Need a low side LED driver IC - Page 1
Forum section: electronics / projects

author: John B
author_rank: Frequent Contributor
timestamp: September 30, 2020, 07:27:59 am
content: I have to power a load of LED panels with a dual colour temp arrangement, where there's a common anode and two cathodes. That rules out using the high side drivers I know. Does anyone have a recommendation for a basic low side driver? The specs would include:Analogue dimming inputi2c dimming could also be an optionExternal switch is OK, maybe even preferablePanel is supplied with around ~36V (maybe bumped to 38V or so for headroom), max differential across the LED panel would be 35VDriver IC can have separate and lower VccGeneral basic overvoltage and overcurrent protectionSwitching frequency around 50-100kHz

author: ebclr
author_rank: Super Contributor
timestamp: September 30, 2020, 08:52:08 am
content: https://www.analog.com/en/technical-articles/accurate-pwm-led-dimming.html

author: opampsmoker
author_rank: Regular Contributor
timestamp: September 30, 2020, 01:51:29 pm
content: HV9910B is one of my favorites. You can add an external opamp error amp. Plus add OV protection if its not a buck.LM3423 is a well known one.Linear.com (now analog) , as above by ebclr are the best but pricey.

author: Benta
author_rank: Super Contributor
timestamp: September 30, 2020, 05:54:47 pm
content: Check Toshiba. They have a large portfolio of LED drivers:https://toshiba.semicon-storage.com/ap-en/semiconductor/product/power-management-ics/led-driver-ics.html

author: radzimir
author_rank: Newbie
timestamp: September 30, 2020, 08:23:56 pm
content: Hi,Funny accident, but I'm facing currently the same problem with very similar LED panel.All the LT37* ICs form analog (LT3761, LT3755-2, LT3756-2) and LM342x from TI requires high-side current sensing, that is impossible with common anode.LM342x seams to be possible choice, but.... in my case I don't want to build the whole SMPS from scratch.Additionally, my panel is actually an array of 36 parallel strains with 12 LEDs in each one, it means current limiting can't work at all, so why bother using complex solutions designed for one strain.I overloaded it with my bench power supply up to 40V, there were no sins of spontaneous rise of the current. I assume, one can drive it safely with 36V voltage source.I'm going to apply low profile MeanWell LRS-150-36 as voltage source and for dimming a sink current controller presented by Dave in "EEVblog #102 - DIY Constant Current Dummy Load for Power Supply and Battery Testing".Power loss on MOSFET will be maximal for dimming by 2V, but only at about 1.3W, only 5% of power consumed. I can live with that.I intend to use ESP32 with IRLZ44 and LM358.One LRS-150-36 can power at least 3 panels. Cheapest are on mouser.com if you buy at least 3.If 3 panels are placed in one room, my material cost per panel may be even under 10€.I appreciate in advance any negative feedback :-)

author: John B
author_rank: Frequent Contributor
timestamp: September 30, 2020, 11:48:14 pm
content: Thanks for the suggestions. The HV9910B looks like a good candidate and they're fairly cheap too. The datasheet recommends a gate charge of less than 25nC for the external FET, so I might opt for something like the IRFZ34N rather than the usual IRFZ44N. Even then the IRFZ34N has a total gate charge of 34nC. Maybe something like the IRF520 would work better.So far I've been trying to avoid the PWM dimming input available on most controllers, because my understanding is that it will cause the output current waveform to cycle between 0mA and the set current limit. Or roughly so, since the inductor current will decay to zero in most applications with typical inductor values and the PWM input frequency being low compared to the IC switching frequency.Due to the nature of the application, I want to keep the output current as DC as possible. I'm aware that there may be a colour temp shift in the LEDs with lower current (with DC only), but I've never found that to be an issue. Plus I tested these panels with my bench supply and they look good at any current. They have a CRI of >90.I could still potentially use the PWM input if I brute force the output with a larger inductor, plus large amounts of capacitance.

author: opampsmoker
author_rank: Regular Contributor
timestamp: October 01, 2020, 12:44:38 pm
content: yes PWM dimming is often used instead of analog because its easy to get a pwm dimming signal out of a micro...most uC based dimmers for analog dimming just filter a micro's pwm output anyway, to give the analog dimming voltage....so may as well just pop the pwm straight into the driver.But yes, PWM dimming is ON/off....PWM dimming comes into its own when you need really low llight levels and you cant really get there with analog dimming.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 01, 2020, 04:03:50 pm
content: Have you only considered FET's in TO220?Why?If I interpret the string: 8/29/95 from:https://pdf1.alldatasheet.com/datasheet-pdf/view/68616/IRF/IRFZ34N.htmlcorrect, then it's a 25 year old datasheet / FET.More modern fets have smaller gate charges, which means faster switching which results in less dissipation. TO220 is mostly useful if you need the power dissipation. SMT FET's can go upto 300A these days and Rds-on of less than a milli ohm.Just now I have a datasheet of the STD20FN06 open.Datasheet is from 2007, so this is also an old FET.It's an SMT DPAK, and further:60V 40mOhm, 24Aand for gate chages:31nC "(Max) total gate charge" (23nC typical)5nC "Gate-source charge"7.5nC "Gate-Drain charge"This seems to be a common FET, which probably means low price. But it's likely there are better candidate's around.