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HeNe Laser Power Supply

October 2, 2009
 
So this is a blast from the past. At least for me anyway. I built this Helium-Neon Laser power supply back on Augugst 8th, 1991 (at least that is what the home etched PCB says anyway). I cannot seem to remember where I got the plans for this, but I am sure it was from the now no longer published Modern Electronics Magazine (anyone remember that one?). Anyway the unique thing about this is that it uses a Ford Delco Starter Coil as the high-voltage transformer required to excite the laser tube. I can still remember going to a junk yard to find those. The laser tube itself is a Siemens HeNe 1mW laser tube...yep that's right a whole whopping 1mW!
 
Well it was kind of fun to build back in the day. I don't have any schematics for it, but it looks pretty simple. It consists of an 8V DC power supply (why 8V??? I have no idea) with a 555 configured in astable mode. The 555 has adjustable timing resistors but it looks like they work best when placed in the mid range around 470k and 47k. It generates an approximate 250 Hz signal at about 90% duty cycle.
 
The 555 output drives an RC snubber consisting of a paralleled 100-ohm and 0.22uF capacitor into the base of a TIP31 power transistor. The TIP31's emitter is connected to ground while the collector goes to the primary of the starter coil and up to 8VDC. This generates the high-voltage required by the HeNe tube.
 
I have no idea why I chose to build an 8V DC power supply, but I did. Plus it looks like the power to the primary is coming from the 8V regular which probably in hind site is a bad idea. It should probably just come off the bridge rectifier since it doesn't really require any regulation. Plus the drive frequency is probably pounding that regulator pretty significantly.
 
Anyway, I found I still have another spare Ford Delco starter coil so I might try and make a quick "updated version" which is a little better executed.
 
Here's the very crude PCB mask I created for this project long ago. It's amazing this thing even worked with how badly this was done. Oh well :)
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