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The GhostDrive is Coming...

Ghostchrome

Ghostchrome

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Being a hardcore do-it-yourselfer, I embarked on a journey to design my own linear driver that I could use use in my laser builds. It's been a fun project that I've been working on for quite a while now, so it's pretty neat to start seeing it actually start to come together.

I finally bit the bullet and ordered the boards after spending many moons figuring out the features that I wanted, the components that I should use, the size of the components, etc. Everything that I learned along the way has been self-taught through either reading as much as I possibly could on the subject, or by trial and error. Seriously... it's been holding me back from working on ACTUAL LASERS. :p

I've made many Mouser orders, done lots of testing, and redesigned the board several times due to reasons like: picking the wrong package size for the resistors, not realizing at first that the smaller package size weren't rated for the wattage that I was going to be putting through them. DOH! :banghead: Luckily I never actually ordered the boards before figuring that out.

I finally received the boards today after waitng for what seemed like an eternity for them to arrive. Here's a peek:

b8sc39.jpg



Ooooh I'm excited! :D



So the features that I wanted the driver to have are:

1) It had to be able to run both red and blu-ray diodes with 2 cells.

2) I wanted reverse polarity protection.

3) I wanted ripple protection.

4) I wanted it to be small... micro-sized even. It needed to at least fit in the rear part of an Aixiz module. I finally got the board down to 8.96mm x 12.8mm. Not too shabby.


I chose the 1117 series voltage regulator because it's low-dropout, it's tried and tested, it's cheap, and it's power is limited to 800mA.


I realize that there are a few of you guys out there selling linear drivers right now. Just so things are clear here, I'm not trying to take away your business or compete with you. I'd like to offer a low-powered, entry-level solution to builders. I have a pretty wide assortment of set resistors, but none of which will power a laser diode over 502mA, so rest assured, this is not a driver that can power the big guns.


Anyway, I'm going to assemble a couple of these boards this weekend, fire them up, and see what they can do. I'll let you know how things go!


EDIT:

Here's a couple pics of the assembled driver.

esjl0j.jpg


epehk1.jpg
 
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Very nice! +:beer:

I am very interested to see how it turns out. The more availability and variety of different drivers for our hobby the better :)
 
So, this morning I put together a 456mA version of the driver. Hooked it up to 7.5V and boosh, it's alive!

Here's my observations:

1) The actual measured out put across the testload was 450mA (vs. 456mA). I guess I'll attribute this to varying tolerances in the resistors.

2) She's gets hot. If you're running at the top end of it's capabilities you'll definitely need to heat sink it.

3) At 7.5V, I couldn't maintain 450mA longer than a second or two when using a test load for a blu-ray (6 diodes + a resistor). At 9V, no problem, it holds 450mA just fine. Fully charged batteries should work fine for a blu-ray, but technically the driver should be able to light up a blu-ray diode at 7V, so I'll have to do a little more experimenting. I'd like to figure out what's going on.

It could be the testload I guess? I was using a solderless breadboard and some pretty well-used diodes that may or may not have been used and/or abused. :D

Anyone have any ideas?
 
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Ghostchrome said:
At 7.5V, I couldn't maintain 450mA longer than a second or two when using a test load for a blu-ray (6 diodes + a resistor). At 9V, no problem, it holds 450mA just fine. Fully charged batteries should work fine for a blu-ray, but technically the driver should be able to light up a blu-ray diode at 7V, so I'll have to do a little more experimenting. I'd like to figure out what's going on.
Click to expand...

Yep, the answer is an easy one. You're underestimating the dropout of that driver. You should be factoring in 2.3V dropout voltage:
DDL Driver Dropout = IC Dropout (@ your current level) + 1.25V

So, the LM1117 drops ~1.1V @ a current of 450mA. Add in the 1.25V from the current setting resistor, and you've got a total driver dropout of 2.35V. That means that 7.5V of input, will result in a maximum of 5.15V to the blu-ray diode, which isn't enough. The PIV curve of your 405nm diode (or simulation via a test load) is the limiting factor.

Simply put, a DDL LM1117 driver can't run a 12X 405nm diode at much higher than around 400mA from two lithium ion cells.
 
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rhd said:
Yep, the answer is an easy one. You're underestimating the dropout of that driver. You should be factoring in 2.3V dropout voltage:
DDL Driver Dropout = IC Dropout (@ your current level) + 1.25V

So, the LM1117 drops ~1.1V @ a current of 450mA. Add in the 1.25V from the current setting resistor, and you've got a total driver dropout of 2.35V. That means that 7.5V of input, will result in a maximum of 5.15V to the blu-ray diode, which isn't enough. The PIV curve of your 405nm diode (or simulation via a test load) is the limiting factor.

Simply put, a DDL LM1117 driver can't run a 12X 405nm diode at much higher than around 400mA from two lithium ion cells.
Click to expand...

Ah ok, thank you.

Yeah, I was just figuring 4.5V for a PHR. :( So 12Xs with currents above 400mA are out - at least with this version using an LM1117. welp... When I get a chance I'll assemble a driver for around 100mA and see how she does.
 
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Looks cool! I have a few suggestions:

- the LM1117 requires input AND output caps to remain stable
- you might want to increase your trace sizes
 
Yeah traces look thin.

Whilst I agree that competition is good, I cant be the only one thinking , not another linear driver on the market?!..how many do we need? , need a good reliable alt to the flex/ boost drive thats a little cheaper.
 
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rhd said:
Looks cool! I have a few suggestions:

- the LM1117 requires input AND output caps to remain stable
- you might want to increase your trace sizes
Click to expand...

Thanks.

Yeah, I think you're right. The next version I'm going increase the trace sizes as well as try to fit in as much extra metal in between the layers as I possibly can in order to help dissipate heat.

As far as the caps go, I've seen a few different datasheets for the LM1117. Some recommend two caps, some one; some need two tantalum, some just any old capacitor. I've tried using two caps vs one, but haven't had a problem when using this regulator. Here's the datasheet for the LD1117 that is used in the driver, they only recommend one:

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000544.pdf

I actually had two caps in the design at one time but got rid of it in order to simplify the design and to get it a bit smaller.
 
ped said:
Whilst I agree that competition is good, I cant be the only one thinking , not another linear driver on the market?!..how many do we need? , need a good reliable alt to the flex/ boost drive thats a little cheaper.
Click to expand...

Yeah, I think that myself sometimes too. heh.

I ordered these boards before Moh released the Mohgasm, and it's been in the works before kiyoukan announced his. it's just taken a while to get things moving. So now you have another alternative. :D

A boost driver is a bit beyond my capabilities - I think it's beyond most people, otherwise there'd be more of them out there. We've got one or two on the horizon, so perhaps one day we'll have more.
 
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^^ Fair comment, and I neglected to say kudos to you for doing this driver.

I agree that boost drivers are more complicated, but we have some highly skilled electronics enthusiasts on here, pity we couldnt all pull together to get one out there.
 
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