Testing DDl's circuit

You would normaly have the switch on the input of the regulator. To switch in a capacitor discharge resistor, whilst turning off the supply, your would need to rig a DPDT switch, it could be done and if you are using the circuit to test LD's it would take the worry out of making connections.

Regards rog8811

Hey, I don't have any 1 ohm resistors, so would it work if I placed a 10 ohm resistor, and then divided the output by 10? :-?
Thanks for the help and sorry if I sound like a noob.

You can leave out the 1ohm and test across the 100ohm load resistor if you are testing for a blue, or replace the 1ohm for a 10ohm if testing for a red, then just do the maths as you suggest..... The main reason for using the 1ohm is to get a direct conversion between mv and ma  (the lazy way )

Regards rog8811

Ok man thanks a lot. ;D

umm... isn't +Vin pin 1? or does it matter?

Either way this was very very helpfull.

isn't +Vin pin 1?

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The drawing on post 2 of the regulator package is correct showing pin 3 as Vin, the original thread was notated differently for some reason. Connect using leg descriptions rather than numbers and you won't go wrong.

Regards rog8811

To the top.

Radio shack has a nice 2.47v 300mA screw base lamp #272-1132 If you use this in place of your diode you can tweek the pot and see if your circuit acts as it should for far less then a diode costs. The easy way is to solder on a pair of leads and then substitute it as a diode until u feel comfortable with your circuit. Radio shack has various light bulbs and if your voltage / current will be different, then find a more appropriate bulb or consider a series or parallel combo to provide the proper "dummy load" for testing ..

Additionally, I have noticed that grounding your circuit to say a "alligator hand soldering station" helps dissipate the current upon removing power as the residual heat produced from the components dissipates faster and after a couple minutes there is no need to discharge the cap manually as it bleeds out on its own.

I use this with the light bulb, not the diode, its good in the test mode, but i am not sure i want the diode itself grounded to my tools. I have had 0 issues with it on the lightbulb tho and I appreciate its quick dissipation in testing with the 50 cent bulb.
SN

In addition, the bulb and tweeking the pot is a cool way to learn how non linear most pots are and should give a nice appreciation for how delicate the turn is on a mini pot and how drastic the gain becomes on approaching the max.

SN

Sure, you can use the bulb, we just use the four diodes because they all have a voltage drop of 2.8v which kind of simulates an LD. There's some people who use a 100ohm resistor to simulate a blu ray LD too. But it's up to you what kind of dummy load you want to use.

Yepper,

It's all good. I just like to see the light and realize the range/gain the pot provides as it approaches 0. It can also help when deciding if you can decrease the resister if your bulb is in line with your LD spec v and mA

SN

Oh and on a side note,

If your volts are a bit lower and your current is a bit higher then this causes more heat. This indicates that a higher volt with a matching lesser current should provide a cooler and more reliable circuit (within reason). In theory yes. With a laser diode? I dunno. But it works in basic electronic ideology. So it seems to me that i would prefer to stay near the top end of volts and thus my current would be less fatal, although pushing the max is the same, riding in the middle should be more safe at a lesser current at a higher volt (within the parameters of the device)

SN

I thought that when you are measuring current, that you should put your multi meter in series, not in parallel with the circuit... I'm confused! :'(

laser_freak said:

I thought that when you are measuring current, that you should put your multi meter in series, not in parallel with the circuit... I'm confused! :'(

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That's true. But if using a 1 ohm resistor in series with the load, you will measure the voltage across it. The reading you get on your DVM will be the current.

What mA range should I be expecting when using the 25ohm 3W pot from radioshack linked in DDL's circuit thread?

Over the 1ohm resistor, I read 30-40 at max resistance to 180-190 at lowest.

Fusion2004 said:

What mA range should I be expecting when using the 25ohm 3W pot from radioshack linked in DDL's circuit thread?

Over the 1ohm resistor, I read 30-40 at max resistance to 180-190 at lowest.

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The mA range will depend on the least resistance vs the max resistance. For example, if you had a 25 ohm pot along with two 10 ohm resistors in parallel (5 ohms), The least resistance would be 5 ohms (1.25/5 = 250mA's). The max resistance would be 30 ohms (1.25/30 = about 42mA's).
So the driver would have a range from 42mA's to 250mA's. As long as the supply voltage is over 6 volts (for the red builds). 2 X 3.6 volt batteries is perfect.
Jay