# What is the difference in these setups?

Discussion in 'General Electronics Chat' started by vijaybala85, Mar 9, 2010.

1. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
Hi Guys,

It has been quite sometime since I have dealt with electronics. But, I kinda have this question lingering in my mind. What is the difference between these setups I am describing below. I would really appreciate it if someone can explain. I am unable to understand or am I looking at it differently.

Basically, I have an opamp in non inverting setup to give and output of 24V when input is 5V and 0V when input is 0V. Using an Opamp for digital setup and especially for working like a switch is not ideal I presume. But now that I have done it, I want to make it work until the next design.

Difference between :-
A non inverting opamp with R1=10k and R2=100k.
A non inverting opamp with R1=1k and R2=10k

Both have gain of 10. I am assuming that there will be current limitations. Although for my requirement, a gain of 5 would suffice with R1=1k and R2=4.7k, but I didnt realize this before while designing.

My requirement is 24V output @ 11.2mA. My source or input is 5V @ 5mA. Any help or explaination would be amply appreciated.

Thanks!

VJ

2. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
I am sorry .. gain of 11. for 100k and 10k...

3. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
Can someone help me out with this question?

Vj

4. ### dsp_redux Active Member

Apr 11, 2009
182
5
Your guess was good. The difference between the two lies on current limitation/thermal noise. I'm not sure if that answers your question?

5. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
Thanks dsp_redux!! I guessed it right then. But how will it affect my load requirements? My load requires 24V and the current it needs is 11.2mA. And, all that the input does is drive the opamp. The load draws its output voltage and current from Vcc and GND.

What I dont get is my circuit with 100k and 10k worked for a while and then failed. I changed it to 10k and 1k and it seems to be working fine. I am just wondering if this would eventually fail too or will I be ok.

VJ

6. ### dsp_redux Active Member

Apr 11, 2009
182
5
Can you post a schematic of your circuit?

7. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
Here is the circuit diagram (did it quickly in pain(ful)t ) But describes what my question is.

Thanks!

V

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8. ### vijaybala85 Thread Starter Member

Jan 7, 2010
92
0
I know this is not a good way of designing for this application but I have already done it. I am looking for replacing this design in a month. But, for tnow this has to work

V