how should i design a linear current to voltage converter without power supply from transmitter circuit .i should convert 4-20ma current from transmitter circuit to equivalent 0-5v using diodes and transistor s

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electronic projects

 

You need to be far more specific as to your needs, it's not very obvious what you are trying to do, nor what you want.

But, a simple resistor does everything you've asked so far!.

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i need it using some diodes and transistors with resistors to convert from 4-20ma to equivalent 0-5v.

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electronic projects

 

Are you sure you want the low end to be 0 volts? Many, but not all interfaces start at some point above zero because zero is hard to measure.

In some applications the normal way to handle this is select a resistor that will have a voltage drop of 5 volts when the current is 20 ma. The voltage drop is 1 volt when the current is 4 ma so the span is 1 to 5 volts. This works if anything connected does not significantly load the circuit.

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stevez

 

In the industrial world, we use a 250 ohm precision resistor to accomplish exactly what stevez wrote about. We put the 4-20mA loop current thru the resistor and measure the voltage across it.
JB

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jbeng,

Yes this is standard but there is one problem, freak123 wants 0V at 4mA and the 250ohm resistor will supply 1V.

 

Unless this is a homework assignment, think OPAMP. It would be simple to do, take less power, less board space, and be more accurate.

Re-evaluate the specs .

j.

 

just wondering about that, if the 4-20mA mentioned was the actually the output from a sensor, would there be enough power to reach 5V just by the use of a simple 250 ohm resistor? Or would a op amp do a better job

 

Most often, the 4-20 ma does not come from or thru the sensor but is the result of a transducer or convertor that is attached to the sensor, computer, etc. You'd have to check mfr's specs to see just how much voltage/power is available.

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stevez