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Registered Member #621
Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119
I have decided that I need to encorperate a voltage regulator into my low voltage power supplies of my laser project. I am going to full wave bridge rectify a 12 volt AC 3 amp transformer, run it into a smoothing capacitor, then put an adjustable voltage regulator on it this way I can obtain the 3 volts (and a smooth 3 volts) necessary to run my little 5 milliwat Diode Laser that put a spot on the target to aim my Ruby Laser. Now my question is, I am reading that a voltage regulator has a current limit. The ones I am looking at are from Radio Shack and have a 1 amp current limit.
Is this the current they can pass from left leg 1 to right leg 3 and to my device? Or is there any sort of current limit between leg one and the COMMON middle leg 2? Like can I have say...heck, a 100 amp source to Leg 1 and the middle leg, but only draw 50mA from leg 3 and be allright with a 1 amp regulator?
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
The regulator only has the middle leg to know how far above ground level it is operating. It should not sink any significant current there. The max. current is a question of heat dissipation, so fora 5mW diode you don't need to worry about it.
I would also suggest you to run a fixed voltage of say 5V which gives you some headroom to drop voltage over a potentiometer. Otherwise you would need a current source since laser diodes have a highly nonlinear voltage/current relationship. I.e. You can't just feed it 3V, you have to feed it 5mA.
Registered Member #621
Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119
Thanks man. The diode I was looking at says it has a "built in driver", will this take care of the current draw for me and let me just supply the 3 volts and it will siphon off whatever current it needs? About the fixed voltage regulator, I was looking at them too. I plan on having 4 separate voltage levels in my Laser's internals (unfortunately!!! LOL!), I plan on using 3 volts for the diode, 12 volts to run tons of relays, 24 volts to run the darn vacuum relay with its stupid wacky 26.5 volt coil LOL, and of course my 5656 volts of my 244uF capacitor bank. (the high kvp wont be regulated of course, not worried about that as my caps can hold 6,400 volts and my NST I am charging them with is 4,000 volts (rectified to 5656volts)
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
3V is a rather odd specification, but you can derive it from 5V by having three silicon diodes in series with the supply. Each drops 0.7V, so you will be left with 2.9V, close enough. I suggest you use a 12V AC wall wart transformer, that way you can obtain the 24V with a voltage doubler and the 3 and 12V with regultators.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Four voltage levels really isn't anything spectacular. A computer has +12, -12, +5, -5, +3.3, +2.5 and +1.8, and I have a stereo amp with +5, +15, -15, +50, -50, +65 and -65V.
Your original question about current limits is confusing. Pretty much all electronic subsystems are designed to be powered from a voltage source, and "siphon off only the current they need" as you put it. When a power supply (which is after all a voltage source) has a current rating, that doesn't mean that anything you connect to it will have that amount of current forced through it. For instance, a car battery might have a 300 amp cranking rating, but if you connect it to a car headlight bulb, the bulb only draws about 5 amps.
Hardly any current flows in the middle leg of a voltage regulator, maybe a milliamp or two. The 1 amp rating refers to the current it can supply to your load.
Voltage regulators are not suitable for running bare laser diodes. A bare laser diode needs a current regulator instead. However, a diode with a built-in driver should work off one fine.
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Voltage Regulator question.
