Objective and use case

You will construct an LR low-pass filter using an RF choke to isolate a DC power line from high-frequency AC noise. By superimposing an AC signal onto a DC voltage supply, you will observe how the inductor’s frequency-dependent reactance permits DC to pass while heavily attenuating high-frequency noise before it reaches the load.

This circuit concept is highly useful in the real world for:
* Preventing high-frequency switching noise from entering sensitive analog sensor circuits.
* Filtering out radio frequency interference (RFI) from long power supply lines.
* Isolating different functional blocks that share a common power rail on a PCB.
* Protecting automotive audio and communication electronics from alternator whine.

Expected outcome:
* The mixed input signal (V_IN_MIX) will display a steady DC offset combined with significant high-frequency ripples.
* The output voltage (V_OUT_CLEAN) across the load will show a stable DC level with the AC noise vastly reduced.
* An FFT (Fast Fourier Transform) analysis of the input will reveal a large 0 Hz (DC) component and a prominent high-frequency peak.
* An FFT analysis of the output will show the high-frequency peak almost completely suppressed, confirming the choke’s blocking action.

Target audience: Intermediate electronics students learning about reactive components and AC/DC superimposition.

Materials

• V1: 5 V DC source, function: main DC power supply
• V2: 500 mV peak sine wave AC source at 100 kHz, function: high-frequency noise simulator
• L1: 1 mH inductor, function: RF choke to block high-frequency noise
• R1: 100 Ω resistor, function: load simulation

Wiring guide

• V1: connects between V_DC and 0
• V2: connects between V_IN_MIX and V_DC
• L1: connects between V_IN_MIX and V_OUT_CLEAN
• R1: connects between V_OUT_CLEAN and 0

Conceptual block diagram

Measurements and tests

1. Connect an oscilloscope probe to V_IN_MIX with the ground clip attached to node 0. Set the channel coupling to DC. You should observe a 5 V DC baseline with a 1 V peak-to-peak 100 kHz sine wave riding on top of it.
2. Connect a second oscilloscope probe to V_OUT_CLEAN. Observe that the DC voltage remains at approximately 5 V, but the high-frequency 100 kHz ripple is drastically attenuated due to the high inductive reactance (XL = 2\pi fL) of the choke.
3. Activate the FFT (Fast Fourier Transform) math function on the oscilloscope for the V_IN_MIX channel. Note the massive spike at 0 Hz (representing the 5 V DC component) and the distinct noise spike at 100 kHz.
4. Apply the FFT function to the V_OUT_CLEAN channel. Compare the magnitude of the 100 kHz spike against the input measurement; it should be significantly reduced, successfully proving the inductor’s high-frequency blocking capabilities.

Common mistakes and how to avoid them

• Using an inductor with a low self-resonant frequency (SRF): All inductors have parasitic winding capacitance. If the noise frequency exceeds the inductor’s SRF, the component behaves like a capacitor and allows high-frequency noise to pass straight through. Always verify the SRF is well above your target noise frequency.
• Neglecting the inductor’s DC resistance (DCR): Inductors are made of coiled wire which naturally possesses resistance. High load currents passing through an inductor with high DCR will cause an unacceptable DC voltage drop. Choose a choke with an appropriately low DCR for your load.
• Core saturation due to high DC current: If the load draws more continuous current than the inductor’s saturation rating (Isat), the core’s magnetic flux saturates. This causes the inductance to drop sharply, destroying its filtering capability. Always check the saturation current rating.

Troubleshooting

• Symptom: High-frequency noise is still heavily present at V_OUT_CLEAN.
• Cause: The inductor value is too low to provide significant reactance at the simulated noise frequency, or its SRF has been exceeded.
• Fix: Increase the inductance value (e.g., scale from 10 µH to 1 mH) or verify the frequency limits of the specific choke being used.
• Symptom: Significant DC voltage drop at V_OUT_CLEAN under load (e.g., reading 4 V instead of 5 V).
• Cause: The inductor’s internal DC resistance (DCR) is too high relative to the load resistor R1.
• Fix: Replace the inductor with a physically larger one that uses thicker wire, which lowers the DCR, or increase the load resistance if it’s drawing more current than intended.
• Symptom: The choke gets excessively hot during operation.
• Cause: The DC current drawn by the load exceeds the continuous thermal current rating (Irms) of the inductor.
• Fix: Select a higher-rated power inductor capable of safely handling the steady-state load current.

Objective and use case

In this practical case, you will build a parallel LC tank circuit driven by an AC sine wave source through a series resistor. By sweeping the input frequency, you will observe the precise point where inductive and capacitive reactances cancel out, maximizing the circuit’s impedance.

Understanding LC resonance is essential in modern electronics because these circuits are the fundamental building blocks of frequency selection. Real-world applications include:
* Radio frequency (RF) tuning: Selecting a specific station’s frequency while rejecting others.
* Audio and signal filtering: Creating band-pass or band-stop (notch) filters to eliminate noise.
* Wireless power transfer: Maximizing the efficiency of inductive coupling between transmitter and receiver coils.
* Oscillator circuits: Generating stable clock signals for microcontrollers and transceivers.

Expected outcome:
* You will calculate the theoretical resonant frequency based on the chosen $L$ and $C$ values.
* The total current drawn from the source (Itotal) will drop to its minimum value at resonance.
* The voltage across the LC tank (VLC) will peak at the resonant frequency.
* You will observe how energy continuously sloshes back and forth between the capacitor’s electric field and the inductor’s magnetic field.

Target audience: Intermediate electronics students transitioning from DC basics to AC reactive circuits.

Materials

• V1: 5 V peak-to-peak AC voltage source, function: sine wave generator for frequency sweep
• R1: 1 kΩ resistor, function: source impedance to allow voltage variations across the tank
• L1: 10 mH inductor, function: magnetic energy storage
• C1: 100 nF ceramic or film capacitor, function: electric energy storage

Wiring guide

• V1: Connect the positive terminal to node IN and the negative terminal to node 0 (GND).
• R1: Connect one pin to node IN and the other pin to node TANK.
• L1: Connect one pin to node TANK and the other pin to node 0 (GND).
• C1: Connect one pin to node TANK and the other pin to node 0 (GND).

Conceptual block diagram

Measurements and tests

1. Calculate the theoretical resonant frequency (fr):
   Use the formula fr = (1 / 2\pi\sqrtLC). With L = 10 mH and C = 100 nF, the expected resonant frequency is approximately 5032 Hz.
2. Set up the frequency sweep:
   Configure V1 to output a 5 V peak-to-peak sine wave. Begin with a frequency of 1 kHz and gradually increase it up to 10 kHz.
3. Measure VLC (Tank Voltage):
   Monitor the voltage amplitude at node TANK relative to node 0 (GND) using an oscilloscope or an AC voltmeter. As you approach 5 kHz, the voltage amplitude will rise steadily, hitting a sharp maximum exactly at resonance, and then fall as the frequency increases further.
4. Measure Itotal (Source Current):
   Measure the current flowing through R1 (this can be done by observing the voltage difference between IN and TANK and applying Ohm’s law: Itotal = ((VIN – VTANK) / R1)). Note that at resonance, the parallel LC tank exhibits maximum impedance, meaning Itotal will drop to its minimum.
5. Calculate the circuit’s Q-factor:
   Identify the -3dB (half-power) frequencies above and below the resonance peak to find the bandwidth ($BW$). The Quality Factor is Q = (fr / BW).

Common mistakes and how to avoid them

• Using a polarized capacitor in an AC circuit: Electrolytic capacitors are generally polarized and can fail or explode if subjected to reversing AC voltages. Always use non-polarized capacitors (like ceramic or film) for an LC tank.
• Ignoring the inductor’s Equivalent Series Resistance (ESR): Real inductors consist of long coils of wire, adding parasitic DC resistance to the tank. If the measured Q-factor is much lower than expected (resulting in a wider, flatter peak), inductor ESR is usually the culprit.
• Confusing angular frequency (\omega) with standard frequency ($f$): Remember that \omega = (1 / \sqrtLC) yields results in radians per second. You must divide by 2\pi to get the frequency in Hertz.

Troubleshooting

• Symptom: The measured resonant frequency is significantly higher or lower than the calculated 5032 Hz.
  • Cause: Component tolerances. Standard ceramic capacitors can have a ±20% tolerance, and inductors often have ±10%.
  • Fix: Measure the exact values of L1 and C1 using an LCR meter and recalculate the expected frequency.
• Symptom: VLC shows no noticeable peak during the sweep; the voltage remains relatively flat.
  • Cause: The chosen frequency sweep range does not cover the resonant point, or R1 is too small, effectively shorting the tank to the rigid voltage source.
  • Fix: Double-check the math for your specific $L$ and $C$ values to ensure the sweep range encompasses fr. Ensure R1 is adequately sized (1 kΩ is a good starting point).
• Symptom: Signal distortion or clipping is observed at node TANK.
  • Cause: The AC source might be overdriving the circuit, or core saturation is occurring in the inductor (if using a very small ferrite core at high currents).
  • Fix: Reduce the amplitude of V1 from 5 V to 1 V peak-to-peak and check if the sine wave becomes clean again.

Objective and use case

In this practical case, you will build a basic open-loop Boost converter to demonstrate how an inductor stores and releases magnetic energy to step up a DC voltage.

Why it is useful:
* Allows battery-powered devices to operate at higher voltages (e.g., generating 5 V from a single 3.7 V Li-ion cell).
* Drives strings of LEDs that require a constant, high forward voltage.
* Captures and steps up voltage in energy harvesting and regenerative braking systems.
* Provides versatile power rails in compact portable electronics without requiring multiple batteries.

Expected outcome:
* You will observe the inductor current (I_inductor) ramping up when the switch is closed and ramping down when it opens.
* The output voltage (V_out) will be demonstrably higher than the input voltage source.
* You will record the direct relationship between the switch’s Duty Cycle and the resulting V_out magnitude.

Target audience and level:
Intermediate electronics students learning the fundamentals of switch-mode power supplies.

Materials

• V1: 5 V DC source, function: main power input
• V2: Pulse voltage source (0-5 V, 100kHz, 50% duty cycle), function: PWM signal for the switch
• L1: 100 µH inductor, function: magnetic energy storage
• M1: N-channel MOSFET (e.g., IRLZ44N), function: main switching element
• D1: Schottky diode (e.g., 1N5819), function: prevents reverse current from capacitor
• C1: 47 µF capacitor, function: output voltage smoothing
• R1: 100 Ω resistor, function: basic load to discharge capacitor

Wiring guide

• V1: connects between VIN and 0 (GND).
• V2: connects between GATE_PWM and 0 (GND).
• L1: connects between VIN and SW_NODE.
• M1: Drain connects to SW_NODE, Gate connects to GATE_PWM, Source connects to 0 (GND).
• D1: Anode connects to SW_NODE, Cathode connects to VOUT.
• C1: connects between VOUT and 0 (GND).
• R1: connects between VOUT and 0 (GND).

Conceptual block diagram

Measurements and tests

1. Initial state check: Apply V1 (5 V) with V2 turned off (0% duty cycle). Measure VOUT. The voltage should be roughly 4.7 V (the 5 V input minus the forward voltage drop of the Schottky diode).
2. Switching activation: Activate V2 to supply a 100kHz square wave at a 50% duty cycle. Measure VOUT across R1. The voltage should rise to approximately 9 V-10 V, demonstrating the step-up action.
3. Inductor current observation: Probe the current flowing through L1 (I_inductor). You will observe a triangular waveform. The upward slope occurs while M1 is ON (energy storage), and the downward slope occurs while M1 is OFF (energy release to VOUT).
4. Duty Cycle mapping: Adjust the Duty Cycle of V2 from 30% to 70% in 10% increments. Record VOUT at each step to verify that a higher duty cycle yields a higher output voltage.

Common mistakes and how to avoid them

• Using a standard rectifier diode (e.g., 1N4007): Standard diodes are too slow to turn off at 100kHz, leading to massive switching losses and poor voltage conversion. Always use a fast-recovery or Schottky diode like the 1N5819.
• Inductor core saturation: If the inductor’s maximum current rating is lower than the peak switching current, the magnetic core will saturate. The inductor will then act as a short circuit, potentially destroying the MOSFET. Always verify the inductor’s saturation current rating.
• Operating without a load: Running a boost converter with no load resistor (R1) can cause the output voltage to continuously rise with every switching cycle, theoretically reaching infinity and destroying the output capacitor or MOSFET. Always include a minimum load.

Troubleshooting

• Symptom: Output voltage equals the input voltage (minus diode drop).
• Cause: The MOSFET is not switching. V2 might be disconnected or the voltage level is too low to surpass the MOSFET’s gate threshold.
• Fix: Check the GATE_PWM signal with an oscilloscope. Use a logic-level MOSFET if your PWM signal is limited to 3.3 V or 5 V.
• Symptom: MOSFET becomes extremely hot very quickly.
• Cause: The inductor is saturating, or the MOSFET has a high ON-resistance (RDS(on)) and is experiencing high conduction losses.
• Fix: Swap the inductor for one with a higher current rating. Ensure the gate drive voltage is sufficient to turn the MOSFET completely ON.
• Symptom: Unstable or highly rippled output voltage.
• Cause: The output capacitor C1 is too small for the load or has a high Equivalent Series Resistance (ESR).
• Fix: Increase the capacitance of C1 or place a ceramic capacitor in parallel with the electrolytic capacitor to lower the overall ESR.

Objective and use case

In this practical case, you will build a switched inductor circuit monitored by an oscilloscope to observe the destructive voltage spike (inductive kickback) that occurs when current is abruptly interrupted. You will then install a flyback diode in parallel with the inductive load to safely clamp this transient voltage.

Why it is useful:
* Prevents catastrophic overvoltage damage to sensitive switching components such as transistors, MOSFETs, and microcontroller pins.
* Significantly reduces electromagnetic interference (EMI) and radio frequency interference (RFI) caused by high-voltage arcing across mechanical switch contacts.
* Increases the reliability, safety, and lifespan of power supply systems, motor controllers, and relay-driven circuits.

Expected outcome:
* Without the diode, opening the switch will produce a massive negative voltage spike on the oscilloscope, often reaching hundreds of volts.
* With the flyback diode installed, the transient spike will be immediately clamped to a safe level of approximately -0.7 V.
* The stored magnetic energy will safely dissipate as a steadily decaying circulating current through the inductor-resistor-diode loop.

Target audience and level: Intermediate electronics students learning about reactive components, energy storage, and circuit protection techniques.

Materials

• V1: 12 V DC supply, function: main power source
• SW1: SPST toggle or push-button switch, function: circuit connection control
• L1: 100 mH inductor, function: magnetic energy storage
• R1: 100 Ω resistor, function: limits steady-state current to 120 mA
• D1: 1N4007 rectifier diode, function: flyback protection

Wiring guide

• V1: connects between node VCC (positive) and node 0 (ground).
• SW1: connects between node VCC and node SW_OUT.
• L1: connects between node SW_OUT and node L_MID.
• R1: connects between node L_MID and node 0.
• D1: connects between node 0 (Anode) and node SW_OUT (Cathode) for reverse bias during normal closed-switch operation.

Conceptual block diagram

Measurements and tests

1. Connect the oscilloscope probe to node SW_OUT and attach the ground clip to node 0. Set the oscilloscope trigger to a falling edge, single-shot mode.
2. Begin with the flyback diode (D1) completely disconnected from the circuit.
3. Close the switch (SW1) to allow current to flow. Wait a moment for the magnetic field in the inductor to fully build up.
4. Quickly open the switch (SW1). Observe the oscilloscope capture; you will see a massive negative voltage transient as the inductor acts as a current source, forcing current across the open switch gap.
5. Connect the flyback diode (D1), verifying that the cathode (striped end) connects to node SW_OUT and the anode connects to node 0.
6. Repeat the switching process. The oscilloscope trace will now show the negative transient safely clamped at roughly -0.7 V as the diode forward-biases to provide a safe discharge path.

Common mistakes and how to avoid them

• Reversing the diode polarity: Placing the diode with the anode pointing to the positive voltage node creates a direct short circuit to ground when the switch is closed. This will destroy the diode or trigger the power supply’s overcurrent protection. Always ensure the cathode faces the higher potential.
• Using a diode with inadequate current rating: The flyback diode must safely handle a peak forward current equal to the steady-state current of the inductor just before switching. Always use properly rated rectifier, Schottky, or fast-recovery diodes.
• Omitting the series resistor: Connecting a pure inductor directly across a high-current DC source acts as a near short-circuit once the magnetic field is fully established. Always include a current-limiting series resistor, or ensure the inductor (such as a relay coil) has sufficient internal DC resistance.

Troubleshooting

• Symptom: The power supply shuts down or its current limit LED turns on immediately upon closing the switch.
  • Cause: The flyback diode is installed backwards, creating a short circuit from the power source to ground.
  • Fix: Disconnect power immediately and flip the diode so its striped end (cathode) faces the switch node.
• Symptom: A massive voltage spike still appears on the oscilloscope even with the diode supposedly installed.
  • Cause: The diode may have blown open due to a previous overcurrent event, or the breadboard connection is loose.
  • Fix: Verify diode continuity using a multimeter’s diode mode, and check the physical seating of the pins at the switch and ground nodes.
• Symptom: The oscilloscope trace shows high-frequency ringing instead of a clean clamp.
  • Cause: Parasitic capacitance in the switch, wiring, or oscilloscope probes interacting with the inductor.
  • Fix: Ensure the oscilloscope probe is properly compensated (x10 mode recommended for high voltage spikes) and keep ground leads as short as physically possible.

Objective and use case

In this practical case, you will construct a fundamental electromagnetic induction demonstrator using a hand-wound copper coil and a high-strength neodymium magnet. You will observe how kinetic energy is converted into electrical energy via Faraday’s Law of Induction.

Why it is useful:
* Power Generation: This mechanism illustrates the core principle behind electric generators, alternators, and wind turbines.
* Audio Technology: This is the operating principle for dynamic microphones and electric guitar pickups (transducers).
* Sensors: Used in automotive ABS speed sensors and industrial position sensors.
* Wireless Charging: Demonstrates the basics of magnetic coupling used in phone chargers.

Expected outcome:
* A measurable voltage spike (positive or negative) on the multimeter when the magnet moves relative to the coil.
* The LED flashes briefly when the magnet is moved rapidly, indicating a voltage peak exceeding the diode’s forward voltage (~1.8 V).
* Reversing the direction of the magnet’s movement reverses the polarity of the induced voltage.

Target audience: Students and hobbyists introducing themselves to Faraday’s Law and passive components.

Materials

• L1: Air core coil (approx. 500–1000 turns of enameled copper wire), function: induction element.
• MAG1: Cylindrical Neodymium magnet (fit to pass inside L1), function: source of magnetic flux.
• D1: Red LED, function: indicator for positive phase induction.
• D2: Green LED, function: indicator for negative phase induction (connected in anti-parallel).
• M1: Multimeter (set to 200 mV or 2 V DC range), function: voltage monitor.

Wiring guide

The circuit consists of the coil connected directly to the indicators in parallel. We define the coil terminals as nodes COIL_A and COIL_B.

• L1: Connects between node COIL_A and node COIL_B.
• D1: Anode connects to COIL_A; Cathode connects to COIL_B.
• D2: Anode connects to COIL_B; Cathode connects to COIL_A (anti-parallel to D1).
• M1: Positive probe connects to COIL_A; Negative probe connects to COIL_B.

Conceptual block diagram

Measurements and tests

1. Static Test: Place the magnet inside the coil and hold it completely still. The multimeter should read 0 V, and no LEDs should light up. This confirms that a changing magnetic field is required.
2. Slow Insertion: Set the multimeter to the lowest DC voltage range (e.g., 200 mV). Slowly push the magnet into the coil. Observe a small voltage reading (e.g., +10 to +50 mV).
3. Fast Action: Quickly thrust the magnet into the coil. You should see a significantly higher voltage spike (potentially > 1 V) and D1 (Red) may flash briefly.
4. Reverse Motion: Quickly pull the magnet out of the coil. The voltage polarity on the multimeter will flip (negative sign), and D2 (Green) should flash.
5. Oscillation: Move the magnet back and forth rapidly inside the coil. The LEDs should flicker alternately, demonstrating the generation of Alternating Current (AC).

Common mistakes and how to avoid them

1. Using weak magnets: Standard black ferrite magnets are often too weak to generate visible voltage on an LED. Solution: Use rare-earth Neodymium magnets.
2. Moving too slowly: Faraday’s Law (V = – N · d\Phi / dt) depends on the rate of change. Solution: Move the magnet as quickly as possible to maximize the voltage spike.
3. Insulation issues: Enameled wire has a clear coating that blocks electricity. Solution: Ensure the ends of the coil wire are sanded or scraped down to bare copper before connecting to the LEDs or multimeter.

Troubleshooting

• Symptom: Multimeter shows voltage, but LEDs never light up.
  • Cause: The induced voltage is lower than the LED forward voltage threshold (~1.8 V).
  • Fix: Add more turns to the coil (increase $N$) or move the magnet faster.
• Symptom: No reading on the multimeter even with fast movement.
  • Cause: Open circuit or poor connection at the coil tips.
  • Fix: Check continuity (resistance mode) across the coil terminals; it should read a few Ohms, not infinite.
• Symptom: Voltage reading is erratic or hard to see.
  • Cause: Digital multimeters have a slow sample rate.
  • Fix: Use the «Max/Min» hold function if available, or use an analog (needle) multimeter which responds better to transient pulses.

Objective and use case

In this practical exercise, you will build a passive RL low-pass filter using a series inductor and a shunt resistor. This circuit demonstrates the inductive reactance property, where impedance increases with frequency, effectively blocking high-frequency signals while allowing low-frequency signals to pass through to the output.

Why it is useful:
* Audio Electronics: Used in crossover networks to direct low frequencies (bass) to woofers while blocking treble.
* Power Supplies: Essential for smoothing output currents and reducing ripple in DC/DC converters.
* Noise Suppression: Filters out high-frequency interference (EMI) on signal lines.
* Signal Conditioning: Removes high-frequency noise from sensor data before processing.

Expected outcome:
* Low Frequency Input (< Cutoff): The output amplitude (VOUT) is approximately equal to the input amplitude (VIN).
* Cutoff Frequency (fc): The output amplitude drops to roughly 70.7% of the input amplitude (-3dB point).
* High Frequency Input (> Cutoff): The output amplitude is significantly attenuated (reduced).
* Target audience: Basic electronics students and hobbyists exploring AC circuit theory.

Materials

• V1: Function Generator (Sine wave source), function: AC signal injection
• L1: 10 mH inductor, function: series reactive element (impedance increases with frequency)
• R1: 100 Ω resistor, function: load/shunt resistor (output taken here)
• Scope: Dual-channel Oscilloscope, function: visual comparison of Input vs. Output

Wiring guide

Construct the circuit using the following node connections. The output voltage is measured across the resistor.

• V1 (Signal Source): Connects between node VIN (Positive) and node 0 (GND).
• L1: Connects between node VIN and node VOUT.
• R1: Connects between node VOUT and node 0 (GND).
• Oscilloscope Channel 1: Connect probe tip to VIN and ground clip to 0.
• Oscilloscope Channel 2: Connect probe tip to VOUT and ground clip to 0.

Conceptual block diagram

Measurements and tests

Follow these steps to validate the frequency response of the filter.

1. Setup: Configure the Function Generator (V1) to output a Sine Wave with 5 Vpp amplitude.
2. Low Frequency Test (Pass Band):
   • Set V1 frequency to 100 Hz.
   • Observe Channel 1 (Input) and Channel 2 (Output) on the oscilloscope.
   • Result: The output wave (VOUT) should be almost identical in amplitude to the input (VIN).
3. Cutoff Frequency Test (fc):
   • Calculate the theoretical cutoff: fc = (R / (2\pi L)) ≈ (100 / (2\pi × 0.01)) ≈ 1.59 kHz.
   • Set V1 frequency to 1.6 kHz.
   • Result: VOUT should be approximately 3.5 Vpp (roughly 0.707 × 5 Vpp). You will also notice a phase lag of -45°.
4. High Frequency Test (Stop Band):
   • Set V1 frequency to 50 kHz.
   • Result: The output wave (VOUT) should be very small (highly attenuated) compared to the input.

Common mistakes and how to avoid them

1. Measuring across the Inductor: If you measure voltage across L1 instead of R1, you create a High-Pass filter (passing high frequencies). Solution: Ensure the oscilloscope probe monitors the node between L1 and R1 relative to Ground.
2. Using DC Input: An inductor acts as a short circuit in DC (after the transient). Solution: Ensure the function generator is set to AC (Sine Wave) to observe reactance effects.
3. Inductor Saturation: Using a very small inductor core with high current can saturate the magnetic field, distorting the waveform. Solution: Use an appropriate inductor or keep signal current within the component’s rating.

Troubleshooting

• Symptom: VOUT is zero at all frequencies.
  • Cause: Open circuit in the wiring or broken inductor wire.
  • Fix: Check continuity of L1 and connections at VIN and VOUT.
• Symptom: VOUT equals VIN at all frequencies.
  • Cause: The inductor L1 is shorted or R1 is disconnected (open).
  • Fix: Measure the resistance of L1 (should be non-zero but low) and ensure R1 is properly grounded.
• Symptom: No attenuation observed at 50 kHz.
  • Cause: Inductor value is too small or Resistor value is too large (cutoff frequency is too high).
  • Fix: Verify component values. Try increasing L1 or decreasing R1 to lower the cutoff frequency.