are DDL circuits different for each laser diode maker. or laser diode. or are them the same structure for all laser diodes.?

This is a constant current source. The LM 317 is a voltage regulator. it holds the voltage constant between the output and the reference.

The right pin is the input and if it is at least 1.25V above the output the circuit will work. I is better to hold it at least 1.5 v above the output to give it headroom.

This circuit is difficult to understand. a better circuit to explain it is here:

http://users.telenet.be/davshomepage/current-sourc...

The right side of the LM317 is the output, It drives current through the resistor.

The Ref reads the voltage past the resistor and holds it at 1.25 v lower than the output.

If the resistor is 1 ohm the current is 1.25/1 or 1.25A. if the resistor is 100 ohms the current is 1.25/100= 12.5Ma.

In the circuit you referenced the output is the center pin and the reference is the left pin. R is two resistors in parallel and a potentiometer, the blue square, a variable resistor so the resistance can be changed.

Some lasers are spikey and make lots of noise. The output should be steady so there is a transient diode(reverse biased) to clip off noise and a capacitor to absorb noise. They are between the Reference and the Laser diode. This circuit is also used for LED's.

This LM 317 is not a DDL circuit.

If you have more questions email me. If you want a reply, you must open your file to replies or just send me your email address in your message.

YOU ARE ALL CONFUSED !

DDL WAS THE FIRST GENERATION LOGIC CIRCUIT TO MAKE " AND , OR GATE " WITH JUST DIODES. DDL APPEARED THE YEAR BEFORE 1970 AND NO MORE USED AFTER TTL WAS INVENT.

LASER DIODE OR BETTER CALL IT LED HAS A COMPLETELY DIFFERENCE BEHAVIOUR COMPARE TO ORDINARY DIODE AND ITS SEMI CONDUCTOR MATERIAL BEING USED IS NOT THE SAME. BUT THEIR STRUCTURES ARE THE SAME, ONE ANODE AND ONE CATHODE.