Hi, i need to build a circuit with the following spec:

using a 12v supply I need to run a 6v servo motor (with internal resistance of 10ohms)
-when the current on the motor will be more than 1A, i need to cutoff the power to it, and light a red led light.
-when the current goes down 1A, the power can only be restored by pressing a reset switch (which will also will turn the led light off).

the thing is i can only use simple components (diodes, transistors, resistors, op amps etc, NO IC, relays, software...)

Thanks



Moderator's Note.
Please don't do double post, one thread is enough.

 

An OP-amp is typically an IC, so now what?

Every time the motor starts, there will be a surge which is probably on the order of 5x the running current.

 

Hi, i need to build a circuit with the following spec:

using a 12v supply I need to run a 6v servo motor (with internal resistance of 10ohms)
-when the current on the motor will be more than 1A, i need to cutoff the power to it, and light a red led light.
-when the current goes down 1A, the power can only be restored by pressing a reset switch (which will also will turn the led light off).

the thing is i can only use simple componenets (diodes, transistors, resistors, opamps etc, NO IC, relays, software...)

Thanks

Do you want the power to shutdown (no current to motor) or do you want it to just get limited to 1 amp.

 

I need the power to be shut down

 

I mean i cant use programmable chips

 

Naughty to post the same problem twice. The other one is in Analog. Mods informed.



Moderator's Note:
Merged another post to this thread, thanks for your help.

 

You wind 10 turns of the wire entering the motor around a reed switch.
Problem fixed.

 

You wind 10 turns of the wire entering the motor around a reed switch.
Problem fixed.

I cant use reed switches.

I need to use BASIC components. Diodes, transistors, Op-Amp, resistor and capacitors nothing fancy.

 

Are you joking ????

 

Are you joking ????

no I'm not..

 

no I'm not..

I would do something like this...

Can you figure it out?

It works but there may be some improvements possible.

 

I would do something like this...

Can you figure it out?

It works but there may be some improvements possible.
View attachment 120818

it looks great thanks!!

-where should i place the LED warning light?
-what is Q3? i couldnt figure it out

 

it looks great thanks!!

-where should i place the LED warning light?
-what is Q3? i couldnt figure it out

Q3 is a p-channel MOSFET

Are you going to make an attempt to describe how it works? Then I'll post the LED.

Note: simply placing an LED in the existing circuit will alter the operation.

 

Q3 is a p-channel MOSFET

Are you going to make an attempt to describe how it works? Then I'll post the LED.

Note: simply placing an LED in the existing circuit will alter the operation.

I need the LED to be turned ON when overcurrent of 1A was detected (and the motor is without power)
and to be turned OFF when i press the reset switch (and than the power to the motor is restored).

 

I need the LED to be turned ON when overcurrent of 1A was detected (and the motor is without power)
and to be turned OFF when i press the reset switch (and than the power to the motor is restored).

I know.

I need some investment from you to look at what I've done for you and make sure you know how it works. Imagine your professor asking you the same thing snd having no lifeguard (me) there to protect (help) you?

 

I understand that.
i was mange to build a different circuit and came across the same problem of "where to put the LED" .
That's why i'm asking.

My knowledge in the electronics field is limited, that's why i'm asking for help.

and again, thank you for you help.

 

I understand that.
i was mange to build a different circuit and came across the same problem of "where to put the LED" .
That's why i'm asking.

My knowledge in the electronics field is limited, that's why i'm asking for help.

and again, thank you for you help.

the triangles are best described as Comparitors with 12V supply. Op amps may not give the desired response if they are not rail to rail inputs and outputs.

 

the triangles are best described as Comparitors with 12V supply. Op amps may not give the desired response if they are not rail to rail inputs and outputs.


View attachment 120847

only when i disconnect this part, i can get more than 36mA to the motor

 

it looks like some connections are missing.

Q4 drain

The (-) input of Op_Amp_3T_Virtual is not connected correctly.

The transistor you are using ZTX694 is rated for 0.5 A max - you should use a transistor (preferably a Darlington) rated over 5A and Hfe of 1000.

Your probes are not in the correct location to measure current flow through the motor.

I don't see any connections for your 20 ohm "load" to a 6V supply. Probe 2 should connect to the Top-most connection of that 20 ohm pot, NOT TO THE BASE OF THE ZTX694.

 

it looks like some connections are missing.

Q4 drain

The (-) input of Op_Amp_3T_Virtual is not connected correctly.

The transistor you are using ZTX694 is rated for 0.5 A max - you should use a transistor (preferably a Darlington) rated over 5A and Hfe of 1000.

Your probes are not in the correct location to measure current flow through the motor.

I don't see any connections for your 20 ohm "load" to a 6V supply. Probe 2 should connect to the Top-most connection of that 20 ohm pot, NOT TO THE BASE OF THE ZTX694.

I did some changes, now the current is very low,
what am I doing wrong?