Hello everyone. I made a current source/sink circuit with the help of a lot of you.
Now I'm testing it, and at first it appeared it worked ok, but now I've found some unexpected behavior.
The circuit is a classic op amp + transistor current sink, and it has an H Bridge to alternate the polarity of the current PULSES through the resistor which represents my load. The H bridge has been tested previously and it is working correctly .
The current sink is made in a way that the voltage at Vin(+) of the op amp creates the desired current in Rsense. This is true because ideally, Vin(+) = Vin(-). Thus, I_rsense = Vin(+)/Rsense. Since Rsense is 10 Ohms, I'm using an input voltage range from 0.2V to 1 V to get 20mA to 100mA.
When I apply say 0.5V, I get the desired Voltage drop at the load, hence the current, since I know Rload's value (been testing with 100Ohm for RLOAD) . HOWEVER, as I increase the voltage at the op amp's input (0.5V - 0.7V), Im getting a bigger error for the expected voltage drop at the load, then when I reach 0.8V the voltage drop at Rload reaches a maximum value and remains the same, regardless of going up to 1V, even 1.5V at the input.
With an oscilloscope I saw that the op amp's output reaches a maximum value of 920mV aprox when applying 0.8V, and remains the same for bigger inputs.
I'm not sure what is limiting the op amps output. the op amp is an LM324n, with +5V and GND as supplies. I am aware that regular op amps don't go as high as the rail, but less than 1V is way below.
The shape of the signal is correct, it doesn't look clipped or something, its just of less amplitude, if that makes any sense...
If anybody has experienced this before, please I would appreciate any help. Muchas Gracias!
Now I'm testing it, and at first it appeared it worked ok, but now I've found some unexpected behavior.
The circuit is a classic op amp + transistor current sink, and it has an H Bridge to alternate the polarity of the current PULSES through the resistor which represents my load. The H bridge has been tested previously and it is working correctly .
The current sink is made in a way that the voltage at Vin(+) of the op amp creates the desired current in Rsense. This is true because ideally, Vin(+) = Vin(-). Thus, I_rsense = Vin(+)/Rsense. Since Rsense is 10 Ohms, I'm using an input voltage range from 0.2V to 1 V to get 20mA to 100mA.
When I apply say 0.5V, I get the desired Voltage drop at the load, hence the current, since I know Rload's value (been testing with 100Ohm for RLOAD) . HOWEVER, as I increase the voltage at the op amp's input (0.5V - 0.7V), Im getting a bigger error for the expected voltage drop at the load, then when I reach 0.8V the voltage drop at Rload reaches a maximum value and remains the same, regardless of going up to 1V, even 1.5V at the input.
With an oscilloscope I saw that the op amp's output reaches a maximum value of 920mV aprox when applying 0.8V, and remains the same for bigger inputs.
I'm not sure what is limiting the op amps output. the op amp is an LM324n, with +5V and GND as supplies. I am aware that regular op amps don't go as high as the rail, but less than 1V is way below.
The shape of the signal is correct, it doesn't look clipped or something, its just of less amplitude, if that makes any sense...
If anybody has experienced this before, please I would appreciate any help. Muchas Gracias!
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