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Author Topic: Tact switch and mosfet transistor questions  (Read 137911 times)

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Offline CraigHB

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Re: Tact switch and mosfet transistor questions
« Reply #350 on: March 27, 2015, 05:43:30 PM »
A charge pump is a type of DC-DC converter that uses capacitance instead of inductance to control output voltage.  They are limited in output power compared to an inductive converter because of the difference between an inductor and a capacitor.  To try to use terms simple as possible, it's the difference between current flowing through a wire coil and charge building up on a set of plates.  Current flowing through a wire coil is going to be much less limited in terms of power.  The advantage is charge pumps are simple devices and easy to employ.

The charge pump simply boosts voltage so the MOSFET can be driven with a higher voltage than what's available from the battery.  This puts the MOSFET in a lower resistance on-state and removes the requirement to use MOSFETs with extra low gate-source threshold.  It really frees up the range of MOSFETs that can be used, but also adds more parts.  Kind of a 6 of one half dozen of the other situation.

For any current path the limitation is going to be heat.  If the current paths on PCB heat up to much that can be a problem as much as MOSFETs overheating themselves.  The current paths he's using on the PCB are pretty ample so I imagine the MOSFET would overheat before the PCB traces would.  Can't say for sure without torture testing it, but the current tolerances are so high it would not be easy to build a test rig for that, and who wants to burn perfectly good parts anyway.

Offline fsors

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Re: Tact switch and mosfet transistor questions
« Reply #351 on: March 27, 2015, 08:40:17 PM »
  Kind of a 6 of one half dozen of the other situation.

 and who wants to burn perfectly good parts anyway.

Talking my lingo Craig ;bow; and I might be able to open the mouser box of goodies this weekend who knows?  scared:  might need your  :help:


Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #352 on: March 27, 2015, 09:07:28 PM »
A charge pump is a type of DC-DC converter that uses capacitance instead of inductance to control output voltage.  They are limited in output power compared to an inductive converter because of the difference between an inductor and a capacitor.  To try to use terms simple as possible, it's the difference between current flowing through a wire coil and charge building up on a set of plates.  Current flowing through a wire coil is going to be much less limited in terms of power.  The advantage is charge pumps are simple devices and easy to employ.

The charge pump simply boosts voltage so the MOSFET can be driven with a higher voltage than what's available from the battery.  This puts the MOSFET in a lower resistance on-state and removes the requirement to use MOSFETs with extra low gate-source threshold.  It really frees up the range of MOSFETs that can be used, but also adds more parts.  Kind of a 6 of one half dozen of the other situation.

For any current path the limitation is going to be heat.  If the current paths on PCB heat up to much that can be a problem as much as MOSFETs overheating themselves.  The current paths he's using on the PCB are pretty ample so I imagine the MOSFET would overheat before the PCB traces would.  Can't say for sure without torture testing it, but the current tolerances are so high it would not be easy to build a test rig for that, and who wants to burn perfectly good parts anyway.

Thanks for taking the time to explain that.

I can see how it can be a benefit, or a necessity depending on which MOSFET is used, and I can see how it opens doors to other options which have a higher Rds On.

I guess my real question was in regards to the parts lists between the two projects listed under the OSH Park for David4500.  I’m still learning here, so please excuse me if this is an elementary question, but two boards use the same (PSMN1R1-25YLC,115) MOSFET, one with the charge pump and one without. At least that’s what he selection in both the parts list/project carts on mouser.  I understand I can use whatever I want within the same package size, but I just want to compare the two boards using the same MOSFET.

http://www.mouser.com/Search/ProductDetail.aspx?R=PSMN1R1-25YLC%2c115virtualkey66800000virtualkey771-PSMN1R125YLC115
The PSMN1R1-25YLC,115 shows an Rds On of 4.5v, does that mean when using a single cell that the MOSFET is in an active state and its acting as a variable resistor?

Based on the spec sheet chart Figure 7, it looks like the fet is right on the curve?  So as the charge drops low, or if there is a great deal of voltage drop across the coil, the fet resistance will shoot up to an unsafe zone?

Am I reading the spec sheet correctly?

If not using a charge pump, you basically want as low as a resistance as possible for drain-source on-state resistance correct?  So if one fet is 1.5mOhms and the other is 2.0mOhms at the same voltage, than the lower resistance 1.5mOhms selection would be better?

Offline CraigHB

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Re: Tact switch and mosfet transistor questions
« Reply #353 on: March 28, 2015, 11:15:54 AM »
For any MOSFET used as a switch you want the on-state to be in the flat part of the curve.  As the consideration is "gate-source voltage versus on-state resistance" the gate-source threshold and on-state resistance stated in the data sheet determine the shape of the curve.  You always want an on-state resistance as low as possible and you always want the applied gate-source voltage to put the transistor in the flat part of the curve.   

You may wonder why MOSFETs vary so much in these specifications.  There is a reason for it.  There are trade-offs with respect to the speed and cost of a MOSFET.  Some applications may require a fast switch and the trade-off there comes in on-state resistance.  For some applications on-state resistance is not as important.  It becomes of great importance when dealing with higher currents.  Some applications may require higher voltage tolerance and the trade-off there comes in higher gate-source threshold.

There's also the advancement of tech.  Transistors improve over time getting faster with lower on-state resistance.  Parts become more available at wider ends of the spectrum such as transistors with very low gate-source threshold.  The through-hole parts are pretty much obsolete in terms of new parts which don't come in through-hole packages.  Though through-hole parts are handy for free wiring stuff, they are limited in performance.

Offline fsors

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Re: Tact switch and mosfet transistor questions
« Reply #354 on: March 28, 2015, 07:38:25 PM »




Just want to say Thanks to David for Great Markers!  :thankyou: :yes" :beer-toast:

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #355 on: March 29, 2015, 03:06:59 PM »
Looks good! Which mosfet did you decide on?

Got some new boards assembled:





« Last Edit: March 29, 2015, 05:19:58 PM by david4500 »

Offline Rigure

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Re: Tact switch and mosfet transistor questions
« Reply #356 on: March 29, 2015, 08:23:24 PM »
Love those boards David, now I just wish I could get it to work right.  Iv been thru two of then and thay seem to get really HOT.  here's some pic, if you spot anything, let me know.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #357 on: March 29, 2015, 08:58:28 PM »
Hmm... what resistance coil were you firing? Is it the v1.3 version of the board? Any boards earlier had errors and won't function properly.

Looks like you may have not have used flux while soldering. I would recommend that to ensure proper flow and resulting solder joints. I used MG Chemicals 8341 paste flux.
« Last Edit: March 29, 2015, 09:01:59 PM by david4500 »

Offline Rigure

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Re: Tact switch and mosfet transistor questions
« Reply #358 on: March 29, 2015, 09:00:33 PM »
Ah, no wonder...I got the v2 board befor the added resister for series.... oh, and a .5 ohm coil build.

Offline Rigure

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Re: Tact switch and mosfet transistor questions
« Reply #359 on: March 29, 2015, 09:04:10 PM »
I have the radio shack brand, but I did use for each joint, just not alot of it.so you seen the version 2 board is not functional?

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #360 on: March 29, 2015, 09:05:25 PM »
Ok... on that board, it still should function ok, it's just that a pull down resistor was recommended to be added to the series link mosfet to discharge to gate while in series and idle. Don't think that's the cause of the heat issue.

Offline Rigure

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Re: Tact switch and mosfet transistor questions
« Reply #361 on: March 29, 2015, 09:07:34 PM »
Can I ad a resister to the circuit on the series mosfet? Like a thru hole one?

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #362 on: March 29, 2015, 09:27:19 PM »
With a 0.5 ohm coil, the mosfets shouldn't be dissipating very much heat.

8.4v with a 0.5 ohm coil would be 16.8 ohms.

http://www.wolframalpha.com/input/?i=8.4%2F0.5%3DCurrent

For single mosfet with an RDS ON of .001 ohms and seeing current of 16.8 ohms, it only 0.28 ohms

http://www.wolframalpha.com/input/?i=Power%3D%2816.8^2%29*.001

Here is a screenshot of the most recent board in Diptrace:



One end of the resistor is connected to a trace leading to the Bat2- pad. The other end is connected to a trace leading to the series link mosfet gate by why of a via (red highlighted hole on left). Along that same trace, the via on the right connects to the lower middle pad of the slide switch. The vias aren't pads... but maybe you could manage to solder a through hole resistor to one of them and the Bat2- pad.
« Last Edit: March 30, 2015, 01:18:34 AM by david4500 »

Offline Rigure

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Re: Tact switch and mosfet transistor questions
« Reply #363 on: March 29, 2015, 10:10:55 PM »
Thanks david, I'll try that in the morning.

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #364 on: March 30, 2015, 04:19:47 AM »
Hi everyone, this is my first post here in this forum, but have been lurking a long time. Some very interesting stuff discussed here! I have been thinking of drawing up a simple mosfet board for a wooden mod I have, and have had various pcb's made for guitar effects pedals (very low current devices) at a hobby level in the past. So thought I would try a pcb for my mod, but this high current stuff seems to be a totally different ball game!

I have a question regarding the current carrying capacity of copper traces. According to online calculators, if I use a trace from say the drain of a PSMN1R1-25YL and its 200 mil wide and say 100mil long (to get to the atty negative pad) and I'm using 1 oz copper, that trace will only handle 13.4A for a 30 degrees C temp rise. I used this calc (but the several ones I used to cross-check each other were similar)

http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/

Yet the resistance for the track is given as 0.2 milliohms. Given such low resistance, how can it only be rated to take 13.4A? And with a 30 degree C (86F) temperature increase? Does the intermittent use factor help us, given that we can't vape continually?

You can see the resistance is negligible, am I missing something? 2 oz copper is considerably more expensive :(

I have another question regarding the use of the MHP-TA15-9-77 as a resettable fuse. It looks to me that its actually a temperature cut-off device designed to be installed in a lipo battery pack, so it can sense temperature and cut the power if the temp reaches 77 degrees C. Am I missing something here too?
Any input appreciated guys.

BTW for those that just can't wrap their head around the pcb layout softwares available (like me), I eventually found a quick and easy one that got me going. You don't need a schematic to make it work, you can just draw the pcb, and easy to learn. Its called Sprint Layout and I use version 5.0, I don't like the later one. Its not free, it was about $50 when I got it years ago, but they have a free trial version that will let you see if you like it or not.

Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #365 on: March 30, 2015, 11:39:39 AM »
I have another question regarding the use of the MHP-TA15-9-77 as a resettable fuse. It looks to me that its actually a temperature cut-off device designed to be installed in a lipo battery pack, so it can sense temperature and cut the power if the temp reaches 77 degrees C. Am I missing something here too?
Any input appreciated guys.

I just took a look at the spec sheet and you seem to be on point...
http://www.mouser.com/ds/2/418/NG_DS_DS28403_A-109895.pdf

I am a bit new at this too but the spec sheet would lead me to believe the same thing.  The vendor website does show a Hold/Trip current values for amperage but its design application for LiPoly packs does make a lot of sense too.

http://www.mouser.com/ProductDetail/TE-Connectivity-Raychem/MHP-TA15-9-77/?qs=1vPsWa5aeatw7frgf8Ap9Q%3D%3D

I am going to order these anyways and test them out…  I’ll put a current clamp meter which can record peak valves in line and create an intentional short just to see what it does.
« Last Edit: March 30, 2015, 11:43:19 AM by Emex »

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #366 on: March 30, 2015, 08:03:58 PM »
Exceeding the current hold of 15 amps, the temp of the fuse will rise along with the resistance of the fuse. If it reaches the thermal cutoff, the fuses will fully trip and cutoff the flow of current. Removing the over current, the fuse will cool off and return to its normal state.

On the data sheet, check out page 2, under "design concept" which detail how the fuses function.

This data sheet from TE will have charts showing the relationship between current and temp with the different value thermal fuses: http://www.te.com/content/dam/te/global/english/products/Circuit-Protection/knowledge-center/documents/mhp-devices.pdf

Using two of those 15 amp fuses in parallel, with a mosfet, and installed in a mod, I've intentionally shorted the 510 with a piece of metal. The fuses functioned exactly as them should. The current flow was stop quite quickly. Once the fault was removed, the fuses were slightly more resistive but settled back to normal once cooling off.
« Last Edit: March 30, 2015, 08:18:39 PM by david4500 »

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #367 on: March 31, 2015, 03:17:02 AM »
Thanks David,

It appears that it functions for our purpose then, maybe the bimetal strip heats up anyway with the high current and breaks the circuit.

From this datasheet, it clearly states "During an abnormal event, the device reacts to the rise in cell temperature causing the bimetal contact to open at the specified temperature". Hence the reason for my question. It looks like a good alternative to polyfuses and one-shot fuses, and they are cheap, I'll get a couple and test them. I might get a MHP-TA15-9-72 to compare to the MHP-TA15-9-77 as well.

Are you using 1 oz copper on your boards David, or 2 oz? Have you ever felt the large copper areas at the drains and sources getting warm during your testing?

Actually I just realized I have some 1 oz copper-clad board here somewhere, maybe I should cut a small piece off, solder a wire on each end and run some current through it, to see if my intended track width and length will handle the intended current.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #368 on: March 31, 2015, 04:41:12 AM »
1oz on Oshpark. I'd have to get them somewhere else for 2oz. I just tin the exposed traces or copper fills and it's worked out.

None of the boards or mosfets have been excessively warm after firing. One with 3 parallel mosfets I fired a 0.2 ohm coil for 4 minutes straight. There was a slight temp increase on the board, that was it. No where near hot or burning. I'll get an infrared temperature gun so I can get some actual temp readings.
« Last Edit: March 31, 2015, 04:46:43 AM by david4500 »

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #369 on: March 31, 2015, 07:05:31 AM »
Sounds like the 1 oz copper has it all running sweet if it only gets a bit warm after 4 mins firing 0.2 ohms. Very nice.

On second thoughts, you are spreading the power between 3 mosfets, each is only taking 1/3 the power, and there would be more copper for the three compared to just one. Also, I stumbled across a PSMN1Rsomething datasheet suggesting 2 oz copper, but that is for a single mosfet at max power with a 1" square of copper on the pcb to act as a heatsink. I'm gonna have to be careful because I only want to use one mosfet, due to not much room in there. Thanks for your comments, very much appreciated.



Nice board you did there.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #370 on: March 31, 2015, 01:47:30 PM »
The power dissipation for 3 in parallel is dramatically lower than for a single.

Say the current draw is 30 amps and the RDS ON of the mosfet is 0.0015 ohms (1.5 millohms)

Current^2 * Resistance = Power

30^2 * 0.0015 = 1.35 watts

http://www.wolframalpha.com/input/?i=30^2*0.0015%3DPower

With the multiple mosfets in parallel, the current and RDS ON would be fractionally split. 1/3 in this example, so 10 amps and 0.0005 ohms.

10^2 * 0.0005 = 0.05 watts per mosfet

http://www.wolframalpha.com/input/?i=10^2*0.0005%3DPower

Enormous difference right...? 0.15w vs 1.35w, 9 times lower

Offline fsors

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Re: Tact switch and mosfet transistor questions
« Reply #371 on: March 31, 2015, 05:11:26 PM »
Looks good! Which mosfet did you decide on?

Got some new boards assembled:







Hey Looks good! For the box posted above I use the 3034 but the ones I am about to make will use the same as yours with the boards mosfets x 3 and fuses. Thanks for the Markers too they are fantastic!  :thankyou: ;hubba; :wave:

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #372 on: April 06, 2015, 05:10:40 AM »







Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #373 on: April 06, 2015, 08:51:49 AM »
David, is that a micro on this board? If it is, what is it doing? Intriguing...I am dabbling with an Atmel micro much the same size.


Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #374 on: April 06, 2015, 03:37:19 PM »
That's the Quad Mosfet board...

I think the part you are referring to is the ADM660ARZ charge pump which doubles the voltage to the gate of the mosfet.

http://www.mouser.com/ProductDetail/Analog-Devices/ADM660ARZ/?qs=BpaRKvA4VqGx3CPq2l2ChQ%3D%3D


Offline dc99

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Re: Tact switch and mosfet transistor questions
« Reply #375 on: April 06, 2015, 05:09:37 PM »
David, did you pull the board with the fuses?

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #376 on: April 06, 2015, 06:15:36 PM »
David, did you pull the board with the fuses?

If a link here is dead, the board was revised and the old version was deleted.

This should be what you're looking for: https://oshpark.com/shared_projects/o7NrTQMe

Check out the project page for the others: https://oshpark.com/profiles/david4500
« Last Edit: April 06, 2015, 06:20:26 PM by david4500 »

Offline dc99

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Re: Tact switch and mosfet transistor questions
« Reply #377 on: April 06, 2015, 06:28:17 PM »
Thanks. Im giving up learning the software for now. 

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #378 on: April 06, 2015, 08:06:43 PM »
Were you trying to make a board with a p-channel and voltage detector?

Offline dc99

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Re: Tact switch and mosfet transistor questions
« Reply #379 on: April 06, 2015, 08:28:11 PM »
Originally yes. The board you have is perfect for the box Im doing now. Neg. is fine for this one. Plus I like the fuses.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #380 on: April 07, 2015, 08:09:48 AM »
Were you trying to make a board with a p-channel and voltage detector?

Schematic only at the moment.

Thanks Craig for the part recommendations throughout this thread.

Pfets: SI7157DP-T1-GE3
Voltage Detector: TPS3700

Low voltage cutoff ~3v

It's quite possible I've fucked something up, but this is what I have so far.

« Last Edit: April 07, 2015, 08:33:49 AM by david4500 »

Offline dc99

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Re: Tact switch and mosfet transistor questions
« Reply #381 on: April 07, 2015, 03:51:47 PM »
You really didn't have to work on this. It is appreciated though. I may just have to contract you with my ideas. Haha.

Offline tj138waterboy

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Re: Tact switch and mosfet transistor questions
« Reply #382 on: April 07, 2015, 08:51:32 PM »
David, I have a quick question.  On all of your boards with solder points for the vm, How much space saving could be accomplished if it were just combined with atomizer + & - ?  I know it probably would be very little if at all but just throwing that out there.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #383 on: April 07, 2015, 11:54:44 PM »
The voltmeter pads are usually put in an area where there just so happens to be space. Space isn't made for them. So removing them, there would just be empty space.

Thanks for that thought though. I'll certainly consider that on future boards if space is at a minimum.

Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #384 on: April 09, 2015, 12:12:42 PM »
My Mouser order came in (easy to run up a tab over there) yesterday and I couldn't wait to get the iron fired up... Just sharing.

My first board (thanks David4500) for sharing your project.

My only concern is the tinning of the traces for the MOSFETs... not sure if I need to lay on some more solder to make it a bit thicker... any suggestions? (see Picture 2)

I also whipped up a test bed with a 510 connection using some banana jacks...  it also doubles as a ohm meter breakout adapter for a DMM.  Added a little push button switch to it as well to make REL/Zeroing out the lead resistance easier.

« Last Edit: April 09, 2015, 12:17:39 PM by Emex »

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #385 on: April 09, 2015, 04:49:47 PM »
Nice! Looks like you've got plenty of solder on the traces. I think I fired that board for 4 minutes continuous and it barely even rose in temperature.

Offline dc99

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Re: Tact switch and mosfet transistor questions
« Reply #386 on: April 09, 2015, 05:21:27 PM »
I ordered enough of that board to keep me busy for a while.

Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #387 on: April 09, 2015, 05:31:37 PM »
Nice! Looks like you've got plenty of solder on the traces. I think I fired that board for 4 minutes continuous and it barely even rose in temperature.

Good to know... I wanted to test this extensively but I started thinking about each individual MOSFET...  is there a way to test each one to make sure none of them were damaged from soldering/heat/or ESD?

I am very excited to get this thing into a box... it will be my FIRST DIY mod.

I was thinking of going with 3 x 18650 and hopefully cram it all into a 1590B, but not sure how I should do that since each fuse on this board was supposed to have its own dedicated connection to the positive on each cell.  I was thinking of just making the bridge/parallel connection at the battery sled level and then both fuses would give me a combined 30A hold / 60A trip for the entire bank of batteries.

I might be better off just using 2 x 18650 in a 1590G.

Another thing I noticed was my DMM picking up 0.0407v @ the 510 connection at rest... im guessing there is some voltage leakage / idle drain?

Offline Visus

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Re: Tact switch and mosfet transistor questions
« Reply #388 on: April 09, 2015, 09:55:58 PM »
Emex gr8 job bu I think your resistor is 1k not 10k 1002 is usually 1k 1003 is 10k may be wrong but on my 4 digit smd's thats how it is..

If so it wouldn't possibly shut the mosfets down and you get the leaks?

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Re: Tact switch and mosfet transistor questions
« Reply #389 on: April 09, 2015, 10:01:50 PM »
Im  ordering  your 555 board David as soon as ya say its golden which I may have missed the post,  but if its golden ya-- gonna poss. put  it in a aa 2s box mod,  it will fit perfectly per specs and look awesome..   :thumbsup:

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #390 on: April 09, 2015, 10:26:59 PM »
Another thing I noticed was my DMM picking up 0.0407v @ the 510 connection at rest... im guessing there is some voltage leakage / idle drain?

What's the voltage on the gates at rest?

Emex gr8 job bu I think your resistor is 1k not 10k 1002 is usually 1k 1003 is 10k may be wrong but on my 4 digit smd's thats how it is..

I'm pretty sure 1002 is 100 with 2 extra zeros = 10k

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Re: Tact switch and mosfet transistor questions
« Reply #391 on: April 09, 2015, 11:39:42 PM »
What's the voltage on the gates at rest?

I'm pretty sure 1002 is 100 with 2 extra zeros = 10k

It  is, 

 :thumbsup:

I was confused on the 3 digit to 4 digit smd resistor values but,  "I'm pretty sure 1002 is 100 with 2 extra zeros = 10k;" made logic in my brain so off the top of memory it will be correct..  ... :laughing:


http://www.hobby-hour.com/electronics/smdcalc.php





Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #392 on: April 10, 2015, 12:22:12 AM »
What's the voltage on the gates at rest?


Battery / Input Voltage = 4.17v
Gate @ Rest = 4.17v  (measured from battery Positive to Gate)
510 @ Rest = 0.0488v (with minor fluctuations)
510 @ fire (no atty / load) = 4.17v

Is that normal?

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #393 on: April 10, 2015, 01:00:39 AM »
Battery / Input Voltage = 4.17v
Gate @ Rest = 4.17v  (measured from battery Positive to Gate)
510 @ Rest = 0.0488v (with minor fluctuations)
510 @ fire (no atty / load) = 4.17v

Is that normal?

I don't think so, otherwise you would be pulling near 50mA of current from the battery all the time with a 1 ohm coil. I have one mod with a mosfet in it and it doesn't have any voltage at all when off, its 0.000V across the coil. Your circuit board looks like a clean build too. No idea on how to check each individual mosfet at this stage. If I think of something I'll let you know.

On another point, these mosfet-switched devices have no reverse-polarity protection. If the battery is put in backwards it appears the body diode conducts and fires the atty, with the 0.7V approx diode drop. Is there anything else to be aware of? Is there an easy reverse-polarity protection circuit for a mosfet?

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #394 on: April 10, 2015, 01:00:40 AM »
Im  ordering  your 555 board David as soon as ya say its golden which I may have missed the post,  but if its golden ya-- gonna poss. put  it in a aa 2s box mod,  it will fit perfectly per specs and look awesome..   :thumbsup:

I had some issues on the first version.

Mainly the pfet pads for gate and source were reverse of what they should have been. Diodes were in the wrong direction causing the duty cycle to increase when turning counterclockwise instead of clockwise.

Fixed those issues, most recent update: https://oshpark.com/shared_projects/4JRetcg2

Can't say 100% everything is perfect at the moment, although it should be. Should be getting the boards from Oshpark tomorrow and will test to confirm.
« Last Edit: April 12, 2015, 01:59:37 AM by david4500 »

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Re: Tact switch and mosfet transistor questions
« Reply #395 on: April 10, 2015, 01:07:15 AM »
510 @ Rest = 0.0488v (with minor fluctuations)

Should be from drain current leakage. Pretty sure I've had a similar reading on every mosfet mod I've made.
« Last Edit: April 10, 2015, 01:12:05 AM by david4500 »

Offline Emex

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Re: Tact switch and mosfet transistor questions
« Reply #396 on: April 12, 2015, 12:45:46 AM »
Man... cramming the fused TriParaMos into a 1590G is proving to be a challenge...

I feel like I should just use the 1590B and call it a day.

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #397 on: April 12, 2015, 01:54:41 AM »
Man... cramming the fused TriParaMos into a 1590G is proving to be a challenge...

I feel like I should just use the 1590B and call it a day.

Not sure of the exact issue but if it's clearance along side the battery holder, try one of the 3d printed dual 18650 holders. Or if using a keystone or mpd holder, modify to minimal width about 37mm.
« Last Edit: April 12, 2015, 01:59:08 AM by david4500 »

Offline Ian444

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Re: Tact switch and mosfet transistor questions
« Reply #398 on: April 18, 2015, 04:32:13 AM »
I tested the MHP-TA15-9-77 today, it looks really good, much to my surprise.
It will hold 15A no worries.
At 22A goes open in around 7 secs.
28A 5 secs.
43A maybe 1 sec.
47A maybe half a second if that.
It resets pretty quick and the resistance at 10A flow was measured around 2.25 milliohms, (22.5mV AC on Fluke187), at 5.5A it was about 1.9 milliohms (10.5mV AC).

The testing was done with a high current transformer from a circuit breaker test set, fed with a variac, so AC, but I think the results should be OK and in the ballpark.

So now David, you can say "I told you so" :)

Offline david4500

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Re: Tact switch and mosfet transistor questions
« Reply #399 on: April 28, 2015, 11:05:50 PM »
Schematic only at the moment.

Thanks Craig for the part recommendations throughout this thread.

Pfets: SI7157DP-T1-GE3
Voltage Detector: TPS3700

Low voltage cutoff ~3v

It's quite possible I've fucked something up, but this is what I have so far.



Assembled (used a 30K instead of a 15K for the pullup res)


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