6 questions and answers about regulators you most want to know

The regulator produces a fixed output voltage with a constant preset amplitude, regardless of whether its input voltage or load conditions change.

Regulators fall into two categories: linear and switching -

Linear regulators use active (BJT or MOSFET) current-through devices (in series or parallel) that are controlled by high-gain differential amplifiers. It compares the output voltage to a precision reference and adjusts the through-current device to maintain a constant output voltage.

The switching regulator converts the DC input voltage to a switching voltage applied to the power MOSFET or BJT switch. The filtered power switch output voltage is fed back to the circuit that controls the power switch on and off times so that the output voltage remains constant regardless of changes in its input voltage or load current.

What are the topology of the switching regulator?

There are three common topologies: buck, boost, and buck/boost. Other topologies include flyback, SEPIC, Cuk, push-pull, forward, full-bridge, and half-bridge topologies.

How does the switching frequency affect the regulator design?

Higher switching frequencies mean that the regulator can use smaller inductors and capacitors. This also means higher switching losses and greater circuit noise.

What are the losses of the switching regulator?

The power required to turn the MOSFET on and off causes losses and is related to the MOSFET gate driver. Similarly, it takes a certain amount of time to switch from the on state to the non-conduction state, thus generating MOSFET power consumption. In addition, the energy required to charge and discharge the MOSFET gate capacitance between the threshold voltage and the gate voltage can also cause losses.

What are the common applications for linear and switching regulators?

Given the input and output voltages, the linear regulator's power dissipation is proportional to the output current, so the typical efficiency can be 50% or less. By optimizing the device, the switching regulator achieves 90% efficiency. However, the linear regulator's noise output is much lower than the switching regulator of the same output voltage and current requirements. Typically, switching regulators can drive higher current loads than linear regulators.

How does the switching regulator control its output?

Switching regulators need to change their output voltage in some way in response to input and output voltage changes. One method is to use PWM to control the input of the associated power switch to control its switching time (duty cycle). During operation, the regulated output voltage of the regulator is fed back to the PWM controller to control the duty cycle. If the filtered output changes, the feedback applied to the PWM controller changes the duty cycle to maintain a constant output voltage.

Which design specifications are important to the regulator IC?

The basic parameters include input voltage, output voltage, and output current. Other parameters may also be important depending on the application, such as output ripple voltage, load transient response, output noise, and efficiency. Important parameters of the linear regulator include differential voltage, PSRR (power supply rejection ratio), and output noise.