Monday, April 25, 2011

Stanham driver

To run a CNC laser you'll need a laser diode driver (current source) that can be modulated. I wanted a driver that can be modulated with an analog voltage as well in case I want to give EMC control over the laser power output. After some searching I settled on a modified StanHam. I changed the design by adding soft-start capacitors (though not tested yet) and made it all surface mount components and a beefier output transistor as I intend to run this up to one amp for my 445nm diode. The board layout is as follows:

The board works well though the transistor gets hot, so do add a heat sink. The bare board etched at home using toner transfer looks like

and once populated it looks like this:

Pardon the messy tin, I'm trying to protect the copper layer from oxidizing away. Be careful when trying to run this for the first time. Most likely you'll short circuit the power supply :) The driver is very sensitive to the position of the POTS RV1 and RV2. Start with RV2 set so that R6 is connected to ground and set RV1 so that R3 is connected to ground. Then apply power to P3 (0-5V) and start increasing RV1. You can estimate the current that will be flowing even before you attach your dummy laser by measuring the voltage over C4 multiply that by two and assume 1V=1A. So if you read 125mV, you driver would output 250mA. The voltage at pin1 of the IC should be twice the voltage at pin 3 and equal to the voltage over R10 when a diode or dummy load is present.

1 x Transistor 2SD1758TLR
3 x Diodes 1N4148WS
1 x Dual opamp LM358MX
2 x 10k Trim pots PVG5A103C03R00
1 x 1 Watt 2512 SMD 1 Ohm transistor
1 x 100uF capacitor
1 x 100nF SMD805 ceramic capacitors
7 x 10k SMD805 resistors
2 x 1k SMD805 resistor
2 x 470pF 805 SMD ceramic capacitors (optional)


  1. hello,
    what about softstart feature,
    Do you have tested it?

  2. Hey! ...people here is not happy because the blogger doesnt give replies! ;)