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Help with circuit diagram

ericgibbs

Well-Known Member
Most Helpful Member
You're going to have to help me. What exactly am I looking for in that graph?
You said you wanted to understand, one day you may want to use a 555 as a monostable.
That graph shows the signal the threshold requires in order to to trigger the monostable.

You can see its the 1/3 .. 2/3 requirement, which explains the function is common to the mono and astable.
 
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axro

New Member
Here's another question that could fit in with the 555. Do any of these IC's have a limit on current that can be supplied to them on VCC/VDD? It seems that all is every talked about is voltage. Does current not matter or is it one of those "uses what it needs" kind of deals?
 

BrownOut

Banned
is it one of those "uses what it needs" kind of deals?

Yes.

As long as you don't overload the output or mis-wire the device.
 
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ericgibbs

Well-Known Member
Most Helpful Member
Here's another question that could fit in with the 555. Do any of these IC's have a limit on current that can be supplied to them on VCC/VDD? It seems that all is every talked about is voltage. Does current not matter or is it one of those "uses what it needs" kind of deals?
hi,
Look at these two images.
The 7555 is a CMOS version of the 555, earlier 555's were TTL.
 

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axro

New Member
hi,
Look at these two images.
The 7555 is a CMOS version of the 555, earlier 555's were TTL.
To be clear, when they are talking about source current they are talking about how much is coming into the 555 on pin 8 and not how much it is sourcing on the output. Right?
 

audioguru

Well-Known Member
Most Helpful Member
Hi Eric,
Whose datasheet of the 7555 Cmos timer did you post?
It has an error on the output sourcing left side whene it says output sinking by mistake.

It also has the sourcing current at room temperature where its current is fairly high but its sinking current is at a high temperature where its current is fairly low.

Most Cmos 555's have a max sourcing current of only 10mA and a sinking current of 50mA to 100mA when their supply voltage is at almost max.

Hi Axro,
The output sinks when its voltage is low and the output sources when its voltage is high.
Look at the graphs to see the big difference the supply voltage has on how much output current is available. Also look at the high voltage drop.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi Eric,
Whose datasheet of the 7555 Cmos timer did you post?
It has an error on the output sourcing left side whene it says output sinking by mistake.
It also has the sourcing current at room temperature where its current is fairly high but its sinking current is at a high temperature where its current is fairly low.
Most Cmos 555's have a max sourcing current of only 10mA and a sinking current of 50mA to 100mA when their supply voltage is at almost max.
hi agu,

For reference only.:)
 

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audioguru

Well-Known Member
Most Helpful Member
Hi Eric,
You did not post the "sourcing" graph. Here it is with a comparison of the sourcing and sinking output currents when the voltage drop is half the supply voltage:
 

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axro

New Member
Hi Axro,
The output sinks when its voltage is low and the output sources when its voltage is high.
Look at the graphs to see the big difference the supply voltage has on how much output current is available. Also look at the high voltage drop.
Right, but when they are talking about supply current, do they mean Supplying the 555 or supplying to circuit on output.
 
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audioguru

Well-Known Member
Most Helpful Member
Right, but when they are talking about supply current, do they mean Supplying the 555 or supplying to curcuit on output.
The supply current is the current used by the IC and its load into pin8.
The supply current changes depending on what the IC is doing.
The supply current for the Cmos 555 is typically only 60uA when it has a 15V supply and is not driving a load.
The supply current for an NE555 is typically 10mA when it has a 15V supply and is not driving a load.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi Eric,
You did not post the "sourcing" graph. Here it is with a comparison of the sourcing and sinking output currents when the voltage drop is half the supply voltage:
Woops!, I'll take another look, sorry about that.!!

EDIT:
I see my errror, I enclosed the incorrect captions for the plots when I did an off screen capture.
 
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