S
Steve
- Jan 1, 1970
- 0
I've put together a voltage controlled current source for use at high
currents (5 Amps) based on the desgin at
http://www.daycounter.com/Circuits/Current-Servo/Current-Servo.phtml
It uses a single supply op amp (OPA340 or OPA703) driving a low gate
threshold logic level MOSFET (RFP30N06LE). Load connects between
drain and power source. Current sense resistor from MOSFET source to
ground with that junction feeding back through 10 K to inverting
input. Voltage control applied to non-inverting input.
Because of the high current and the desire to minimize power
dissipation in the sense resistor and voltage drop across it, I am
using a 0.1 ohm sense resistor. This is resulting in the current not
following the V=(current / 0.1 ohms) equation. I observe 0.725 A
(expect 1 A) at 0.1 control voltage and 3.5 A (expect 5 A) at 0.5 V.
These large errors are even present at low currents. Things are
better for higher valued sense resistors. For example, output current
is only 5% low when a 1 ohm current sense resistor is used. Is some
resistance not being compensated for or ?
currents (5 Amps) based on the desgin at
http://www.daycounter.com/Circuits/Current-Servo/Current-Servo.phtml
It uses a single supply op amp (OPA340 or OPA703) driving a low gate
threshold logic level MOSFET (RFP30N06LE). Load connects between
drain and power source. Current sense resistor from MOSFET source to
ground with that junction feeding back through 10 K to inverting
input. Voltage control applied to non-inverting input.
Because of the high current and the desire to minimize power
dissipation in the sense resistor and voltage drop across it, I am
using a 0.1 ohm sense resistor. This is resulting in the current not
following the V=(current / 0.1 ohms) equation. I observe 0.725 A
(expect 1 A) at 0.1 control voltage and 3.5 A (expect 5 A) at 0.5 V.
These large errors are even present at low currents. Things are
better for higher valued sense resistors. For example, output current
is only 5% low when a 1 ohm current sense resistor is used. Is some
resistance not being compensated for or ?