switching FETs or relays

[[email protected]]

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?

 

[[email protected]]

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?

A couple of MOSFET switches are going to be cheaper, more compact and
much less power hungry.

Using a TTL output (switching between 0.4V and around 3.0V) to control
a P-channel MOSFET sourcing your +12V and an N-channel MOSFET sourcing
your -12V is going to take a little fiddling.

A 1k pull-up resistor from the TTL output to +5V would give you useful
extra output swing.

You could use a "logic level" N-MOSFET - gate tied to the TTL output,
source tied to 0V and drain tied to the gate of the P-channel MOSFET
to control the +12V rail. You will need a resistor (perhaps100k) tied
to the +12V supply to make sure that the P-channel MOSFET turns off.

Turning on the -12V rail is a little more difficult. Perhaps the
easiest way to do it would to use a second P-channel MOSFET in
parallel with the one switching the +12V rail to drive the gate of the
N-channel MOSFET driving the -12V rail. Again, you will need a
resistor from the drain of the second P-channel MOSFET to the -12V
supply to make sure that the N-channel MOSFET is fully off when it is
supposed to be off.

Hope this helps.

 

[Jamie]

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?

use a hex fet or some logic fet rated for the current and voltage.
pick one that has the lowest On Resistance

 

[Eeyore]

use a hex fet

You only recommend parts from IR do you ?

or some logic fet rated

Since the TTL signal is almost certainly going to be ground referenced and the
load is 'high side', a logic level fet is NOT required.

Graham

 

[Eeyore]

Yeah, I work for them.

They make very good parts for sure but it would have been more helpful to use the
term power mosfet.

Why not?, because it's to simple?

I suggest you think about how a logic level fet helps a 'TTL' 0-5V signal switch the
fets on the +12V and -12V supplies. Answer ..... it doesn't because the control
signal needs to be referenced to +12V and -12V.

You need level translation to drive both fets. Since you work for IR you should know
this since 'high side drivers' are a bit of an IR speciality.

Graham

 

[Jamie]

Jamie wrote:




You only recommend parts from IR do you ?

Yeah, I work for them.

Since the TTL signal is almost certainly going to be ground referenced and the
load is 'high side', a logic level fet is NOT required.

Graham

Why not?, because it's to simple?

 

[Eeyore]

#1.
I don't work for IR. That was just a derogatory remark which you
obvious didn't pick up on. Not surprised considering the heritage
you were born into. No fault on your part. I guess you could blame that
on us also.

#2.
It shows that you haven't worked with Logic Fets that much if
any at all.

#3
Yes, I know about high side drivers, I've designed a few small scale
drives and DC amplifiers using power fets.

You couldn't design yourself out of a wet paper bag.

We've used Logic Fets
down in the range of 2.5 volts for 50 % turn on and at 4.5 volts, full
turn on.
#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 ?

You think TTL circuits output a NEGATIVE output voltage in the OFF state ?
Bwahahahaahahhahaha !!!

That has NEVER been the case.

#5
There is a reason they make P-Channels and N-Channel fets.
You speak of high side ? I assume you mean the + rail maybe?
In which case, you could use a P-Channel, and the - rail an
N-channel.

None of which helps you switch +/-12V from TTL.

Graham, take a tea break. you need the caffeine!

You're a FUCKIN MORON ! As ever, you're just taking waffle.

You haven't the tiniest clue about how to switch +/-12V.

Why don't you just SHUT UP. You have NOTHING to offer this group other than your very
considerable IGNORANCE.

Graham

 

[Jamie]

Jamie wrote:




They make very good parts for sure but it would have been more helpful to use the
term power mosfet.





I suggest you think about how a logic level fet helps a 'TTL' 0-5V signal switch the
fets on the +12V and -12V supplies. Answer ..... it doesn't because the control
signal needs to be referenced to +12V and -12V.

You need level translation to drive both fets. Since you work for IR you should know
this since 'high side drivers' are a bit of an IR speciality.

Graham

#1.
I don't work for IR. That was just a derogatory remark which you
obvious didn't pick up on. Not surprised considering the heritage
you were born into. No fault on your part. I guess you could blame that
on us also.

#2.
It shows that you haven't worked with Logic Fets that much if
any at all.

#3
Yes, I know about high side drivers, I've designed a few small scale
drives and DC amplifiers using power fets. We've used Logic Fets
down in the range of 2.5 volts for 50 % turn on and at 4.5 volts, full
turn on.
#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 ?

#5
There is a reason they make P-Channels and N-Channel fets.
You speak of high side ? I assume you mean the + rail maybe?
In which case, you could use a P-Channel, and the - rail an
N-channel.

Graham, take a tea break. you need the caffeine!

 

[Jamie]

Jamie wrote:




You couldn't design yourself out of a wet paper bag.





You think TTL circuits output a NEGATIVE output voltage in the OFF state ?
Bwahahahaahahhahaha !!!

What an ignorant sap.
Did you really read and understand what I wrote above?

That has NEVER been the case.





None of which helps you switch +/-12V from TTL.

I was unsure about your background, now it's confirmed.

You're a FUCKIN MORON ! As ever, you're just taking waffle.

You haven't the tiniest clue about how to switch +/-12V.

Why don't you just SHUT UP. You have NOTHING to offer this group other than your very
considerable IGNORANCE.

Graham

Your losing it boy!, lack of control !, sign of some one in the rear and
falling ever so more.

Have a good day Eyhaw, Eyhaw.
oh sorry , that of Eeyore. How inconsiderate of me.

 

[Eeyore]

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.

 

[Eeyore]

'High side' has a generic meaning. It's limited to the polarity of a supply or signal.


Still irrelevant to any advantage that logic level fets might offer.

I was unsure about your background, now it's confirmed.

More utter drivel.

The fact you can't understand why a logic level fet is irrelevant to switching +/-12V
simply illustrates you're an IDIOT without the tiniest clue about hardware design.

Is there any limit to your ignorance ?

Graham

 

[Jamie]

Jamie wrote:

Are you really that bad?

 

[Eeyore]

Are you really that bad?

Where does the -2.5V come from Mr Knowall ?

Graham

 

[Eeyore]

Your hole is getting deeper. Keep digging.

I'd say that applies to you actually.

So, Mr Self-appointed Expert. Can I ask you this ?

You suggest the use of a p-channel mosfet to switch the +12V and an n-channel to switch the
-12V.

Since you're such an expert, I'm sure you can tell us what the required gate voltages will
be turn these on and off won't you ?

I'd also like to see you explain how the use of 'logic level' mosfets will make the job any
easier wrt using a standard TTL signal as the control input.

You might also care to give an example of a suitable 'logic level' p-channel mosfet btw.


Graham

 

[Jamie]

Jamie wrote:




'High side' has a generic meaning. It's limited to the polarity of a supply or signal.





Still irrelevant to any advantage that logic level fets might offer.





More utter drivel.

The fact you can't understand why a logic level fet is irrelevant to switching +/-12V
simply illustrates you're an IDIOT without the tiniest clue about hardware design.

Is there any limit to your ignorance ?

Graham

Your hole is getting deeper. Keep digging.
You might end up on the other side. As I
read your never endless sappy posts. It appears
your talents for insults are running dry!

Is that all you got?

I don't know if it would have any relevance but
I was at a chinese restaurant tonight. when it
came time for the fortune cookie. I had to
make a mental note of the script in it.
Something you should of read.

"To get the last word in, Apologize"

 

[Jamie]

Jamie wrote:




Where does the -2.5V come from Mr Knowall ?

Graham

And when speaking of TTL, where does it say that in the last sentence
moron!
You do notice I only spoke of TTL in the last sentence.
Yes, I made a mistake! I forgot to capitalize the "in" so sue me.

You know, my dog has more intelligence. I think i'll take her for a
walk.
Bye idiot.

 

[Jamie]

Jamie wrote:




I'd say that applies to you actually.

So, Mr Self-appointed Expert. Can I ask you this ?

You suggest the use of a p-channel mosfet to switch the +12V and an n-channel to switch the
-12V.

Since you're such an expert, I'm sure you can tell us what the required gate voltages will
be turn these on and off won't you ?

I'd also like to see you explain how the use of 'logic level' mosfets will make the job any
easier wrt using a standard TTL signal as the control input.

You might also care to give an example of a suitable 'logic level' p-channel mosfet btw.


Graham

I'm sorry, if you have never seen this before. It's obvious you're lost.

You should have stopped long ago. It's making you look worse than ever.

If you really read my posts, you would of seen something in there and
you wouldn't be asking this idiot. I don't repeat my self and I won't
give you examples because it would take me to long to set up a
compatible program so that I post something here. I use my own software
for doing the CAD which includes the schematics, boards, cabinet and any
hardware items needed to support all of these component.
You see, unlike you. I program not for fun and games, but for the work
I do that also includes Uc,PLCs, Wonderware, Custom PC GUI for
industrial controls etc.. The software I used is very specific. It does
have a Gerber function that I have been working on. And that is only so
that we can start out souring our board info to others that need Gerber.

See you later jerk.

 

[Eeyore]

And when speaking of TTL, where does it say that in the last sentence
moron!
You do notice I only spoke of TTL in the last sentence.
Yes, I made a mistake! I forgot to capitalize the "in" so sue me.

You said "logic was +2.5 and up for ON State, -2.5 and down for Off state"

Where does the -2.5V come from Mr Knowall ?

Graham

 

[Eeyore]

I'm sorry, if you have never seen this before. It's obvious you're lost.

Is it indeed ? I can certainly see you're incapable of answering a few very simple and very
pertinent questions. The fact of the matter is that you've been talking out of your asshole of
course and just relying on blather to make yourself sound important ! I can supply the answers of
course but you can't.

Since you're such an arrogant whiney PRICK, you can't 'back down' either.

Furthermore, you can't "give an example of a suitable 'logic level' p-channel mosfet " CAN YOU ?
Let me explain why ....

That's because there are NO 'logic level' p-channel mosfets. If you had even the tiniest
knowledge of circuit design you would be able to see why.

Kind of nicely illustrates how STUPID you claim was that logic level mosfets made the job of
switching +/-12V any easier.

Graham

 

[Eeyore]

I use my own software
for doing the CAD which includes the schematics, boards, cabinet and any
hardware items needed to support all of these component.
You see, unlike you. I program not for fun and games, but for the work
I do that also includes Uc,PLCs, Wonderware, Custom PC GUI for
industrial controls etc.. The software I used is very specific. It does
have a Gerber function that I have been working on. And that is only so
that we can start out souring our board info to others that need Gerber.

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

Graham