power supply control transitioning uc3854 customers to the ucc3817 pfc controller power supply...

Power Supply Control

Transitioning UC3854 Customers to the UCC3817 PFC Controller

Power Supply Control Products

Objective:•Review the Similarities and Differences of Both Controllers •Highlight the Application Differences That Transitioning Customers Need to Know About

Rectified Input Voltage

Input Current




Similarities:•Designed to Control PFC Power Stage•Average Current Mode Control•Achieved Near Unity Power Factor by Shaping the Input Current Waveform •These Controllers Are Typically Designed in Two-stage Systems

Typical Two Stage Power Converter With PFC Front End

Vout

+

-

PFC Controller PWM Controller

VLINE85-265 VAC

Stage 1 Stage 2




Differences:•PWM Modulation

–UC3854 Uses Traditional Trailing Edge PWM Modulation–UCC3817 Uses Leading Edge Modulation

•Current Amplifier–UC3854 Is Set up in a Non Inverting Configuration–UCC3817 Is Set up in an Inverting Configuration

•Voltage Feed Forward(VFF)–UC3854 Generates VFF From the Input and Requires a Two Pole Filter–UCC3817 Generates VFF Internally From the Iac Current and Only Requires a Single Pole Filter

•Multiplier–The Older UC3854 Required a Bias Resistor From the Internal Reference to the Iac Pin for Proper Operation –The UCC3817 Multiplier Has Better Overall Parametric Performance




Q 2

C BULKQ 1

L1

B U C K D E R IV E D C O N V E R TE RP FC B O O S T

C IR C U IT

D 1IA C

IQ 1 IC

IQ 2ID 1 IL

L2

C o u tD 2 R L oa d

C t

G ate D rive Q 1 T ra ilingE dge M odula tion

G ate D rive Q 2 T ra ilingE dge M odula tion

Ic w ith T ra iling E dge/T ra iling E dge M odu la tion

Ic w ith Lead ing E dge/T ra iling E dge M odu la tion

G ate D rive Q 1 LeadingE dge M odula tion

PWM Modulation•UC3854 Uses Traditional Trailing Edge PWM Modulation•UCC3817 Uses Leading Edge PWM Modulation

–When Properly Synchronized With a Down Stream Converter Can Have up to 40% Less RMS Current Through the Boost Capacitor

Ct

C1

G ate Drive fromDown Stream PW M

D1

D2UCC3817

Ct

Rt

R t

Boost Capacitor Ripple Current Comparison Synchronization Circuit




Current Amplifier Configuration•UC3854 Uses a Non Inverting Amplifier Configuration•UCC3817 Uses a Inverting Amplifier Configuration That Can Have Better

Noise Rejection Than the Non Inverting Configuration

+

–ZF

RINRIN

RSENSE

CA

-

+

PWM

PFC GATE DRIVE

UC3854 CURRENT AMPLIFIER CONFIGURATION

IMULTIPLIER

-

+

ZFRINRIN

RSENSE

CA

+

-

PWM

PFC GATE DRIVE

UCC3817 CURRENT AMPLIFIER CONFIGURATION

IMULTIPLIER

1Zin

ZfGCA +=

Zin

ZfG CA -=

Vnoise

Vnoise




Voltage Feed Forward(VFF)•UC3854 Generates VFF From a Voltage Divider That Requires a Two Pole Filter

–5 Components Required to Generate the VFF•UCC3817 Generates the VFF From an Internal Current Source That Requires a Single Pole Filter

–2 Components Required to Generate the VFF

+–ACin

UC3854

VFF

UC3854 External Circuitry that Creates the Feed Forward Voltage

Rsense

Iac

+–

UCC3817

VFF

Circuitry that is Required to Configure UCC3817 Feed Forward Voltage

Rsense

Iac

Rvff Cvff Iac/2ACin




Multiplier:•The Older UCC3854 Required a Bias Resistor From Vref to Iac For Proper Operation

Bias Resistor




Multiplier:•The UCC3817’s Improved Multiplier Performance Improves System Operation Over a Wider Load Range•Performance Curves Can Be Found in the Data Sheet

00

1 2 3 4 5

50

100

150

200

250

300

350

VO - Voltage Error Amplifier Output (VAOUT) - V

VAO(V)

IMO

(uA

)

Multiplier Output Current Imout vs. VAOUT

01 2 3 4 50

100

200

300

400

500

Feed Forward Voltage - (VFF) - V

VAOUT = 5V

VAOUT = 4V

VAOUT = 3V

VAOUT = 2VV

FF

*IM

O(u

W)

Multiplier Constant Power Performance




Recap Reasons For Transitioning From The UC3854 to The UCC3817•The UCC3817 Has Better Noise Immunity Because of the Current Amplifier Configuration•It Takes Fewer Components to Use the UCC3817 in the Application•Leading Edge Modulation When Synchronized Correctly Will Reduce the RMS Current in the Boost Capacitor•Improved Multiplier Performance Allows the System to Operate With a Wider Load Range




UCC3817 EVM Availability•EVMs Are Available Presently but in Limited Quantities

–Contact Judy Pacheco •EVMs Are Presently Being Put Into the TI System and Will Be Available in August

power supply control transitioning uc3854 customers to the ucc3817 pfc controller power supply...

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