Losses are also due to the energy needed to charge and discharge the capacitance of the MOSFET gate between the threshold voltage and gate voltage. However, the noise output from a linear regulator is much lower than a switching regulator with the same output voltage and current requirements. Typically, the switching regulator can drive higher current loads than a linear regulator. Switching regulators require a means to vary their output voltage in response to input and output voltage changes.
One approach is to use PWM that controls the input to the associated power switch, which controls its on and off time duty cycle. If the filtered output tends to change, the feedback applied to the PWM controller varies the duty cycle to maintain a constant output voltage.
Among the basic parameters are input voltage, output voltage, and output current. Depending on the application, other parameters may be important, such as output ripple voltage, load transient response, output noise, and efficiency.
There are various topologies for linear and switching regulators. Linear regulators often rely on low-dropout LDO topologies. For switching regulators, there are three common topologies: step-down converters, step-up converters, and buck-boost converters.
Each topology is described below:. One popular topology for linear regulators is a low-dropout LDO regulator. Linear regulators typically require the input voltage to be at least 2V above the output voltage. However, an LDO regulator is designed to operate with a very small voltage difference between input and output terminals, sometimes as low as mV. Step-down converters also called buck converters take a larger input voltage and produce a lower output voltage.
Conversely, step-up converters also called boost converters take a lower input voltage and produce a higher output voltage. A buck-boost converter is a single-stage converter that combines the functions of a buck and a boost converter to regulate the output over a wide range of input voltages that can be greater or less than the output voltage.
The four fundamental components of a linear regulator are a pass transistor, error amplifier, voltage reference, and resistor feedback network.
One of the inputs to the error amplifier is set by two resistors R1 and R2 to monitor a percentage of the output voltage. The other input is a stable voltage reference VREF.
Linear regulators typically only require an external input and output capacitor to operate, making them easy to implement. On the other hand, a switching regulator requires more components to create the circuit. The power stage switches between VIN and ground to create charge packets to deliver to the output. Similar to a linear regulator, there is an operational amplifier that samples the DC output voltage from the feedback network and compares it to an internal voltage reference.
Then the error signal is amplified, compensated, and filtered. This signal is used to modulate the PWM duty cycle to pull the output back into regulation. For example, if the load current increases rapidly and causes an output voltage droop, the control loop increases the PWM duty cycle to supply more charge to the load and bring the rail back into regulation.
Linear regulators are often used in applications that are cost-sensitive, noise-sensitive, low-current, or space constrained. Some examples include consumer electronics such as headphones, wearables, and Internet-of-Things IoT devices. Moreover, if designers are mainly interested in creating a low-cost application, they need not be as concerned with power dissipation, and can rely on a linear regulator.
Switching regulators are beneficial for more general applications, and are especially useful in applications that need efficiency and performance, such as consumer, industrial, enterprise, and automotive applications see Figure 3. For example, if the application requires a large step-down solution, a switching regulator is better suited, since a linear regulator could create high power dissipation that would damage other electrical components.
Some of the basic parameters to consider when using a voltage regulator are the input voltage, output voltage, and output current.
Other parameters — including quiescent current, switching frequency, thermal resistance, and feedback voltage — may be relevant depending on the application. Quiescent current is important when efficiency during light-load or standby modes is a priority.
When considering switching frequency as a parameter, maximizing the switching frequency leads to smaller system solutions. Additionally, thermal resistance is critical to remove heat from the device and dissipate it across the system. The Linear regulator acts as a voltage divider.
In the Ohmic region, it uses FET. The resistance of the voltage regulator varies with load resulting in constant output voltage. Linear voltage regulators are the original type of regulators use to regulate the power supplies. Once a load is allied, the changes in any input otherwise load will consequence in a difference in current throughout the transistor to maintain the output is constant. To change the current of the transistor, it should be worked in an active otherwise Ohmic region.
Throughout this procedure, this kind of regulator dissipates a lot of power because the net voltage is dropped within the transistor to dissipate like heat. Generally, these regulators are categorized into different categories.
A series voltage regulator uses a variable element placed in series with the load. By changing the resistance of that series element, the voltage dropped across it can be changed. And, the voltage across the load remains constant.
The amount of current drawn is effectively used by the load; this is the main advantage of the series voltage regulator. Even when the load does not require any current, the series regulator does not draw full current. Therefore, a series regulator is considerably more efficient than a shunt voltage regulator.
A shunt voltage regulator works by providing a path from the supply voltage to the ground through a variable resistance. The current through the shunt regulator has diverted away from the load and flows uselessly to the ground, making this form usually less efficient than the series regulator. It is, however, simpler, sometimes consisting of just a voltage-reference diode, and is used in very low-powered circuits wherein the wasted current is too small to be of concern.
This form is very common for voltage reference circuits. A shunt regulator can usually only sink absorb current. A switching regulator rapidly switches a series device on and off.
This is controlled by a feedback mechanism similar to that of a linear regulator. Switching regulators are efficient because the series element is either fully conducting or switched off because it dissipates almost no power. Switching regulators are able to generate output voltages that are higher than the input voltage or of opposite polarity, unlike linear regulators.
The switching voltage regulator switches on and off rapidly to alter the output. It requires a control oscillator and also charges storage components.
In a switching regulator with Pulse Rate Modulation varying frequency, constant duty cycle and noise spectrum imposed by PRM vary; it is more difficult to filter out that noise. A switching regulator with Pulse Width Modulation , constant frequency, varying duty cycle, is efficient and easy to filter out noise.
In a switching regulator, continuous mode current through an inductor never drops to zero. It allows the highest output power. It gives better performance.
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