DC-DC Converter – 12V to 3.3V Step Down at Low Current

The large inductor value does have some design implications:

1. It's going to make the converter tend to operate in continuous conduction mode, which has loop stability ramifications (you generally need a type-3 compensator with low gain)

2. It's going to affect the transient response of the converter by limiting the current slew rate.

3. Is this inductor intended to carry DC current? Such high values are common for EMI inductors, not output chokes.

If you're experimenting with a reference design, it's always recommended to start with the exact BOM that the manufacturer suggests - at least you get some assurance that the circuit will work to some degree.

Edit #1

Your input is 24V, and when you try and adjust the output higher than 7V, the controller loses regulation. The output is essentially rising up to a voltage just below the input, most likely only limited by the maximum duty cycle supported by the part. This could be for several reasons.

Your voltage feedback should be via a resistor divider from the output to ground, with the midpoint going to pin 11. The converter will regulate the output so that pin 11 is at 5.1V.

Is your clock stable? You should be able to see a clean ramp on the timing capacitor (no jitter).

Is your reference stable? The 5.1V on pin 14 should be rock-solid.

What compensation components do you have from pin 10 to ground? I would suggest removing what's there and replacing it with a fairly large capacitor (1uF ceramic), and try your experiment again. The impedance from pin 10 to ground is your loop compensation, which determines the overall stability of the converter (along with operating frequency, output RC filter and load). Since you have a radically different inductor, you'll probably need to change the compensation for stability.

In principle, what you want to do will work. But as you say, it's a matter of risk and peace of mind. It is possible, though unlikely, that the unit you are considering (and widely available for almost nothing on ebay) could fail in such a way as to deliver a damaging voltage to the camera, which would be expensive to fix.

The main situation to avoid is over voltage. To avoid that you could add a crowbar circuit (see google if interested), but that seems like work.

The other issue is whether or not the camera presents a highly variable load, as Dave suggests. In that case the 3A rating on the ACK-E6 may be an average that doesn't represent the peak required, which the capacitors on your regulator board may not be sufficient to supply.

A possible workaround for both these problems is to take your existing ACK-E6 and interpose a connector between the brick and the "battery" block. Connect the brick for mains power, and instead connect your DC-DC converter (set to 8V I think from the spec) for alternate power. The ACK-E6 spec suggests that there's some active regulation in the "battery" block, and that would help moderate any over-voltage accident, and I would expect provide sufficient capacitance to handle transient demand.

But all of this is somewhat speculative without schematics!