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You don't want a depletion mode mosfet for Q1. With the switch off you want no current to travel between drain and source. An enhancement mode mosfet will protect the circuit fine. Depletion mode mosfets are generally used for dual-rail powered circuits... cheers, kernelpanic

You can use that p-channel there.But you have to reverse your source and drain. Mosfets are controlled by the gate to source voltage. So upon closer examination of your circuit, even putting an n-channel mosfet there for Q1 wouldn't work. (Since the gate-source on Q1 will be too low through the...

o.k. That looks like it'll work. Just make sure to use logic-level mosfets and you're golden. I still think Q1 might be overkill for a handheld(nice addon for a labby though). But having it would make multiple modes possible with a little control circuitry... cheers, kernelpanic Oops. No it...

Re: pre-order phr803 #6 is now a sale Drew, payment sent via google checkout for 3 sleds and 3 modules ($66). Your link worked fine... cheers, kernelpanic

IC1 needs to be a single supply rail to rail op-amp. The lm358 is a good choice. The mosfets aren't critical. But Q1 may be redundant. Q2 will protect the diode. Q1 only protects the op-amp, which probably doesn't need it. But the zener diode/op-amp portion of your circuit probably wont work...

Re: Simple Adjustable Laser driver (V. 2) It Works Thanks. Yes and no. This circuit as-is works well for phr-803t diodes as the cathode is not grouded to the case. For other (read- 650nm) diodes it'll need to use a p-channel mosfet. I'm still sourcing one small enough to fit in the aixiz...

Re: Simple Adjustable Laser driver (V. 2) It Works The 'spray' is actually butane for the soldering iron. The 'red plastic cover' is a cd envelope. And you missed the steel epoxy-putty. (It was right there too!) ;) Thanks for playing the WTF is all that CRAP- home game! All joking aside, the...

One could use this circuit. It's the p-channel version of the driver on this thread.-> http://www.laserpointerforums.com/forums/YaBB.pl?num=1220866048 You only need to choose R1 and R2. For your app Running 2.9V to the diode from a 3v supply, you want the max voltage at that resistor to be...

Re: Simple Adjustable Laser driver (V. 2) It Works and one of it running... p.s.- Identify everything on my desk and win a prize! (Alas, not really.)

Re: Simple Adjustable Laser driver (V. 2) It Works hello all, Off woork finally. Here's a pic of the host using this driver. I got the diode from drew. It's the second. (The first I blew adjusting up on my v1 driver as the circuit was non-linear in it's response, hence the op-amp and...

The problem with that is that no 2 diodes are exactly alike. Any variance in resistance will cause the load to each diode to differ. In practice, if one diode blows, it might take the other one with it. If you decide to do it anyway, you should test as many diodes as possible and select the 2...

Daguin, Thanks for the heads up! cheers, kernelpanic

There's one for sale on ebay now.-> http://cgi.ebay.com/BECKMAN-GX100-Genomyx-LR-DNA-Sequencer-Electrophoresis_W0QQitemZ220231958971QQcmdZViewItem?_trksid=p3286.m20.l1116 It also is an electrophoresis based sequencer. So there's a laser in there somewhere. If I was in Texas I'd go get it...

Eureka! Hello All, Received my PHR-803T yesterday. It's in the host and working great!!! The only differences between the circuit I built and the schematic are that I used an IRL-520 logic-level mosfet and instead of a 9k resistor, I used an 8.3k (what I had on hand...) Anyway, I now have a...

Re: pre-order phr803  #5  sold out Got mine, very happy ;) Thanks again, kernelpanic

monk, I've been working on this negative regulator- http://www.laserpointerforums.com/forums/YaBB.pl?num=1220866048 The circuit on that thread is for 405nM from a 6v supply. But it could easily be tuned for a different combination. Only the resistor values need changed... The IRL510 can...

Re: Simple Adjustable Laser driver (V. 2) It Works You are absolutely correct. ;) (That's why we're in the 'Experiments' topic...) I'm simply trying to build a cheap DIY circuit capable of lower dropout than the LM317. It's posted here in case anyone else wants to build it. Once I get the...

Better Picture... Hello All, Here's a better picture of the assembled driver in-host. I've run it quite a bit under a test load. I have to say it provides the regulated current all the way up to 98% of supply voltage. For low-dropout, mosfets are the way to go. The op-amp and pot  only eats...

Every 20x LG I've pulled apart has had a long open-can in it... cheers, kernelpanic

Re: Simple Adjustable Laser driver (V. 2) It Works Hello All, Here's a progress report. I've managed to build this small enough to fit in the SKU4171 host. (Pic included) However it's a tight fit. So I ordered all of the parts from digikey to build this surface mount. I ordered enough to build...