Dc Dc Boost Ppt
description
Transcript of Dc Dc Boost Ppt
-
EE462L, Spring 2013DCDC Boost Converter
-
Vin + Vout C iC Iout iinBuck converter Boost converter Vin + Vout C iC Iout iin
-
Boost converter This is a much more unforgiving circuit than the buck converterVin + Vout C iC Iout iin iL LiDIf the MOSFET gate driver sticks in the on position, then there is a short circuit through the MOSFET blow MOSFET!If the load is disconnected during operation, so that Iout = 0, then L continues to push power to the right and very quickly charges C up to a high value (250V) blow diode and MOSFET!Before applying power, make sure that your D is at the minimum, and that a load is solidly connected
-
Boost converter Vin + Vout C iC Iout iin iL LiDModify your MOSFET firing circuit for Boost Converter operation (see the MOSFET Firing Circuit document)Limit your output voltage to 120V
-
Boost converter Using KVL and KCL in the average sense, the average values are Find the input/output equation by examining the voltage across the inductor
-
Switch closed for DT seconds Reverse biased, thus the diode is openfor DT secondsVin + Vout C iin iL LNote if the switch stays closed, the input is short circuited!+ Vin
-
Switch open for (1 D)T secondsDiode closed. Assume continuous conduction.Vin + Vout C iin iL Lfor (1D)T seconds(iL Iout)+ (Vin Vout )
-
Since the average voltage across L is zeroThe input/output equation becomesA realistic upper limit on boost is 5 times
-
Examine the inductor currentSwitch closed,Switch open,DT(1 D)TTImaxIminIavg = IinIavg = Iin is half way betweenImax and IminIiL
-
Inductor current ratingMax impact of I on the rms current occurs at the boundary of continuous/discontinuous conduction, where I =2Iin2Iin0Iavg = IinIiLUse max
-
MOSFET and diode currents and current ratingsUse max2Iin02Iin0Take worst case D for eachVin + Vout C iC Iout iin iL LiD
-
Capacitor current and current rating2Iin IoutIout0Max rms current occurs at the boundary of continuous/discontinuous conduction, where I =2IoutUse maxiC = (iD Iout)Vin + Vout C iC Iout iin iL LiDSee the lab document for the derivation
-
Worst-case load ripple voltageThe worst case is where C provides Iout for most of the period. Then,Iout0iC = (iD Iout)
-
Voltage ratingsDiode sees VoutMOSFET sees VoutC sees VoutDiode and MOSFET, use 2VoutCapacitor, use 1.5VoutVin + Vout C iin iL LVin + Vout C iin iL L
-
Continuous current in L2Iin0Iavg = IiniL(1 D)Tguarantees continuous conductionThen, considering the worst case (i.e., D 1),use maxuse min
-
Impedance matching
DCDC Boost Converter
+Vin+
Iin+VinIinEquivalent from source perspectiveSource
-
Example of drawing maximum power from solar panelIscVocPmax is approx. 130W (occurs at 29V, 4.5A)For max power from panels, attachI-V characteristic of 6.44 resistorBut as the sun conditions change, the max power resistance must also change
-
Connect a 100 resistor directly, extract only 14W130W6.44 resistor100 resistor14WTo extract maximum power (130W), connect a boost converter between the panel and the load resistor, and use D to modify the equivalent load resistance seen by the source so that maximum power is transferredSo, the boost converter reflects a high load resistance to a low resistance on the source side
-
BOOST DESIGN
Worst-Case Component Ratings Comparisons
for DC-DC Converters
Converter Type
Input Inductor Current (Arms)
Output Capacitor Voltage
Output Capacitor Current (Arms)
Diode and MOSFET Voltage
Diode and MOSFET Current (Arms)
Boost
1.5
2
_1221762425.unknown
_1221762461.unknown
_1221762477.unknown
_1221762444.unknown
_1150520753.unknown
-
5A1500F50kHz0.067VBOOST DESIGN
Comparisons of Output Capacitor Ripple Voltage
Converter Type
Volts (peak-to-peak)
Boost
_1221762523.unknown
-
40V2A50kHz200HBOOST DESIGN
Minimum Inductance Values Needed to
Guarantee Continuous Current
Converter Type
For Continuous Current in the Input Inductor
For Continuous Current in L2
Boost
_1221762630.unknown