I've bought a 10-pack of AMC7140 LED drivers to make some high power LED lamps. This regulator was recommended here on the forum a few times, e.g. by DrAzzy and Wawa. So I hope people who have used it already can answer a few questions about it. As usual, I talk too much, so this post is long. I've marked my questions in bold so that other parts may be skipped
This device comes from a Chinese company and unfortunately the datasheet is no on the same level as most other datasheets I've seen. It doesn't even have a functional block diagram of the device, but I assume it's a linear regulator as there is no external inductor which a buck converter would have.
The first page of the datasheet contains a circuit diagram with an output capacitor, however there is no mention of this capacitor (type and value) anywhere else in the document. Other circuit diagrams don't have it either. I was wondering how necessary it is, and what function does it have. A picture of the circuit is attached.
In the datasheet for AMC7135, they do describe the output capacitor, which can be omitted in some cases (depending on lengths of PCB traces/wiring). "Typically, capacitance of 0.1uF ~ 1uF is recommended and 1uF is needed when L2 is much longer than 3cm."
Can I apply the same reasoning to AMC7140? Would I use the same capacitance value recommendations, or would AMC7140 need a larger capacitor?
The device can be dimmed in two ways, either by adjusting the current setting resistor, or by PWM control of the Enable pin.
In the first case, a potentiometer Rset1 can be wired in series with a fixed resistor Rset2 (880 Ohm in a diagram in the datasheet). If a 10K pot is used, the minimum current will be Iout=500Iset=5001.2V/Rset=500*1.2/(880+10000)~=55mA. Max current (@Rset=880) is 682mA.
The datasheet doesn't provide details regarding PWM control of the Enable input. To avoid LED flickering, which can be a problem around machine tools (a "strobe light" effect is highly undesirable) or for photo/video shooting, so it's probably best to use a relatively high PWM frequency. What is the highest (recommended) PWM frequency that AMC7140 can handle?
I will next describe my particular current project in a separate message, if that's interesting to anyone.