advice on blanking circuits......

[monkeypuzzle]

I'm a little lost as to how to blank a laser driver that needs a wire pulling to ground to blank it from an fb3 which will give a +ve to blank.... I'm sure it'll become obvious if someone could point me in the right direction.... I have a good electrical background but my electronics is as rusty as the titanic from my A levels 15 years ago.....

Cheers, Matt.

[stanwax]

Matt
that suggests that its a ttl laser - you will need something between the fb3 to invert the ttl signal, you can do it with a transistor and a couple of resistors or the sledgehammer approach would be to use a ttl inverter chip - cant think what the number is now - but a cmos one is 4069
Rob

ps how did ya get on with the mirrors?

[monkeypuzzle]

thought that migh be the case, got the babani (you remeber them!) books on op amps and basic TTL coming so that should do it... Haven't had a chance to get the mirrors on yet but I'll let you know how it goes when i do......

[stanwax]

bloody hell babani books - what a blast from the past!
Rob

[mixedgas]

I'm a little lost as to how to blank a laser driver that needs a wire pulling to ground to blank it from an fb3 which will give a +ve to blank.... I'm sure it'll become obvious if someone could point me in the right direction.... I have a good electrical background but my electronics is as rusty as the titanic from my A levels 15 years ago.....

Cheers, Matt.

Chinese low cost blanking wants to see a current sink instead of a current source. Since most laser systems output a source, you need to add a simple NPN transistor to ground to "invert" the blanking signal, or use a TTL buffer chip between the laser software and the laser.

For some lasers, a 2n2222 with a 470 ohm base resistor is all you need. Emitter to ground, collector to the laser, base to the laser software via the 470 ohm. In some cases you may need a pullup resistor, perhaps about 1K on the collector to +5. Most lasers have the pull up, and the opamp in the FB3 is not good at fighting them. The FB3 meets the TTL specs, but the Chinese lasers can need more then 20 mA of sink to turn on, which is outside the limits of most opamps.

The Chinese lasers really want to be driven by a TTL totem pole output stage, but only in sink, they do not need the source side, so you need to fake one. Open collector TTL inverters are good for this, as are AC, ACT, HC or HCT series CMOS.

Steve

[monkeypuzzle]

Cheers Steve, I think thats the one.... I'll get a cpc order in and see what happens.