hello
i'm italian, and i'm sorry for my english, i hope to be clear
i need a advice
i'm building a project and i 'd like use a transistor as a switch.
this circuit put in series or parallel two batteries. I need very low energy consumption.
what is the best transistor used as a switch?
what is the resistance value?
i attachment a drawing, in this drawing the optotransistor work when it has value 5V, but in other circuit part i need that, other transistor work when output NE555 has value 0V.someone has suggestions?
thank you in advance.

 

Hello,

I am not going to rotate my monitor to look at the image.
I have rotated, changed perspective and scaled the image using The Gimp :



Bertus

 

Your circuit won't work, but, if we were to replace the transistor with a switch to achieve the series connection; how can the batteries ever be connected in parallel?

Perhaps you should explain what, overall, you are trying to achieve?

 

i want replace variable speed dc motor and brush switch, because i want consume little energy

 

Hello,

I am not going to rotate my monitor to look at the image.
I have rotated, changed perspective and scaled the image using The Gimp :

View attachment 99714

Bertus

For bipolar transistors general rule is a base current 1/10 of collector current. This would be too much for the opto to deliver. At least two options, Darlington NPN or N-MOSFET.

 

For bipolar transistors general rule is a base current 1/10 of collector current. This would be too much for the opto to deliver. At least two options, Darlington NPN or N-MOSFET.

which n mosfet?
what is the resistance value?

 

which n mosfet?
what is the resistance value?

re: which MOSFET
What do you have on hand? Most any "Logic level" N-MOSFET, enhancement mode, TO-220. IRFLxxxx for instance.

 

i want replace variable speed dc motor and brush switch, because i want consume little energy

Ok, I don't understand that diagram, it appears to be nonsense. There are better methods for controlling motor speed than to use battery switching.

There is little point discussing the merits of transistors vs mosfets without an inkling of a viable solution or design.

Do you have any information on the motor?

 

Ok, I don't understand that diagram, it appears to be nonsense. There are better methods for controlling motor speed than to use battery switching.

There is little point discussing the merits of transistors vs mosfets without an inkling of a viable solution or design.

Do you have any information on the motor?

i'm sorry but the diagram has a good sense!
motor turn 3 brush switch each brush switch close one time a contact and other time other contact.

i have done a simple question
how i can have a switch with electronic components?
transistor
mosfet
moc
or?
the think very important is low consume energy
i can't use relay for noise , consume energy and wear parts.

 

i'm sorry but the diagram has a good sense!
motor turn 3 brush switch each brush switch close one time a contact and other time other contact.

i have done a simple question
how i can have a switch with electronic components?
transistor
mosfet
moc
or?
the think very important is low consume energy
i can't use relay for noise , consume energy and wear parts.

Please provide more information on the motor.
From your post, I think you're driving a brushed motor.

Use a low side n-channel MOSFET.
Use a gate driver to turn it on and off fast to reduce switching losses.

Your schematic lacks a method to turn the MOSFET off at all, except relying on gate leakage.
The optocoupler will also be slow for a MOSFET gate driver.
Your schematic also lacks a freewheeling diode, which is essential for a brushed motor.
I think your schematic places the batteries in series with the transistor, which would be wrong.
Which variant of the 555 timer are you using?
What's powering the 555 timer?
Your schematic leaves a lot of important questions unanswered.

 

Please provide more information on the motor.
From your post, I think you're driving a brushed motor.

Use a low side n-channel MOSFET.
Use a gate driver to turn it on and off fast to reduce switching losses.

Your schematic lacks a method to turn the MOSFET off at all, except relying on gate leakage.
The optocoupler will also be slow for a MOSFET gate driver.
Your schematic also lacks a freewheeling diode, which is essential for a brushed motor.
I think your schematic places the batteries in series with the transistor, which would be wrong.
Which variant of the 555 timer are you using?
What's powering the 555 timer?
Your schematic leaves a lot of important questions unanswered.

HI Mr Knight
i don't want use motor and brush switch but i want replace them
i have build ne555 for 800MHz signal
if The optocoupler will also be slow for a MOSFET gate driver, do i can use other transistor?

 

Hello,

The NE555 can never reach the mentioned 800 MHz.
There are versions that can reach 2 MHZ at most.

Bertus

 

Hello,

The NE555 can never reach the mentioned 800 MHz.
There are versions that can reach 2 MHZ at most.

Bertus

i'm sorry i've writed wrong
800 Hz

 

800MHz sounds fast for a motor.

From your messages, it's hard to see what you want. You didn't answer all the questions.

The circuit you use depends on the application.

If you want bidirectional control, use something like this:
http://www.microchip.com/pagehandler/en-us/technology/motorcontrol/motor-types/brushed-dc.html

If you want unidirectional movement, use a circuit that looks like this: http://i.stack.imgur.com/pZM6G.png, with a chip like this to drive an n-channel MOSFET:
http://www.farnell.com/datasheets/1669445.pdf

 

As blocco said above, your circuit WILL NOT WORK as a speed control. When the transistor is off, there is no current flow. When it is on, both batteries are in the circuit, making your circuit unneeded.

And, what is a brush switch?

 

i'm sorry i've writed wrong
800 Hz

This is painful, the solution could be very simple but you aren't making sense.

Forget what you have already presented because it won't work, and instead provide details of the motor, available power-supply, and control requirement? If you can't do this, there is little point continuing.

 

yes the circuit must work so:
When the transistor is off, there is no current flow. When it is on, both batteries are in the circuit

 

This is painful, the solution could be very simple but you aren't making sense.

Forget what you have already presented because it won't work, and instead provide details of the motor, available power-supply, and control requirement? If you can't do this, there is little point continuing.

I'm sorry but i don't want use the motor, in the second drawing the motor and brush switch work like ne555 and i can replace it simply. i need a circuit that work as a switch
for this reason i thought at transistor.