EE152 Green Electronics - Stanford Universityweb.stanford.edu/class/ee152/lecture_slides/Power...•...

EE152 Green Electronics

Power Devices 9/28/15

Prof. William Dally Computer Systems Laboratory

Stanford University

Course Logistics •  HW1 due Today •  HW2 out Today due Monday 10/3 •  Lab1 signed off this week •  Lab2 out

EE155/255 Lecture 3 - Power Devices

Course to Date •  We need sustainable energy systems •  At the core they are voltage converters •  Periodic steady-state analysis, buck and boost •  Embedded software is event driven

Real Switches

High-SideGate Drive

Low-SideGate Drive

Real Switches •  Finite switching time •  Finite voltage blocking •  Non-zero on resistance •  Parasitic L and C

High-SideGate Drive

Low-SideGate Drive

Quick Summary in a Few Pictures

DC I-V Characteristics of On Switches

V(d)0.0V 0.1V 0.2V 0.3V 0.4V 0.5V 0.6V 0.7V 0.8V 0.9V 1.0V 1.1V 1.2V 1.3V 1.4V 1.5V 1.6V 1.7V 1.8V 1.9V 2.0V

50AIx(m:1) Ix(h:2) Ix(i:C) I(Dd)

600V FET FCB36N60

600V IGBT FGH40N60

400V Diode STTH20R04

60V FET IRLB3036

FETs Characterized By RON

IGBT Like a Diode Little Current Until ~0.7V

HV FET has high RON R ~ kV2

Diode and IGBT Resistive at high Current

Transient Response of FET and IGBT

0ns 40ns 80ns 120ns 160ns 200ns 240ns 280ns 320ns0V

V(di) Ix(i:C)

V(dm) Ix(h:2)

ix(i:c)*v(di) ix(h:2)*V(dm)

600V FET FCB36N60

Instantaneous Power

Turn On Turn Off

600V IGBT FGH40N60

36µJ 36µJ 92µJ 428µJ

Boost Configuration for Transient Test

Diode Reverse Recovery

(Amps)

t(sec)t1

0ns 3ns 6ns 9ns 12ns 15ns 18ns 21ns 24ns 27ns 30ns-220A

40AI(D1) I(D2) I(D3) I(D4)

0ns 10ns 20ns 30ns 40ns 50ns 60ns 70ns 80ns 90ns 100ns 110ns 120ns-810A

180AI(D1) I(D2) I(D3) I(D4) I(D5) I(D6) I(D7)

400V Diode STTH20R04

Medium Speed Diode

Area under curve (Charge) is approximately constant QRR

Power MOSFETs

Power MOSFETs are your friends

MOSFET Properties •  Fast switching time 10-50ns

–  Low switching losses

•  Low conduction losses at low voltages –  V2/R of 1-2MW

•  e.g., at 20V R = 0.4mOhm (4mV drop at 10A) –  Typically better than IGBT up to ~400V

•  Easily paralleled for lower Ron, More I, or easier cooling

•  Integral body diode in DMOS FET •  Avalanche breakdown can be used to “snub”

overshoot

MOSFETs are Switches

Source

GateRon

(a) (b)

gaten n

- - - - -

g=0 g=1

s dIDS=0

How do they Work

Power MOSFET (DMOS) Structure

gatesource source

channel

Gate Charge vs VGS

0 10 20 30 40 50 60 70 80 900

QG (nC)

V GS (V

source

Parasitics

130 Green Electronics

source

Figure 17.4: MOSFET parasitic circuit elements. At high operating frequen-cies these parasitic circuit elements have a large e↵ect on the performance andswitching losses of a MOSFET.

Symbol Value Units DescriptionCDS 200 pF Drain-source capacitanceCDG 70 pF Drain-gate (Miller) capacitanceCGS 3600 pF Gate-source capacitanceQG 86 nC Total gate turn-on chargeQGD 35 nC Gate-drain turn-on chargeLS 7 nH Source inductanceLD 3 nH Drain inductanceLG 7 nH Gate inductanceRG 1.5 ⌦ Gate resistance

Table 17.1: Values of parasitic circuit elements for a typical 600V 100m⌦ powerMOSFET in a TO-220 package.

600V 0.1Ω FET TO220 Package

source

Parasitics

CDS – CV2 energy LD, LS – I2L energy

slows switching, overshoot, corrupts gate drive

CDG – slows turn on RG, LG – slow device turn-on

Typical MOSFETs

Copyright

2011-15

Dally,allrights

reserved

Device 20V IRLB3036 IRFB4227 FCB36N60N EPC2010 C2M0025120 Units DescriptionVDSmax

20 60 200 600 200 1200 V Maximum VDS

1.9 20 81 18 25 m⌦ On resistanceQG 91 70 86 5 161 nC Gate chargeCoss 1020 460 80 270 220 pF Output capacitance CSD + CGD

195 65 36 12 90 A Maximum continuous drain currentIDM 1100 260 108 60 250 A Maximum pulsed drain currentEAS 290 140 1800 mJ Single-event avalanche energyP

380 330 312 463 W Maximum power dissipationV 2/R 1.9 2.0 4.4 2.2 58 MW Figure of meritV 2/RQG 21 29 52 440 360 mV/s Figure of merit

Table 17.2: Key parameters of six field-e↵ect transistors.

GaN SiC

Power MOSFETs should be ON or OFF They are not happy in between

•  IRLB3036 •  Can handle 60V (when its off) •  Can handle 195A (when its on – if you can cool it)

–  I2R = (195)2(0.002) = 76W

•  But it can’t handle 60V and 195A at the same time –  P = VI = (60)(195) = 11.7kW –  At least not for very long

•  Turn them on and off quickly •  Best circuits are “soft switching”

–  Zero-current switching (ZCS) or zero-voltage switching( ZVS) or both.

Power Diodes

Diode Properties •  Self-controlling switch

–  Allows current in one direction –  Turns off when current reaches zero (in theory)

•  Relatively fixed voltage drop independent of current –  0.5 to 2.0V –  High losses at low voltages

•  Care required to operate in parallel –  Current hogging

•  Turn-off delay –  Must clear space charge out of junction

•  Turn-on delay –  Negligible for most fast diodes, but some are problematic

Key Parameters •  Reverse breakdown voltage

•  Maximum current

•  Reverse recovery time

•  Junction capacitance

(Amps)

t(sec)t1

Diode Forward Recovery

(Volts)

t(sec)

Diode Forward Recovery

Good Diode Bad Diode

Two 2A Diodes < One 4A Diode

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.10

125°C

VD (Volts)

i D (A

source

Summary – Power Devices •  Finite, non-zero

–  Switching time –  Blocking voltage –  On-voltage (resistance)

•  Parasitics – L and C •  MOSFETs – switches

–  Turn on/off as fast as gate can be charged

–  R = kV2

•  Diodes –  Self-controlled switches –  Reverse recovery loss QRR

Source

Gate RonDbody

(a) (b)

(Amps)

t(sec)t1

Power Circuits

Practical Buck Converter

High-SideGate Drive

Low-SideGate Drive

Simple Model

One Switch May be a Diode

Lower switch for buck Upper switch for boost Other switch does most of the work Synchronous rectification may be used to reduce loss

Turn-On Loss

ILQRR QD

t1 t2 t3

Turn-On Buck w/ Diode

ILQRR QD

t1 t2 t3

t1 – ramp current to IL t2 – diode reverse recovery t3 – discharge drain

capacitance Current waveform in t2 and t3 may vary

Turn-On Buck w/ Diode

t1 =ILs

E1 = 0.5VDDILt1 =0.5VDDIL

t2 =2QRR

sE2 =VDDt2 IL + 0.5t2s( )

t3 ≈2IPQD

E3 = 0.5VDDQD + 0.33VDDILt3

ILQRR QD

t1 t2 t3

Turn-Off Buck with Diode

Excess current charges drain node. Integrate to get switching energy

E =VDDtr16IL +

Turn-Off Buck with Diode

If current ramps faster than voltage nearly ZVS ID

E = 16V1ILtc

Parasitic Losses

Switching Loss with SPICE

Simulation Setup •  Boost configuration 40A, 50V •  IRLB3036 – 60V, 2mΩ FET

Ideal Diode, No Parasitics

22uJ turn-on 22uJ turn-off

Body Diode of IRLB3036

225uJ turn-on

700A peak current EE155/255 Lecture 3 - Power Devices

Inductance on Drain

8uJ turn-on

42uJ turn-off

With Snubber (1nF, 5Ω)

8uJ turn-on

2uJ in snubber

42uJ turn-off

Real Diode and Inductance

14uJ turn-on 26uJ turn-off

720uJ in diode

Gate Drive

Gate Driver

source

Control &Protection+

Gate-driver IC

Effect of Miller Cap on Rise Time

=iGCDG

Δt = ΔVDCDG

Example: i = 0.5A, C = 100pF, ΔV = 400V

Bootstrap Supply

High-SideGate Drive

Low-SideGate Drive

RB DB V

Dead Time

Too Little Dead Time (11.6kW loss)

1.6µs 1.7µs 1.8µs 1.9µs 2.0µs 2.1µs 2.2µs 2.3µs 2.4µs 2.5µs 2.6µs 2.7µs 2.8µs 2.9µs 3.0µs 3.1µs 3.2µs-5V

16V-3.0KA

-2.5KA

-2.0KA

-1.5KA

-1.0KA

-0.5KA

3.0KA-10KW

V(p1l) v(p1h)-v(m1) V(1:gl) V(1:gh)-v(m1)

Ix(1:h:1) Ix(1:l:3)

ix(1:h:1)*(v(d)-v(m1)) ix(1:l:1)*v(m1)

4mJ 3.4mJ

0.6 0.8 1 1.2 1.4 1.6 1.8

v G (V

0.6 0.8 1 1.2 1.4 1.6 1.8

v X (V

0.6 0.8 1 1.2 1.4 1.6 1.8

i M1 (k

t (µ s)0.6 0.8 1 1.2 1.4 1.6 1.8

P M1 (k

The “Real” Gate Signal

Too Much Dead-Time (340W loss) (Still pretty good)

50V-2V

16V-700A

-500A-400A

0A100A

500A600A

800A-4KW

V(p2l) V(p2h)-v(m2) V(2:gl) V(2:gh)-v(m2)

Ix(2:h:1) Ix(2:l:3)

ix(2:h:1)*(v(d)-v(m2)) ix(2:l:1)*v(m2)

700mV diode drop

0.27mJ

Just Right (310W loss)

50V-2V

16V-350A

420A-0.3KW

V(p4l) v(p4h)-v(m4) v(4:gh)-v(m4) V(4:gl)

Ix(4:h:1) Ix(4:l:3)

IX(4:l:1)*v(m4) ix(4:h:1)*(v(d)-v(m1))

0.19mJ 3uJ

Conduction loss is I2R = 502 x 1m ~ 25W

Slower gate rise

Short duration diode drop

Too much dead time is better than too little

Snubbers

Dampen Ringing Nodes

LD and Cj resonate when M is on Parallel RS dampens tank Series CS limits dissipation

Inductance on Drain

8uJ turn-on

42uJ turn-off

With Snubber (1nF, 5Ω)

8uJ turn-on

2uJ in snubber

42uJ turn-off

Design Procedure

Pick RS ~ 1/ωCj Pick CS so

τ >= π/ωOr

Es = CSV2/2

G 50V+-

Move Turn-Off Dissipation to Passive Device

CS slows rise time of drain

CSV2/2RS dissipated in RS when CS discharges

Rarely used today

Other forms slow fall time and rising/falling current EE155/255 Lecture 3 - Power Devices

Lab Half-Bridge Module

The Half-Bridge Module

IRS21834

ComVss

��

C14.7 F

2.2 F200V

D356V5W

VBCSupply

VDCFilter

Bootstrap Supply

Drain Voltage Filter

IRS21834

ComVss

��

C14.7 F

2.2 F200V

D356V5W

VBCSupply

VDCFilter

Drain Voltage Filter 300nH Input Inductance

SPICE Example – A Voltage Divider

A Voltage Doubler * Simple voltage "doubler".include "gel.lib".param td=100n tr=100n tf=100n tw=2.5u tcy=5u ncy=2.param l1=22uH c1=10uF r1=10

* call half-bridge subcircuitxhb vd mid g g 0 v12 gel_hb

* circuitl1 vin mid {l1}c1 vd 0 {c1}r1 vd 0 {r1}

* suppliesv12 v12 0 12vin vin 0 24

* stimulusVG g 0 PULSE(0 5 {td} {tr} {tf} {tw} {tcy} {ncy})

.ic i(l1)=9.2

.ic v(vd)=42.8

.tran {ncy*tcy}

Turn-On Transient

Steady State

Close up of Drain Current

With PID Control

A Warning •  SPICE (or any simulator) is a Verification tool, not a Design tool

•  Design your circuit first –  Use Excel, Matlab, a calculator etc… to calculate component

values •  Then simulate your circuit to check operation and fine-

tune parameters •  Don’t try to design your circuit using SPICE

•  Simulation is not a substitute for thinking

Summary •  Real switches have limitations

–  Conduction losses (RON for FETs, VCE for IGBTs, Diode drop) –  Switching losses (finite ton, toff, trr)

•  With current source load, current ramps, then voltage falls •  And voltage rises before current falls •  May be dominated by reverse recovery time •  Complicated by inductance

•  Power MOSFETs –  Switch quickly, have linear I-V, integral diode

•  IGBTs –  Diode-like I-V, slower switching

•  Diodes –  Have reverse recovery time

•  Switches operate in pairs –  For one-way converters, one switch may be a diode –  Synchronous rectification – make both switches FETs to reduce loss –  Need “dead time” to avoid “shoot through” current

•  Gate-drive circuits control rise and fall times •  Bootstrap supply needed for high-side driver •  Snubbers dampen voltage and current transients •  Use SPICE as a verification tool, not a design tool EE155/255 Lecture 3 - Power Devices

In Upcoming Lectures

No Date Topic HW out HW in Lab out Lab ck Lab HW 1 9/21/15 Intro (basic converters) 1 1 Intro to ST32F3 Periodic Steady State 2 9/23/15 Embedded Programming 3 9/28/15 Power Electronics -‐ 1 (switches) 2 1 2 1 AC Energy Meter Power Devices 4 9/30/15 Power Electronics -‐ 2 (circuits) 5 10/7/15 Photovoltaics 3 2 3 2 PV MPPT PV 6 10/9/15 Feedback Control 7 10/12/15 Electric Motors 4 3 4 3 Motor control Matlab Feedback 8 10/14/15 Solar Day 9 10/19/15 Isolated Converters 5 4 5 4 Motor control -‐ Lab Motors 10 10/21/15 MagneTcs 11 10/28/15 SoU Switching 6/PP 5 6 5 PS Part 1/Proposal MagneTcs and bridge converter 12 10/30/15 Inverters and Power Factor 13 11/2/15 BaWeries 6/PP 7 6 PS Part 2 14 11/4/15 Thermal Design 15 11/9/15 EMI, Grounding, and Debugging P 7 Project 16 11/11/15 Quiz Review 17 11/16/15

11/16/15 Quiz -‐ in the evening 18 11/18/15 C1

11/23/15 Thanksgiving Break 11/25/15 Thanksgiving Break

19 11/30/15 C2 20 12/2/15 Wrapup 21 12/4/15 Project presentaTons P

12/9/15 Project webpage due

EE152 Green Electronics - Stanford Universityweb.stanford.edu/class/ee152/lecture_slides/Power...•...

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