Making TTL driver for DX 200mW greenie

Benm said:

Actually, connecting Q2 over the TL431 is an even better option in terms of 'lowest off current' achieved. You always have the C-E voltage drop of the transistor to consider, which is a few 100 mV typically in saturation.

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Right for this reason i suggested to connect the transistor before the trimmer ..... the drop of a common silicon transistor is around 0,6V, and if the current sense resistor is giving less than this value, there is no shutdown, connecting it directly on the op-amp pin .....

The better solution at all, can be split the 20K resistor in 2 x 10K in serie, and connect the collector in the middle point, but i supposed that, being a SMD module, it was a bit more difficult to do, if someone don't have the needed tools ..... also, the 10uF capacitor must be took out, if you want to modulate it decently ..... can be substituted with a 100nF, or also just 10nF ceramic, if you are sure that your PSU is stable and well built (not too much ripple and spikes from it )

Benm said:

I'd also suggest running the whole thing with a 5 volt power supply so the LM358 has some more room to work with, substituting R6 with a slightly larger resistor (2k2 or so).

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I'm not completely sure about this, cause some of these modules dies joyfully p) if powered with more than 4V ..... better to check first the module type .....

The idea of putting extra capacitors is good too ..... you can be abundant there, nothing bad in adding filters caps ..... 330 or 470 uF plus 100nF is good for all

Also the idea to pull up the positive side of R6 in the laserov schematic is not bad, if you want to have a positive modulation without use an extra transistor, only check that your 5V output can give the needed current (that is not too much high, anyway)

If you set these things up properly, higher supply voltage will not do any harm... at leat to the point where the output transistor cannot handle the dissipation anymore.

As for postitive modulation by yanking R6 high, that works with most drivers. I usually opt from somewhat larger resistors, such as 22 or 33k in series with a 10k resistor, and 2 1n4148 diodes over the 10k te provide a hard upper limit regrardless of drive voltage.

Several similar topologies are used in simple laser pointers like those sold on DX and the like, but they are often ineffective because supply voltage from 2 AAA cells falls way short of the required 3.0 volts for the lm358 under any kind of load.

Are they any to add a TTL to a driver so i can use it with mach3