Achtergrond van Bruco

Automotive alternator voltage regulator

Vehicles with combustion motors make use of an alternator for generating electricity. Within these alternators the voltage is mostly regulated with an alternator voltage regulator IC (AVR). All vehicle makers have their own demands on the regulation, like regulation voltage, temperature coefficient on the regulation voltage, dependence on phase frequency, load response control, remote control, fail safe functions, auto start etc.

This wide variation of demands has resulted in a lot of regulator ICs that differ slightly. Therefore the original equipment manufacturers (OEM) have to deal with a lot of different variants of regulator ICs and modules. With the by Bruco newly designed AVR IC, the OEM is able to fulfill a wide variety of different demands with the same regulator IC and same module by just configuring the module.

Challenge

In an automotive environment there are a lot of electrical sources that introduce noise and voltage spikes on the supply circuit of the vehicle. One can think of noise from switching large inductive loads like wind screen wipers, voltage dips introduced by starting the cars' engine, and high frequency noise from the dynamo itself. Voltages up to 100 V can occur in normal cars with a 12 V power net, or trucks with a 24 V power net.
In this rough environment, the controller has to fulfill its functioning and configuration in a reliable and accurate way.
Alternator module

Solutions

In order to withstand the electrically rough automotive environment, the controller has been designed in a high voltage process that can cope with voltages up to 100V. A voltage clamp will limit the voltage over the IC. The device is protected against accidental reverse battery polarity. The IC has several provisions to cope with fault conditions, like disconnected pins and broken module wires.

The controller can be used to control both low side (switch between load and ground) and high side (switch between battery and load) power switches. In low side applications, the controller is able to steer an NPN Darlington or an N-FET. For high side applications an internal charge pump has been implemented. This charge pump can generate and deliver a voltage higher than the battery voltage, which is needed to steer the gate of the power FET in case of a high side configured switch.

The flexible configuration is achieved by connecting pre-defined resistors to the configuration pins. Since the OEM makes use of trim-able film resistors, the same module can be used at low cost for different alternator and vehicle makers.

The AVR IC can be configured in the following manners:

  • 12 V and 24 V battery system
  • Proportional PWM controlled field current
    • High side or low side configuration
    • Drive low side NFET or NPN Darlington
  • Self-regulating or remote control
  • Temperature coefficient on reference voltage
  • Load response control for low RPM
  • Auto-start condition
  • Field strobe duty factor after start up
  • Diagnostic outputs e.g. indicator light, load indication

Block diagram of the AVR IC in the alternator module