reverse battery protection with single cell - Page 1
Forum section: electronics / beginners

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 05:54:17 am
content: I'm making a small project that uses a single AA battery for power. How does one implement reverse battery protection? Diode drop would be to big and voltage is too low for MOSFET method.I'm using Torex XC9140C331MR-G boost DC to DC converter.

author: c4757p
author_rank: Super Contributor
timestamp: August 10, 2013, 06:16:06 am
content: PTC current limiter, reverse Schottky diode across the circuit, user's fault if they stick the battery in backwards and drain it?

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 10, 2013, 07:37:54 am
content: There's probably some clever IC out there that will do what you're looking for. The attached circuit is my completely untested, unproven idea. If you use it and it breaks then you get to keep all the pieces.It is basically a Joule Thief, self resonating circuit hooked to a shunt regulator. The shunt regulator will be set to an appropriate voltage so that it pulls the N-channel MOSFET's gate up enough to completely turn it on and keep it out of its linear region. (5V to 7V, should work.)It probably isn't particularly efficient but the nice thing about the Joule Thief circuit is that it is known to start-up and work under low-voltage situations. It will start-up and run even when a single cell gets down to 0.7V to 0.8V.The cap across the shunt regulator will have to be big enough so that it doesn't cause the shunt regulator to oscillate. (They don't like certain sized capacitive loads.) A zener can be used instead of a shunt regulator but wouldn't likely be as efficient.You would have to wind your own (tiny) transformer if you use this method. So it would be practical only for small quantities. Use a small toroid ferrite core with as high as flux density you can find and put as many turns of 30 AWG magnet wire as you can get on it for the primary and secondary.Some of the component values may need some tweaking and the particular parts used aren't critical. The BC337-40 can be any NPN BJT with high gain. The 1N5818 can be any Schottky diode.Edit: I forgot to draw the arrow on the MOSFET but, as noted above, it is an N-channel. Also, the resistor on the base of the BJT can probably be made bigger to improve efficiency. You just want to be sure you keep the BJT saturated when it is switched on.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: August 10, 2013, 07:46:35 am
content: If you're using an AA cell or AAA cell, the best bet may be mechanical. Machine a groove for the positive end so that a reversed battery can't make contact.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 10, 2013, 07:53:09 am
content: Quote from: c4757p on August 10, 2013, 06:16:06 amFuse, reverse Schottky diode across the circuit, user's fault if they stick the battery in backwards and blow the fuse?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 10, 2013, 08:53:05 am
content: Do you actually need it? The low voltage may mean that a reverse connection won't actually kill anything. If you can afford to put a few ohms in series with anything critical, that may be enough.A simple reverse parallel diode may also be a possible solution.Some low-voltage boost regs have internal protection - check the datasheet.In the case of a boost reg, you may be able to use resistive protection in the supply to the boost chip, but have the inductor connected direct to the supply - the inductor's resistance may be enough to limit current to a safe level without the losses of a resistor.

author: amyk
author_rank: Super Contributor
timestamp: August 10, 2013, 10:19:26 am
content: Quote from: TerminalJack505 on August 10, 2013, 07:37:54 amIf you're going to use a boost converter to drive the MOSFET gate, how about using the output of the original one to do it? (Rely on the body diode to pass a low-enough voltage to start it up.)

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 10, 2013, 10:38:56 am
content: Quote from: amyk on August 10, 2013, 10:19:26 amGood point. I kind of missed the fact that he was already using a boost converter. It would probably be a good idea to put a Schottky diode between the source and drain parallel to the body diode to lower the voltage drop.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 10, 2013, 11:25:44 am
content: Hi,The original poster does not say how big the load current is.Here is an idea that uses a single PNP transistor to provide reverse voltage protection. The transistors base current should be 1/50th of the load current.Here are the waveforms from the simulation:The input waveform is +/- 1.5V. The output does not go negative.If you only have a NPN transistor you can use this:This is the best version, but it requires a MOSFET that has been carefully selected with a low gate threshold version. The reason it is the best is that there is no additional battery current.Jay_Diddy_B

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 01:17:04 pm
content: Here is the data sheet for the boost converter I'm using.http://www.torex.co.jp/english/products/dcdc_converters/data/XC9140.pdfit generates 3.3v from single AA cell. Current draw idle is 350ua, max current draw is 3.8ma.Does this mean the IC protects itself from reverse polarity battery?* Diodes inside the circuits are ESD protection diodes and parasitic diodes.

author: Marco
author_rank: Super Contributor
timestamp: August 10, 2013, 01:19:40 pm
content: It clamps the reverse voltage itself ... but without an external fuse the internal diodes can become the fuses.

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 01:54:45 pm
content: I do have an external 125ma fuseI'm also willing to change the boost converter to something that works of single cell (0.8v-1.5v) and has the protection built in. I prefer fixed output of 3.3v, but adjustable is ok too.

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 02:33:58 pm
content: maybe something can be wired up to use the enable pin on the MCP1640http://ww1.microchip.com/downloads/en/DeviceDoc/22234B.pdf

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 03:01:40 pm
content: I checked the battery holder and it does not offer a mechanical solution.If I reverse wire a Schottky diode what would be a good choice for low power draw, and low voltage drop? Through hole is preferred, but SMT is ok.

author: grips03
author_rank: Contributor
timestamp: August 10, 2013, 06:37:11 pm
content: I ended up using STPS2L60RL schottky diode in series. I have so little current draw that I'm only losing .1v so this is fine.

author: alank2
author_rank: Super Contributor
timestamp: August 11, 2013, 12:11:12 am
content: Quote from: grips03 on August 10, 2013, 06:37:11 pmThis is what I do as well. This configuration also allows for a dual power source as well, you can feed each power source through a schottky and they can't back feed into each other.

author: bsodmike
author_rank: Regular Contributor
timestamp: October 18, 2020, 09:22:17 am
content: Quote from: Jay_Diddy_B on August 10, 2013, 11:25:44 amHi Jay, I'd like to use a MOSFET and I have a few spare IRL640A on hand. Sure, totally over kill, but it has low Rds(on) = 0.18 ohm and Vgs(th) = 1 to 2V typical.With an input supply of 12VDC would this suffice? What's a "less over the top" MOSFET I could use here (TO-220 package)? Load current draw is under 200mA, max 500mA.Thanks.Edit: Responded to old thread as the topic is on point and Jay has already shared relevant information; he is still super active on the forums. Hope this is OK!

author: bsodmike
author_rank: Regular Contributor
timestamp: October 18, 2020, 11:55:58 am
content: I've ordered a few of these to test out, specs look good and relatively low Vgsth:https://export.farnell.com/rohm/rtr040n03tl/mosfet-n-30v-4a/dp/1525562?ost=1525562