Not complex, but still handy to know
Added 2024-10-03 05:23:56 +0000 UTCThis is a very common battery level indicator used with many cheap power tools (including from Aldi and LIDL). The one interesting twist in this module is the time delay circuit with a simple MOSFET, capacitor and resistor arrangement.
That's maybe an idea for a project. A night light that you press the button for full intensity and it then fades slowly away over several minutes.
Comments
With just resistors the LEDs would always glow and increase in intensity as the voltage rose. With the zeners there's a more decisive turn on. Two resistors per LED, acting as a potential divider, would be a crude alternative.
Big Clive
2024-10-04 04:05:31 +0000 UTCIt's a very interesting design. I think if you did the math correct. You would only need the four resistors and the four LEDs.
Jonathan Hughes
2024-10-04 02:29:18 +0000 UTCIdeally yes. The OnSemi datasheet says 20V continuous or 40V for 50ms non-repetitive suggesting there may be some overload tolerance. But having dealt with Chinese factories and seen how they're happy to fit counterfeits I can 100% say they are crossing their fingers.
Mike Page
2024-10-03 18:18:38 +0000 UTCThat 4k7 is odd. It should be higher because a common absolute max gate voltage on a 2n7002 seems to be 20 volts. They are really pushing their luck or they have to be very careful and spec one of the rare 30 volt VgsMax models.
Zac
2024-10-03 13:16:03 +0000 UTCThat 4k7 was probably carried over from a Darlington design. Or - since Vgss max is 20V, a current limit in case of gate breakdown?
Mike Page
2024-10-03 10:41:08 +0000 UTCYes - would love to see a new project build video. It's been a while!
Todd Sharp
2024-10-03 07:13:00 +0000 UTCAldi has some battery operated tools running at 40volts- even some of their chargers are dual 20/40 volt as are their battery packs for some tools- which would explain the mosfet gate to drain voltage peak of 40 v,
Mike Hughes
2024-10-03 06:06:29 +0000 UTC
