Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

A analogue circuit that spit out the resistance desired

henry kissinger

Newbie level 6
Joined
Nov 19, 2021
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
130
I am thinking about a analogue circuit that should work like this.
Right now I have 2 values known, these are the voltage of a node (38V) and a resistor (158.4ohm).
This circuit need to interpret 38V as 38ohm, and then tune the adjustable resistor to 50ohm (because the 158.4ohm and 50ohm in parallel give us the 38ohm resistance.
Any idea is appreciated.
The result circuit should work for all the values of known values of the voltage node and the resistor.
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,349
Helped
1,551
Reputation
3,104
Reaction score
1,422
Trophy points
1,393
Location
Turkey
Activity points
32,163
If you design a constant current source with a 1A value, you can measure this voltage then adjust the resistance to maintain this voltage as 38V.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
21,990
Helped
4,591
Reputation
9,196
Reaction score
4,812
Trophy points
1,393
Activity points
145,178
Hi,

please draw a sketch.

As far as I understand .. BigBoss´ idea is O.K.
On the other hand this means a lot of power dissipation = a lot of heat
38W on 38 Ohms ... or 158W on 158 Ohms.

Does this make sense?

What is it for?

Klaus
 

henry kissinger

Newbie level 6
Joined
Nov 19, 2021
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
130
I am thinking about a analogue circuit that should work like this.
Right now I have 2 values known, these are the voltage of a node (38V) and a resistor (158.4ohm).
This circuit need to interpret 38V as 38ohm, and then tune the adjustable resistor to 50ohm (because the 158.4ohm and 50ohm in parallel give us the 38ohm resistance.
Any idea is appreciated.
The result circuit should work for all the values of known values of the voltage node and the resistor.
 

Attachments

  • 擷取.PNG
    擷取.PNG
    194.4 KB · Views: 17

stenzer

Advanced Member level 2
Joined
Oct 1, 2012
Messages
639
Helped
106
Reputation
213
Reaction score
140
Trophy points
1,323
Activity points
6,835
Hi,

where does this 38 V requirement comes from? Only to intrepret the reading easy? Is the “parallel“ resistor your unknown one? If facilitating a constant current source, I would choose 100 mA or even 10 mA. At the moment, your compliance votage is 158.4 V at 1 A. And as @KlausST already mentioned, the power losses are huge.

BR
 

henry kissinger

Newbie level 6
Joined
Nov 19, 2021
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
130
If you design a constant current source with a 1A value, you can measure this voltage then adjust the resistance to maintain this voltage as 38V.
right, the issue I am facing is how to generate this resistance automatically
If you design a constant current source with a 1A value, you can measure this voltage then adjust the resistance to maintain this voltage as 38V.
You are right!
but I am facing is how to tune this resistance to 50ohm so I can get the 38V at Va. This should be a automatic process. I can not simply change the resistance value manually.
 

Attachments

  • 擷取.PNG
    擷取.PNG
    59.1 KB · Views: 13

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
5,349
Helped
1,551
Reputation
3,104
Reaction score
1,422
Trophy points
1,393
Location
Turkey
Activity points
32,163
right, the issue I am facing is how to generate this resistance automatically

You are right!
but I am facing is how to tune this resistance to 50ohm so I can get the 38V at Va. This should be a automatic process. I can not simply change the resistance value manually.
If you cannot manually adjust the resistance value, you have to use discrete resistance bank so you will able to change the resistance values by adding or substracting resistances to fix the value. You cannot use small signal variable resistance like FET too. So, resistance bank is the most reliable solution.

It's needles to say to use ADC or similar control circuit.
 

stenzer

Advanced Member level 2
Joined
Oct 1, 2012
Messages
639
Helped
106
Reputation
213
Reaction score
140
Trophy points
1,323
Activity points
6,835
Hi,

I still do not get the aim of the circuitry. Do have to keep a certain voltage "stable" or do you want to perform a measurement of an unknown resistor? As you are controlling the parallel resistor (Z Ohms) it does not seem like a measurement task to me, as the parallel configuration has only a single solution to fullfil the condition

38 V = 1A • (158.4 Ohm || Z Ohm) --> 49.9934 Ohm


If your parallel resistor is unknown (Z Ohms) and you are not able to control it, I would use the parallel configuration of the zwo resistors (Y || Z) to set the output current of a constant current source e.g. with an LM317HV [1]. This tutorial might be useful [2].

[1] https://www.ti.com/lit/ds/symlink/l...=https%3A%2F%2Fwww.ti.com%2Fproduct%2FLM317HV
[2] http://imajeenyus.com/electronics/20160530_adjustable_current_source/index.shtml

BR
 

LaTeX Commands Quick-Menu:

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top