Monday, March 16, 2015

LED Driver Boost Converter

So, it's time for an update on the LED driver I'm designing.  I think I have the final design of the circuit and have most of the components selected.  I haven't bothered selecting actual parts for non critical components yet.  The design is mostly locked in, a value may change here or there but it's pretty much final.  The input filter added to remove conducted EMI may need some improvement as there may be the possibility of ringing.

I'll admit that this has taken longer than I would have liked, but I took it as an opportunity to learn how all the components of a boost converter interact and change the overall operation.  I didn't want to blindly follow a reference design and not know what I was doing.  I still have a lot to learn, particularly about compensation and stability, but it's been fun.

Boost Converter LED Driver - with PWM and Analog Dimming

The plot below shows the circuit starting up.  The PWM dimming function is in use with the frequency being swept from 0 to 3kHz.  The output slew rate limiting circuit does its job and brings the output voltage up gradually without causing too much current to flow through the main inductor.

LED Driver Sweeping the PWM Frequency from 0 to 3 kHz over 60 ms

In the plot below you can see a cycle of the converter operating.  The LED currentin dark blue slightly overshoots its target but comes into regulation rather quickly.  The main inductor current is shown in light purple and can be seen to have ripple, but nothing that wasn't anticipated.  The main supply current is shown in dark purple and has no noticeable high frequency component, but there is some ringing,  I don't want that.  So this area needs some attention.  If anyone has experience with this I'd be glad to take suggestions.

I've simulated the snot out of this thing, but that can only get you so far.  So it's time to actually do a board and see what happens.

Main Inductor Current, Supply Current and LED Current

You can grab the associated files from the GitHub Repository

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