I've been trying to troubleshoot this for a while, but I think it's time to get some second opinions. Any ideas what might be the problem?
What country has a black flag ie your flag ? I think this is the first one I have seen. If a forum glitch maybe someone can fix it or maybe you could try reload the image (unless it really is black). Or maybe a black flag has a meaning I do not know, then my stupid.
it isn't holding at ~4V, but dropping to 3.6V. My reading of the various tutorials and descriptions suggest that once you meet the minimum regulation current (10mA) it should be pretty solid.
Where are you measuring this? Try and measure right at the regulators output terminal not at the load, that way you can eliminate resistance between the output and the load as a cause. ... What is the timebase set at on that scope mS or seconds?
I'm using an LM317 to regulate a 12VDC input down to the ~3.9V required to emulate the camera's original battery.
I just tested 2 x 2200uF caps in parallel on the output to try and deal with any sudden current spikes - it doesn't seem to have made much difference, unfortunately.
Is it normal to expect the voltage to drop from the compensated* target output voltage when ANY load is applied?
* I mean compensated for the drop caused by the current sink resistor + LED that I added to ensure I'm meeting the minimum regulation current requirement.
Are those carbon composition resistors?
Quote from: AcHmed99 on Today at 09:32:46 AM
Where are you measuring this? Try and measure right at the regulators output terminal not at the load, that way you can eliminate resistance between the output and the load as a cause. ... What is the timebase set at on that scope mS or seconds?
Answer to these questions, please.
Quote from: NotionalLabs on Today at 12:25:40 AM
I'm using an LM317 to regulate a 12VDC input down to the ~3.9V required to emulate the camera's original battery.
Can you confirm precisely which LM317 variant you're using? Manufacturer and P/N? If I trust your single-shots, the 2nd plot suggests you're using a IOmax=500mA variant, whereas your application requires more current. This is my initial suspicion and I wouldn't bother pressing forward until this has been validated.
Quote from: NotionalLabs on Today at 07:17:15 AM
I just tested 2 x 2200uF caps in parallel on the output to try and deal with any sudden current spikes - it doesn't seem to have made much difference, unfortunately.
If part of the problem is in fact a consequence of insufficient decoupling, then it's not so much the size of the cap that matters, but it's equivalent series resistance spec. Unfortunately, aluminum electrolytics (like the one used in your pic) are good for cheap low frequency bulk decoupling, but are ineffective for fast transients (apologies for the handwavy explanation). Tantalum (for large values) and ceramic (for smaller values) are best suited for this.
Other than that, mikerj's comment on breadboard contact resistance and high current, and mariush's on linear regulators and heat dissipation are important and need to be kept in mind.
P.S.
With R1=120R, R2=270R, and without LED, you're pretty much at threshold for min. load current to maintain stability. If you want to remove the LED to allow for more current to the real load, try R1=100R and R2=220R. That should give you 12.5mA load @ 4V output.
Quote from: bson on Today at 09:46:30 AM
Are those carbon composition resistors?
They look like standard carbon film.
The output voltage is still all over the place. You have a variation of more than 500 mV. Normally the LM317 can regulate its output within a few mVolts.
Sorry, but even if the camera works now, I don't see the problem as solved.
The output voltage is still all over the place. You have a variation of more than 500 mV. Normally the LM317 can regulate its output within a few mVolts.
Something is horribly wrong here. Are you sure your 12 Volt power supply is up to the task? Do the same test as before but plot the 12 Volt input instead. Maybe it is because the input is drooping and causes the LM317 to go out of regulation.
What is providing 12V DC input power? Input current may be inadequate.
an old 12VDC 2000mA adapter from an old router or something
Don't forget it's still on a breadboard. Clearly a better version than the original, but that's exactly the kind of performance issue I would expect from a breadboard, especially since the output wires are a long way from the regulator itself.
I'm going to work it up on a protoboard when I get a moment, but to help aid my understanding could you explain why the distance of the load affects the regulator's performance?
I'm going to work it up on a protoboard when I get a moment, but to help aid my understanding could you explain why the distance of the load affects the regulator's performance?Because the additional wiring (and especially breadboard traces) between the LM317 output pin and the load +ve, and between the load 0v and the bottom of the lower LM317 adjustment resistor introduce a load dependant voltage drop that the regulator can not compensate for. Try connecting your meter directly to the LM317T output pin and the bottom of the lower voltage adjust resistor (ground side of R1 in the schematic below). If the regulation looks much better at these points, you know the breadboard and wiring is the problem.
What I suspect is that the input actually droops a lot more than that, but your meter isn't fast enough to record it.
Instead of that wall wart, supply your circuit with 12 Volts from a computer PSU, or a lead-acid battery (car battery or UPS battery) so you'll be sure that the input is not drooping, no matter what.