Reverse diode current problem - Page 1
Forum section: electronics / projects

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: November 20, 2017, 06:38:01 am
content: Hello there,Take a look the schematic, I have observed this circuit in maximum and minimum temperature, the problems areThe gate of Q3 will be turned on at maximum temperature, while MAIN_PWR_EN is 0(disable).1. D7 shows reverse diode current.2. Q10 is also malfunctioning.According to datasheet, torexsemi.com/file/xbs053v13r/XBS053V13R.pdf, the reverse current at 20V reverse volatge is 100u A. We are expecting a unidirectional current path towards R41 and R68 junction. Somehow in this circuit, current is producing,,,,The parameters from datasheet of Q3 (onsemi.com/pub/Collateral/NTR2101P-D.PDF) says, if you calculate the gate current,Ig = Qg/(td(on)+tr); (Total Gate Charge) / (Turn-on delay time + rise time of MOSFET) it will about 0.37 A. (at VGS = ?4.5 V, VDD = ?4.0 V, ID = ?1.2 A, RG = 6.0 ohm) Reverse leakage might be temperature dependent, if you can see the circuit, a voltage difference between VIN(4.2v) and V_3V3 if Q3 is turned on that could make reverse path for diode conduction.

author: danadak
author_rank: Super Contributor
timestamp: November 20, 2017, 10:45:28 am
content: Downsides of schottky diodes are precisely what you observe,high reverse leakage.You might look around for a better part, 100 uA does seem a tad high.Regards, Dana.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: November 20, 2017, 07:23:05 pm
content: I agree with Dana that that 100µA spec is pretty high. And that's at 25°C!By comparison, the RB168LAM-30 (https://www.digikey.nl/product-detail/en/rohm-semiconductor/RB168LAM-30TR/RB168LAM-30CT-ND/7243343) is spec'd for 0.6µA max at 30V Vr.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: November 21, 2017, 04:10:19 am
content: QuoteDo you mean downside diode D7?QuoteCan you compare my calculated gate current in actual case?

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: November 21, 2017, 04:14:35 am
content: QuoteMy company wish to replace,http://www.mouser.com/ds/2/348/rb520s-30-209876.pdfand I wanna do heat chamber test again.Do you agree with this part?

author: danadak
author_rank: Super Contributor
timestamp: November 21, 2017, 11:49:32 am
content: Yes on question D7, it is D7 being discussed.Your Mouser replacement shows no high temp leakage performance.You could contact vendor and ask for characterization data at hightemp.I would sim this design to get at peak gate drive current. You coulduse LTCspice, Tina TI spice, many vendors have simulators that wouldhandle this.http://www.ti.com/lit/ml/slua618/slua618.pdfhttps://www.semikron.com/dl/service-support/downloads/download/semikron-application-note-igbt-driver-calculation-en-2007-10-31-rev-00/https://www.infineon.com/dgdl/an-944.pdf?fileId=5546d462533600a40153559eb9841190Regards,. Dana.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: November 22, 2017, 01:40:17 am
content: Thank you sir Danadak,QuoteI will talk to them, but already the circuit is ready for production repair department.I think, the suitable diode what RobK_NL has said is OK.QuoteWell said, I have been used those tool.But, if you see the circuit we need to generate some shots of signal like MAIN_PWR_EN, PWR_HOLD, PWR_IND signal.As this device is OS related firmware, we can just make signal conditioning by the circuit.Can you suggest which tool I need to apply here?Any OR, AND, NOR, gate signal?