4A Laser Driver

[electrophile]

I'm fairly new to lasers but an old hand at electronics. I started working with lasers about 2 years ago and since then I've been hooked! I came up with this 4A laser driver recently and the one shown here is a prototype that I use with my laser engraver that is powered by a 3.5W NUBM06 laser. A 10A driver prototype is also in the works. If this is something you folks would be interested in, I can start making more.

Here are the specs:

1. 4A max current out at 5.5V
2. Max VIN is 75V (recommended Max VIN is 60V)
3. Two modes of current adjustment - PWM and potentiometer. Suggested method is to set the max current limit using the pot and then use to the PWM to vary power output. PWM frequency can be between 400Hz to about 100KHz.
4. Soft start of about 5ms.
5. Cycle by cycle current limit with low-power and thermal shutdown
6. 500KHz switching frequency
7. Terminal tabs on the board to attach external current meters for continuous current readout.
8. JST VH connectors for input and output rated at 10A.

 

[Alaskan]

Nice, I might be interested in a 10A version, not many of those available yet. What would the maximum input voltage be for it?

Please post an introduction in the welcome section, a general geo location is also welcome. I guess your last post is an introduction too, but members like to see more, if you are willing to share more. I started in electronics in high school back in the early 70's, but lasers are fairly new to me too, just a few years since I started this as my new hobby, used to be Ham radio and flying private aircraft.

 

[RedCowboy]

An output of 10a @ 5v is something I could make use of, do you have these for sale, ebay perhaps ?

p.s. Yes do post a simple introduction in the welcome thread here >>> https://laserpointerforums.com/f37/

 

[electrophile]

used to be Ham radio and flying private aircraft.

Learning to fly has been on my bucket list for a while now but its just so expensive :| Someday perhaps... I've posted an introduction just now.

Nice, I might be interested in a 10A version, not many of those available yet. What would the maximum input voltage be for it?

Max VIN is 75V but realistically I'd recommend not to go higher than 60V.

 

[electrophile]

An output of 10a @ 5v is something I could make use, do you have these for sale, ebay perhaps ?

p.s. Yes do post a simple introduction in the welcome thread here >>> https://laserpointerforums.com/f37/

Just posted an introduction!

The 10A driver is not yet in production. Still testing it. I'll be sure to post my results once I get a production ready version and a subsequent purchase link too.

 

[Alaskan]

That's great, I have a problem finding drivers which allow me to put a high enough VIN to allow stringing several laser diodes in series. What is the drop out voltage?

 

[electrophile]

I haven't tested these with LDOs in series. Do you mean the voltage drop when operating at full load? At the full rated 4A, the voltage across the single LDO was about 5.2V. The output voltage can be adjusted to be higher though. I'd just have to use a different combination of certain components which wouldn't be too big a deal.

 

[Alaskan]

I just meant how much voltage is lost from the VIN to the Out, in other words, if supplying 8.2 VDC, what is the maximum output voltage at the rated full current the device can produce?

 

[paul1598419]

As you should know, the Vf of a laser diode depends on the current your driver allows it to draw. To string laser diodes in series is the easiest way to hold all their currents to a single value, regardless of the voltage drop across each one. That is why people are interested in the limit of its forward voltage.

It might be easier to let us know the topology of the driver. Is it linear, bucking, sepic.....

 

[RedCowboy]

Also many of our favorite LD's live around 4.5a @ 4.5v but I am interested in 10a @ 4.7v and can supply DC in from 12v to 36v within my device size.

 

[electrophile]

As you should know, the Vf of a laser diode depends on the current your driver allows it to draw. To string laser diodes in series is the easiest way to hold all their currents to a single value, regardless of the voltage drop across each one. That is why people are interested in the limit of its forward voltage.

It might be easier to let us know the topology of the driver. Is it linear, bucking, sepic.....

Ah I see. Its a buck driver with an external FET. I guess if you are going to string LDOs in series then the driver will have to be modified to account for the drop across each LDO. In which case, the output voltage will change from the design value of 5.5V to whatever is needed for the # of LDOs in series.

 

[electrophile]

Also many of our favorite LD's live around 4.5a @ 4.5v but I am interested in 10a @ 4.7v and can supply DC in from 12v to 36v within my device size.

Got it. Yes the max VIN is about 75V so it should be ok to drive it with those supplies.

 

[Alaskan]

A high VIN sure allows a string of diodes in series, but how much voltage VIN is required to produce, for example, 5 volts out at a constant current value if using batteries with a much lower voltage? The difference is considered the drop-out voltage loss through the driver.

 

[electrophile]

Since this is a buck driver the input voltage has to be higher than the output. Theoretically it can still operate if the output voltage becomes equal to the input voltage. Thereafter the output voltage is directly proportional to the input voltage. The output current however is at the peak value the driver was designed for since the FET is ON all the time. To be on the safe side, the input voltage should be at least 2V above the needed output voltage. I've operated the above design from a 9V battery and it works great. If you are using 3.7V LiIon cells then you may want to have a 3S-xP combination for a 5V output.

 

[Alaskan]

Thank you, that's the number I was looking for, 2 volts input above needed output voltage.

 

[RedCowboy]

That's why I like to run 3 li cells in my builds, the SXD needs 6.8vin at minimum under load IINM and running 2 cells means more frequent charging, a lot of videos I watch I suspect the operator is not getting full power due to running 2 poor quality cells and sag below minimum vin, also I use IMR/INR formulated cells with low sag, but I have seen people driving nubm's with two ultrafire cells and I know they are not getting full power.