A Simple Current Sensor Probe
Make floating current measurements with ground-referenced ‘scopes

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Extra info / Update
• Current sensor probe for oscilloscopes
• Common mode voltages: min. ±200 V at ±5 V for IC1 up to ±600 V at ±15 V for IC1
• Common mode suppression: min. 90 dB
• Measured voltages: up to ±4.7 V at ±5 V for IC1 up to ±14.7 V at ±15 V for IC1
• Input impedance: 2 Mohm for voltage across shunt
500 kOhm for common mode voltage
• Bandwidth: 0 up to 130 kHz (–3 dB)
• Amplification factor: x 1
• Amplification: max. 0.001 % errors
max. 5 ppm nonlinearity
max. 5 ppm drift
• Offset voltage: max. 1 mV
• Noise max. 35 µVpp at 0.01 to 10 Hz
typ. 1.6 µV/√Hz at ≥100 Hz
Component list
Resistors
All SMD 0603
R1 = 50Ohm
R2,R3 = 560Ohm
Capacitors
All ceramic
C1,C2 = 10µ 10V*, SMD 1206
C3..C6 = 100n 50V, SMD 0603
C7,C8 = 330n 25V*, SMD 1206
Semiconductors
D1–D4 = 1N4148, DO214AA
D5 = LED, red, SMD 0805
D6 = LED, blau, SMD 0805
IC1 = AD8479, SOIC-8
IC2 = 78L05F*, SOT89
IC3 = 79L05F*, SOT89
Miscellaneous
Coaxial cable*
Microphone cable*, 2-wire, shielded
Pin probes*
PCB
* see text
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