switching FETs or relays

[[email protected]]

#4
Last time I went to school for this (years ago, experienced
followed) logic was +2.5 and up for ON State, -2.5 and down for Off
state. Anything between that was undefined. in the case of TTL , +2.5
and up was on, anything below was off.

Maybe things have changed ?

No, nothing has changed. TTL was always driven between a +5V rail and
a 0V rail. A low output was always between 0V and 0.4V, and a high
output between 2.4V and 5V.

Check any data sheet.

focus.ti.com/lit/ds/symlink/sn7400.pdf

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

 

[Eeyore]

You know, my dog has more intelligence.

I expect it has more intelligence than YOU !

It would be difficult for it not to have a more pleasant character too. I
suggest you leant how to temper your arrogant IGNORANCE from your dog.

Graham

 

[MooseFET]

On Sep 2, 9:15 pm, [email protected] wrote:
[... logic with +/- 2.5V levels.

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

How old is Jamie? If he is over about 65, there may be a good reason
he was taught those values for "logic". Notice that he said "logic"
in that part and TTL in a later part.

 

[Eeyore]

On Sep 2, 9:15 pm, [email protected] wrote:
[... logic with +/- 2.5V levels.

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

How old is Jamie? If he is over about 65, there may be a good reason
he was taught those values for "logic". Notice that he said "logic"
in that part and TTL in a later part.

And who actually uses true TTL these days ? I'd be shocked to see any genuine
TTL in any modern kit.

Aside from a casual reference to 'TTL levels', I'd specify CD4000/ HC/HCT output
levels.

Graham

 

[[email protected]]

On Sep 2, 9:15 pm, [email protected] wrote:
[... logic with +/- 2.5V levels.

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

How old is Jamie? If he is over about 65, there may be a good reason
he was taught those values for "logic". Notice that he said "logic"
in that part and TTL in a later part.

And who actually uses true TTL these days ? I'd be shocked to see any genuine
TTL in any modern kit.

Aside from a casual reference to 'TTL levels', I'd specify CD4000/ HC/HCT output
levels.

Input levels are rather more important than unloaded output logic
levels.

CD4000 input logic level thresholds are specified as 1/3rd and 2/3rd
of the rail voltages, which can be anything from 3V to 18V.

HC is more or less the same, but the maximum rail voltage is rather
lower.

HCT input levels are specified for compatibility with TTL, assuming a
5V supply rail - anything from 0V to 0.8V is guaranteed to be
recognised as a low, anything between 1.4V and 5V is guaranteed to be
recognised as a high. Rather different from CD4000 or HC.

 

[Guy Macon]

The statement quoted appears to be a simple typo.
Replace the "-" with a "+" and it becomes:

"Last time I went to school for this (years ago, experienced
followed) logic was +2.5 and up for ON State, +2.5 and down
for Off state. Anything between that was undefined. in the
case of TTL , +2.5 and up was on, anything below was off."

....which does not imply that TTL 0 is a negative voltage.

Jamie did misremember the voltage, though. That's the typical
(as opposed to guaranteed) switching voltage for 74HC logic.
For TTL, the levels are:

Assuming Vcc=5.0V and maximum fanout:
A TTL output 1 is guaranteed to be +2.4V or higher.
A TTL input is guaranteed to accept +2.0V or higher as a 1.
A TTL output 0 is guaranteed to be +0.5V or lower.
A TTL input is guaranteed to accept +0.8V or lower as a 0.
Typical switching level is roughly +1.5V

There are some nice articles here:
http://www.interfacebus.com/Logic_Family_Noise_Margin.html
http://www.web-books.com/eLibrary/Engineering/Circuits/Digital/DIGI_3P10.htm
http://www.interfacebus.com/Design_Logic_Family_Selection.html
http://www.twysted-pair.com/74xx.htm

 

[neon]

you are making the thing more unreliable by sticking fets and so forth a switch on the other hand is reliable and generaly accepyed as a device to turn on things.

 

[Eeyore]

On Sep 2, 9:15 pm, [email protected] wrote:
[... logic with +/- 2.5V levels.

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

How old is Jamie? If he is over about 65, there may be a good reason
he was taught those values for "logic". Notice that he said "logic"
in that part and TTL in a later part.

And who actually uses true TTL these days ? I'd be shocked to see any genuine
TTL in any modern kit.

Aside from a casual reference to 'TTL levels', I'd specify CD4000/ HC/HCT output
levels.

Input levels are rather more important than unloaded output logic
levels.

In the context of the OP's question it was only the output drive levels he mentioned.
These might reasonably be taken to be 'close to' 5V and 0V where a CMOS output stage
device (such as CD4000/74HC/74HCTetc) is used.

CD4000 input logic level thresholds are specified as 1/3rd and 2/3rd
of the rail voltages, which can be anything from 3V to 18V.

HC is more or less the same, but the maximum rail voltage is rather
lower.

HCT input levels are specified for compatibility with TTL, assuming a
5V supply rail - anything from 0V to 0.8V is guaranteed to be
recognised as a low, anything between 1.4V and 5V is guaranteed to be
recognised as a high. Rather different from CD4000 or HC.

Indeed.

Graham

 

[Eeyore]

The statement quoted appears to be a simple typo.
Replace the "-" with a "+" and it becomes:

So Jamie is just an IDIOT who doesn't know his + from his - ?

Sure, I can believe that.

Graham

 

[Genome]

I want to run my amplifier via batteries and use a TTL driven switch
to turn it ON, only when it's needed - to save power. So for +/- 12
volts with 20 mA should i go with FETs or just used mechanical
switches?

Here you go. This uses a pair of N and P channel mosfets along with
some level shifting. It also incorporates current limiting for start
up and just in case. Sorry about the limited, lack of, explanation and
component values.

Grab hold of LTSpice.....

http://www.linear.com/designtools/software/switchercad.jsp

Then cut and paste the text below into Notepad and save the file with
an .asc extension. Then you can load it into LTspice to look at it.


Version 4
SHEET 1 880 920
WIRE -208 -224 -256 -224
WIRE -176 -224 -208 -224
WIRE -64 -224 -96 -224
WIRE 0 -224 -64 -224
WIRE 352 -224 96 -224
WIRE -64 -192 -64 -224
WIRE -208 -128 -208 -224
WIRE -112 -128 -208 -128
WIRE 16 -128 16 -176
WIRE 16 -128 -16 -128
WIRE -208 -48 -208 -128
WIRE -192 -48 -208 -48
WIRE 16 -48 16 -128
WIRE 16 -48 -112 -48
WIRE 16 -16 16 -48
WIRE 16 96 16 64
WIRE 112 144 80 144
WIRE 160 144 112 144
WIRE 288 144 240 144
WIRE 416 144 352 144
WIRE 112 176 112 144
WIRE 16 240 16 192
WIRE 112 288 112 256
WIRE 112 288 80 288
WIRE 352 288 352 160
WIRE 352 288 112 288
WIRE 352 320 352 288
WIRE 16 368 16 336
WIRE -192 480 -224 480
WIRE 16 480 16 448
WIRE 16 480 -112 480
WIRE -224 560 -224 480
WIRE -112 560 -224 560
WIRE 16 560 16 480
WIRE 16 560 -16 560
WIRE 16 608 16 560
WIRE -224 656 -224 560
WIRE -224 656 -256 656
WIRE -192 656 -224 656
WIRE -64 656 -64 624
WIRE -64 656 -112 656
WIRE 0 656 -64 656
WIRE 352 656 96 656
FLAG 352 320 0
FLAG 416 144 CTRL
IOPIN 416 144 In
FLAG -256 -224 +12
IOPIN -256 -224 In
FLAG -256 656 -12
IOPIN -256 656 In
FLAG 352 -224 +12S
IOPIN 352 -224 Out
FLAG 352 656 -12S
IOPIN 352 656 Out
SYMBOL pmos 96 -176 M270
WINDOW 0 98 83 VLeft 0
WINDOW 3 74 83 VLeft 0
SYMATTR InstName M1
SYMBOL nmos 96 608 R90
WINDOW 0 71 47 VRight 0
WINDOW 3 95 10 VRight 0
SYMATTR InstName M2
SYMBOL npn 80 96 M0
WINDOW 0 79 36 Left 0
WINDOW 3 61 60 Left 0
SYMATTR InstName Q1
SYMBOL pnp 80 336 R180
WINDOW 0 83 60 Left 0
WINDOW 3 70 34 Left 0
SYMATTR InstName Q2
SYMBOL Digital\\buf1 352 80 M0
SYMATTR InstName TTL
SYMBOL res -208 -32 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 0 56 VBottom 0
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL res -96 464 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL res 96 160 R0
WINDOW 0 38 50 Left 0
SYMATTR InstName R3
SYMATTR Value 2K2
SYMBOL res 256 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 4K7
SYMBOL res -80 -240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 6R8
SYMBOL res -96 640 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 6R8
SYMBOL pnp -16 -192 R90
WINDOW 0 83 42 VRight 0
WINDOW 3 108 26 VRight 0
SYMATTR InstName Q3
SYMBOL npn -16 624 M270
WINDOW 0 104 72 VLeft 0
WINDOW 3 79 70 VLeft 0
SYMATTR InstName Q4
SYMBOL res 0 -32 R0
WINDOW 0 36 51 Left 0
SYMATTR InstName R7
SYMATTR Value 4K7
SYMBOL res 0 352 R0
WINDOW 0 40 50 Left 0
SYMATTR InstName R8
SYMATTR Value 4K7

 

[Eeyore]

Jamie did misremember the voltage, though. That's the typical
(as opposed to guaranteed) switching voltage for 74HC logic.
For TTL, the levels are:

Just how low are your prepared to GROVEL or arse-lick ?

This is a group for electronics designers and you would apparently seek to
promote those idiots who can't even do basic arithmetic or even understand what
supply voltages are in normal use over experienced 'real world' designers !

Go **** YOURSELF Macon !

Graham

 

[Genome]

I want to run my amplifier via batteries and use a TTL driven switch
to turn it ON, only when it's needed - to save power. So for +/- 12
volts with 20 mA should i go with FETs or just used mechanical
switches?

This one has some more meaningful values on it and you get to run an
analysis.

Version 4
SHEET 1 988 920
WIRE -224 -240 -272 -240
WIRE -176 -240 -224 -240
WIRE -64 -240 -96 -240
WIRE 0 -240 -64 -240
WIRE 672 -240 96 -240
WIRE 752 -240 672 -240
WIRE 864 -240 752 -240
WIRE -64 -208 -64 -240
WIRE -224 -144 -224 -240
WIRE -112 -144 -224 -144
WIRE 16 -144 16 -192
WIRE 16 -144 -16 -144
WIRE -224 -64 -224 -144
WIRE -192 -64 -224 -64
WIRE 16 -64 16 -144
WIRE 16 -64 -112 -64
WIRE 16 -32 16 -64
WIRE 672 -16 672 -240
WIRE 752 -16 752 -240
WIRE -224 80 -224 -64
WIRE 16 80 16 48
WIRE 112 128 80 128
WIRE 160 128 112 128
WIRE 288 128 240 128
WIRE 464 128 352 128
WIRE 560 128 464 128
WIRE 112 176 112 128
WIRE 464 176 464 128
WIRE -224 208 -224 160
WIRE -224 208 -256 208
WIRE -256 240 -256 208
WIRE 16 240 16 176
WIRE -224 256 -224 208
WIRE 112 288 112 256
WIRE 112 288 80 288
WIRE 352 288 352 144
WIRE 352 288 112 288
WIRE 464 288 464 256
WIRE 464 288 352 288
WIRE 672 288 672 48
WIRE 672 288 464 288
WIRE 752 288 752 64
WIRE 752 288 672 288
WIRE 464 320 464 288
WIRE 16 368 16 336
WIRE -224 480 -224 336
WIRE -192 480 -224 480
WIRE 16 480 16 448
WIRE 16 480 -112 480
WIRE 752 512 752 288
WIRE 672 528 672 288
WIRE -224 560 -224 480
WIRE -112 560 -224 560
WIRE 16 560 16 480
WIRE 16 560 -16 560
WIRE 16 608 16 560
WIRE -224 656 -224 560
WIRE -224 656 -256 656
WIRE -192 656 -224 656
WIRE -64 656 -64 624
WIRE -64 656 -112 656
WIRE 0 656 -64 656
WIRE 672 656 672 592
WIRE 672 656 96 656
WIRE 752 656 752 592
WIRE 752 656 672 656
WIRE 848 656 752 656
FLAG 464 320 0
FLAG 560 128 CTRL
IOPIN 560 128 In
FLAG -272 -240 +12
IOPIN -272 -240 In
FLAG -256 656 -12
IOPIN -256 656 In
FLAG 864 -240 +12S
IOPIN 864 -240 Out
FLAG 848 656 -12S
IOPIN 848 656 Out
FLAG -256 240 0
SYMBOL pmos 96 -192 M270
WINDOW 0 98 83 VLeft 0
WINDOW 3 74 83 VLeft 0
SYMATTR InstName M1
SYMATTR Value BSS84
SYMBOL nmos 96 608 R90
WINDOW 0 71 47 VRight 0
WINDOW 3 95 -1 VRight 0
SYMATTR InstName M2
SYMATTR Value BSS123
SYMBOL npn 80 80 M0
WINDOW 0 107 36 Left 0
WINDOW 3 61 60 Left 0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL pnp 80 336 R180
WINDOW 0 101 60 Left 0
WINDOW 3 57 34 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL Digital\\buf1 352 64 M0
SYMATTR InstName TTL
SYMATTR SpiceLine Vhigh=5V Vlow=0V Trise=100n Tfall=100n
SYMBOL res -208 -48 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 0 56 VBottom 0
SYMATTR InstName R1
SYMATTR Value 100K
SYMBOL res -96 464 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 100K
SYMBOL res 96 160 R0
WINDOW 0 38 50 Left 0
SYMATTR InstName R3
SYMATTR Value 47K
SYMBOL res 256 112 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 47K
SYMBOL res -80 -256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 6R8
SYMBOL res -96 640 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 6R8
SYMBOL pnp -16 -208 R90
WINDOW 0 76 48 VRight 0
WINDOW 3 100 1 VRight 0
SYMATTR InstName Q3
SYMATTR Value 2N3906
SYMBOL npn -16 624 M270
WINDOW 0 104 81 VLeft 0
WINDOW 3 79 82 VLeft 0
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL res 0 -48 R0
WINDOW 0 36 51 Left 0
SYMATTR InstName R7
SYMATTR Value 47K
SYMBOL res 0 352 R0
WINDOW 0 40 50 Left 0
SYMATTR InstName R8
SYMATTR Value 47K
SYMBOL cap 656 -16 R0
WINDOW 0 -59 28 Left 0
WINDOW 3 -61 52 Left 0
SYMATTR InstName C1
SYMATTR Value 100µ
SYMBOL cap 656 528 R0
WINDOW 0 -58 16 Left 0
WINDOW 3 -60 40 Left 0
SYMATTR InstName C2
SYMATTR Value 100µ
SYMBOL voltage 464 160 R0
WINDOW 0 43 56 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 5 1 100n 100n 1 2)
SYMBOL res 736 -32 R0
WINDOW 0 39 43 Left 0
WINDOW 3 39 69 Left 0
SYMATTR InstName R9
SYMATTR Value 220R
SYMBOL res 736 496 R0
WINDOW 0 36 53 Left 0
SYMATTR InstName R10
SYMATTR Value 220R
SYMBOL voltage -224 64 R0
WINDOW 0 36 46 Left 0
WINDOW 3 35 70 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12V
SYMBOL voltage -224 240 R0
WINDOW 0 37 45 Left 0
WINDOW 3 38 70 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 12V
TEXT 112 320 Left 0 !.tran 0 10 0

 

[Fred Bloggs]

And you have never seen negative rail logic circuits?
pity.

Not in the context of TTL. The actually logic family may be relegated to
replacement purposes only, but the input levels and loading have become
a de facto standard of input specification.

 

[Jamie]

No, nothing has changed. TTL was always driven between a +5V rail and
a 0V rail. A low output was always between 0V and 0.4V, and a high
output between 2.4V and 5V.

Check any data sheet.

focus.ti.com/lit/ds/symlink/sn7400.pdf

I can't imagine who might have taught you +/-2.5V - do let us know the
name of the school that you think taught you that. You may be able to
sue them for fraud, but if you are sufficiently out of touch with
reality not to have learned better, I can't hold out much hope..

And you have never seen negative rail logic circuits?
pity.

 

[Jamie]

Jamie wrote:




You'd better stick to software because for sure you know NOTHING of value about hardware design

Graham

And you don't seem to know the difference of a lot of things.
Your statements proves it. I don't need to go into details, others here
that know their field can see in your posts.

Just goes to show how much of an insignificant little twit you are.

I'm having fun watching you dig your self in deep.

better start making friends here, you'll need them. That is, if you can
find any that are as mindless and dead to reality as you are.

 

[Jamie]

The statement quoted appears to be a simple typo.
Replace the "-" with a "+" and it becomes:

"Last time I went to school for this (years ago, experienced
followed) logic was +2.5 and up for ON State, +2.5 and down
for Off state. Anything between that was undefined. in the
case of TTL , +2.5 and up was on, anything below was off."

...which does not imply that TTL 0 is a negative voltage.

Jamie did misremember the voltage, though. That's the typical
(as opposed to guaranteed) switching voltage for 74HC logic.
For TTL, the levels are:

Assuming Vcc=5.0V and maximum fanout:
A TTL output 1 is guaranteed to be +2.4V or higher.
A TTL input is guaranteed to accept +2.0V or higher as a 1.
A TTL output 0 is guaranteed to be +0.5V or lower.
A TTL input is guaranteed to accept +0.8V or lower as a 0.
Typical switching level is roughly +1.5V

it's true they will switch at much lower levels how ever, I
was referring to the design standard of guaranteed levels which
means. Those that design circuits should insure the (1) state is
2.5 or more even though we know, many will switch way below that but
not advised. This was one of the faults of circuit designed that caused
many TTL circuits to generate excessive heat due to insufficient input
levels to force the device into saturation state.

Dense input types of AND/OR's were noted to miss behave if the
minimum on all inputs were not up to spec. there were also a few logic
series that used diodes on the inputs so that the (1) state would turn
on closer to the 2.5 point.

Oh well.
Have a good day.,

 

[Fred Bloggs]

This one has some more meaningful values on it and you get to run an
analysis.

Very nice...

 

[[email protected]]

And you have never seen negative rail logic circuits?
pity.

Do a google groups search on "Bill Sloman"+ECL - you will get 243
hits. Adding in PECL still leaves 34 hits.

Scarcely relevant in a discussion with someone who thinks that TTL
swings between +2.5V and -2.5V.

 

[Eeyore]

And you have never seen negative rail logic circuits?
pity.

*TTL* does not run from a negative rail.

Graham

 

[[email protected]]

This one has some more meaningful values on it and you get to run an
analysis.

Version 4

Great, this does make sense. I Appreciate that Genome. Thank you