SLUAAY5 December   2024 UCC21551-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Automotive PTC Heater Module Overview
    1. 2.1 Automotive Heating Architectures
      1. 2.1.1 Positive Temperature Coefficient Heaters
      2. 2.1.2 Heat Pumps
    2. 2.2 Automotive Heating Architectures
    3. 2.3 PTC Heater Topologies
  6. 3Design of Automotive PTC Heater Controller
    1. 3.1  Block Diagrams
    2. 3.2  Designing the Power Supplies
    3. 3.3  Picking Low-Dropout Regulators
    4. 3.4  Designing of the Communication Interface
    5. 3.5  Implementation of the Digital Isolator
    6. 3.6  Implementation of the Microcontroller Unit
    7. 3.7  Designing of the Switch Driver Stage
    8. 3.8  Selection of the Power Switches
    9. 3.9  Considerations of the PTC Load
    10. 3.10 Designing the Load Current Monitoring
    11. 3.11 Selection of the Temperature Sensing
  7. 4Summary

1 Introduction

PTC heaters generate heat via resistive heating. Current flows through the PTC heating element (thermistor) and generates instantaneous heat to either heat the coolant or the cabin directly, with the heat increasing as more current flows through. Once a specified temperature is achieved, the resistance in the heating element rises significantly. This limits the chance of overheating. This application has the advantage of simplicity of use and system design. The control for this application is responsible for supplying current within the rating of the PTC load over a period of time and shutting off that current once heating is completed. The drawback to PTC heaters is that their Coefficient of Performance (CoP), the ratio of useful heat or cooling to energy needed for said system, can be at most 1:1, as opposed to heat pumps which can achieve a much higher CoP. This is accomplished by the heat pump using the power it gets from the battery to move hot air to and from the outside environment instead of generating the heat like the PTC heater does. So, more heat energy is transferred into the cabin than electrical energy is used to operate the system. The higher CoP results in a longer driving range for the EV, making this system attractive to automakers. However, a designer may still want to use a PTC heater solution instead of/in addition to a heat pump due to its simplicity and cost advantage over a heat pump system. The designer may also deem the PTC heater as a more practical heating system than the heat pump if the EV end user is in a very cold climate. The heat may have to be generated if it is not available in the outside environment of the car.