Electronics > Beginners
Heating operational amplifier OP284FSZ-REEL7
Jwillis:
--- Quote from: Glebiys on February 01, 2020, 10:00:59 am ---@Jwillis, thank you for the answer!
I already created a board, so, unfortunately, adding a resistor at the moment will not work. This can be done in the next version of the board.
Then what are the options:
1) Change the value of the resistor on the voltage divider so that the voltage difference is in the range of 0.6 V.
2) Buy another operational amplifier that corresponds to a large difference in inputs.
The LM258W came up, but it's not Rail-To-Rail.
--- End quote ---
I've only worked with a very few op amps and mostly for high voltages. I'm sure some one else would be able to say what would be a more suitable Op amp .
Just changing the voltage divider at the inverting input won't help because it has current limit with the 100K resistor. It's more on the non inverting input . How much current is the PWM putting out.
wraper:
--- Quote from: Glebiys on February 01, 2020, 10:00:59 am ---@Jwillis, thank you for the answer!
I already created a board, so, unfortunately, adding a resistor at the moment will not work. This can be done in the next version of the board.
--- End quote ---
Resistor will do nothing since input current is already limited by high resistance of divider connected to negative input. You should use different op-amp or comparator if you manage to find one with push-pull rail-to-rail output in the same package and high enough supply voltage.
Kleinstein:
The current limiting at the negative input should be enough. However the OPA284 seem to no like the circuit. There is nothing absolutely wrong with the circuit, though the OPA284 is not a good choice with the limited input range.
I have found a similar problem with the TLE2071: it does not like to have it's output driven hard negative and than consumes a lot more current (some 20 mA) and gets warm :rant:. Looks like the OPA284 may have a similar problem.
So the best is to use a different OP or comparator. My suggestion would be OPA2170. It is not fully rail to rail at the input, but at the output.
TerminalJack505:
The OP284 has two op amps so the other op amp may be causing the problem. How is it hooked up?
wraper:
--- Quote from: Kleinstein on February 01, 2020, 11:05:39 am ---My suggestion would be OPA2170. It is not fully rail to rail at the input, but at the output.
--- End quote ---
Nope, don't use OPA2170. It has back to back diodes between inputs.
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