Using a DC/DC converter to power the laser

phenol · Mar 2, 2008

the typ Vfb is 190mV and it should equal exactly the voltage across the shunt. you dont have to break the circuit to measure the current. just measure the voltae on R shunt. if all is ok, it should be around 190mv

IgorT · Mar 2, 2008

phenol said:
the typ Vfb is 190mV and it should equal exactly the voltage across the shunt. you dont have to break the circuit to measure the current. just measure the voltae on R shunt. if all is ok, it should be around 190mv

You are right.. The voltage across the Rsense is 193mV...

So why don't i get the correct current?

I have two resistors in parallel.. One is blue and says 1R00 and the other is black and says 2R0..
I'm guessing the blue is 1% and the black 5%?

Also, my IC is now heating up to 39°C (It was 30°C at 213mA with a blue R910 resistor)

IgorT · Mar 2, 2008

I found the problem... My tantalums were bleeding.. They were actually getting warmer, than the catch diode, so i unsoldered the LD and measured the resistance across the output.. My tantalums are presenting 96 Ohms parallel resistance to the LD.

No wonder my IC is warming up much more than yesturday.. It's pumping out more, than the current going through the LD..

I'll replace the tantalums, and everything is going to be fine. Mystery solved...

drlava · Mar 2, 2008

were the tantalums underrated? it's possible there are voltage spikes from your unit that wnet over the tant's rating.

IgorT · Mar 2, 2008

drlava said:
were the tantalums underrated? it's possible there are voltage spikes from your unit that wnet over the tant's rating.

No, i don't think it's that.. It's possible, they were the ones connected the wrong way for a split second, a while ago.. Looks like that killed them both. Just my luck, that i picked exactly these two for the circuit..

Should have thrown them away immediatelly, but they still measured correctly.. Luckily i remembered this, when i saw that Vfb is correct, so i knew where to look for the problem.. Oh, them being warm helped a bit as well...

I'll just put two new ones in and everything will be fine.

How's your Blue Ray boost driver doing? Which IC are you using anyway? Looks like this one would do just as well..

drlava · Mar 2, 2008

oh, yes they are very sensitive to revers polarity.

I have built 4 prototypes hand soldering the DFNs it's a treat. Testing phase right now. As far as the construction and chips, that'll come out once I have a contract with an assembly co. For the specs:
2.5-9V operation, up to 85% measured efficiency, compatibility with blu ray or red lasers, current pot adjustable, ramp current startup.

IgorT · Mar 2, 2008

drlava said:
I have built 4 prototypes hand soldering the DFNs it's a treat. Testing phase right now. As far as the construction and chips, that'll come out once I have a contract with an assembly co. For the specs:
2.5-9V operation, up to 85% measured efficiency, compatibility with blu ray or red lasers, current pot adjustable, ramp current startup.

Sounds good..
I'm sure many people will want one. Especially since right now, they have to use three Li-Pos for a blue ray..

I think i'm gonna use the 3410 for the blue rays as well.. But in that case i really am going to add the chokes, just in case.

How do you achieve ramp current start up? Does the IC do this by itself, or did you have to add some additional circuitry?

toked323 · Mar 18, 2008

so how much is this average costs for all the parts?

phenol · Mar 18, 2008

inductors and ic can be ordered as free samples, ceramic caps can be scavenged from a dvd burner drive. all u need to buy is a suitable schottky diode /cheap 1n5817 should do just fine/, a nice assortment of smd shunt resistors and a pcb substrate. makin the pcb/soldering the chip is prolly the trickiest stuff around this convertr. with some dexterity and tons of luck you could solder them by hand

toked323 · Mar 19, 2008

were can i get the free samples?

phenol · Mar 19, 2008

get them @ national.com and coilcraft.com. for national semiconductor you have to provide an email address other than yahoo, gmail etc, ie a what looks like a company email, otherwise you will have to cover shipping costs. coilcraft are more discerning to whom they ship samples. it seems they look you up online to grant or deny sample approval. if you are a student they will probably ship to you without further investigation if you give them your prof's details, which usually they dont check.

IgorT · Mar 19, 2008

If you order samples from CoilCraft, make up a plausible student project, that justifies the amount you're ordering.

toked323 · Mar 19, 2008

like what kind of project?

toked323 · Mar 19, 2008

hey someone want to order the lm3410 and ill pay you for it cause i dont want to pay 8$ for shipping

chimo · Mar 19, 2008

So you want someone else to pay for the shipping?

toked323 said:
hey someone want to order the lm3410 and ill pay you for it cause i dont want to pay 8$ for shipping

woop · Mar 20, 2008

what, do you want someone who can get free shipping, to get national to ship a few to you?

Using a DC/DC converter to power the laser

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