Then the circuit I have provided is more than sufficient
Edit:
If the frequency is actually 0.33Hz, it will require larger caps
@Mooly: The 555 spec sheet specifies, and I have measured it too, there is a large voltage drop as the current increases.
I quote from my first message "For example powering the ICM7555 or SE555 with 10V and drawing about 20mA results in 7.44V at the output, whereas at 1mA gives 9.84V at the output."
@Elvee: yes, but did you notice the T=3 sec? We need to increase the caps to like 470u. It is just too many components, IMHO.
I quote from my first message "For example powering the ICM7555 or SE555 with 10V and drawing about 20mA results in 7.44V at the output, whereas at 1mA gives 9.84V at the output."
@Elvee: yes, but did you notice the T=3 sec? We need to increase the caps to like 470u. It is just too many components, IMHO.
I just did it again (for sanity)
V=10V.
ICM7555:
0mA = 10V
1mA = 9.79V
2mA = 9.551V
13.54mA = 6.364V
18.22mA = 4.291V
SA555:
0mA = 9.339V
0.86mA = 8.664V
1.84mA = 8.648V
18mA = 8.546V
35.95mA = 8.470V
So the ICM7555 is useless for large currents, but better for small currents.
The SA555 is better for large currents, but still quite a distance from the rail voltage.
I do not think there is much discrepancy here, the SA555 is less than 1.6V off the rail (10V to 8.47V at 36mA) and the trend seems to be holding. Your museum piece LM555 is 1.7V off the rail at 180mA, I think we are the same more or less.
But the BIG problem is that the LM555/SA555 right off the bat loses over 1V off the rail, increasing to 1.5V at 35mA converging or plateauing at 1.7V. This 1.5V below the rail means that you can easily light up an LED or two when you do not mean it. And if those LEDs happen to be controlling SSRs or LDRs you will have leaks.
But the BIG problem is that the LM555/SA555 right off the bat loses over 1V off the rail, increasing to 1.5V at 35mA converging or plateauing at 1.7V. This 1.5V below the rail means that you can easily light up an LED or two when you do not mean it. And if those LEDs happen to be controlling SSRs or LDRs you will have leaks.
OK, I realise its going to very application specific with regard to what problems the limitations cause.
Could you run your loads from two single ended outputs if its a case of one or other being on at any one time ? Just thinking something like an N channel fet or an NPN to drive a load tied to V+ and a P channel FET or PNP to drive a ground referenced load.
Could you run your loads from two single ended outputs if its a case of one or other being on at any one time ? Just thinking something like an N channel fet or an NPN to drive a load tied to V+ and a P channel FET or PNP to drive a ground referenced load.
Which is really what you had with the FET's connected as you did. Transistors with level shifting on the base would work too.
separating the two loads means I will have to include the P-channel FET (top) and NPN (bottom) at the load location. If I have more than one loads, in separate locations, I will have to run two signal lines and include local FET/NPN at the locality. Therefore the solution of the two FETs to boost the output of the 555, means I can now distribute this boosted line everywhere and know that this line can source and sink lots of mA and be really close to the rails at the same time, as if it were coming out of a super-555.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.