Schematics for Scanditronix Diolase I and II Laser Line Generators

The following have been extracted from the chapter on diode laser power supplies in Sam's Laser FAQ. I don't know how many variations there are on these - I only checked one sample of each type.

Laser Diode Power Supply 1 (RE-LD1)

This is the circuit from a Scanditronix "Diolase 1" laser line generator, a unit designed for patient positioning in medical diagnostic and treatment applications like radiation therapy. No, it doesn't actually engrave the patient but just projects a red line to aid in placing the patient on the couch and adjusting couch position in relation to semi-indelible ink marks drawn on the skin surface.

It will run from a (wall adapter) power supply of about 6 to 9 VDC.


            D1
  Vcc o-----|>|-------+-----------+-------------------+--------+-----+
           1N4001     |           |                   |        |     |
          Rev. Prot.  |           |    Pwr Adj       _|_     __|__  _|_ C4
                      |           /   R3 10K (2)  PD /_\  LD _\_/_  --- .01uF
                      |       R2  \     +----+        |        |     |
                      |      560  /     |    |        |        |     |
                      |           \     +---/\/\--+---+        +-----+
                      |           |     |         |                  |
                      |           |     |         +-------||---+     /
                    +_|_          |     |       __|__   C2 (1) |     \ R4
                 C1  ---          |     |     E /   \ C 100pF  |     / 3.9
               10uF - |           +-----|------' Q1  '---------+     |
                      |           |R    |    BC328-25 (5)      |    C|
                      |       +---+     |       (PNP)          |   |/ Q2 (5)
                      |       |  _|_.   |                      +---|  BD139
                      |   VR1 +-'/_\    |                      |   |\ (NPN)
                      |   LM431   |     |                 C3 +_|_   E|
                      |   2.5V    |     |               10uF  ---    |
                      |   (3)     |     |X                   - |     |
            R1 3.9    |           |     |Y                     |     |
  Gnd o------/\/\-----+-----------+-----+----------------------+-----+

Note the heavy capacitive filtering in this circuit. Changes would be needed to enable this circuit to be modulated at any reasonable rate.

Notes:

Capacitor C4 value estimated.
Potentiometer R3 measured at 6K.
LM431 shunt regulator set up as 2.5 V reference. A 2.5 V zener or even a visible LED could also be used.
Supply current measured at 150 mA (includes power on LED not shown).
Transistor types do not appear to be critical.

Laser Diode Power Supply 2 (RE-LD2)

This is the circuit from a Scanditronix "Diolase 2" laser line generator, similar to the Diolase 1 described above but containing a pair of diode laser modules, normally adjusted to produce a horizontal and vertical line. It appears to be an improved design including a soft-start (ramp-up) circuit and an inductor in series with the laser diode. Otherwise, it is virtually identical and will run from a 6 to 9 VDC source.

Since both units were from the same company, I assume that these refinements were added as a result of reliability problems with the previous design - in fact, I have recently discovered that the unit from which I traced that schematic is not as bright as it should be!

Interestingly, there does not appear to be any reverse polarity protection on the input - I don't know why that would have been removed! C1 and Q1, at least, would likely let their smoke out if the power supply was connected backwards.


           2SC517 (NPN) (6)
 Vcc o----+--.  Q1 .---+---------+---------------+--------+----+-----+
          |  _\___/_E  |         |               |        |    |     |
          |     |      |         |              _|_     __|__  \ R5 _|_ C4
       R1 \     |      |         |           PD /_\  LD _\_/_  / 1K --- .01uF
     3.3K /     |      |         /               |        |    \     |  (2)
          \     |      |     R2  \               |        |    |     |
          |     |      |    390  /         R3    |        +----+-----+
          |     |      |         \    +---/\/\---+--+                |
          +-----+      |         |    |   2.2K      |                +
                |      |         |    |             +----||----+      )
                |    +_|_ C2     |    |           __|__ C3 (1) |      ) L1
                |     --- 33uF   |    |   R4    E /   \  47pF  |      ) (3)
                |    - |         +----|--/\/\----' Q2  '-------+     +
                |      |         |R   |  220   BC328-25 (6)    |     |
           C1 +_|_     |     +---+    \           (PNP)        |   |/ Q3 (6)
          1uF  ---     |     |  _|_.  /<-+ R6                  +---|  BD139
              - |      | VR1 +-'/_\   \  | 10K                 |   |\ (NPN)
                |      | LM431   |    |  | Power Adjust   C5 +_|_   E|
                |      | 2.5 V   |    +--+ (4)          10uF  ---    |
                |      | (5)     |    |X                     - |     |
                |      |         |    |Y                       |     |
 Gnd o----------+------+---------+----+------------------------+-----+

Note the heavy capacitive filtering in this circuit. Changes would be needed to enable this circuit to be modulated at any reasonable rate.

Notes:

Capacitor C3 was marked n47 and very small, probably .47nF (470pF).
Capacitor C4 was marked 10n and very small, probably 10nF (.01uF).
Inductor marked Red-Black-Black-Silver, probably 20uH.
Potentiometer R6 setting not measured.
LM431 shunt regulator set up as 2.5V reference. A 2.5V zener or even a visible LED could also be used.
Transistor types do not appear to be critical.