Limpkin's blog - Tag - boost<div>An electronics geek blog, dedicated to sharing and open source. Check out my stores: <a href="https://lectronz.com/stores/stephanelec" hreflang="en" title="Lectronz store">EU</a> / <a href="https://www.tindie.com/stores/stephanelec" hreflang="en" title="tindie store">EU & US</a>.</div>2024-03-27T19:19:38+00:00Mathieuurn:md5:51de6a3d917257edeff5a252fe925b02DotclearCurrent controlled boost LED driver and black soldermasksurn:md5:cc9f9a12b8a91a3a167556ab468a87352012-08-12T19:37:00+01:002023-04-14T13:52:18+01:00limpkinMy Projectsboostledpcb<p>Ok I agree, the two are not connected :-) ...<br /></p>
<p><img src="https://www.limpkin.fr/public/max16834/.MAX16834_PCB_m.jpg" alt="MAX16834_PCB.JPG" style="display:table; margin:0 auto;" title="MAX16834_PCB.JPG, août 2012" /></p> <p>Unfortunately I can't reveal the schematics and production files this time :-( , as this board is some contractor work I've done for a company and also because it <strong>wouldn't be much use to you</strong> (it highly depends on your LED power requirements).<br />
<strong>However</strong> I can tell you all you need to know to design your own LED driver based on the <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/5876" hreflang="en" title="MAX16834">MAX16834</a> and also give you the design spreadsheets <strong>that are quite long to get</strong>.<br /><br /></p>
<h2>The theory<br /><br /></h2>
<p>First, if you don't already know it, a LED's brightness is controlled by the <strong>current</strong> going through it.<br />
I know you're gonna tell me that voltage and current are related to each other, and you'd <strong>be right</strong> to do so. However, a LED intensity/voltage curve can <strong>be non linear</strong> and therefore better brightness adjustment can only be done by <strong>current control</strong>.<br />
There are several ways to do current control and I'm not going to detail them here. The main difference between them is their <strong>efficiency</strong>.<br />
For example, using a simple transistor is highly inefficient as it will dissipate the heat caused by the voltage drop * current going through it. Not important if you're driving a few LEDs, but <strong>very</strong> if you're driving 60W of LEDs.<br />
Therefore, you need some way to adjust your LED string voltage <strong>depending on the current going through it</strong> in an highly efficient way.<br />
That's just what a design based on a <a href="http://en.wikipedia.org/wiki/Boost_converter" hreflang="en" title="Boost converter">Boost converter</a> does:<br /><br /></p>
<h2>The MAX16834<br /><br /></h2>
<p><a href="https://www.limpkin.fr/public/max16834/MAX16834_schem_ex.png" title="Boost LED driver based on the MAX16834"><img src="https://www.limpkin.fr/public/max16834/.MAX16834_schem_ex_m.jpg" alt="MAX16834_schem_ex.png" style="display:table; margin:0 auto;" title="MAX16834_schem_ex.png, août 2012" /></a><br />
The MAX16834 is a neat little chip (it's not the only one, there are plenty of others out there) that allows high efficiency designs for LED string driving.<br />
It provides a platform for a Buck or Boost converter design, as well as <strong>brightness adjustment</strong> via analog/<strong>PWM</strong> input pins, as well as a <strong>fault output</strong> (in case of open/short circuits for example) and also diverse other functionalities that can be quite useful.<br />
Using a resistor in series with your LED string, it will <strong>sense the current</strong> going through it and adapt the LED string voltage accordingly.<br /><br /></p>
<h2>What you need to take care of<br /><br /></h2>
<p><a href="https://www.limpkin.fr/public/max16834/P1030004.JPG" title="PCB for a MAX16834 design"><img src="https://www.limpkin.fr/public/max16834/.P1030004_m.jpg" alt="P1030004.JPG" style="display:table; margin:0 auto;" title="P1030004.JPG, août 2012" /></a><br />
As my main goal is not to promote Maxim-ic components (even if you can get samples quite easily!), I'm gonna write a few advices for the design of this kind of electronics:<br />
- be aware of the <strong>minimum required traces widths</strong>, which depend on the current going through them (duh...). You'll find <a href="http://www.desmith.net/NMdS/Electronics/TraceWidth.html" hreflang="en" title="Trace width calculators">a</a> <a href="http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/" hreflang="en" title="Trace width calculator">few</a> <a href="http://www.armisteadtechnologies.com/trace.shtml" hreflang="en" title="Trace width calculator">calculators</a> on the internet for it.<br />
- create <strong>large copper areas</strong> on the top and bottom layers around the components that generate heat. Connect the two planes with a lot of vias (but not too many, that would compromise the PCB strength). Obviously, this advice is only valid if you use SMD components, which use the PCB <strong>as their heatsinks</strong>. The hot components are the 2 mosfets, the coil and diode<br />
- if you're powering other circuits with the same power supply, be aware of the <strong>voltage ripple this circuit will introduce.</strong> This is caused by the boost switching frequency as well as the PWM's.<br />
- get some <strong>cheap IR thermometer</strong> from ebay, that will allow you to check that all the temps are within the chips working range<br />
- be aware that PCB temperature can <strong>affect components' characteristics</strong> (such as oscillators)<br />
- with a scope, <strong>look how long it takes for the MAX16834 to attain stable current regulation</strong> by measuring rsense voltage. This will give you the maximum PWM frequency.<br />
- directly measure the voltages with your oscilloscope probe. Don't forget that if you add wires for measurement, they will <strong>act as inductors</strong>, which is very annoying for <strong>fast rising signals</strong> such as the mosfet gate control.<br />
- don't forget the MAX16834 heatpad (woups :-D ).<br />
- protect your voltage input for transients with a TVS diode<br />
- if you need an advanced input protection (such as reverse polarity protection), look at the <a href="http://www.linear.com/product/LTC4365" hreflang="en" title="LTC4365">LTC4365</a><br /><br /></p>
<h2>The design spreadsheets & the final result<br /><br /></h2>
<p><a href="https://www.limpkin.fr/public/max16834/LED_PS.png" title="LED_PS.png"><img src="https://www.limpkin.fr/public/max16834/.LED_PS_m.jpg" alt="LED_PS.png" style="display:table; margin:0 auto;" title="LED_PS.png, août 2012" /></a><br />
Here are two design spreadsheets (<a href="https://www.limpkin.fr/public/max16834/MAX16834_CCM_Boost_LED_driver_V1.xls">here</a> and <a href="https://www.limpkin.fr/public/max16834/MAX16834_BOOST_DCM_updated.xmcd">here</a>) that I managed to obtain from Maxim. I personally used the excel sheet, as it seems it was the one used for the application notes.<br />
For your information, I didn't have any bad surprises when assembling my first prototypes.<br />
The black solder mask was just for fun... it feels like it is <strong>thicker</strong> than the conventional one, which makes the assembly process a bit trickier :-) .<br />
It also hides all the PCB traces, so I would only recommend it once you are sure that your schematics are ok.<br />
That's all for now! Not a lot of advanced information in this post, but at least I hope it gave you some ideas ;-) .</p>