Microchip E-Bike Tech Q&A - Will E-Bike Positioning System Power Supply Be Interrupted?

Semiconductor Integrated Circuits (ICs)
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Q: In the E-Bike scheme, will there be an interruption in the power supply of the positioning system?

A: Whether it is E-Bike , three/four-wheeled vehicles, or passenger cars, there may be cases of system power supply interruption or undervoltage. For example, during start-up or high-load power-on (such as catapult start), abnormal power supply may occur due to the discharge rate of the battery pack—for instance, the voltage drops from 48V to several volts.

We try to avoid this through design, such as optimizing the VCU control strategy to prevent sudden high-load situations.

If abnormal power supply occurs, more considerations need to be taken for such scenarios in design: conduct FTA/FMEA (Fault Tree Analysis/Failure Mode and Effects Analysis) for system design, add a voltage detection circuit at the hardware level, and enable the BOD (Brown-Out Detect) undervoltage reset protection built into the MCU in software to realize system voltage abnormality detection. These measures help the system better respond to such situations.

In general, voltage abnormalities are unavoidable.

Why Does Power Supply Interruption or Undervoltage Occur?

The power source of electric vehicles mainly comes from the traction battery (e.g., 48V, 60V, 72V).

In some extreme load scenarios, such as:

  • Start-up (especially the moment the motor starts, the current is very large);
  • High-load power-on (e.g., catapult start, climbing, sudden acceleration);

The instantaneous discharge rate of the battery will be insufficient → leading to a sharp drop in the bus voltage.

Example: A 48V battery may drop to several volts instantly, which will cause the low-voltage power supply (for the positioning module) to be directly cut off or under-voltage.

Why Is It “Unavoidable”?

Whether it is an E-Bike, three- or four-wheeled electric vehicles, or passenger cars, instantaneous voltage abnormalities of the power supply may occur.

The reason lies in the internal resistance of the battery and current transients: instantaneous large currents will cause the voltage to drop rapidly.

We can only reduce the probability through design optimization, but it is almost impossible to avoid it completely.

Design Response Ideas

(1) System-Level Optimization

VCU (Vehicle Control Unit) control strategy: Avoid instantaneous high loads, such as limiting the start-up acceleration or the rising rate of motor current.

(2) Hardware-Level Protection

  • Voltage detection circuit: Monitor the power supply voltage in real time to determine undervoltage or power failure.
  • Backup power supply: A small-capacity battery/supercapacitor can be added to the positioning module to ensure that the short-term power supply is not interrupted.

(3) Software-Level Protection

  • BOD (Brown-Out Detect) undervoltage reset protection built into the MCU: Reset or enter a safe mode when the voltage is lower than the safe value to prevent program abnormalities.
  • Abnormality handling algorithm: Automatically recover after power failure/undervoltage to avoid system crash.

(4) Reliability Design

FTA/FMEA analysis: Start with system failure mode and effect analysis, evaluate the risks caused by power supply abnormalities in advance, and optimize during the design phase.

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