Current reversal in push/pull?

Must be high power...

Or maybe it was this: View in a fixed-width font such as Courier.

. . . V+ . | . +---+----|>|----+------+-------+----+ . | | | | | | . [Rp] | | + | | | . | e === - S - . | |/ | ^ S ^ . +-| | | S | . | |\\ | | | | . | c-----------+------+ +----+ . [Rb] | | . | | | . | | | . +---------------|--------------+ . | | . | | . ON [Rc] c . -- | |/ . | | >--|-----[Rb]-+-| . | | | | |\\ . - - | [Rp] e . | | | . +----------+---+ . | . .--- . GND . .

Or maybe this for fast recovery- IIRC you posted several mods: View in a fixed-width font such as Courier.

. . . V+ . | . +---+---+------|>|-+---+----------------+----+ . | | | | | | | . [Rp] | | | + | | | . | e | === - S - . | |/ | | ^ S ^ . +-| | | | S | . | |\\ | | | | | . | c--------------+---+ +----+ . [Rb] | | | . | | [Rc] | . | | | | . +------------------|--------------------+ . | | | | . - | | | . ^ [Rbc] c ON c . | | |/ -- |/ . +-------+-|>|--+-| | | >-[Rb]-+-| . | |\\ | | | |\\ . [Rp] e - - [Rp] e . | | | | . +---+----------------+---+ . | . .--- . GND . .

Should have bought latching relays- too late now-)

There may have been some issue about even a single reverse diode drop across the storage capacitor- so this will guarantee 0V reverse voltage- but I still like the feel good diode there anyway- you lose a diode drop in the drive: View in a fixed-width font such as Courier.

. . . V+ . | . +---+---+----|>|---+---+----------------+----+ . | | | | | | | . [Rp] | | | + | | | . | e | === - S - . | |/ | | ^ S ^ . +-| | | | S | . | |\\ | | | | | . | c--------|>|---+---+ +----+ . [Rb] | | | . | | [Rc] | . | | | | . +------------------|--------------------+ . | | | | . - | | | . ^ [Rbc] c ON c . | | |/ -- |/ . +-------+-|>|--+-| | | >-[Rb]-+-| . | |\\ | | | |\\ . [Rp] e - - [Rp] e . | | | | . +---+----------------+---+ . | . .--- . GND . .

Maybe use a Schottky diode and linearizing resistor to bleed the few nanoamps around the capacitor. View in a fixed-width font such as Courier.

. . . V+ . | SD . +---+---+----|>|---+---+----+-----------+----+ . | | | | | | | | . [Rp] | | | + | | | | . | e | === - [10K] S - . | |/ | | ^ | S ^ . +-| | | | | S | . | |\\ | PND | | | | | . | c--------|>|---+---+----+ -+----+ . [Rb] | | | . | | [Rc] | . | | | | . +------------------|--------------------+ . | | | | . - | | | . ^ [Rbc] c ON c . | | |/ -- |/ . +-------+-|>|--+-| | | >-[Rb]-+-| . | |\\ | | | |\\ . [Rp] e - - [Rp] e . | | | | . +---+----------------+---+ . | . .--- . GND . .

Nah- what am I thinking- now the capacitor maintains a few 100mV forward bias: View in a fixed-width font such as Courier.

. . . . . V+ . | SD . +---+---+----|>|---+---+----------------+----+ . | | | | | | | . [Rp] | | | + | | | . | e | === - S - . | |/ | | ^ S ^ . +-| | | | S | . | |\\ | PND | | | | . | c--------|>|---+---+--[10K]--|>|----+----+ . [Rb] | | | . | | [Rc] | . | | | | . +------------------|--------------------+ . | | | | . - | | | . ^ [Rbc] c ON c . | | |/ -- |/ . +-------+-|>|--+-| | | >-[Rb]-+-| . | |\\ | | | |\\ . [Rp] e - - [Rp] e . | | | | . +---+----------------+---+ . | . .--- . GND . .

Geez, Fred, would you please make up Tony's mind? :-)

Ed

P.S. Thanks for posting

Similar to that one afair. Although it would be nice for the pnp to go Off early to get longest re-charge time for the C.

Fred seems to have it in hand. :-)

I also recall on that thread a relay driver chip that put full voltage on initially, then pwm'd to reduce the relay power.

Okay- then since the storage capacitor is not exactly a precision component and can be oversized slightly, a one-shot based on worst case solenoid pull-in time using low Vgs MOSFETs works- the sim looks good for 2n7000's and 500mA @24V loads- can be scaled up if necessary: View in a fixed-width font such as Courier.

. . . +------------[Rg]----------+ . | | . | V+ | . | | SD | . | +-------+----|>|-------+---+--------------+---+ . | | | | | | | . | | | | + | | | . | d | C === - - S . | |-+ [Rb] S | ^ ^ S . +-|N | | | | S . | |-+ | | | | | . | s----------------------+---+ +---+ . | | | | . c | | | . \\| | | | . |--+--|-[Rg]-+-|N . | | | - - | |-+ . | | | [Rp] s . | | | | | . +----+---------------------+------------------+---+ . | . --- . GND . .

"Tony Williams" a écrit dans le message de news: snipped-for-privacy@ledelec.demon.co.uk...

I remember doing that with a 555 in the 80s.

If one have enough relays to justify 2 supply voltages and don't want high toggle rate, then this simple one will do:

Vsust -------------. | | C| C| C| | | ,-----+ | | V --- - === | +| ___ `-----+---|___|--> Vstart > Vsust | | ||-+ ||

I suppose this could be made into a real workhorse: View in a fixed-width font such as Courier.

. . +----------------------------------+ . | | . | | . e | . \\| | . |---------------------+---[Rp]---+ . /| | | . c | | . | V+ | | . | | SD | | . | +-----|>|---------------+----+---------+ . [100] | | | | | . | | | | | | . | d | | | +---+ . | |-+ | | + | | | . +--------|N [Rbg] C === - - S . | |-+ | S | ^ ^ S . | s | | | | S . | | | | | | | . | | | | | +---+ . | SD | | | | | . +-|--+-|N . | - - | |-+ . | [Rp] s . | | | . +--------------------------+------------------+---+ . | . --- . GND .

Some clamp diodes: View in a fixed-width font such as Courier.

. . +----------------------------------+ . | | . e | . \\| | . |---------------------+---[Rp]---+ . /| | | . c | | . | +---|>|----+ . | V+ | | . | | SD | | . | +----+--|>|-------------+----+---------+ . [100] | | | | | | . | | | | | | | . | d | | | | +---+ . | |-+ | | | + | | | . +--------|N - [Rbg] C === - - S . | |-+ ^ | S | ^ ^ S . | s | | | | | S . | | | | | | | | . | | | | | | +---+ . | SD | | | | | | . +-|--+-|N . | - - | |-+ . | [Rp] s . | | | . +--------------------------+------------------+---+ . | . --- . GND .

I suppose this could be made into a real workhorse: View in a fixed-width font such as Courier.

. . +----------------------------------+ . | | . | | . e | . \\| | . |---------------------+---[Rp]---+ . /| | | . c | | . | V+ | | . | | SD | | . | +-----|>|---------------+----+---------+ . [100] | | | | | . | | | | | | . | d | | | +---+ . | |-+ | | + | | | . +--------|N [Rbg] C === - - S . | |-+ | S | ^ ^ S . | s | | | | S . | | | | | | | . | | | | | +---+ . | SD | | | | | . +-|--+-|N . | - - | |-+ . | [Rp] s . | | | . +--------------------------+------------------+---+ . | . --- . GND .

Some clamp diodes: View in a fixed-width font such as Courier.

. . +----------------------------------+ . | | . e | . \\| | . |---------------------+---[Rp]---+ . /| | | . c | | . | +---|>|----+ . | V+ | | . | | SD | | . | +----+--|>|-------------+----+---------+ . [100] | | | | | | . | | | | | | | . | d | | | | +---+ . | |-+ | | | + | | | . +--------|N - [Rbg] C === - - S . | |-+ ^ | S | ^ ^ S . | s | | | | | S . | | | | | | | | . | | | | | | +---+ . | SD | | | | | | . +-|--+-|N . | - - | |-+ . | [Rp] s . | | | . +--------------------------+------------------+---+ . | . --- . GND .

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 | | | | | | . +-|---+ | . N|--------------+ | | | | | | . +-| | | | - - | | . s | | | | | . | +--|

Whoops- just spotted an opportunity to add two more diodes:-) View in a fixed-width font such as Courier.

. . . +----------------------------------+ . | | . e 2N4403 | . \\| | . |--------------+----------[1K]---+ . /| | | . c 12V | | . | | | SD | . | +---------------+---|>|-+----+---------+ . | | | | | | | . [100] | | - | | | . | | | v | | | . | d | | | | +---+ . | |-+ c - | + | | | . +--------|N \\| v C === - - S . | |-+ |-------+ S | ^ ^ S . | s /| | | | | S . | | e | | | | | . | | |2N4401 | | | +---+ . | SD | | | | | | . +-|---+ | . N|--------------+ | | | | | | . +-| | | | - - | | . s | | | | | . | +--|