Transcript UCC38500 PFC/PWM Combination Controller

Power
Supply
Control
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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
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Power
Supply
Control
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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
Stage 1
Stage 2
VLINE
85-265 VAC
+
Vout
-
PFC Controller
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PWM Controller
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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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
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Power
Supply
Control
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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
PFC BOOST
CIRCUIT
BUCK DERIVED CONVERTER
ID1
L1
IQ2
D1
Gate Drive from
Down Stream PWM
IL
L2
Q2
IAC
Q1
CBULK
IQ1
D2
Cout
RLoad
IC
C1
Ct
D2
UCC3817
Gate Drive Q2 Trailing
Edge Modulation
Ct
Gate Drive Q1 Trailing
Edge Modulation
Ct
D1
Ic with Trailing Edge/
Trailing Edge Modulation
Rt
Rt
Gate Drive Q1 Leading
Edge Modulation
Ic with Leading Edge/
Trailing Edge Modulation
Boost Capacitor Ripple Current Comparison
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Synchronization Circuit
Power
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Control
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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
UC3854 CURRENT AMPLIFIER CONFIGURATION
RSENSE
RIN
ZF
+
–
CA
PWM
+
RIN
IMULTIPLIER
PFC GATE DRIVE
G CA =
Zf
+1
Zin
Vnoise
UCC3817 CURRENT AMPLIFIER CONFIGURATION
RSENSE
ZF
+
CA
G CA = PWM
+
-
RIN
IMULTIPLIER
RIN
Vnoise
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PFC GATE DRIVE
Zf
Zin
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Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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
UC3854 External Circuitry that Creates the Feed Forward Voltage
UC3854
+
Iac
ACin
–
VFF
Rsense
Circuitry that is Required to Configure UCC3817 Feed Forward Voltage
UCC3817
Iac
ACin
–
+
VFF
Rvff
Rsense
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Cvff
Iac/2
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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Multiplier:
•The Older UCC3854 Required a Bias Resistor From Vref to Iac For Proper Operation
Bias Resistor
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Power
Supply
Control
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
Multiplier:
•The UCC3817’s Improved Multiplier Performance Improves System
Operation Over a Wider Load Range
•Performance Curves Can Be Found in the Data Sheet
Multiplier Constant Power Performance
Multiplier Output Current Imout vs. VAOUT
500
350
VAOUT = 5V
300
400
VAOUT = 4V
VFF*IMO(uW)
IMO(uA)
250
200
150
100
300
VAOUT = 3V
200
VAOUT = 2V
50
100
0
0
1
2
3
4
5
VAO(V)
VO - Voltage Error Amplifier Output (VAOUT) - V
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0
1
2
3
4
Feed Forward Voltage - (VFF) - V
50
Transitioning UC3854 Customers to the
UCC3817 PFC Controller
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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
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Transitioning UC3854 Customers to the
UCC3817 PFC Controller
Power
Supply
Control
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
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