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Transient Stability Testing of Transmission Line Fed LED Driver

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TDFS Impedance Stability of Transmission Line Fed LED Driver - Switching

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This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure impedance stability ratio. The system is a switching DC/DC step-down power converter used for LED lighting, supplied by a battery through a long power cable.The TDFS impedance stability measurement model applies a 0.2A sinusoidal stimulus current at the point where the cable connects to the converter. The voltage at that point, as well as the stimulus current splits (toward the source and the load) are measured, and the associated source and load impedances vs. frequency are computed.The ratio of the source to load impedance is the impedance stability ratio (Tm). Similar to the open-loop frequency response requirement for closed-loop stability, Tm must not have magnitude = 1.0 at phase = 180 degrees, at any frequency.For this system, with a cable length of 400 meters and 8 AWG wire, the results show that the impedance ratio magnitude (green waveform) reaches unity (0 dB) at close to 2 kHz, where the phase (light blue waveform) is approximately 165 degress. This implies a "phase margin" of only 15 degrees, For a longer cable, this margin is further reduced. As shown in the companion example, "Transmission Line Fed LED Driver - Switching", for the cable length = 800 meters the system is unstable.This instability is the result of the "source" impedance (which includes the cable) variation over frequency, interacting with the varying load impedance. Note that at low frequency, the load effectively has a negative impedance, due to the constant power nature of the DC to DC converter.

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CAN Network Signaling

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Copy of CAN Network Signaling - on Fri, 02/13/2026 - 15:05

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Copy of Transient Stability Testing of Transmission Line Fed LED Driver - on Thu, 01/22/2026 - 14:29

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Copy of Transient Stability Testing of Transmission Line Fed LED Driver - on Fri, 11/28/2025 - 14:51

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ES1

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This 4-node CAN network model is a "Live" design, meaning the user can change or "tune" various parameters shown in blue, and then run a new simulation to see the corresponding change in the signals received at each CAN node. These "tunable" parameters include the transmission line lengths, termination and choke parameter values, as well as select which of the CAN nodes is the transmitter.

In the network configuration shown, the parasitic capacitance at Node 4 causes asymmetric transitions. This asymmetry would normally result in EMI-causing even-mode propagating currents on the transmission lines, but the choke greatly reduces this effect. One interesting change the user can make is to set the choke inductance values to 0.0, effectively removing the choke from the network, and note the increase in the even-mode voltage wave on the adjacent transmission line.

The user can also save a copy of this design and enjoy full editing capability of the network configuration.

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Copy of CAN Network Signaling - on Fri, 06/13/2025 - 09:41

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Description

This 4-node CAN network model is a "Live" design, meaning the user can change or "tune" various parameters shown in blue, and then run a new simulation to see the corresponding change in the signals received at each CAN node. These "tunable" parameters include the transmission line lengths, termination and choke parameter values, as well as select which of the CAN nodes is the transmitter.

In the network configuration shown, the parasitic capacitance at Node 4 causes asymmetric transitions. This asymmetry would normally result in EMI-causing even-mode propagating currents on the transmission lines, but the choke greatly reduces this effect. One interesting change the user can make is to set the choke inductance values to 0.0, effectively removing the choke from the network, and note the increase in the even-mode voltage wave on the adjacent transmission line.

The user can also save a copy of this design and enjoy full editing capability of the network configuration.

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Copy of CAN Network Signaling - on Mon, 02/17/2025 - 12:45

Designer

Description

This 4-node CAN network model is a "Live" design, meaning the user can change or "tune" various parameters shown in blue, and then run a new simulation to see the corresponding change in the signals received at each CAN node. These "tunable" parameters include the transmission line lengths, termination and choke parameter values, as well as select which of the CAN nodes is the transmitter.

In the network configuration shown, the parasitic capacitance at Node 4 causes asymmetric transitions. This asymmetry would normally result in EMI-causing even-mode propagating currents on the transmission lines, but the choke greatly reduces this effect. One interesting change the user can make is to set the choke inductance values to 0.0, effectively removing the choke from the network, and note the increase in the even-mode voltage wave on the adjacent transmission line.

The user can also save a copy of this design and enjoy full editing capability of the network configuration.

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Copy of CAN Network Signaling - on Mon, 02/17/2025 - 09:35

Designer

Description

This 4-node CAN network model is a "Live" design, meaning the user can change or "tune" various parameters shown in blue, and then run a new simulation to see the corresponding change in the signals received at each CAN node. These "tunable" parameters include the transmission line lengths, termination and choke parameter values, as well as select which of the CAN nodes is the transmitter.

In the network configuration shown, the parasitic capacitance at Node 4 causes asymmetric transitions. This asymmetry would normally result in EMI-causing even-mode propagating currents on the transmission lines, but the choke greatly reduces this effect. One interesting change the user can make is to set the choke inductance values to 0.0, effectively removing the choke from the network, and note the increase in the even-mode voltage wave on the adjacent transmission line.

The user can also save a copy of this design and enjoy full editing capability of the network configuration.

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