BioMedical Instrumentation Lab., BME, Yonsei University 윤 자 웅윤 자 웅 The Design of Output Stages & Driver Section in SMPS Power Supply CookBook (2 nd ) – Marty Brown

Contents BioMedical Instrumentation Lab., BME, Yonsei University 1.The Design of Output Stages - Passive Rectifier and Output stage - Active Rectifier and Output stage 2. The Design of Driver Section - BJT ( fixed base, proportional base ) - MOSFET - IGBT

The Design of Output Stages BioMedical Instrumentation Lab., BME, Yonsei University A good design of the Output stage -> High efficiency of Power Supply Two Basic types of Output stage : ( Forward-Mode, Boost)

The Design of Output Stages - Rectification BioMedical Instrumentation Lab., BME, Yonsei University The designer should choose the type of rectification technology that is most appropriate for the application. Synchronous rectification (vs Passive rectification) 1.More effiicient 2.Typically, used in battery operated product 3.Restricted only to continuous forward-mode output 4. Need the added cost of the driving circuit. Adv. Dis Adv.

The Design of Output Stages – Passive Output Stage BioMedical Instrumentation Lab., BME, Yonsei University Traditional passive semiconductor rectifier based design Recommended to the SMPS those efficiencies of 72 ~ 84% How to choose ? ( k = 1 (full-wave), 2 (center-tapped) )

The Design of Output Stages – Schottky vs Ultrafast Diode BioMedical Instrumentation Lab., BME, Yonsei University Schottky Ultrafast P-N 0.3 – 0.6 V0.8 – 1.1 V Drop Out 35 – 85 ns Reverse recovery time Less than 15VDC out Less than 10ns Recommendation Junction Semiconductor - SemiconductorSemiconductor - Metal Characteristic Curve

The Design of Output Stages – Schottky vs Ultrafast Diode BioMedical Instrumentation Lab., BME, Yonsei University

The Design of Output Stages – Active Output Stage BioMedical Instrumentation Lab., BME, Yonsei University Active Output Stage = Synchronous Rectifiers Used in higher current (power) outputs. Power MOSFETs : Turned on whenever the rectifier is required to conduct. Very low resistance when conducting, On-Resistance (Rds(on))

The Design of Output Stages – Active Output Stage BioMedical Instrumentation Lab., BME, Yonsei University

The Design of Output Stages – The Output Filter BioMedical Instrumentation Lab., BME, Yonsei University Convert the rectified rectangular ac waveform into the dc output Forward Mode - 2 LC filter, Boost Mode – 1 LC filter Key Design factor 1. Inductor (L) : To operate in the continuous current mode 2. Capacitor (c) : Determine the ripple peak to peak voltage ( Usually, 30mVpp)

The Design of Output Stages – The Output Filter BioMedical Instrumentation Lab., BME, Yonsei University

The Design of Driver section BioMedical Instrumentation Lab., BME, Yonsei University Power Switch : BJT, Power MOSFET – needed a driver IGBT ( Integrated gate bipolar transistor) -> Higher power industrial applications, such as >> 1 kW

The Design of Driver section - BJT BioMedical Instrumentation Lab., BME, Yonsei University Current Driven Device. Full Saturation, Full Cutoff -> Switch-like operation Symbol & Equivalent Circuit

The Design of Driver section - BJT BioMedical Instrumentation Lab., BME, Yonsei University Current Driven Device. Full Saturation, Full Cutoff -> Switch-like operation Symbol & Equivalent Circuit

The Design of Driver section – Fixed base drive circuit BioMedical Instrumentation Lab., BME, Yonsei University

The Design of Driver section – Proportional base drive circuit BioMedical Instrumentation Lab., BME, Yonsei University

The Design of Driver section – Power MOSFET Power Switch BioMedical Instrumentation Lab., BME, Yonsei University The most common choice as a power switch Voltage-controlled current source. - to drive a MOSFET into saturation, enough voltage must be applied between the Gate – Source terminal. D-MOSFET, E-MOSFET Ciss, Coss, Cres

The Design of Driver section – IGBT Power Switch BioMedical Instrumentation Lab., BME, Yonsei University IGBT = Insulated Gate Bipolar Transistor Advantage of BJT + MOSFET Slow switching time ( < 100 kHz)

Selecting the optimum Control Method BioMedical Instrumentation Lab., BME, Yonsei University Selection of the control IC is very important Voltage-Mode control : Forward Mode Converter Current – Mode control : Buck, Boost, Buck-Boost, Flyback Needed some additional protection & feedback circuit 1. Voltage-Mode : Error Voltage Feedback 2. Current – Mode : Overloaded current protection circuit

Epilogue – Q&A BioMedical Instrumentation Lab., BME, Yonsei University Thank you for your attention !