Linear and Switching Voltage Regulators

Voltage regulators

A voltage regulator is a device, IC, or circuit that outputs a fixed voltage to it’s loads. For example, a 5v regulator outputs 5v to the loads which can be 100 Ohms which will result in 50mA of current. Each regulator has its own limitation in terms of current and total power.

Types of voltage regulators

Basically 2 main types: linear and switching. Each of them has its own advantages and disadvantages, as well as, field of application.

Both types has an electronic switch (transistor) as well as other elements. The main difference is the utilization of this transistor element in each topology.

It is better to view the slides version (attached in the last step) of this instructable.

Linear regulator

Figure 1 shows the typical linear regulator, the transistor here is called “pass element” which is delivering power continuously to the load.

The transistor here can be BJT or MOSFET and it will be operating in the “linear region”.

A feedback signal and a reference signal is compared together using an error amplifier (Op-amp), which in turns controls the transistor to keep it’s output voltage stable.

Switching regulator

Figure 2 shows the typical switching regulator, the transistor here is called “switching element” which is connecting and disconnecting input power to the load.

The transistor here can be BJT or MOSFET and it will be operating in the “saturation” or “cut off” region.

Switching regulators have an energy storage element to store energy and discharge it continuously. Thus power is in a form of pulses in the transistor not a continuous flow of current.

See the slides for a better table and better explanation.

Linear regulators:

Advantages: low noise, simple design, small size, and low cost.

Disadvantages: low efficiency, offers only "step-down" operation, and doesn't offer isolation.

Switching regulators:

Advantages: High efficiency, offer isolation, and has step-up, step-down, and inverting typologies.

Disadvantages: High noise and ripple, hard to design, large board space, and more expensive than linear ones.

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Dropout voltage:

it is the voltage difference between input and output voltage. It is what determines the efficiency of the linear regulator. LDOs are low dropout regulators which operates at a very low dropout such as 1v.

Example: input voltage = 10v, output voltage = 7v, and 1A of current will have 3v dropout (10-7). Thus the wasted power in the transistor of the linear regulator is 3v * 1A = 3W which is too much. Efficiency is 7W/10W = 0.7 = 70%, while similar switching regulator of the same specs can easily reach 95%. Many linear regulators do not have such low dropout like regulating 12v to 5v (at 2A) which has ~ 41.7% efficiency. Heatsinks are a must in most linear regulators.

See the attached slides to see schematics and images.

Linear: NPN, PNP, Quasi, P-MOSFET, and N-MOSFET.

Switching: Buck, boost, buck-boost, SEPIC, push-pull, flyback....etc.

These are circuits which combines both switching and linear regulators. Linear regulator is the final output regulator while the switching one is before it so that the switching one provides the linear one with an input of the output voltage + a small dropout to enhance efficiency while keeping the useful and clean linear regulator output.

Such switching regulators are called “Pre-regulators” and the linear regulators are sometimes called “Post-regulators”. It is a relatively new method in power supplies to gain high efficiency and low dropout at the same time. The pre-regulators might be controlled by a feedback from the linear output voltage, in this case the switching regulator is called “tracking pre-regulator”. Figure 2 below shows an example of the hybrid regulator.

I attached slides and simulation files with this instructables post. Simulation is done in LTSpice with 2 regulators, one is linear and the other is switching.

This is the video tutorial where I explain all that in details:

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