why not LM317 instead of Flexdrive?

[sampson]

GBD

Thanks for the info! Unfortunately I don't have an oscilloscope at home but I do work for a major CPU/GPU manufacturer that has awesome equipment :eg:

I'll take my boards up to work in the next week or so and see how nasty my circuit is. I figured there would be oscillations/ringing so I tried to minimize the possibility by building the circuit compact and keeping leads short. I didn't think much about spikes so I'll definitely be looking for that. As for wrecking the driver circuit.. I stress tested this setup for 96 hours with success using an heatsinked NTE1900 based driver @ 250ma OUT w/ 50% duty cycle.. frequency was only around 100hz though. V+in was 12V driving a 650nm diode so there was a very healthy Vdrop on the NTE1900; temps stayed under 130F w/ ambient at ~76F.

ALSO.. you don't have a resistor between PIN 3 OUT on the 555 to the NPN.. when I tried this I let the smoke out of the 555 and that thing POPPED! Any ideas here or did you forget that R?

Your solution is good and the result on the scope is beautiful.. awesome work. IF my circuit isn't a complete piece of crap I will post it up as it MIGHT be useful.. especially for low frequency situations.

sometoymachine - Yea.. sorry for the threadjack.. I just had a nerdgasm when I saw that PWM enabled driver. :beer:

 

[GBD]

Im glad your driver worked out for you, but geez, sorry about that man, yes there is a 1/4W resistor (I belived I used 100 ohm) between the second 555 to the NPN, I just hastly drew this schematic and forgot to use it

also note, another I think I excluded in the schematics
all the 555s have decoupling capacitors, that is, there is a 100nF (non-polar) capacitor soldered directly on pin 8 and pin 1 (or V+ and GND).

this isnt critical to its function, but helps out against interferance

 

[sampson]

Im glad your driver worked out for you, but geez, sorry about that man, yes there is a 1/4W resistor (I belived I used 100 ohm) between the second 555 to the NPN, I just hastly drew this schematic and forgot to use it

also note, another I think I excluded in the schematics
all the 555s have decoupling capacitors, that is, there is a 100nF (non-polar) capacitor soldered directly on pin 8 and pin 1 (or V+ and GND).

this isnt critical to its function, but helps out against interferance

OK awesome. I used a decoupling capacitor in mine.. but didn't notice it missing in yours. Thanks for the info man!!!

 

[sometoymachine]

Its all good. Once i saw all the foreign language I tuned out anyway

 

[Johnyz]

GBD: Another question about your driver: If i used a N FET, would it be possible to drive it using analog voltages?

 

[GBD]

As long as your drive voltage is enough to charge the gate of your fet, ( whatever the datasheet specifies) it should work fine. but however for larger fets, an amp may be required to meet sufficient gate requirements.

 

[qumefox]

I think he's asking if it can be used for analog modulation. While it would probably work, there are more efficient ways to go about this by manipulating the feedback to the regulator rather than just dumping current to ground.

 

[Johnyz]

qumefox: Exactly. I found some schematics of Die4Drive, Robin was gladly presenting them on PL. I guess I will use these.