Newbie- transistor as switch

[methuso]

HI
First off. I am electrically retarded
there.

I have gotten a couple of transistors from a friend that i'de like to use to switch on and off a 300mw red laser-diod thru a laserdriver, EMC2 and stepper driver/breakout board.
i have soldered everything together like in my attached picture (not good at that either)
problem is that when i turn it on i only get 110mw out of it but when i bridge the emitter and collector with a screwdriver (I should wear jeans and flanellshirts) i get the full 300mw that i have set on the laserdriver.

on the transistors i can make out c548b and under that ph 8.7
and on the reeltape it comes on its written 500mah and 30V by hand.

in the picture the diod symbolises the laserdriver. p14 is pin14 on my Hobbycnc card, the 6v is a adjustable "wallwart" and the resistor is 470 ohm.

what am i missing??

hmm i see not that i might have turned the diod the wrong way in the picture... in real life it works but with too little power. sorry for that

[Al_The_Man]

If I were you I would use a power Hexfet, these have very little on resistance and can be switch by 5v gate signal.
It sounds like your transistor is not being fully switched on, the bipolar transistor is a current operated device whereas the Hexfet is voltage operated.
Do you know the nature of the operating device at p14 or is that PP output??
Al.

[methuso]

"Do you know the nature of the operating device at p14 or is that PP output??":
p14 is a output pin directly connecter to the parallellport.

"It sounds like your transistor is not being fully switched on, the bipolar transistor is a current operated device ":
My friend talked some magic stuff about letting a resistor tickle the amps for the emitter (or was it the collector) or something. i think he was sober... doesn't sound like it thou
but he said he mend putting a resistor between the laserdriver and the transistor.
might this get it to open fully?? in that case how large?

best regards /Ulf

[Al_The_Man]

You could try a 1kohm from p14 to +v.
I would go for the Hexfet for the price of probably @ $1.00 ea.
Don't put a resistor in either the emitter or collector, it will only make matters worse.
Al.

[methuso]

ok thanks.
I'll try to find out how to get hold of one and then how to connect it

but since i already got these i'll try the 1kOhm too

/Ulf

[methuso]

hmm... well i have 21pcs of these http://www.irf.com/product-info/data.../irlml2502.pdf left since i was into modding PiccoZ helis
Would they do? and how would i connect them? I really cant read specs that good.

/Ulf

[Al_The_Man]

You are looking a logic level gated power fet, the one you show is SMT or surface mount technology, you will be better off getting a leaded one with three pins.
I will see if I have a suitable number handy and post it.
Al.
.

[Al_The_Man]

The 2n7000 goes up to 600ma, these are usually around 10c each, and available anywhere.
Digikey should have them.
Al.

[methuso]

ok thanks. really had liked no use the stuff i already have. (Hate waiting)
I dont find SMT hard at all but is its the "logic level gated power fet" that doesnt fit I guess i'll have to order.

thankt /Ulf