1. Chapter 9 Practical Application Issues of Power Semiconductor Devices
Power Electronics
Chapter 9 Practical Application Issues of Power Semiconductor Devices

2. Outline 9.1 Gate drive circuit
9.2 Protection of power semiconductor devices
9.3 Series and parallel connections of power semiconductor devices

3. 9.1 Gate drive circuit Basic function of gate drive circuit:
Generate gate signals to turn-on or turn-off power semiconductor device according to the commanding signals from the control circuit.
Other functions of gate drive circuit:
Reduce switching time (including turn-on time and turn-off time)
Reduce switching loss (including turn-on loss and turn-off loss) and improve efficiency
Improve protection and safety of the converter
Gate drive circuits provided by power semiconductor
manufacturers and Integrated gate drive chips are
more and more widely used.

4. Electrical isolation in the gate drive circuit
Gate drive circuit usually provides the electrical isolation between control circuit and power stage.
Two ways to provide electrical isolation
Optical
Optocoupler, fiber optics
Transformer
Magnetic
Schematic of an optocoupler

5. Thyristor gate current pulse requirments
Shape of gate current pulse waveform:
Enhanced leading part
Magnitude requirement (for the enhanced leading part and the other part)
Width requirement (for the enhanced leading part and the whole pulse)
Power of the triggering signal must be within the SOA of the gate I-V characteristics
Ideal gate current pulse waveform for thyristors

6. Typical thyristor gate triggering circuit

7. Typical gate signal and gate drive circuit for GTO

8. A typical gate drive circuit for IGBT based on an integrated driver chip
M57962L integrated driver chip

9. 9.2 Protection of power semiconductor devices
Protection circuits
Overvoltage protection
Overcurrent protection
Snubber circuits—specific protection circuits that can limit du/dt or di/dt
Turn-on snubber
Turn-off snubber

10. Causes of overvoltage on power semiconductor devices
External reasons
Overvoltage caused by operation of mechanic swithes
Overvoltage caused by thunder lightening
Internal reasons
Overvoltage caused by the reverse recovery of diode or thyristor
Overvoltage caused by the turning-off of fully-controlled devices

11. Measures to protect power semiconductor devices from overvoltage
Lightening arrestor
RC or RCD snubbers (will be discussed later)
Zener diode, Metal Oxide Varistor (MOV), Break Over Diode (BOD)

12. Measures to protect power semiconductor devices from overcurrent
Fuse
Circuit breaker
Protection with current feedback control in the control circuit
Protection with overcurrent detection in the gate drive circuit—the fastest measure

13. Functions and classifications of snubbers
Limiting voltages applied to devices during turn-off transients
Limiting device currents during turn-on transients
Limiting device current rising rate (di/dt) at device turn-on
Limiting the rate of rise (du/dt) of voltages across devices during device turn-off
Shaping the switching trajectory of the device
Classifications
According to different switching transients
Turn-off snubber (sometimes just called snubber)
Turn-on snubber
According to the treatment of energy
Power dissipating snubber
Lossless snubber

14. Operation principle of typical snubbers
Circuit configuration
Switching trajectory

15. Other turn-off snubbers

16. 9.3 Series and parallel connections of power semiconductor devices
Object
To increase the capability to deal with voltage or current
Issues and solutions
Series connection
Issue: even voltage sharing
Solutions:
Selection of devices that are closer to each other in the characteristics
Voltage sharing circuit
Parallel connection
Issue: even current sharing
Current sharing circuit and symmetrical circuit layout

17. Series Connection of thyristors
Voltage sharing circuit
Steady-state voltage sharing circuit
Dynamic voltage sharing circuit

18. Parallel Connection of Power MOSFETs
Easy to realize because of the positive temperature of their on-state resistance
Need a small damping resistor in series with the individual gate connections
Still need to select devices that are closer to each other in the characteristics
Circuit layout should be symmetrical