Soft-Start Circuits: An In-Depth Look скачать в хорошем качестве

Soft-Start Circuits: An In-Depth Look

In this video we discuss soft-start circuits which are used to limit inrush current during power-up of a circuit. We go into detail on three different soft-start circuit architectures and test example versions of them in the lab. Concepts discussed: What soft-start circuits are and why they're important NTC Thermistor architecture overview and lab testing Resistor and switch architecture overview and lab testing Ramp rate controller architecture overview and lab testing Overview on selecting the best architecture for your application Chapter Descriptions Intro o Overview of what a soft-start circuit is Circuit Input Capacitance o Using an example of an AC Adapter to a voltage regulator, we discuss why large input capacitances are often desirable and how they can lead to high currents during turn-on and how this large current must be reduced with a soft-start circuit NTC Thermistor Overview o We explain the general operation of the NTC Thermistor-based soft-start circuit NTC Thermistor Lab Results o I show some oscilloscope and digital multimeter (DMM) measurements I made in the lab with an NTC thermisor and "example" inrush circuit, as well as some static measurements of a bunch of different thermistor circuits Table of NTC Thermistor Test values o I show a table containing several thermistors I tested to help get a rough feel for the resistances you can expect how various thermistors NTCs in Series and Parallel o I discuss some things to keep in mind when putting NTCs in series and parallel (generally don't put them in parallel) NTC Circuit Pros and Cons o I discuss the advantages and disadvantages of the NTC circuit Resistor and Switch Overview o I explain the general operation of the resistor and switch-based soft-start circuit Resistor and Switch Lab Results o I go over the test circuit I designed for the lab demo, show the results, and discuss them Resistor and Switch Pros and Cons o I discuss the advantages and disadvantages of the resistor and switch circuit Ramp Rate Controller Overview o I explain the general operation of the ramp-rate-controller -based soft-start circuit using a MOSFET as the transistor element Mechanics of Power MOSFET Turn-on o I go over the mechanics of power MOSFET turn-on and how gate-source and gate-drain capacitance affects the mechanics of that turn-on. An understanding of the turn-on mechanics is required to understand how the ramp rate controller circuit operates and how to tweak the design to serve your application o I show that the results from our examination of the general power MOSFET turn-on pretty straightforwardly apply to the ramp rate controller circuit Ramp Rate Controller Design Flow and Analysis o I go through an example design flow for a ramp rate controller to show how you come up with the various parameters to set everything up for the ramp rate controller o I also perform all the necessary calculations to get predicted results from our lab test Ramp Rate Controller Lab Results o I go over the test circuit I designed for the lab demo, show the results, and discuss them A Note about MOSFET Safe Operating Area o I go over what a MOSFET's "Safe Operating Area" is and how to incorporate this into your design The Importance of Gate-Source Capacitance o If the gate-source capacitance is too low relative to the gate-drain capacitance, it will close the MOSFET right at turn-on and cause surge currents o I derive the relevant equations and use some example calculations to indicate what happens with a couple different capacitor values to illustrate the point Ramp Rate Controller Pros and Cons o I discuss the advantages and disadvantages of the ramp rate controller circuit Ideal Applications For Each Circuit o I briefly go over the ideal applications for each circuit to help decide which one is best to use for your specific application 00:00:00 Intro 00:02:02 Circuit Input Capacitance 00:06:05 NTC Thermistor Overview 00:09:07 NTC Thermistor Lab Results 00:12:02 Table of NTC Thermistor Test Values 00:13:28 NTCs in Series and Parallel 00:14:43 NTC Circuit Pros and Cons 00:19:43 Resistor and Switch Overview 00:20:55 Resistor and Switch Lab Results 00:27:36 Resistor and Switch Pros and Cons 00:30:06 Ramp Rate Controller Overview 00:32:29 Mechanics of Power MOSFET Turn-on 00:43:00 Ramp Rate Controller Design Flow and Analysis 00:47:13 Ramp Rate Controller Lab Results 00:51:34 A Note about MOSFET Safe Operating Area 00:55:45 The Importance of Gate-Source Capacitance 01:00:20 Ramp Rate Controller Pros and Cons 01:01:53 Ideal Applications For Each Circuit 01:02:40 Outro