MOSFET gate driver keeps on burning - Page 1
Forum section: electronics / projects

author: kasunch
author_rank: Newbie
timestamp: October 30, 2015, 12:24:17 am
content: Hi all,I have a simple circuit to drive a high power LED with a N-channel MOSFET. The LED is powered with a liner regulator to have constant current supply. As seen in the attached schematic, I am using a gate driver to drive the gate of the MOSFET. However, the gate driver keeps on burning all the time. I could not figure out the reason for this. Any help would be appreciated.DatasheetsFQP50N06 -http://www.farnell.com/datasheets/299068.pdfUCC27524P -http://www.farnell.com/datasheets/1806027.pdfThanks

author: Phoenix
author_rank: Frequent Contributor
timestamp: October 30, 2015, 01:33:00 am
content: Though I can't directly seeing it kill the gate driver... You are turning off a current source by causing an open circuit. This will cause the current source output to shoot up rapidly in voltage.

author: nuno
author_rank: Frequent Contributor
timestamp: October 30, 2015, 01:38:44 am
content: You do have lots of inputs floating...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 30, 2015, 01:39:48 am
content: Quote from: Phoenix on October 30, 2015, 01:33:00 amThat, and no decoupling capacitor and no idea of the layout. Probably some huge oscillation somewhere.Floating inputs are OK as per datasheet, but if there is a huge oscillation somewhere it could be causing false triggering/ground bounciness, itself causing even more oscillation...

author: moffy
author_rank: Super Contributor
timestamp: October 30, 2015, 01:43:52 am
content: Quote from: Phoenix on October 30, 2015, 01:33:00 amI agree. Could be that your 12v supply is having voltage spikes which are killing your driver.

author: kasunch
author_rank: Newbie
timestamp: October 30, 2015, 01:53:14 am
content: Quote from: Alex Eisenhut on October 30, 2015, 01:39:48 amActually, I am just using the application diagram of UCC27524P (Figure 27) with a bench power supply.

author: mij59
author_rank: Frequent Contributor
timestamp: October 30, 2015, 04:53:13 am
content: What are the voltage levels and frequency of the pwm signal ?Check the gate source resistance of Q1.Please describe the "burning" in more detail.Pictures of the actual circuit may be useful.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 30, 2015, 05:00:18 am
content: I suspect that parasitic inductance is causing ringing well above the 20v max for that device. The gate output current is pretty high on that device and you have no bypass caps and presumably a fast-ish rise time on the PWM input. The rail voltage is probably a total mess.Do you have a scope that you can monitor the voltage on pin 6 on the driver? I suspect you may see big voltage swings. Add a bypass cap on the driver and an output cap on the linear reg to start. Also consider a filter cap on the whole circuit.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 30, 2015, 05:03:58 am
content: Quote from: kasunch on October 30, 2015, 01:53:14 amDatasheet circuits are a reference for the important concepts. They tend to leave out many of the assumed parts like filter caps and bypass caps. They are also ideal, not taking parasitic problems into account that will be in the actual physical build.

author: DanielS
author_rank: Frequent Contributor
timestamp: October 30, 2015, 05:22:25 am
content: Decoupling caps for the driver or any other chip that drive high-speed signal edges are definitely a must.Otherwise, wiring inductance might be high enough to drop the driver's voltage below its cut-off and then cause it to oscillate between driving and cutting itself off. You don't power something that drives a 7ns rising edge at 5A with power supply wiring that has 1µH worth of parasitic inductance. You need enough local decoupling to charge the FET's gate.

author: kasunch
author_rank: Newbie
timestamp: October 31, 2015, 12:55:05 pm
content: As I have burned all of the UCC27524P gate drivers previously while trying to figure out what is going on, I could not do more experiments with those.However, I have couple of MIC4422YN and tested the same with those.Unlike UCC27524P, MIC4422YN is a single input/output gate driver.I have added 4.7 uF and 0.1 uF & 0.01 uF decoupling capacitors to near the gate driver.Moreover, I also used a 200 k resister to pull down the input of MIC4422YN.I have attached the output of the scope that show voltages at three locations along with the PWM signalpwm_vs_power_source.png - PWM signal and the power sourcegate_driver.png - Output of the gate driverdrain_to_source.png - Voltage between drain and source of the MOSFETNote also that I used 10 V as the supply voltage while using the scope.Datasheet:MIC4422YN -http://www.farnell.com/datasheets/8670.pdfInterestingly, MIC4422YN appears to be working fine without burning out.Any idea?Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2015, 01:18:12 pm
content: Zoom in on the rising edge. You aren't properly resolving it at that scale.Tim

author: DanielS
author_rank: Frequent Contributor
timestamp: October 31, 2015, 02:40:16 pm
content: Quote from: kasunch on October 31, 2015, 12:55:05 pmRemove the decoupling caps and see what happens then.

author: kasunch
author_rank: Newbie
timestamp: October 31, 2015, 02:42:25 pm
content: Quote from: T3sl4co1l on October 31, 2015, 01:18:12 pmHi Tim,Are you thinking about the overshooting at some of the rising edges?

author: kasunch
author_rank: Newbie
timestamp: October 31, 2015, 02:55:05 pm
content: Quote from: DanielS on October 31, 2015, 02:40:16 pmEven before I was connecting the caps, the power supply noise is more or less the same.I am wondering whether MIC4422YN is not being burned due to the construction of its output unit.For an example, MIC4422YN uses two MOSFETS in its output unit while UCC27524P uses another method (looks like a high current buffer)Datasheets:UCC27524P -http://www.farnell.com/datasheets/1806027.pdfMIC4422YN -http://www.farnell.com/datasheets/8670.pdf

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 31, 2015, 03:11:39 pm
content: Can you please show the Drain-to-Source trace channel and the Gate trace channel simultaneously, and at a faster timebase, so that we can see the spike and ringing a little better? I think if you do this you may experience a "flash" of enlightenment. Maybe.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 31, 2015, 06:10:38 pm
content: Quote from: kasunch on October 31, 2015, 02:42:25 pmThat it appears onsomeedges is indicative of it being present onalledges. The random appearance is due to aliasing: your sample rate is not high enough. Hence, zoom in!Tim

author: georges80
author_rank: Frequent Contributor
timestamp: October 31, 2015, 08:15:45 pm
content: You would need to probe with one of those spring clips on the probe head to get rid of any flying ground probe/lead.Looking at spikes etc requires you to measure the signal, not the signal + probing artifacts.An ACTUAL picture of your setup would help determine if you have wiring/probing issues...cheers,george.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 31, 2015, 08:36:36 pm
content: Yep, three dittoes in a row.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 31, 2015, 09:02:15 pm
content: +1probing technique is very important. I have chased my tail more than once learning how to probe circuit. Do it the wrong way creates artifacts that are not necessarily part of your circuit.As Tim says, zoom in to just the rising edge of the pulse AFTER you get the probing challenge solved. You cant fix anything until you can see it and measure it.

author: kasunch
author_rank: Newbie
timestamp: October 31, 2015, 10:14:24 pm
content: Thanks a lot to all for the great inputs.I attached the scope to gate-source and drain source. Then I zoomed in with a trigger as it is easier to get a clear shot when the desired voltage is reached.Here, I attached the output of the scope (see "without_snubber_cap.png"). Looks like the ringing voltage shoots to 16.6 V (may have gone even higher). Note that the supply voltage is still 10 V.Then I attached A snubber capacitor (0.02 uF) to drain and source of the MOSFET. I have read somewhere that this would reduce the ringing. Indeed it did. See "with_snubber_cap.png" (this is a different edge though).I am making this for a student project. So I do not plan to make a PCB. Instead I plan to use a breadboard/strip board for this. For the moment, I have this assembled on a project board.See "current_assembly.jpg" (consider only the bottom part of the project board).

author: georges80
author_rank: Frequent Contributor
timestamp: October 31, 2015, 10:48:39 pm
content: 1) probing like that sucks for any kind of signal fidelity, especially high frequency stuff like edges,glitches,spikes. Most of what you see on the scope will just be probing artifacts.2) those kind of prototype panels suck for anything high frequency, high edge rate, high current etc.cheers,george.

author: bitslice
author_rank: Frequent Contributor
timestamp: October 31, 2015, 11:13:11 pm
content: Quote from: georges80 on October 31, 2015, 10:48:39 pmJust so I know, what should he be doing?(I was simply thinking the scope ground should be nearer the mosfet...)

author: georges80
author_rank: Frequent Contributor
timestamp: October 31, 2015, 11:23:03 pm
content: What he needs to do is stop using those proto boards. A FET driver has some very fast edges and high current to charge/discharge the gate capacitance and charge. Proto boards are nasty for any such circuit. Those protoboards are 'ok' for little flip flop circuits with LEDs flashing and similar type projects, not for this application.Probing of signals that have fast edges needs a probe spring clip that gets rid of the probe hat and also the flying ground clip. Most of the ringing and edge overshoot etc that are on those scope images are due to the probing the OP is using.E.g. (and this is only ONE example picture) ->http://electronics.stackexchange.com/questions/136123/how-do-you-attach-an-oscilloscope-ground-springcheers,george.

author: bitslice
author_rank: Frequent Contributor
timestamp: November 01, 2015, 12:20:37 am
content: Quote from: georges80 on October 31, 2015, 11:23:03 pmGotcha, thanks George

author: Siwastaja
author_rank: Super Contributor
timestamp: November 01, 2015, 07:11:32 am
content: Definitely use a series resistor with the snubber capacitor (hence called RC snubber). It can't really work without; you are shorting the capacitor now with the FET, and it may generate more problems than it solves. There are manuals on the web how to calculate it, but you always need some experiments. Try something like 3-4 ohms first with your 0.02 uF cap.Once you have proper layout (I'm surprised your breadboard worksat all), you may not need the snubber, or you may use much smaller snubber capacitor, which reduces snubber loss. Only the capacitor size defines the amount of power loss, but the loss happens in the resistor.