Hi, Just used some parts on PPTC fuse and one Zener diode on our rc2 board: ** tried parts** Zener diode: A 5W ON-semi 1N5338BG http://www.onsemi.com/pub/Collateral/1N5333B-D.PDF PTC fuses: brand Tyco a) microSMD075F-2, hold 0.75A, trip 1.5A, 6V, 0.4 Ohms, PD MAX 0.8W b) miniSMDC075F-2, hold 0.75A, trip 1.5A, 13.2V, 0.45 Ohms, PD MAX 1W c) microSMD110F-2, hold 1.1A, trip 2.2A, 6V, 0.21 Ohms, PD MAX 0.8W d) miniSMDC125F-2, hold 1.25A, trip 2.5A, 6V, 0.14 Ohms, PD MAX 0.8W
**MM1 needs 0.42A under reconfiguration** **MM1 needs 0.79A after booted** http://en.qi-hardware.com/wiki/Protection_of_Reversed_Polarity_on_DC_plug-in#Experimental_Results This email focuses on *Sch. B*. last time I used a 1W zener which doesn't meet our goal. This time used 5W of 1N5338BG; So* *did *NO LOAD*(MM1) firstly: from this, we can know how many current goes through Zener diode along with fuse trip function on both non-reversed/reversed polarity injection(DC Jack side). A rating current goes through Zerner 5W is 0.98A while normal non-reversed without MM1 load. a)* Sch. B-1-1, *MINISMDC075F-2, 13.2VDC/0.45Ω ; -4.5V ~ -20V inputs fuse trips immediately. b)* **Sch. B-1-1-1*, MINISMDC125F-2, 6VDC/0.14Ω ; trip time happens 2s after from 2.85A non-reversed power on to 0.05A/20V or 0.26A/7.5V input. zener consumption varies from 14.5W max. to 1.35W. i.e. during this 2 seconds, this is over 5W limitation of Zerner. c) *Sch. B-1-1-2*, MICROSMD110F-2, 6VDC/0.21Ω; trip time happens less than 0.5s after from 2.85A non-reversed power on to 0.05A/20V or 0.12A/12V input. A reversed input -5.25V, -12V, -20V fuse trips immediately down to 0.04A. and *LOAD*(MM1) on d) *Sch. B-1-2*, MINISMDC075F-2, 13.2VDC/0.45Ω; +12 V input fuse trips and MM1 doesn't work by protection. +5.25V input, Voltage of symbol 5V marked on M1 RC2 is 4.489V. e) *Sch. B-1-2-1*, MINISMDC125F-2, 6VDC/0.14Ω; +12V, fuse trips after sustaining 2s. +7.5V, fuse trips when tried to boot. still work after power up(reconfiguration stage) +6V, fuse has not yet reached to holding current 1.25A when booted(1.12A). +5.25V input, Voltage of symbol 5V marked on M1 RC2 is 4.833V. f) *Sch. B-1-2-2*, MICROSMD110F-2, 6VDC/0.21Ω; +9V, +12V, +20V inputs fuse trips after sustaining less than 0.5s +6.75V, +7.5V; fuse trips when tried to boot. still work after power up(reconfiguration stage) +6V, fuse has not yet reached to holding current 1.1A when booted(0.94A). +5.25V input, Voltage of symbol 5V marked on M1 RC2 is 4.814V. +4.5 ~ +5.25V, MM1 work well. -5V ~ -20V, fuse trips less than 0.5s. Since our goal is to let fuse quickly trip current when fault over-voltage or reversed polarity occurs, I finally decided that using *MICROSMD110F-2*(size 3225mm) and *1N5338BG* in next rc3 run. Since I forgot to order samples of MINISMDC110F-2(size 4532mm) which is hold 1.1A, trip 2.2A, 8V, 0.21 Ohms, so I would also want to put bigger footprint for it. So rc3 would have an ability to accept DC adapter with outputs: * +6.75V ~ + 20V inputs, tripped. * +6.1 ~ +6.74V inputs, I didn't test. * +4.5 ~ +6V, work. * -4.5V ~ -20V inputs, tripped, no work. **layout criteria** *** place Zerner diode & fuse away from existent parts around DC jack due to heat. *** place size 4532mm footprint for fuse. *** still keep "DC 5V IN" & polarity texts in silkscreen. Thanks, -adam
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