Hi I am currently designing a current loop circuit based on this Maxim's app note: **broken link removed**
I attached my circuit. The problem is that the op-amp is heating. I have tried different op-amp and it is always heating. I tried LM2904 and LM7332. When I disconnect the op-amp output from the transistor it is not heating so it is a problem with the circuit not the op-amp.
Could someone help me and/or explain me why the circuit would make heat the op-amp.
Hi I am currently designing a current loop circuit based on this Maxim's app note: **broken link removed**
I attached my circuit. The problem is that the op-amp is heating. I have tried different op-amp and it is always heating. I tried LM2904 and LM7332. When I disconnect the op-amp output from the transistor it is not heating so it is a problem with the circuit not the op-amp.
Could someone help me and/or explain me why the circuit would make heat the op-amp.
hi,
The transistor connected to the OPA output is effectively shorting out the OPA, so the OPA will get hot.
EDIT:
Resistor Ry, transistor base resistor shown in the datasheet is missing from your circuit.
Yes I tried a 5k.. but there's no result. The op-amp is still heating, not alot but still. I really need it to not heat because it's a small temperature sensor application.
I'm not sure you are using the circuit as the Maxim ap note shows. The +24V supply return (V-) must be connected to the output, not GNDV. Is that the way you connected it? If not, that would explain the overheating of the op amp. The 20mA loop is through the supply voltage and thus the supply must be isolated from circuit gnd.
I'm not sure you are using the circuit as the Maxim ap note shows. The +24V supply return (V-) must be connected to the output, not GNDV. Is that the way you connected it? If not, that would explain the overheating of the op amp. The 20mA loop is through the supply voltage and thus the supply must be isolated from circuit gnd.
Isolated means the minus side of the power supply is not connected to ground. Your "full" schematic does not show where the minus side of the power supply is connected. It should be connected to the output, as I previously stated, and as the Maxim article shows.
It would be a courtesy to read my previous posts before replying.
Ok im sorry I have read your posts. But in my schematics I can't connect something on the op amp V+ and V- but I said that V+ was at 24V and V- at GNDV.
But Ill try to connect Vminus to the output instead.
I simulated you circuit (see below), and it worked if I changed the value of R11 to 1k ohm. Since this is a 20mA loop, it's obvious that R11 can't be greater than that or you can't get 20mA from a 24V supply.
I also put a 1k ohm pot between 5V and ground with the wiper connected to R7 to vary the input. The output current goes from about 4mA to 20mA as is desired when the input goes from 0 to 5V.
Edit: So if your circuit is not working (after changing R11) I suspect you have a misswire somewhere.