XTR 117 help!!!

[paddy]

Hi,

I have assembled the circuit of XTR 117 on breadboard as provided on pspice.

Input voltage of 0-5 V is provided through variable power supply.(Positive terminal of supply connected to IN terminal via 33K resistor and negative terminal of supply connected to IRET.)

Supply voltage is 20V, load resistor of 100 E and BC 547 transistor is used and results are as mentioned below.

Voltage at pin no. 2- 0.15 V to 0.5 V (for 0 to 5 V input)

Voltage at pin no.3- 0V

Voltage across load resistor(100 E)-0.06 V (constant for entire input range)

Voltage at base terminal of transistor- 3.8 V (constant for entire input range)

Voltage at VREG terminal- 5.24 V (constant for entire input range)

Kindly check and suggest.

Thanks,

paddy

 

[KrisBlueNZ]

1. The power supply that you're using to provide the input voltage must be FULLY ISOLATED from the other components. I recommend using a potentiometer or trimpot (5k resistance) between VREG and IRET to generate the test voltage.

2. You said "BC547 transistor is used". In which circuit position? You have marked the VREG transistor and the main transistor as TIP41C devices.

3. You haven't stated which pin the voltages are measured relative to. I assume they're all measured relative to IRET.

4. You should mark the pin numbers on your schematic. You are quoting voltages on pins, but these pins are not labelled, so I have to look at the data sheet to tell where you're measuring. Add numbers on your schematic.

5. The voltage at pin 2 should always be zero relative to pin 3.

6. What type of op-amp are you using for IOP1?

7. What type of op-amp are you using for IOP2? (In the 5V regulator.)

8. Where have you connected the power and ground connections of the IOP1 op-amp?

9. Where have you connected the power and ground connections of the IOP2 op-amp?

10. When you have updated your schematic to show the correct component types, pin numbers, and connections of power supply rails of the op-amps, post it again. Trim off the whitespace first using the "crop" function of an image editor.

11. Why are you breadboarding a discrete version of the XTR117?

12. What is the aim of your project?

Respond to EVERY point in this post, by number. Include as much information as you can.

 

[paddy]

I am really sorry KrisBlueNZ for the inconvenience caused to you because of my improper schematic.

1. The power supply that you're using to provide the input voltage must be FULLY ISOLATED from the other components. I recommend using a potentiometer or trimpot (5k resistance) between VREG and IRET to generate the test voltage.

I have used isolated power supply to give the input voltage. Also as suggested by you I have tried with potentiometer. But I there are same results in both the cases.

You said "BC547 transistor is used". In which circuit position? You have marked the VREG transistor and the main transistor as TIP41C devices.

I have used BC547 instead of TIP41C in between pin no 5,6,and 7. I am attaching new schematic.

You haven't stated which pin the voltages are measured relative to. I assume they're all measured relative to IRET.

I think I did a mistake here!!!! I have measured all the voltages with respect to ground of 20 V supply.

4. I am attaching new schematic.

5.

The voltage at pin 2 should always be zero relative to pin 3.

I will check it once again and update you the results.

Point no 6,7,8 and 9 is related to internal circuitry of XTR 117.

I am designing a circuit of gas detector and in that I need 2 wire 4-20 mA output. So I am trying with XTR chip.

Kindly suggest If you have anything for 2 wire 4-20 mA output.

 

[KrisBlueNZ]

Thanks for the response.

I'm reposting your schematic (from your previous post) here for easy reference.

So you are actually using a real XTR117? You are not trying to simulate it with discrete components and op-amps?

It's very important that all the circuitry on the left side of the diagram is fully electrically isolated from the circuitry on the right side. You need to consider all the circuitry on the left as being completely self-contained and independent of any other circuitry, with no connection at all to any other circuitry at all.

The external pass transistor should be rated for the maximum expected dissipation. The XTR117 limits the current to 32 mA and you have a 100 ohm load resistor and a 20V supply, so the absolute maximum power dissipation in the transistor is roughly V * I = 16.8 * 0.032 = 0.54 watts. The BC547 is rated for 100 mA and 625 mW which is safe and a reasonable choice.

Your design is the same as the suggestion in the data sheet. It should work fine as long as you keep the left side circuitry completely self-contained and not electrically connected to anything else.

 

[paddy]

Thanks for suggestions.

I will test it once again and update you the results.

Thanks a lot for your co-operation.