with the GB diode.

200ma might be OK for short run times. But as I have posted before this diode is a good burner at 160ma's, and for longevity of the diode I do not recommend going higher.

Mah's is used the rate the capacity of batteries.

Make sure before you hook up the diode you shut off the power supply and connect the two wires of the output together. This will discharge any voltage in the circuit. Then hook everything up before applying power.
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
Actually you could get the 3 watt 25ohm rheostat from Radio Shack. This way you can adjust the current and monitor the current with your meter when you get one. I use these and really like them:

http://www.radioshack.com/product/index.jsp?productId=2062299&cp

Just make sure you do as I explained to discharge the capacitors, and make sure everything is hooked up and connected good before you apply power to the diode, including the meter test leads.
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
Thank You Gazoo. I appreciate your help. Now to check the current of the 3.3 volts could I just hook an LED to the 3.3 volts then put the multimeter in series with it, like the (+) probe from the meter to the (+) side of the PSU and then (-) probe from the meter to the LED? Maybe that sound confusing or I just don't know how to word it but could you tell me how to check the current of that 3.3 volts? Also with Daedal's circuit, how much voltage do you have to input into it? You could tell me 9 volts but what if that 9 volts is a high mA? What current does Daedal's ciruit output relative to its voltage input? Again sorry about all these questions. Your help is much appreciated. :)
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
You can do that but you will only be measuring the amount of current the LED is drawing from the power supply. Everything you hook up as a load will give you a different current reading.

Daedal's circuit requires a minimum of 6 volts. Once the pot is adjusted for the current you want to go to the diode, the current will stay the same no matter how much voltage you put into Daedal's circuit...up to 30 volts.
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
But what I mean is if you hook 12 volts to Daedal's circuit at 500 mA, would it be the same as 6 volts only 300 mA? Also if what you said about the current reading only reads depending on the load, then how do I know I am not going to blow the LD. I wanna be sure that the power supply I am using puts out a safe amount of current for the GB LD. That was my main concern was testing the current of MY PSU's 3.3 volts to be sure it is safe for the LD. Now if I can only test the current of that 3.3 volts by hooking a load to it, then if I hooked the LD to it and it ended being 3.3 volts @ 500 mA then my LD is screwed. I hope you can understand what I am trying to say. Hey do you have AIM or MSN? I would appreciate if maybe we can chat about this rather than taking up the thread length on here. Much thanks. :)
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
"then how do I know I am not going to blow the LD"

Exactly.. :) And I do understand perfectly.

This is why you need a meter and a way to control the current. You must also remember that every LD is going to be a bit different even when they come from the same batch. Anyone trying to attempt this hobby is blind with no meter. If you get a meter and the rheostat I linked to, you should not have any trouble using the power supply you have, and your diode should be safe. In fact this will be an excellent way for you to start out since you have the power supply. We don't know what the current rating of the power supply is but I would bet it is enough to power the diode.

Sorry but I hate chatting because I suck at typing...lol. I will PM you.
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
Awesome Gazoo thanks. But lol :p My question still wasnt answered. How do I check the current of the 3.3 volts coming from my PSU? Wait. LOL would I hook the LD to the PSU and have that pot you showed me in series with it? Start with maximum resistance on the pot then slowly turn it until I got a nice bright dot from the LD? Sorry man I guess my whole big deal is this current thing. I am getting a meter soon. But is there in fact no way to measure the current of the 3.3 volts from my power supply? I just wanna know what I am working with here. Because I have seen on all AC to DC converters that the "mA" current is printed right on them. Now how do they determine that with no load like you said? I am under the impression that you cant get a current(mA) reading without a load on the PSU. If this is true then why when you buy AC to DC power supplies, the mA rating is stated right on it? Ok Imma run this by you step by step maybe and if you could tell me if it sounds right.

1. Hook the LD to the PSU with the rheostat at maximum resistance.
2. Turn the PSU on after shorting the capacitors out like you told me.
3. Slowly turn the pot until I get a good bright dot from the LD.

Oh and could you please answer my main concerns about checking the current of my PSU? Thank you so much, your knowledge and help does not go unappreciated. :D
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
1: Connect the output leads of the power supply together for a couple of seconds to discharge the capacitors.

2. Connect ground from the power supply to the ground of the LD. Everything else goes in series on the positive side. Wire up everything and make sure your meter is connected in the circuit before applying power to the LD, and that your meter connections are good. The meter gets connected in series too.

3: Start out with the pot at the maximum resistance, and very slowly turn it until you see the LD begin to laze. Of course, you do not need a meter to do this, but when you get your meter and it gives you a reading of 160ma's, stop there and try out the LD for burning and lighting matches. Focus it about a foot away. You will need protective goggles for this.

Manufactures rate the amount of current their supplies can deliver based on the design of their circuit and load testing. We have no idea what the maximum amount of current is your supply can deliver because we do not have a schematic of the circuit, and it the ratings are not marked on the supply. And honestly I do not know the best way to determine it.

Following is a link that should help you understand what voltage and current are.. :)

http://www.kpsec.freeuk.com/voltage.htm
 

o_DEATH_ANG3L_o

New member
Joined
Sep 7, 2007
Messages
634
Points
0
Thanks a lot Gazoo. I read that and it helped quite a bit. So from my understanding, the current reading from my 3.3 volt PSU will vary depending on the load I put on it? I still do not get why I cant just measure the 3.3 volts current. I know I have to measure it in series but couldn't I find the very last point at which the voltage leaves the PSU and measure it that way. I am still leaning toward the fact that store bought power supplies have the current(mA)output right on them. How do they determine this without hooking the infinity amount of possible loads to it?
 

Gazoo

Active member
Joined
Jun 9, 2007
Messages
3,199
Points
38
If you connect a meter directly to the output of the power supply you will blow the fuse in the meter if you use the low current setting. If you use the 10 amp setting on the meter you will either damage the meter or blow the fuse of the power supply.

As I have already tried to explain, manufacturer's know the current their power supplies are able to deliver because they design the circuits for whatever voltage and current ratings they need for whatever application. A very simple power supply using the LM317 is a good example. The LM317 is rated at 1.5 amps so this is the most a power supply is able to deliver using it.

I am sorry I can not explain any better than I have.
 




Top