TITLE CHANGED, Multi LM317 current syncs..

[rwgast_lowlevellogicdesin]

EDIT: I kind of steered this topic away from the original question in this post, did not want to start a new thread.

So I know you can use PWM to drive the voltage setting of an LM317, but I would like to control it digitally as a constant current source. No digital pots are capable of dissipating two or three watts across the 1.2v on the ADJ and OUT pin. Is there maybe another way to accomplish this?

[rwgast_lowlevellogicdesin]

Ok well this is  a bit off the main topic but I did not want to start a new thread. Basically I have been working on a solder station, for 24v Hakko Irons. I've been basically just using scrapped parts to keep the cost to almost free. The iron handles are 24v 50W so I found two transformers one labeled 60W 24v and the other is about the same size and also 24W.

Now I wanted to test the load on these transformers and find out how well, and cool they handle at 50watts of output. This is why I started using the lm317s I had laying around as a dummy load.

I took two lm317s, and threw wired them both up with 5watt 1.2ohm resistors as current syncs. This way each one would draw one amp. I kind of want to build daves dummy current load for a fine 0 to 1 amp load, and then use a bunch of lm317s to add one amp at a time to the fine adjustment. Well here is the problem with 1 lm317 connected I would draw the expected 1 amp of current, then I hooked up an identical LM317 to the output of the transformer in parallel, but I did not get two amps!! I ended up drawing 3 to 4 amps of current. What is going on here?? Two one amp loads in parallel should draw 2 amps from the voltage supply not 4??!! Wondering if it was a heat issue I stuck the whole device in the freezer for 30 mins then turned it on, still drew 3 to 4 amps! Even more strange when I swapped transformers the circuit drew 4 to 4.5 amps!!!!

[rwgast_lowlevellogicdesin]

Nevermind this was a wiring error, I missed. Cant delete topics