Seems you ignore me, but..
I used the LM324, which while it could source some considerable current, it can only sink a few tens of microamps!!!
Certainly not true, you were doing something wrong. It will sink as much as it can source, enough for this application. The LM324 has different problems with its output stage (significant crossover distortion, being one of them).
Not at all ignoring you! I think I quoted your entire last response with my last response.
Don't believe me, go take a look at the datasheet yourself! I was in just as much disbelief as you originally. Literally jaw dropped!
Could it be possible I am looking at the wrong rating?? It's called "output current" I
O and is split into 2 sections, Source and Sink. I can't imagine what else it might be referring to.
The datasheet specifies the LM324 being capable of
sourcing a minimum figure of 20mA max with a typical figure of 40mA max, but
sinking as little as 12 microamps (50uA typ)!!! Pathetic!
The LM358 is better in this regard, but even it can only sink half the current it can source. It's singing capability is rated at 5mA over the full temperature range, with a typical optimistic figure of 20mA at 25
oC I was able to sink 1mA with my LM324's, but that is well outside of it's limit and explains why my real circuit had trouble when I tried to set the current source higher than a few mA's especially when trying to get near 0V output.
My original design used LM324's, and without those current sinks, I could set the current source so I either had a supply that could provide a stable output voltage down to zero volts but with very little (less than 1A) current capability OR I had a supply which could deliver as much as 3A (maybe more if I had a power supply that could power it better) but incapable of outputting less than 4V! Or something like that, I don't remember anymore. This was mostly fixed by adding those current sources.
I could also replace the schottky diodes with PNP emitter followers but these don't work down below 0.6V above the 1(ish)V minimum output of the op amp, leading to about 1(ish)V minimum output. Then again neither to these current sources so I guess the point is kinda moot, so oh well. Whatever!
I don't suspect they are hurting anything having them there. Do you? If so please to tell me if there is a reason to remove them. As I might not even bother populating them after ordering a PCB.
[url]http://www.ti.com/lit/ds/symlink/lm2902-n.pdf]http://www.ti.com/lit/ds/symlink/lm2902-n.pdf]
[url]http://www.ti.com/lit/ds/symlink/lm2902-n.pdf[/url]
[url]http://www.ti.com/lit/ds/symlink/lm358.pdf]http://www.ti.com/lit/ds/symlink/lm358.pdf]
[url]http://www.ti.com/lit/ds/symlink/lm358.pdf[/url]
Lamp is not suitable for pulse load. Use resistors as load. The lamp/bulb is nonlinear load with current changing both in time and nonlinearly with voltage.
"which draws like 250mA and considerably more when cold" - thats exactly why its useless as a test load. You need a nice square current pulses. Build yourself a pulse load, just 555 + suitable NMOS and a bunch of resistors.
I also used 4 82 ohm resistor to make a 1W 82 ohm resistor as a pulse load when I had the supply set to 15V output. Even used a 2W 5 ohm resistor to draw a "clean" 3A (compared to a large drill motor) and yes, I know I was WAY over pushing it at 15V, don't bother telling me!
I pulsed it (plugging it in and out) for less than a second at a time and it heated up nicely too!