I'm trying to use a nice one-button On|Off latching setup on ATtiny85. See for details the last one of these four: http://www.technoblogy.com/show?VOO In a low-power set-up on my breadboard this is no problem; works like a charm and allows for any delayed auto-off.

However, I want to use this for powering up/down my 400W Ebike.

My question is: how to boost the signal from ATties peak 40mA to an acceptable current that can switch a FET or a relay?

I considered diverse alternatives like transistors or 555 based latching schematics, but choose this one since I have an ATtiny on board already. I have zero experience with FETs or MOSFETs, and I'm stuck.

In this thread (avrFreaks, post #6) a BS170 is mentioned, but I cannot simulate the right circuit and I do not understand yet fully what's going on in that MOSFET.

I have considered using a relay, but these are hard to find in an acceptable price range with specs needed (small footprint, shockproof and allowing to switch 10A at 42V). So I think MOSFET is the way to go.

A detail from the schematic of the on/off wiring:

made with EadyEDA and Nimbus screenshots

PB0 is set high when system is powered up and needs to switch the 42V. Plz feel free to make any changes on the isolated (simplified) part of the schematic on EasyEDA: Go to schematic

Any help will be highly appreciated!

  • \$\begingroup\$ "However, I want to use this for powering up/down my 400W Ebike." NO, JUST NO. Your e-bike draws a lot more current than you seem to think it does, and even if it were only at the level you falsely imagine, the engineering challenges would be far beyond a beginner project. The type of feature you want is one that is either designed into the motor control system from the start by the manufacturer, or not. It is not added later. Don't do this. \$\endgroup\$ – Chris Stratton May 17 at 15:17
  • \$\begingroup\$ Thank you @ChrisStratton for your pointing out. Maybe my words look worse than reality is. The motor controller has an ENABLE pin, which I already drive LOW/HIGH regarding my needs (while accelerating or braking). I could use this pin to switch it ON|OFF, but I'm concerned of the battery drain if the complete system stays powered up. I defenitely will keep your words in mind while exploring the (im)possibities of my idea. I've seen pictures of fried ebikes too, which would be a lot worse than a small energy leak. Thnx again for the reminder! \$\endgroup\$ – BikerMark May 18 at 6:29

You can get MOSFET gate drivers, rated at 6 amps for 100 nanoseconds, to repeat 100,000 times a second. And some suppliers sell 9amp & 12 amp gate drivers, in TO-220 heat-sink-tab packages.

None of these are for continuous DC currents higher than 0.5 amps UNLESS HEATSINK.

They will handle 15 or 18 volts, and control a huge MOSFET gate.

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