Help.
I am trying to determine the worst case power draw from the power rail for a OP07DP and a LM358AN. I have the data sheets for the parts but cant seem to find a definitive characteristic.
For the LM358AN I see the supply current | Icc MAX at infinite load (open) and Vcc=30V to be 2ma so 60mW.
For the OP07DP I see Power dissipation | Pd no load , Supply voltage +- 15V = 150 mW
The circuit is a simple split power supply transformer -> rectifier -> ~16Vdc -> current limit resister -> 7.5 zener -> limit resister -> 2.5V reference device.
I realize that there is more loading the 7.5V zener than the op amp supplies. In fact the entire operations of the 2.5V reference circuit.
These are the steps that I am taking to figure out the load on the power supply;
1. what is the maximum (worst case scenario) needed to run the op amps.
2. what is the load drawn from the 2.5V reference during normal operation plus some % head room.
3. select loading resister appropriately for that need.
4 model circuit and re adjust for increased efficiency of power supply.
*****In order to get past step one I need to know if I am reading the data sheets correctly to find the values I am looking for??
I am willing to do the leg work but can't seem to ask the right question when searching for information about how to read op amp data sheets.
I have watched what seems to be hours of vids and read a lot of information but I am only finding information that deals with ideal power supplies and ideal op amps. When I go the zener route I get lots of information about selecting current limiting resisters according to power need and load. Now I need to figure out the load.
Please Help
Thanks
Jeremy
I am trying to determine the worst case power draw from the power rail for a OP07DP and a LM358AN. I have the data sheets for the parts but cant seem to find a definitive characteristic.
For the LM358AN I see the supply current | Icc MAX at infinite load (open) and Vcc=30V to be 2ma so 60mW.
For the OP07DP I see Power dissipation | Pd no load , Supply voltage +- 15V = 150 mW
The circuit is a simple split power supply transformer -> rectifier -> ~16Vdc -> current limit resister -> 7.5 zener -> limit resister -> 2.5V reference device.
I realize that there is more loading the 7.5V zener than the op amp supplies. In fact the entire operations of the 2.5V reference circuit.
These are the steps that I am taking to figure out the load on the power supply;
1. what is the maximum (worst case scenario) needed to run the op amps.
2. what is the load drawn from the 2.5V reference during normal operation plus some % head room.
3. select loading resister appropriately for that need.
4 model circuit and re adjust for increased efficiency of power supply.
*****In order to get past step one I need to know if I am reading the data sheets correctly to find the values I am looking for??
I am willing to do the leg work but can't seem to ask the right question when searching for information about how to read op amp data sheets.
I have watched what seems to be hours of vids and read a lot of information but I am only finding information that deals with ideal power supplies and ideal op amps. When I go the zener route I get lots of information about selecting current limiting resisters according to power need and load. Now I need to figure out the load.
Please Help
Thanks
Jeremy
The current drawn from the supply usually increases slightly with voltage, so without load, it should be safe to assume 2 mA for the LM358 and 150 mW/30 V = 5 mA for the OP07 when you use them at +/-15 V or less. With load, you need to add whatever current the op-amp output needs to supply to its load (including its feedback network).
I don't understand question 2, so I cannot answer it. It is not clear to me what you intend to connect to the 2.5 V reference.
Question 2 is what I intend to do next. I may or may not have to get help with this. The current | power draw of the output is a subject that is covered very well in vids and articles. I should be able to figure it out with the help of the reference materials available.
The OP07 is used to drive the LM358. The input to the OP07 non inverting is the sum of the high and low reference voltages using resistive summing 500ohm per leg strain gauge, and a 10k potentiometer to add an offset.
This particular strain gauge is a piezo device in a Y configuration. I have yet to analyze it to figure out its actual operating rage so therefore I can not figure out how much it can become unbalanced. I don't know the range of voltage that can come out at the point of summing.
Thank you @MarcelvdG
Jeremy
The OP07 is used to drive the LM358. The input to the OP07 non inverting is the sum of the high and low reference voltages using resistive summing 500ohm per leg strain gauge, and a 10k potentiometer to add an offset.
This particular strain gauge is a piezo device in a Y configuration. I have yet to analyze it to figure out its actual operating rage so therefore I can not figure out how much it can become unbalanced. I don't know the range of voltage that can come out at the point of summing.
Thank you @MarcelvdG
Jeremy