Harry said:
Hey FB
You should get a job as a field apps. engineer for a semi house. They love
circuits with lots of semis.
You had it optimized way back when, just change Rb to a cap to turn off the
high side driver for quicker recharge. In that older circuit, I changed the
high side PNP to a PMOS and low side NPN to a NMOS, added high side turn off
cap and filed it away.
Cheers,
Harry
I suppose that will do most of the time but this thing evolved into
three main goals:
o super-low RDS,ON N-MOSFETs throughout,
o zero OFF state current,
o crowbar re-charging of the storage capacitor.
That capacitor coupling into the MOSFET for long timeouts is way too
slow at turn-off. I can't get zero OFF state current, but the 100u of
the LMC555 is close enough- so this circuit is low stress on the
components, and does the job:
View in a fixed-width font such as Courier.
..
.. +----------------------------------+
.. | |
.. e |
.. \| |
.. 2N4403 |--------------+----------[1K]---+
.. /| | |
.. c | |
.. | | |
.. | 12V c 2N4401 |
.. | | |/ SD |
.. | +---+-----------+---|>|-+----+---------+
.. [100] | |\ | | | |
.. | | e | | | |
.. | d | | | | +---+
.. | |-+ | | | + | | |
.. +--------|N [1K] | C === - - S
.. | |-+ | | S | ^ ^ S
.. | s | | | | | S
.. | | | | | | | |
.. | | | | | | +---+
.. | SD | | | | | |
.. +-|<|-[1]--+-----------------------+----+ |
.. | | | |
.. | | | ON |
.. d | +---------+ -- |
.. +-| | | V+/RST | | | >---+ |
.. N|--------------+ | | | | | |
.. +-| | | | - - | |
.. s | | | | |
.. | +--|<|---+----|OUT THR|---+--||-----+ |
.. | | |_ | | | 1n | |
.. | | |/| | LMC555 | | | |
.. | | [pot] | | +---+ | |
.. | | /| | | | | | |
.. | +-[1K]---+----|TRG | [10K] | | d
.. | |+ | | | | | |-+
.. | === | GND | | - +-|N
.. | |C +---------+ | ^ | |-+
.. | | T | | | [Rp] s
.. | | | | | | |
.. +----------------+---------+--------+---+-----+---+
.. |
.. ---
.. GND
..
..