Switching speed of 7805

[p.gholap93]

Hello everyone.I have an obstacle detection sensor whose output voltage is 0.72V when obstacle is detected and it is 11V when obstacle is not detected.Now I want to convert this output into 0V to 5V range so as to drive controller input pin. I am thinking of using 7805 for the same.Following are the problems I am facing-
1- If obstacle's presence and absence changes rapidly/abruptly,then can 7805 regulator provide such fast and sharp response? (Is there any delay in its op?)
2-Maximum controller input current is 30mA. So, is it fine to put a resistor in series with output of 7805 to limit current?

 

[JimB]

Sounds like a waste of 7805 and money to me.

Just use a resistive divider to reduce the 11 volts to 5 volts.

JimB

 

[savvej]

I agree with JimB ..

 

[4pyros]

You would need caps on the 7805 and that would slow things down.

 

[p.gholap93]

Ya its fine, but the output won't be "REGULATED" 5V. Resistance tolerances may cause problems. Power dissipation across resistances is another problem.

 

[MrAl]

Hi,

Is a zener good enough? That would be very fast too.

 

[Nigel Goodwin]

A single resistor and clamp diodes to 5V and chassis - or depending what your controller is?, just a resistor (if it's a PIC for example).

 

[panic mode]

i agree with Nigel, does not get simpler than that.

 

[p.gholap93]

A single resistor and clamp diodes to 5V and chassis - or depending what your controller is?, just a resistor (if it's a PIC for example).

I am using atmega 128 controller. But I didn't understand your solution. Clamp diode to 5V means what? How should I connect resistor?

 

[alec_t]

its fine, but the output won't be "REGULATED" 5V

Why do you want it to be regulated? The controller will be happy with an input anywhere in the region of 3.5-5.5V as a logic high signal. The clamp diode suggested is just to prevent the input going above 5.6V (which the controller wouldn't like!).

 

[p.gholap93]

Why do you want it to be regulated? The controller will be happy with an input anywhere in the region of 3.5-5.5V as a logic high signal. The clamp diode suggested is just to prevent the input going above 5.6V

But,I am not getting what is this clamp diode you are talking about.Are you talking about zener diode or general purpose diode?

 

[ericgibbs]

But,I am not getting what is this clamp diode you are talking about.Are you talking about zener diode or general purpose diode?

Look at this image, there are three simple options.