DC Voltage level sensing

A comp would be fine, but the TL431 has a built-in precision voltage ref, comes in a 3-pin TO-92, what's not to like?

--
 Thanks, 
    - Win

With a little extra information, an ambient temp rule could be had, and it'd be relatively easy to modify the circuit to automatically adjust its setpoint.

--
 Thanks, 
    - Win

h r

Periodically "tweaking a pot" is exactly the reason why digital is so much better than analog for a host of problems. People who can't hack digital m ay be loath to use it, but this is the sort of problem that can be addresse d with a $0.50 MCU on a $4 board off the shelf and a few lines of code. No need to order many different parts although you will need a couple of resi stors to reduce the voltage being measured to an acceptable value, so it st ill has an analog component. lol

In all seriousness, for either solution you will need to ruggedize against the voltage excursions seen in a car. So there's more analog for the digit al solution.

--

  Rick C. 

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Ruled what out, using a comparator? That's what his circuit is, a comparator with added hysteresis.

--

  Rick C. 

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That's right, we're warned about 60V load-dump surges.

--
 Thanks, 
    - Win

In addition to a deficit in basic English comprehension, you also clearly couldn't be bothered to follow up on the reference I provided. Here for your benefit, is what Win wrote verbatim further up the thread:

"No, sorry, not Figure 25. Although this is a perfect application for a TL431, none of the figures in any of the datasheets show it. "

See that? The bit where he explicitly states, "NOT FIGURE 25". Maybe you are looking at a different datasheet to everyone else after all. Sigh...

Did you look at figure 25. It is for a comparator circuit. Win's design is simply using the part as a comparator with the output driving a FET gate with an added resistor to add hysteresis.

As to your insults and reference to a link, I saw no functional link. I clicked it and it accomplished nothing. Win himself suggested we were looking at different data sheet. Why don't you save your insults for the playground?

--

  Rick C. 

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Hey dumbass, I'll post the entire quote for you in context since you're clearly so lame with Usenet you need to be spoon-fed everything. Here we go:

*********************************************************************** *************************************************************************

Capiche now?

Thank you for the very informative profanities. If you would refer to my previous post you will find that everything I wrote there still applies. Enjoy your weekend.

--

  Rick C. 

  ---+ Get 1,000 miles of free Supercharging 
  ---+ Tesla referral code - https://ts.la/richard11209

Capiche what? I'll have to confess I don't understand what you two are arguing about. Or maybe you're just discussing something.

--
 Thanks, 
    - Win

He is saying I am mistaken about the fact that you are using the part as a comparator. That's all. Are you using the TL431 as a comparator in your d esign?

Not sure why he's making such a big deal about this. He seems to think it all revolves around the fact that we were looking at different data sheets and so Fig 25 is a comparator in the TI data sheet I found and it's a crowb ar circuit in the one you found.

--

  Rick C. 

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  --+- Tesla referral code - https://ts.la/richard11209

Winfield Hill wrote:

Here's a TL431 overvoltage protection circuit I posted on Sat, 28 Sep 2019. It triggers at 48V.

Version 4 SHEET 1 2876 1700 WIRE 224 -256 160 -256 WIRE 384 -256 224 -256 WIRE 624 -256 384 -256 WIRE 928 -256 624 -256 WIRE 1184 -256 928 -256 WIRE 384 -208 384 -256 WIRE 624 -208 624 -256 WIRE 1184 -208 1184 -256 WIRE 928 -192 928 -256 WIRE 1072 -192 1024 -192 WIRE 1120 -192 1072 -192 WIRE 1136 -192 1120 -192 WIRE 1072 -128 1072 -192 WIRE 160 -96 160 -256 WIRE 256 -96 160 -96 WIRE 384 -96 384 -128 WIRE 480 -96 384 -96 WIRE 624 -96 624 -128 WIRE 688 -96 624 -96 WIRE 768 -96 688 -96 WIRE 912 -96 848 -96 WIRE 976 -96 976 -128 WIRE 976 -96 912 -96 WIRE 160 -80 160 -96 WIRE 256 -80 256 -96 WIRE 384 -80 384 -96 WIRE 1184 -80 1184 -112 WIRE 1264 -80 1184 -80 WIRE 1280 -80 1264 -80 WIRE 480 -48 480 -96 WIRE 544 -48 480 -48 WIRE 560 -48 544 -48 WIRE 1184 -48 1184 -80 WIRE 1072 -32 1072 -48 WIRE 160 16 160 0 WIRE 384 16 384 0 WIRE 624 32 624 0 WIRE 624 48 624 32 WIRE 1184 48 1184 32 WIRE 256 64 256 0 WIRE 288 64 256 64 WIRE 576 64 288 64 WIRE 256 96 256 64 WIRE 576 112 560 112 WIRE 560 128 560 112 WIRE 624 144 624 128 WIRE 256 192 256 176 FLAG 160 16 0 FLAG 624 144 0 FLAG 224 -256 Vin FLAG 256 192 0 FLAG 912 -96 Q1B FLAG 1072 -32 0 FLAG 1184 48 0 FLAG 1120 -192 M1G FLAG 1264 -80 Vout FLAG 560 128 0 FLAG 288 64 R1R3 FLAG 688 -96 R2R4 FLAG 384 16 0 FLAG 544 -48 Q2B FLAG 624 32 Q2E SYMBOL voltage 160 -96 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -44 320 Invisible 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 608 -224 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 240 -96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 240 80 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 1024 -128 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 89 64 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL res 864 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 1136 -112 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 1056 -144 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 1168 -64 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 624 144 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 SYMBOL npn 560 -96 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 368 -224 R0 SYMATTR InstName R7 SYMATTR Value 10K SYMBOL res 368 -96 R0 SYMATTR InstName R8 SYMATTR Value 10k TEXT 488 -328 Left 2 !.tran 0 1m 0 1u TEXT 488 -360 Left 2 ;'48V Overvoltage Protection TEXT -64 256 Left 1 !.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=100 Bf=

132.1 Ne=1.375 Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 Nc=2 Isc=0 Ikr=0 Rc= 1.6 Cjc=17.63p Mjc=.5312 Vjc=.75 Fc=.5 Cje=73.39p Mje=.3777 Vje=.75 Tr= 1.476n Tf=641.9p Itf=0 Vtf=0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild) TEXT -64 280 Left 1 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=-2.4 mtriode=2.2 Kp=35 lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cgs=4n cjo=200p M=.3 VJ=.9 Is=3.6p Rb=5.5m mfg=Siliconix ksubthres=.1 Vds=-100 Ron=34m Qg=106n pchan) TEXT 472 184 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0) TEXT 696 88 Left 2 ;Replace the switch with a TL431

Never said any such thing. I suggest you learn to read properly before posting any more of your nonsense.

Whatever he is going on about, he certainly has his knickers in a knot about it.

--

  Rick C. 

  --++ Get 1,000 miles of free Supercharging 
  --++ Tesla referral code - https://ts.la/richard11209

TVS diodes are commonly used to absorb the load dump energy. Newer cars use TVS diodes in the alternator to take care of the entire vehicle (TVS diodes are still used in the electronics. 27V is a common withstand voltage to allow for double battery cause by a moron jump starting the car - backwards. 42V is the "normal" ABS MAX for devices hanging off the vehicle bus (with local TVS).

There are some problems with the .asc text, LTspice kicks it out with an error, even after I edited the overflow lines near the end.

Unknown schematic syntax

--
 Thanks, 
    - Win

Winfield Hill wrote:

I'm very sorry, Win. You are right.

The line wrap in SED makes it very difficult to post files containing models. I have tried many different ways of getting around the problem with random results. Sometimes it works, sometimes not.

The only solution seems to be to get rid of model statements. The trick now is to find components that exist both in IV and XVII. That is trickier than it sounds, but I finally managed. Try this version. Thanks!

Version 4 SHEET 1 1940 1700 WIRE 144 -240 -80 -240 WIRE 384 -240 144 -240 WIRE 640 -240 384 -240 WIRE 832 -240 640 -240 WIRE 944 -240 832 -240 WIRE 832 -224 832 -240 WIRE 144 -160 144 -240 WIRE 384 -160 384 -240 WIRE 944 -160 944 -240 WIRE 640 -144 640 -240 WIRE 832 -144 832 -160 WIRE 832 -144 736 -144 WIRE 880 -144 832 -144 WIRE 896 -144 880 -144 WIRE 832 -80 832 -144 WIRE -80 -48 -80 -240 WIRE -32 -48 -80 -48 WIRE 16 -48 -32 -48 WIRE 144 -48 144 -80 WIRE 240 -48 144 -48 WIRE 384 -48 384 -80 WIRE 448 -48 384 -48 WIRE 480 -48 448 -48 WIRE 624 -48 560 -48 WIRE 688 -48 688 -80 WIRE 688 -48 624 -48 WIRE -80 -32 -80 -48 WIRE 16 -32 16 -48 WIRE 144 -32 144 -48 WIRE 944 -32 944 -64 WIRE 1024 -32 944 -32 WIRE 1040 -32 1024 -32 WIRE 240 0 240 -48 WIRE 304 0 240 0 WIRE 320 0 304 0 WIRE 944 0 944 -32 WIRE 832 16 832 0 WIRE -80 64 -80 48 WIRE 144 64 144 48 WIRE 384 80 384 48 WIRE 384 96 384 80 WIRE 944 96 944 80 WIRE 16 112 16 48 WIRE 48 112 16 112 WIRE 336 112 48 112 WIRE 16 144 16 112 WIRE 336 160 320 160 WIRE 320 176 320 160 WIRE 384 192 384 176 WIRE 16 240 16 224 FLAG -80 64 0 FLAG 384 192 0 FLAG -32 -48 Vin FLAG 16 240 0 FLAG 624 -48 Q1B FLAG 832 16 0 FLAG 944 96 0 FLAG 880 -144 M1G FLAG 1024 -32 Vout FLAG 320 176 0 FLAG 48 112 R1R3 FLAG 448 -48 R2R4 FLAG 144 64 0 FLAG 304 0 Q2B FLAG 384 80 Q2E SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -8 -211 Left 2 SYMATTR Value PULSE(0 100 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 368 -176 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 0 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 0 128 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 736 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 45 161 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 576 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 896 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 816 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 928 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 384 192 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 SYMBOL npn 320 -48 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 128 -176 R0 SYMATTR InstName R7 SYMATTR Value 10K SYMBOL res 128 -48 R0 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL zener 848 -160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BZX84C12L TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'48V Overvoltage Protection TEXT 200 248 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0) TEXT 456 136 Left 2 ;Replace the switch with a TL431

Here's the PLT file

[Transient Analysis] { Npanes: 1 { traces: 2 {524290,0,"V(vin)"} {524291,0,"V(vout)"} X: ('m',1,0,0.0001,0.001) Y[0]: (' ',0,0,10,100) Y[1]: ('_',0,1e+308,0,-1e+308) Volts: (' ',0,0,0,0,10,100) Log: 0 0 0 GridStyle: 1 } }

There is no line wrap in usenet, but there is a 998 octet line length limit it is probably your user-agent software mangling long lines

TEXT -64 280 Left 1 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=-2.4 mtriode=2.2 Kp=35 lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cgs=4n cjo=200p M=.3 VJ=.9 Is=3.6p Rb=5.5m mfg=Siliconix ksubthres=.1 Vds=-100 Ron=34m Qg=106n pchan)

--
  When I tried casting out nines I made a hash of it.

I don't see why it would. Modern cars have to have very good regulation, so I've only seen 12.4V when idle and 14V when running. Ergo, no need to worry about hysteresis AFAICS.

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