12v verses 5v
- Thread starter whills
- Start date
westaust55
Moderator
555 Timer
The 555 is not specifically rated at 12V. It can operate at voltages from 4.5 to 16V.
Note the Sandbox is more for experimenation and testing. Not for actual questions.
You should be posting your questions in the Active PICAXE Forum at the top of the home page.
The 555 is not specifically rated at 12V. It can operate at voltages from 4.5 to 16V.
Note the Sandbox is more for experimenation and testing. Not for actual questions.
You should be posting your questions in the Active PICAXE Forum at the top of the home page.
1. As ICs shrink in size and increase in complexity, the tiny IC level traces get closer together and the voltage stresses are able to bridge the gaps or punch through the insulation. Likewise with surface mount components - conductive dirt on the boards starts to get critical - and miniaturization is one of the goals of design - saves space, power and money while improving performance.
2. Mosfets working at low voltage need a thin insulating gates. So if they made them for HV applications they wouldn't work over low voltages.
3. IC logic is traditionally 5 volts since it CONSUMES LESS POWER, produces less heat, and is now a standard. New designs are moving to 3.3 and 1.6 volts.
The 555 is very old technology. c.'70's
2. Mosfets working at low voltage need a thin insulating gates. So if they made them for HV applications they wouldn't work over low voltages.
3. IC logic is traditionally 5 volts since it CONSUMES LESS POWER, produces less heat, and is now a standard. New designs are moving to 3.3 and 1.6 volts.
The 555 is very old technology. c.'70's
fernando_g
Senior Member
Actually, 1972.
If you want to read an extremely interesting story on the 555, by its actual designer, Hans Camenzind:
http://semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Index.htm
The Picaxe has been called the 555 of the new millenium....... Not because of the volume produced (that is an extremely difficult target) but because its simplicity and versatility.
If you want to read an extremely interesting story on the 555, by its actual designer, Hans Camenzind:
http://semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Index.htm
The Picaxe has been called the 555 of the new millenium....... Not because of the volume produced (that is an extremely difficult target) but because its simplicity and versatility.
Andrew Cowan
Senior Member
It also means it can run on batteries!
3 AAs = 4.5V
8 AAs = 12V
A
3 AAs = 4.5V
8 AAs = 12V
A
szd51pilot
Member
Fernando g -
Many thanks for the reference to the interview with the designer of the 555 - I didn't know of that web site. The original Signetics 555 had a design weakness when used in the oscillator mode due to the collectors of the Trigger Input PNP darlington pair being connected together. Circa 1973 a colleague and myself spent days trying to work out why a 555 timer using the Signetics' part would not work as expected. In the end we called the distributor (or maybe it was Signetics) and were told what the problem was (the circuit diagram on page 6 of the interview shows this problem) One of those "Doh!" moments since we had the internal circuit diagram of the device in front of us all of the time....
Nat Semi brought out the LM555 shortly after that and their version took the collector of the first PNP of the Triggr Input to the 0V rail and so overcame the problem.
His description of making the masks brought back memories of the IC design course I attended at Plesey Microelectronics in 1969. I nearly burnt the semiconductor fab down - but that's another story....
For longish duration timers that I have made recently I have gone away from the CMOS version of the 555 and used the PICAXE-08M!
Richard
Many thanks for the reference to the interview with the designer of the 555 - I didn't know of that web site. The original Signetics 555 had a design weakness when used in the oscillator mode due to the collectors of the Trigger Input PNP darlington pair being connected together. Circa 1973 a colleague and myself spent days trying to work out why a 555 timer using the Signetics' part would not work as expected. In the end we called the distributor (or maybe it was Signetics) and were told what the problem was (the circuit diagram on page 6 of the interview shows this problem) One of those "Doh!" moments since we had the internal circuit diagram of the device in front of us all of the time....
Nat Semi brought out the LM555 shortly after that and their version took the collector of the first PNP of the Triggr Input to the 0V rail and so overcame the problem.
His description of making the masks brought back memories of the IC design course I attended at Plesey Microelectronics in 1969. I nearly burnt the semiconductor fab down - but that's another story....
For longish duration timers that I have made recently I have gone away from the CMOS version of the 555 and used the PICAXE-08M!
Richard
BeanieBots
Moderator
The reason for ever decreasing voltage is to meet the demand for ever increasing speed. Getting circuits to work at 1.8v is a major hurdle for the semiconductor industry to achieve both from a circuit design point of view and from the semiconductor point of view. The advantage gained, is reduced junction capacity and hence increased switching speed. The disadvantge is noise immunity. Memory elements are now so small that the charge required to change state can be just a few electrons. Even background radiation can effect such small charges.
Safety logic is still run at 24v. The shear mass of legacy 5v logic makes it remain the most common and cheapest. However, for sensitive applications, the 15v 74C.. & CD40.. ranges are still very popular. Personally, I prefer to use 15v logic because it is very supply rail immune and also interfaces directly with the more common 15v supply used in analogue electronics. Many 15v logic chips are however limited to about 10Mhz which is snail's pace by todays standards.
Safety logic is still run at 24v. The shear mass of legacy 5v logic makes it remain the most common and cheapest. However, for sensitive applications, the 15v 74C.. & CD40.. ranges are still very popular. Personally, I prefer to use 15v logic because it is very supply rail immune and also interfaces directly with the more common 15v supply used in analogue electronics. Many 15v logic chips are however limited to about 10Mhz which is snail's pace by todays standards.
Michael 2727
Senior Member
Hippy did you brush off the excess Sand before shifting the Post ? 
Michael 2727
Senior Member
Hippy, sorry to break your concentration, I was referring to part 2 of Westy's post #3
westaust55
Moderator
Why PICAXE and most digital ICs use lower voltages
Back to the 5V vs 12V topic . . . .
Some very early diode logic called "high-threshold logic" incorporated Zener diodes to create a large offset between logic 1 and logic 0 voltage levels. These devices usually ran off a 15 volt power supply and were found in industrial control, where the high differential was intended to minimize the effect of noise.
TTL ICs (74xx and 74LSxx series) require a power supply voltage of 5V (+/- 0.5V).
The 74HCxxx (High performance silicon gate) family can be used with both 3.3V and 5V power supplies.
The 4000 series CMOS works with a wider range of power supply voltage – usually anywhere from 3 to 15V.
But a key reason for using a lower voltage level is that, by lowering the supply voltage the current required to charge stray capacitance reduces, and so reduces the current drawn. This in turn reduces the heat dissipation of the IC. By lowering the power supply from 5V to 3.3V, the switching power is typically reduced by around 60 percent (power dissipation is proportional to the square of the supply voltage). Newer IC's and in particular CPUs have lowered their core power supply voltages even further.
Back to the 5V vs 12V topic . . . .
Some very early diode logic called "high-threshold logic" incorporated Zener diodes to create a large offset between logic 1 and logic 0 voltage levels. These devices usually ran off a 15 volt power supply and were found in industrial control, where the high differential was intended to minimize the effect of noise.
TTL ICs (74xx and 74LSxx series) require a power supply voltage of 5V (+/- 0.5V).
The 74HCxxx (High performance silicon gate) family can be used with both 3.3V and 5V power supplies.
The 4000 series CMOS works with a wider range of power supply voltage – usually anywhere from 3 to 15V.
But a key reason for using a lower voltage level is that, by lowering the supply voltage the current required to charge stray capacitance reduces, and so reduces the current drawn. This in turn reduces the heat dissipation of the IC. By lowering the power supply from 5V to 3.3V, the switching power is typically reduced by around 60 percent (power dissipation is proportional to the square of the supply voltage). Newer IC's and in particular CPUs have lowered their core power supply voltages even further.
westaust55
Moderator
Maybe that's why they call us West Aussies "Sandgropers"Hippy, sorry to break your concentration, I was referring to part 2 of Westy's post #3