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## SEPIC-Ćuk split-rail converter average model

Tutorial

SEPIC-Ćuk split-rail converter can be used to make positive and negative supplies from a single input voltage for relatively well-matched loads like operational amplifiers.

Transient models are time consuming. Average models reduce modeling time drastically.

The PWM switch average models for current- and voltage-mode are described in details in Christophe Basso’s book “Switch-Mode Power Supplies, Second Edition: SPICE Simulations and Practical Designs”. Using of these models for SEPIC and Ćuk converters is also shown.

This text shows how to use the PWM switch average model to design a split-rail SEPIC-Ćuk converter.

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## A note on small-signal modeling of SEPIC CM CCM

Tutorial

Knowing parameters of small-signal control-to-output transfer functions makes it easier for engineers to design compensation networks of DC/DC converters. The equations for SEPIC can be found in different works and Application Notes, but there are differences. A work has been done to solve this problem.

Simplified design equations for SEPIC with Current Mode control (CM) in Continuous Conduction Mode (CCM) suitable for practical design of compensation networks are shown.

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## 4th Order Low-pass Filter with 1 Op Amp

Tutorial

The idea to build a 4th order low-pass filter looks simple: add one more feedback loop. But there are pitfalls, as always.
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## Gyrators

Tutorial

Gyrators are impedance converters usually used to simulate inductance in circuits. Though they are rarely used in discrete electronics, they are interesting circuits looking like pole dancers in pictures. There are studies on gyrators, but still something is missing, so it is interesting to do another one.
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## 3rd Order Low-pass Filter with 1 Op Amp

Tutorial

Common approach to build a 3rd order low-pass filter is to use two circuit stages and two Op Amps. Making a good One Op Amp design is not always easy, but it is possible.
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## Active Termination Drivers

Tutorial

The easiest way to build a driver with specified output impedance is to use an amplifier with high load compatibility and add a resistor to its output. The penalty is a voltage drop across this resistor, so there is power loss and we need a higher supply voltage. If our driver is able to deliver the same voltage and current to the same load, but the extra resistor will have a lower value, our device will be able to deliver the same output power at a lower supply voltage. Less power losses, less heat, and longer working time when a battery is used.
There is an idea how to solve this problem: active termination. We can synthesize the output impedance!

Now when we know what we want, go to design our drivers!
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## In-The-Loop Low-pass Filter

Tutorial

If you look through datasheets you will find a strange circuit used in front of some ADCs. It looks like a low-pass filter, but you will not find this topology in books.

Let’s try to figure out what it is, how it works and how to design it.
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## Compensation for Error Caused by Limited Gain-Bandwidth of Operational Amplifiers in Low-pass Filters

Tutorial

An operational amplifier has the internal compensation circuit for stability which limits its working bandwidth. Frequency response of the compensated Op Amp has slope of −6 dB/octave or −20 dB/decade. Unity gain frequency defines the bandwidth where the Op Amp is able to amplify a signal. If we multiply the gain and frequency at any point, the result is the same, allowing us to use this parameter to select the appropriate Op Amp. It is called Gain-Bandwidth Product, GBW or GBP. The limited open-loop gain introduces a closed-loop gain and phase error.

But we want to optimize our circuits, right?
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## How to verify Switching-Mode Power Supply circuits

Из песочницы
It is always good practice to verify a circuit before using.

Switching-Mode Power Supplies are the most used circuits nowadays. But there are some difficulties with verifying their circuits: vendors do not publish models for all controllers; a model can be locked to be used with some tool; there can be errors in a model; average models want correct parameters and you need some practice of using them; transient models take a lot of time to get small-signal response and also can have errors.