I was just starting a redesign on some power boards, and really wishing for a simple way to have them switch themselves off. The buzzer and warning lights solution does no good when someone accidentally leaves the thing switched on and goes home for the weekend (we’ve lost a few LiPo packs that way).
One quick question, how would these (potentially) react to being powered backwards? I know they wouldn’t switch properly, but would they be damaged, and/or let current flow?
Just started the wheels turning to order a couple through work.
Unfortunately, connecting power backwards will let current flow and can destroy the unit. We haven’t fully characterized the behavior yet, but the MOSFET’s body diode will be forward biased, allowing the reversed power to get to your load. We’ll be adding a unit with reverse protection this summer; until then, you can add your own P-channel MOSFET for reverse protection (for an example, see the Orangutan LV-168 schematic).
Thanks, I was more curious than anything else. This is going to be embedded in a larger board with polarized connectors and a big protection diode. Maybe I’ll wait on the reverse protection version for personal projects though, I’m really good at plugging things like that in backwards.
Another quick question, the answer is probably no, but is there a simple way to completely bypass the power button? I have two boards I want to throw these on right away, and one would benefit from the pushbutton power-on, but on the other it would be redundant.
Lets say I have a physical power switch in line with my batteries, and with the Pololu power switch. I would like power to flow when I make the physical switch connection, and to only have the Pololu switch cut power the “off” pin is pulled high (and leave the power off until the physical switch is toggled). I don’t suppose I could do something cute like just bridge the two pushbutton pins with a resistor, or maybe something like a small capacitor/large resistor pair?
If not it’s no big deal, I’ll just have to add some more buttons. Wow, they haven’t even arrived yet and I’m already hacking them in my mind.
I was going to say that the answer is no, but I tried it out and shorting out the pushbutton seems to work! However, the off state will not be as completely off: the switch will look like a 360k resistor (so typically less than 50 uA load). That current goes through the pushbutton bypass, so you could improve the situation slightly by using a resistor instead of the pushbutton; how big of a resistor will work will depend on your application.
Any thoughts on a resistor size for a 3-5amp load running off of a 14.8V battery pack? Actually by the time we want to cut it off it’ll probably be down to 13.5V, if that makes a difference.
When my switches come I can try and see, or even just use a wire jumper. Our battery cutoffs are always a little conservative (Lithium Polymer after all) and at that current 100maH would buy over 80 days!
Campus mail likes to sit on USPS packages for a day or two, but my pushbutton switches just arrived and they work fantastically, both with the button and with just a jumper instead.
I still can’t get over how tiny it is though! Before it arrived I had been describing it to my coworkers as the size of half a stick of chewing gum, but really it’s more like half a postage stamp. Very Nice!
Hi Everyone! Just joined the forum, after discovering the PB pwer switches recently. Got 20 of them, and am thoroughly impressed!
(Jan, we spoke on the phone the other day about a possible 48V version.)
Anyway, I have a situation similar to Adam’s, but not exactly. I’m using two of the switches side-by-side, controlling two separate channels of LED lights. But by pressing the first switch, I’d like to turn on the second channel automatically when it’s powered up, still retaining the ability to turn the 2nd switch off with the pushbutton. In other words, the 2nd switch would be powered by the 1st.
So, is there a simple way to have these beauties default to the On state when powered up?
I also appreciate that they’re truly only .4" wide, with tight tolerances, because they gang up perfectly that way, side-by-side. Nice work!
Many thanks for a very useful (and TINY!) product!!
I did have one teensy suggestion about the PB switches. The holes that the included pins fit into have a bit too much play in them, making it difficult to get the pins soldered in exactly on center, or straight.
I somewhat solved the problem by plugging the pins into a solderless breadboard and then fitting the PCB over them, but the pins still weren’t quite centered in the PCB holes. Nevertheless, the results are excellent, so I have no complaints!
But still, if the holes were a bit smaller, so the pins fit snuggly when soldering them in, it would make it easier to center them at exactly .3" and .8".
Perhaps you already thought of that, but left them larger to accomodate large wires? Anyway, just a thought… the only improvement I could think of.
Unfortunately, I don’t know of a really simple modification you could make to the board to make the switch come up in the on state. It should generally be possible, and we could add that to the requirements list if you’re interested in getting a custom 48V version made.
I was just curious if anything ever came of the higher-voltage pushbutton power switch?
I’ve been using the SV model in some custom wearable computer packs. They work really well, but they’re currently the limiting component in the maximum voltage battery pack I can use. It’s not something I need custom-made, but if there were one that worked at higher voltages (or a component swap modification I could make to the existing boards) I would be very interested.
Sorry, we don’t have a higher-voltage version yet. What kind of voltage are you talking about? We might lose some range on the low end, so it would be good to know what range you need from a single switch.
It’s probably asking too much from one FET, but ideally I would like to be able to use a 3-cell Lithium Ion pack, or a 12V or 24V Lead Acid battery (even while charging) all through the same switch. I guess that means an operational range from 9V to 27V. If that’s impossible, 12V-26.4V would still be useful for a 4-cell LiIon pack or a separately-charged 24V Lead Acid Battery.
Also, we’ve noticed that with enough equipment powered through the SV switch (i.e. two big DC/DC converters and a PC/104 computer) when you press the button to turn it off the voltage drops momentarily, but then comes back on. Driving the off pin high works every time though, so we think of the button as more of an on/reset function.
I don’t think it’s necessarily asking a lot of the FET, but it might make the control circuit more complicated. What you’re seeing with the existing switch is probably due to a combination of the voltage being high and there being a lot of ripple on the supply. If the supply voltage is alternating faster than other nodes in the control circuit, the circuit can switch back on. Can you see what happens at a lower voltage or with less ripple (if there is a lot)?