ir2110 low side problems, VCC and LO short - Page 1
Forum section: electronics / projects

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 05:19:44 am
content: i am trying to make bldc motor drive with charge pump. i have designed a circuit and have made it on a vero board, the problem that i am facing is that sometimes during testing, any one of the bridges' low side will turn on, and upon inspection see that vcc and lo are shorted,did anybody else have ever faced this problem?the motor right now is 24 volts, but it could go up, in voltage, switching frequency is 2 khz.attached is the schematic of one of the halfbridge.any help would be appreciated. i have blown around 8 ir2110s....P.S. flyback diodes, which ones should i use, ryt now i have used 1n5822, but these have blown too before.P.P.S dead time is around 500ns. (through software)

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 31, 2014, 05:43:27 am
content: AamirI can't give you a definative answer but I have noticed a couple of things that need attention.1. I don't see a good high frequency bypass cap across the 48VDC rail right at the MOSFET's.2. I see D4 is a normal mains rectifier diode. It should be a fast recovery such as UF4007 or similar. Even though the operating frequency is only 2khz the turn on and off edges will have rise times of around 50ns. This means that the diode capacitance has a huge effect on the charge pump performance.3. Veroboard is not the correct type of proto board to be using for this application. You need something with a ground plane that you tie all the ground connections to. Also, try to minimise the lead lengths between the source of the lower MOSFET, the bypass cap negative, the IR2110 ground pin, the IR2110 supply bypass cap and the control IC ground pin. The problem with high speed high current switching is that even a small series inductance can cause an appreciable voltage across it. ie V=Ldi/dt. The groundplane acts as a low inductance equipotential surface.Good luckDick

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 05:52:54 am
content: Quote from: Richard Head on March 31, 2014, 05:43:27 amthanks for replying, really appreciate it.will change D4,will add caps, btw how does one select a cap?cant do anything about the veroboard man, these are the only resources i got. however the entire circuit is outlined by a think ground solder connection.could LO be getting damaged because it has to source a high current? or sink it? should i limit it by increasing the gate resistance?

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 06:33:25 am
content: Quote from: AhhhChoo on March 31, 2014, 06:15:33 amso what i understand here is that you are saying that the damage to the ic is due to the transients, that will be eliminated with proper layout? PCBs take time man, i have to be absolutely sure before i make one.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 31, 2014, 07:14:57 am
content: AamirI would use a couple of low ESR 105 deg. C paralleled electrolytic capacitors across the 48V rail. They should be located as close as practical to the MOSFETS. You could also parallel them with a small value (1uF) film cap that has a high-ish self resonant frequency.I would suggest rebuilding the control electronics on a proper piece of proto board with a ground plane before you go mad.Also, why did you use optos to drive the IR2110 when the grounds are the same? Optos are generally very slow and that is the last thing you need when you need to switch off a MOSFET during a short circuit condition.

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 07:43:33 am
content: Quote from: Richard Head on March 31, 2014, 07:14:57 ami have gone mad, destroying one ic after another,i used opto to isolate mc from ir2110, these one work fine till 20k, and umm, grounds have to be same, dont they?12 volt supply and 5 volt supply both use their respective versions of LM2576, to which the input voltage is main supply...

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 31, 2014, 08:08:27 am
content: could LO be getting damaged because it has to source a high current? or sink it? should i limit it by increasing the gate resistance?I'm not sure why the LO output is failing but if you have a poor ground ANYTHING can happen.If the IR2110 ground is not directly connected to the lower MOSFET ground then the ground bounce could be enough to damage the IR2110. Try to aim for a lead length between the driver ground and the lower MOSFET source lead of less than about 30mm total.Get rid of the optos if you don't need them.

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 09:37:31 am
content: Quote from: Richard Head on March 31, 2014, 08:08:27 amthanks for the help man, really appreciate it.btw flyback diodes.. which ones should i use?

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 31, 2014, 09:59:37 am
content: AamirWhat flyback didoes are you refering to? I can't see any on the schematic or am I missing something?1N5822 is a Shottky diode. Although their forward voltage drop is low and quite often suitable I have found that their reverse capacitance is so high that the ringing becomes uncontrollable.I tend to use low voltage (+/- 200V) fast recovery diodes due to their much lower capacitance.Is this a 3-phase motor controller? It looks like it.Dick

author: diyaudio
author_rank: Frequent Contributor
timestamp: March 31, 2014, 10:17:04 am
content: Quote from: aamir on March 31, 2014, 05:19:44 amQuoteOuch thats alot.How did you realize the value of C2 as 100nf? the bootstrap cap needs to be enough to charge Q1. 100nf cannot supply sufficient charge to the gate of Q1. use a 22uf or so. tantalum type recommended.Also use a fast recovery diode as suggested.Shoot through, measure the output(s) timings A and B with a scope and make sure you don't have pulse overlap, you maybe need to add some dead-time use a simple RC constant at the input.Probe the gates, make sure you don't have erratic noise, they should be clean if not its a result of a few things.1) Absence of a drain to source snubber.2) Free-wheel diode to clamp spikes, will help as well.3) Layout, keep the traces connections short around the high current paths and add snubbing.You need to probe "all" the switching nodes, you need to be able read the waveforms it will tell you a story of what's happening . going through "8" ir2110s is not a rational way to problem solve the issue.

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 11:06:32 am
content: Quote from: Richard Head on March 31, 2014, 09:59:37 amyeah i am sorry, i added them latter, i am thinking of replacing the flyback by 1n5408, simply because i have them..in case i do find some fast diodes later, what should be their current rating, should i consider the continuous current or the other one, the Ifsm one?and which diodes do you use? model number?and it is a brushless dc motor controller, quite similar to 3 phase ac motor.

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 11:12:14 am
content: Quote from: diyaudio on March 31, 2014, 10:17:04 amthe bootstrap cap only acts as a storage tank, the 555 timer refreshes the charge for bootstrap cap at 7.5 khz, so this design can work for 100% duty cycle as long as i want it to. no need to switch the low side on,there is no shoot through, 500ns dead time is there.dont have oscilloscope.also didnt knew this was happening just kept changing the ir2110 again and again. (yeah i am quite stupid)drain to source snubber: wouldn't this affect the switching speed?

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 31, 2014, 11:33:23 am
content: AamirI agree with DIYaudio's comments. Snubbers are a must.Also, 1N5408's are just big 1N4007's. They are useless for high frequency operation. You may be able to use PR3007. If a lower voltage is tolerable then a BYV28-200 may be suitable.If this is your first project I think you should have started with something like a PWM controlled DC brushed motor. The 3-phase design multiplies your problems by three!Dick

author: aamir
author_rank: Contributor
timestamp: March 31, 2014, 11:51:02 am
content: Quote from: Richard Head on March 31, 2014, 11:33:23 amhow fast frequency are we talking about here? i am switching it at 2 khz... well lemme see what i can get. i cant get things easily here man..and how should i use snubbers?this is not my first project, but i am quite inexperienced when it comes to circuit design. and yeah, driving bldc is a bitch. it does run though... but then any one low side will blow, and the motor stops.

author: diyaudio
author_rank: Frequent Contributor
timestamp: March 31, 2014, 12:14:50 pm
content: double ouch.You need a scope, you are flying blind anything timing related calls for a scope I suggest you start saving up for one now or burrow one from a good friend. if you serious save up and buy one.Quoteno. that's incorrect. the low side charges the high side the boostrap cap is always charged at Vcc the lower FET will charge the negative plate of the cap, so when Q1 is switched the cap will supply the charge,its essentially floating.Quotedrain to source snubber does not effect switching speed "if" selected correctly its used to tame di/dt parasitics as a result of inductive layout, package parasitics and other layout phenomenon.Quotewith no scope to determine the timings you cannot assume this or even assume the waveforms are shaped correctly.im sorry, but even if you get it to work you still need a scope to verify all switching operations are reliable.

author: ali80
author_rank: Contributor
timestamp: March 31, 2014, 03:57:35 pm
content: i dont agree that a snubber is a must, especially for low power drives, but as others mentioned a scope or maybe a logic analyser is a must and the charge pump capacitor only charges when the low side switch is turned on.

author: Niklas
author_rank: Frequent Contributor
timestamp: March 31, 2014, 11:05:09 pm
content: 1. Check the datasheet for the optocouplers, specifically the part with response time. Then compare the values for rise and fall time with the dead time mentioned in the first post.Do you really need the optocouplers? If yes, can you move them somewhere else in the circuit where the timing is not as critical?2. Skip the charger pump. Replace D2 with a Schottky diode. Add capacitors similar to C3 and C4 to pin 3 Vcc.3. Check the routing between the driver IC and the MOSFETs. Pin 5 Vss and pin 2 COM should be tied with short traces to the Source pins of the corresponding MOSFET. Perhaps also add 10k resistors between Gate and Source on the MOSFETs to bleed out stray charges and keep the MOSFETs off if the IR2110 is disabled.

author: aamir
author_rank: Contributor
timestamp: April 01, 2014, 04:42:44 am
content: Quote from: Niklas on March 31, 2014, 11:05:09 pmthank you all for replying,the optocoupler i am using is 817c. a similar device to is 817p from vishay, and according to them, it takes 10us for it to turn offhttp://www.vishay.com/docs/83522/k817p.pdfpage 4, test bench is almost same as my circuit.what should i do new? change the opto coupler?remove it?use a buffer?

author: Niklas
author_rank: Frequent Contributor
timestamp: April 01, 2014, 05:44:56 am
content: Quote from: aamir on April 01, 2014, 04:42:44 amIn the original posting you wrote that the dead time was 0.5 us, which is obviously too short given the 10 us turn off time. The result is that both MOSFETs could be conducting at the same time, which is not good for their health. Most failed MOSFETs I have encountered had short circuit between all three pins. That could cause the IR2110's output driver to fail as it can appear as a short to GND or to 12 V.I would have had a look at the complete schematics and see if the optical isolation could be placed somewhere else instead. In speed controllers for electrical motors in radio controlled model aircraft the optocoupler is placed on the control signal from the receiver. Connect the microcontroller directly to the HIN and LIN signals on the IR2110.That 10 us turn off time is probably also dependent on a lot of parameters, such as: individual IC, temperature, LED current, aging, the circuitry itself etc. That said, just changing the software to handle a longer dead time, is not a good option as this problem can occur again later.

author: aamir
author_rank: Contributor
timestamp: April 01, 2014, 06:09:19 am
content: Quote from: Niklas on April 01, 2014, 05:44:56 amso how should i introduce the dead time than? change the driver ic, with built in hardware dead time?also gonna try by removing the optocoupler, i am thinking abut pulling down the lin and hin too, just for now, or should i rely on the internal pulldown resistors?

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 01, 2014, 06:18:42 am
content: AamirYou have to have a scope to do this kind of work.

author: aamir
author_rank: Contributor
timestamp: April 01, 2014, 07:37:30 am
content: Quote from: Richard Head on April 01, 2014, 06:18:42 ami know man, i am all about timings and waveforms. i used to work on FPGA so this kind of work is so frustrating.

author: Niklas
author_rank: Frequent Contributor
timestamp: April 01, 2014, 09:08:38 am
content: With the IR2110 you will need some dead time control in your software/ PWM peripheral anyway. The problem is that this timing is dependent on several parameters, just like the optocoupler.There are half bridge MOSFET drivers available with internal comparators for adaptive shot-through protection. Basically they check the gate voltage levels to see if they are below a threshold before enabling the outputs. LTC4444 is one example.

author: aamir
author_rank: Contributor
timestamp: April 01, 2014, 09:25:42 am
content: Quote from: Niklas on April 01, 2014, 09:08:38 ami know about them, the only one i could find in me country was ir2104, but the problem with them is that one side is always on or you need to use the enable pin to tun both sides off, i needed independent control of all 6 pins, for rapid switching.i dont know about LTC4444,

author: aamir
author_rank: Contributor
timestamp: April 01, 2014, 09:27:31 am
content: the place i am working for have gotten a external drive from the same vendor they got their motors from. What a waste of time

author: eneuro
author_rank: Super Contributor
timestamp: April 01, 2014, 09:57:23 am
content: Quote from: Richard Head on March 31, 2014, 07:14:57 amThis PC817 used here has cut-of 80kHz only and additionaly this 1k resistor at its inputs gives maybe too small current (about 4mA @ 5V, 11mA @ 12V while voltage drop is about 1.2V in PC817 input diode), so maybe those delays in software misses optoisolators switching to level that Schmitts at IR2110 input HIn & LIN goes High/Low and this way gives not expected switching speeds even at 2kHz.There are many fast optoisolators with Schmitt trigered ouputs like 6N137, but they need correct input current.

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 01, 2014, 12:29:18 pm
content: Under short circuit conditions and a high switching frequency you may need to switch off the MOSFET in 100-200ns which I don't think any optos can achieve. On the larger lower frequency converters maybe one can get away with fast optos. I normally steer clear of them due to speed limitations. If you use a small transformer 200ns in no problem at all, and they transfer power as well which can be a help.

author: eneuro
author_rank: Super Contributor
timestamp: April 01, 2014, 03:55:22 pm
content: Quote from: Richard Head on April 01, 2014, 12:29:18 pmLooking into datasheet ot fast optoisolator 6N137 we get its tdelay time <100ns.For 1k load its @ 5V 10mA IF we get delay time <50ns.TC4426 gate driver has typical delay time 40ns, so we are <200ns in theory.In practice did not tested 6N137 & TC4426 as optoisolated gate driver yet, but datasheets looks good and I will do it as soon as those new elements are shipped to me

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 02, 2014, 05:58:55 am
content: eneuroThose optos are certainly faster than I expected. I think it may be worth a try.I still don't know why an opto should be required as the micro and driver share the same gnd.

author: eneuro
author_rank: Super Contributor
timestamp: April 02, 2014, 07:55:05 am
content: Quote from: Richard Head on April 02, 2014, 05:58:55 amThey are also not too expensive.I'd like to use them with TC4426 drivers in half bridges with galvanic isolated gate power supplies 15V to drive BLDC or 230VAC AC motors.Below is my optoisolated gate driver circuit under tests-logic connections simulated in software based on its truth tables looks good.I'd like to add there also detection of conducting mosfets using another one 6N137 to have feedback when turning ON/OFF each half bridge side and this will be done in a way similar to fault (desaturation) detection in some optoisolated gate drivers like HCPL316J.I've skipped from IR2110 gate driver while need for this boost voltage for high side is a little bit tricky and sometimes may be problematic, so decided to do it maybe not the chippest way, but while PCB size is not my concern, make it as reliable as possible with additional isolated power supply for gate drivers.

author: aamir
author_rank: Contributor
timestamp: April 07, 2014, 09:40:45 am
content: so a little updateremoved them opto couplers, added 10uf tantalum on all 3 supplies, increased the dead time to 2 us,and so far the ir2110s are fine....however, during operation, my controller resets, i am thinking of adding 6n137 to isolate the controller, should i use a different supply for controller? isolate them grounds?

author: aamir
author_rank: Contributor
timestamp: June 06, 2014, 04:25:54 am
content: So another update.i went on and isolated the signals using 817c and 2630(dual version of 6n137) and it worked fine, operated it at 48 volt and it also worked fine, however another problem that i faced was the the capacitor recharge frequency from 555 did not increase from 2.5k, as a consequence my switching frequency was limited to 2.5k.