Can this threshold circuit be improved - Automotive Key 15

Are those F or C degrees? At 125, it matters and since this is automotive I assume C.

What have you got against a reference and comparitor method? It would be a lot less parts total.

What is the 74HC14 running on?

Maybe use another TLV431 instead of D30 and Q5? Its gate could be driven from a voltage divider that hangs on "Key" and it will draw cathode current when the gate level exceeds the threshold. Cost-wise it shouldn't be a huge difference, but it'll be more precise.

Sharper over the range ...

You can eliminate many of those components with this concept, let Klaus work it out, there are pitfalls here: View in a fixed-width font such as Courier.

. . . . . 'HC14 . _____ /| . KEYON -[Rs]-+----+-----e c ---------+----> SMPS . | | b | 4V7 . | | | | input . | [R1A] | | . | | | | --------- . | | --- '431 [RF2] | | . === +------/ \\ | | | . C| | --- | | | . | [R1B] | | --------- . | | | | 4v 7v . | +-------|------------' . | | | key->

. | [RF1] | . | | | . ----+----+-------+------------------------ . .

Isn't the quiescent current of the TL431 going to f*ck up the works? Place a bleed e-b

...Jim Thompson

Yep, but doesn't have to be much. The cathode current becomes miniscule when it drops out of regulation.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Hey Jim, two can play that game! Short R1b, not needed. Cheers, Harry

Yep, Iq is low (a few uA), but regulation accuracy is only spec'd for cathode current >= 400uA.

...Jim Thompson

What does that fix? Are we playing "shoot from the hip" ?:-)

...Jim Thompson

Most definitely over temperature, and then he has that POWER_KEEP override thing: View in a fixed-width font such as Courier.

. . 'HC14 . _____ /| to . KEYON |->SMPS . \\| | VDD . | .PWR_KP>-|>|--. | . | BC857 | . | | to . KEY >-|>|--+-[Rs]-+----+-----+- e c ---+----> SMPS . | | | | b | 4V7 . | | | [R2] | | input . | | | | | | . | | [R1A] '----+ | . | | | | | 4v7 ------- . | | | --- [RF2] | | . [RPD] === +---------/ \\ | | | . | C| | --- | | | . | | [R1B] |'431 | 0 -------- . | | | | | 4v 7v . | | +----------|------' . | | | | KEY->

. | | [RF1] | . | | | | . ----------+------+----+----------+------------>to SMPS GND .

Well that possibly messes up the KEY_STATUS logic. I think it would be simpler to use the '431 or a ZD to establish any kind of 5V logic level and then clean up all this battery level KEY and POWER_KEEPER logic with a '393 pulled up to the 5V, and route that around to the SMPS and his control computer...

=A0 =A0 ...Jim Thompson

=A0 =A0 =A0 =A0 =A0 =A0to

=A0 =A0 =A0 | =A0 =A0 =A0VDD

=A0 =A0 =A0 =A0 |

=A0 =A0|

=A0 =A0 =A0 | =A0 =A0 =A0 to

=A0 =A0| =A0 =A0 =A0 4V7

=A0| =A0 =A0 =A0 input

=A0 =A0|

=A0 =A0 =A0| =A0 =A0 =A0 =A04v7 =A0 -------

=A0 [RF2] =A0 =A0 =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0|

=A0 | =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0|

=A0| =A0 =A0 =A0 =A0 0 --------

=A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 4v =A0 7v

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 KEY->

Thanks for the inputs ;-)

I was sick last week with pneumonia and has been to weak to use the keys on the keyboard (almost)

Well, I did find an alternative way:

This uses an 100uA LDO to be used both as reference and as the KEY control. It has a precise input, so the issues of temperature drift etc are solved. The Flag output clamps the reference in the other schematics, so this upower LDO is always enabled

Regards

Klaus

Sorry to hear that, hope nobody around you got it. Grandma would hang us over a pot of steaming water with chamomile buds in there and a towel over the head. It worked ...

Wow, those are expensive. Looks like tke KEY_STATUS would still need work since it won't reliably transition at 4V. Can the FLAG output be used for that as well? Also, you might need a hysteresis back to MON so the thing doesn't get the shakes when KEY comes a bit sluggish.

Personally I am not a fan of LDOs, seen too much grief with them. Including stuff where the manufacturer's app engineers said "oh, oh!" and pretty much gave up.

If Klaus had been visiting me, as planned, he wouldn't have pneumonia, he'd have sun burn ;-)

...Jim Thompson

When he comes and you don't want to fire up the grill at home maybe take him to Rustler's Roost at South Mountain. I don't know if they still have the live bull out front but Europeans usually can't believe that they are really serving rattle snake as an appetizer. Great view and good beers, too.

That's actually not far from my location... I'm due south of the transmitter towers on South Mountain.

...Jim Thompson