Hall Effect Sensor Voltage Regulation and Power Management

Hall Effect Sensor Voltage Regulation and Power Management

Most digital-output Hall Effect sensors contain internal voltage regulators that allow them to operate over an extended range of power supply voltages, most linear output sensors do not and require a regulated power supply. If microcontrollers, discrete logic  or other kinds of circuitry are used then a source of regulated power internal to the sensor assembly may be needed to power the other devices.

A regulated power supply may be done in two main ways, design it from discrete components or buy an  integrated regulator in the form of an off-the-shelf integrated circuit.

LM78xx Family of Linear regulators

When discussing linear in the context of a voltage regulator, it means that the device does not contain any switching elements and operates in a continuous manner without oscillators or clocks. The 78L05 and it’s related variants provide a regulated 5V output voltage with a peak current output of 100mA in many of the versions. The device is available in both TO-92 3-leaded transistor and SOIC-8 surface mountable packages. To use one of these parts an input voltage ranging from 8-24V connects to one pin and the second pin gets tied to the system ground., a 5V connects to the third pin.  Small capacitors can be connected from both of the inputs and outputs to the ground to reduce noise levels and provide power supply decoupling.

An understanding of certain characteristics helps to be able to employ these devices effectively. First, they have definite limits to the power they can safely dissipate. If 100mA is drawn from the 5V output while running from a 24V input to these devices the regulator will dissipate nearly 2W of power, in the form of heat. Neglecting this power consumption for internal “housekeeping” functions can severely limit the amount of current one can draw from a linear regulator because of the large differences in the input and output voltages.   For regulators in smaller packages (TO-, SOIC-8) it can be easy to exceed the devices maximum power ratings. If the ambient room temperature increases, the maximum power rating for integrated regulators decrease.

The second important characteristic of these devices is that there is a “drop-out” voltage for the input below which regulation is lost and the output is not guaranteed to be 5V (for a 5V regulator).The dropout voltage for 78Lxx devices is usually specified as 2-3V, a 5V regulator would begin to dropout at about 7-8V of input voltage. There is a low-drop-out regulator for when lower power supplies are required, it is referred to as a LDO.