What does TTL really do?

[sometoymachine]

Hi everyone, I'm very wet behind the ears here. Working on my first laser build now. Red diode powered by 5v input from old PSU. I purchased an AixiZ driver and come to realize that some were having issues with the driver.

Firstly, what is transistor-transistor logic and how do you use it? I also hear that on this driver, you must run a 1n4xxx diode between Vcc and TTL. Not sure why that is.

I was told that 5v input, the max output is slightly over 310ma. That seems like a lot for reds doesn't it? If I turn the pot on the driver down I could adjust it but wouldnt that excess power generate more heat and lower the life span? FYI, I am heatsinking the driver and output regardless. How would I go about handling this, or is it even an issue?

Thanks for reading

 

[Gryphon]

TTL modulation is generally only used on drivers found in things like lab lasers or those in projectors as a way of remotely modulating their output. If you don't care to use the modulation capabilities of the driver, there are several different driver options available to you that are more plug-n-play. Drivers like rckstr, flexdrive, even diy builds like the DDL.

 

[anselm]

TTL in this here context apparently means that the laser can be turned on or off
via a TTL-level logical signal (usually 0V = false and 5V = true).
This provides for a simple on/off modulation if you input a suitable control signal.
The other kind of modulation is "analogue" which can smoothly give you a wide range of
brightness from 0% to 100%.

 

[sometoymachine]

Ok , so in my case It is a shut off if the power exceeds 5v or so, protecting the driver or more importantly, the diode.

However, what about the heat issue-- powering a red with nearly 350ma? Should I simply turn the adjustment down on the driver or use some sort of resistance just after the PSU?

 

[anselm]

Ok , so in my case It is a shut off if the power exceeds 5v or so, protecting the driver or more importantly, the diode.

Hmm, I don't think you understood that right, see:
The TTL signal is not where the diode gets its power from, it is a logical signal
that you can supply to the driver in order to turn the beam on or off.
An electrical switch, if you like.
If you put a voltage (usually around 5V) across the TTL input of the driver,
the switch will activate, turning the beam off (or on maybe).
Take away the voltage (put 0V across the TTL input) and the switch toggles to
it's other state.

If do that fast enough (say a few kHz) you can modulate the beams intensity.

 

[sometoymachine]

Thanks for the responses guys. Unfortunately I didn't get the driver working for whatever reason. I then got impatient and wanted to find out if the LD was even working so I found a 3.4vdc wire on the PSU and hooked it up to the diode. It's only producing a very small amount of red light. Surely with that little power, I couldn't I've LED'd my diode? Perhaps the DVD-R I got it from was less than 16x? I dont know if that would matter :-/ either way I'm very discouraged.

 

[HIMNL9]

Are you sure it's not the IR diode ?

IR diodes from CD / DVD burners emits that what, at eyes, appear as very dim dark red, also if they are emitting all the power ..... have you checked with a camera or webcam, that the diode is emitting really red and not IR ?

Seen through a webcam or camera, an IR diode looks as it's emitting bright pink light .....

 

[qumefox]

Are you sure it's not the IR diode ?

IR diodes from CD / DVD burners emits that what, at eyes, appear as very dim dark red, also if they are emitting all the power ..... have you checked with a camera or webcam, that the diode is emitting really red and not IR ?

Seen through a webcam or camera, an IR diode looks as it's emitting bright pink light .....

It came out in another thread that the PSU he used was a 3.3v 20A non-current limited supply... his diode is toast heh.

 

[Mohrenberg]

oh, is 20A bad for a red diode? :crackup:

 

[sometoymachine]

Bleah :-/ yeah I seemed to have learn that a little late. Didn't catch that bit on the power supply. I just assumed all the current was the same. Rookie mistake. Another thing I am confused about is the (-) voltage on the ouput.. Such as -5V /.3A -- what would a negative voltage do?

 

[anselm]

what would a negative voltage do?

Makes current flow in the opposite direction.

 

[sometoymachine]

the opposite direction? That sounds like its getting really intense. So, you couldnt use + voltage and - voltage to form a circuit then could you?

 

[qumefox]

It's the voltage referenced to ground. Like anselm said, the direction the electrons flow is backwards. It's used in some circuits... Amplifiers for instance, will always have + and - voltage rails. Like +40v and -40v.

If you have 3.3V@20A and -5V@.3A, it sounds to me like your using a PC power supply.

Keep in mind PC power supplies don't regulate worth a crap on any output unless they have a load on the 5V. I use them all the time for 12V supplies you just have to remember to put enough resistance between 5V and ground to draw about an amp or so so they'll regulate properly.

 

[sometoymachine]

Yeah its a PC PSU. I connected the 5w green (some called it the PSU-ON) to ground. Does that take care of the load on the PSU you mentioned or do mean a load on that particular lead?

 

[qumefox]

The 5V rail is what needs an actual resistive load. Jumpering the turn on doesn't put a load on it, only turns on the PSU.

Newer power supplies might not need it, it's been a few years since i've used one in this fashion. Measure the 12v out(or any of the other voltages but the 12V is most noticeable fluctuating) with a DMM, If it's waving all over the place, you need a load on the 5V. The 12V should stay stable and really close to 12V when the psu is regulating properly.

 

[anselm]

Look here:
http://laserpointerforums.com/f67/12v-5v-power-supply-58484.html
inside that thread there are two great links to some HOW-TOs about PC PSUs.