Pnp transistor

Thread Starter

Peter basolo

Joined Nov 24, 2014
38
What is the name of a 6 volt pop transistor? I know a lm317t is 1.25. Also is there a name code for transistors? I'm using this for a blue laser diode I have that I am making a diver for. can you check the schematic for me? This is a slightly modified shcem. Form tingawinga7 I didnt make this. Will this give me a final load of 6 volts at 130 ma? I need this fast I'm about to go to radio shack to buy the parts thanks in advance
 

Attachments

ian field

Joined Oct 27, 2012
6,540
What is the name of a 6 volt pop transistor? I know a lm317t is 1.25. Also is there a name code for transistors? I'm using this for a blue laser diode I have that I am making a diver for. can you check the schematic for me? This is a slightly modified shcem. Form tingawinga7 I didnt make this. Will this give me a final load of 6 volts at 130 ma? I need this fast I'm about to go to radio shack to buy the parts thanks in advance
You should be able to do the constant current you need for the laser diode with just the 317 and a current sensing resistor - unless its a very big laser diode.

Feed the 317 output to the laser via the current sensing resistor and connect the voltage sense pin to the diode as well.

As the laser draws current, it develops a voltage across the sense resistor - when that voltage reaches the 317 1.25V threshold; the 317 throttles back and limits the current.

So find out what current the laser needs and calculate the resistor to drop 1.25V at that current.
 

Thread Starter

Peter basolo

Joined Nov 24, 2014
38
You should be able to do the constant current you need for the laser diode with just the 317 and a current sensing resistor - unless its a very big laser diode.

Feed the 317 output to the laser via the current sensing resistor and connect the voltage sense pin to the diode as well.

As the laser draws current, it develops a voltage across the sense resistor - when that voltage reaches the 317 1.25V threshold; the 317 throttles back and limits the current.

So find out what current the laser needs and calculate the resistor to drop 1.25V at that current.
Interesting. Could I cut out the pot? Also does the 317 cut current? A 9 volt puts out 180 ma but I want 130 ma how can I achieve this
 

dl324

Joined Mar 30, 2015
9,111
What is the name of a 6 volt pop transistor?
In the US, 2N3906 or 2N2907 are frequently used for general purpose circuits. Their complements are 2N3904 and 2N2222, respectively.

I assume the voltage you're referring to is collector-emitter or collector-base breakdown voltage. You won't find a discrete general purpose transistor with such a low breakdown voltage. The transistors mentioned above are 40V and 60V, respectively.

One other thing. You seem to be lax in your use of capitalization. In electronics, capitalization is often critical. Milliamps is abreviated mA, not ma.
 

ian field

Joined Oct 27, 2012
6,540
Interesting. Could I cut out the pot? Also does the 317 cut current? A 9 volt puts out 180 ma but I want 130 ma how can I achieve this
If you don't know the correct current to calculate the sensing resistor for, you can temporarily fit a pot and turn it up till the laser starts lasing - but its all too easy to turn it up too far and destroy the laser diode.

If you mean a 9V transistor radio battery - it won't supply 130mA for very long.

Presumably the 180mA you stated is the mA/h capacity of the battery - that doesn't mean it will supply 180mA for an hour, the measure most manufacturers use is that the battery will supply 9mA for 20h. If you draw more current than that, the claimed mA/h capacity starts to shrink.
 

dl324

Joined Mar 30, 2015
9,111
To drive a laser diode?!
Why not? OP said he wanted 130mA. When I worked at HP Labs in the late 70's, laser diodes didn't start lasing until around 100mA. It's generally much lower now, but I just did the calculations the OP needed to get 130mA from an LM317 configured as a current source.
 

ian field

Joined Oct 27, 2012
6,540
Why not? OP said he wanted 130mA. When I worked at HP Labs in the late 70's, laser diodes didn't start lasing until around 100mA. It's generally much lower now, but I just did the calculations the OP needed to get 130mA from an LM317 configured as a current source.
My misunderstanding - I thought you were referring to just a dropper resistor.
 

AnalogKid

Joined Aug 1, 2013
8,137
READ page 14 of the LM317 datasheet. It has the schematic for using the 317 as a constant current regulator, which is what you want for a laser diode. For that schematic, Iout = 1.25 / R1, or R1 = 1.25 / 0.130 = 9.6 ohms. Buy two resistors, 10 and 220 ohms, and put them in parallel as R1.

Delete both 1N4001 diodes from your schematic.

ak
 

ian field

Joined Oct 27, 2012
6,540
If a 317 puts out 1.25 what puts out 6 volts? And I need more than 20ma can I use 2 18650 batteries in series?
The 317 has a 1.25V difference between output and Vin pin - its normally used as an adjustable voltage regulator by connecting a potential divider from output to GND and feeding the tap back to Vin - when the tap is at 1.25V less than the output, the 317 stabilises at that level.

Used as a current regulator, the output current flows through the sense resistor and develops a voltage across it - the Vin pin is connected to the load end of the sense resistor, so when the voltage across that resistor reaches 1.25, the 317 stabilises.
 

atferrari

Joined Jan 6, 2004
3,486
Peter, I do not intend to disturb your way to success but please be aware that the LM317 is not a pnp transistor. It is a three terminal voltage regulator.
 
Top