Voltage regulators are a common feature in many circuits to ensure that a constant, stable voltage is supplied to sensitive electronics.
How Linear Voltage Regulators Work
Maintaining a fixed voltage with an unknown and potentially noisy input requires a feedback signal to clarify what adjustments need to be made. Linear regulators use a power transistor as a variable resistor that behaves like the first half of a voltage divider network. The output of the voltage divider drives the power transistor appropriately to maintain a constant output voltage. Because the transistor behaves like a resistor, it wastes energy by converting it to heat—often lots of heat. Since the total power converted to heat is equal to the voltage drop between the input voltage and the output voltage times the current supplied, the power dissipated can often be very high, demanding good heatsinks. An alternate form of a linear regulator is a shunt regulator, such as a Zener diode. Rather than act as a variable series resistance as the typical linear regulator does, a shunt regulator provides a path to ground for excess voltage (and current) to flow through. This type of regulator is often less efficient than a typical series linear regulator. It is only practical when little power is needed and supplied.
How Switching Voltage Regulators Work
A switching voltage regulator works on a different principle than linear voltage regulators. Rather than acting as a voltage or current sink to provide a constant output, a switching regulator stores energy at a defined level and uses feedback to ensure that the charge level is maintained with minimal voltage ripple. This technique allows the switching regulator to be more efficient than the linear regulator by turning a transistor fully on (with minimal resistance) only when the energy storage circuit needs a burst of energy. This approach reduces the total power wasted in the system to the resistance of the transistor during the switching as it transitions from conducting (very low resistance) to non-conducting (very high resistance) and other small circuit losses. The faster a switching regulator switches, the less energy storage capacity it needs to maintain the desired output voltage, which means smaller components can be used. However, the cost of faster switching is a loss in efficiency as more time is spent transitioning between the conducting and non-conduction states. More power is lost from resistive heating. Another side effect of faster switching is the increase in electronic noise generated by the switching regulator. By using different switching techniques, a switching regulator can:
Step down the input voltage (buck topology).Step up the voltage (boost topology).Both step down or step up the voltage (buck-boost) as needed to maintain the desired output voltage.
This flexibility makes switching regulators a great choice for many battery-powered applications because the switching regulator can step up or boost the input voltage from the battery as the battery discharges.
