Gate driver design and inductance fabrication

Gate Drive Circuit
MOSFET/IGBT
Malaiyappan M
Pantech Solutions

Technology beyond the Dreams™ Copyright © 2006 Pantech Solutions Pvt Ltd.
MOSFET
• Metal Oxide Semiconductor Field Effect
Transistor
– It is the key component in high frequency, high
efficiency switching applications across the
electronics industry.
– It must be driven from a low impedance source
capable of sourcing and sinking sufficient current to
provide for fast insertion and extraction of the
controlling charge

Structure of MOSFET Technology
Using polycrystalline silicon
gate structures and self-aligning
processes, higher density integration and
rapid reduction in capacitances
became possible
V-groove or trench technology to further increase
cell density in power MOSFET devices.
The better performance and denser integration do
not come free; however, as trench MOS devices are
more difficult to manufacture.
power MOSFETs have significantly lower capacitances,
therefore, they can switch much faster and they require
much less gate drive power

MOSFET Models
Epi layer has to withstand most
of the MOSFET's OFF-state
drain-to-source voltage.
Inbuilt dV/dT Function
The switching performance of
the MOSFET transistor is determined by
how quickly the voltages can be
changed across these
capacitors.

TURN – ON Mechanism

MOSFET GATE DRIVE TURN - ON
VGS
VTH
VDS
ID
IG
Turn On
Delay
“Miller Effect”
Turn On
Rise Time

TURN- OFF Mechanism

MOSFET GATE DRIVE TURN - OFF
VGS
VTH
VDS
ID
IG
Turn Off
Delay
“miller effect”
Turn Off
Rise Time

GATE Driver Properties
1. Isolator
2. Amplifier
3. Protection
4. Speed up Mechanism( Turn ON/OFF)

Isolation
1. Opto-coupler
2. Galvanic Isolation
S.N
o
Switching
Frequency
Device
1 25KHz MCT2E
2 25KHz TLP250
3 100KHz HCPL7840
4 250KHz FD3180
5 2MHz 6N135
6 250KHz SID11x2K

Amplifier
Property
1. Totem Pole Driver
2. Most Popular
3. Cost Effective
4. High Reverse Break Down Voltage Protection

Protection
Zener Protection
By Pass Capacitor Protection

dV/dT Protection
1. Pull Down Resistor
… Wtts
Ton-min= 2.5uS
5RC=2.5uS
R can be calculated
2. Snubber Protection

Turn – Off Speed Enhancement
RGATE allows adjustment of the MOSFET turn-on speed.
Schottky anti parallel diode

MOSFET Driver

PCB Consideration
Suggestions
1. Signal and Ground Line Must be short
2. If More Noise at Driver output, RC Filter network is required with Proper Frequency Calculations
3. Proper Isolation have to be placed

High Freq. Isolated Driver

Inductor Design
• Air Core Inductor
• Iron Core Inductor
• Ferrite Core Inductor
• Iron Powder Inductor
• Toroidal Inductor
• Multi-layer Ceramic Inductors
• Film Inductor
• Variable Inductor
• Coupled Inductors

Major Applications
• Filters
• Transformers
• Sensors
• Motors
• Energy Storages

Core Types
• Iron-core inductors
– Large inductance values but have large power losses
at high frequencies
• For high-frequency applications
– Ferrite-core inductors are used

Core Types
E Core EQ Core ER Core
ETD Core PM Core PQ Core
E 30 to 100 EQ 25 to 30 ER 25 to 54
ETD 29 to 59 PM 50 to 114 PQ 32 to 50

Start
Collect L, F, Ipeak
and Temp
Calculate Energy Dissipation
Choose Core Type and Size
Choose Wire size from Peak current
Calculate Airgap and wind the Inductor
Adjust the Airgap and Correct the Inductance
Value

Inductor Design
Specification
1. Inductance Value L
2. Switching Frequency
3. Peak Current

Sample Data 1
L: 1mH,
Switching Frequency: 100KHz,
Peak Current: 15A
Energy Calculation : ½ LI2
: ½ *1*15*15 mJ
: 112.5mJ

No of Turns (N) = ( L x Ipeak x 104 ) / Ac x Bm Nos
= 1x10-3 x 15x104 / (0.3*5.32)
= 94T
Note: 94 Turns if not Possible to wind make 2 Cores in single bobbin, N: 47
Selection of Wire = Ipeak/J
= 15/3 = 5 Sq mm; 12 SWG
Airgap = uoNIp / Bm
= 2.95 mm; 1.5 mm per side

Sample Data 2
S.No Parameters Buck Boost Buck Boost
1 Input Voltage 0-30 0-30 0-30
2 Output Voltage 0-25 45 0-45
3 Output Current 2A 2A 2A
4 Efficiency 90% 90% 90%
5 Inductance 100uH 23uH
6 Sw. Freq 100KHz 100KHz 100KHz
7 Current 2A 2A
8 Peak Current 5A 5A
9 Core Type EE42 EE42 EE42 EE42
10 AWG 24 24 24

Gate driver design and inductance fabrication

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