In the design of power electronic devices, the drive technology for IGBTs directly affects the performance and reliability of the system. Among them, the pulse transformer isolated drive method, due to its simplicity, reliability, low cost, and strong anti-interference ability, is widely used in the industrial field. This article will deeply explore the working principle of this drive method and analyze its typical application scenarios.
The basic principle of pulse transformer isolated drive for IGBTs
Pulse transformer isolated drive is a method that transmits drive signals through magnetic coupling to achieve electrical isolation between the main circuit and the control circuit. Its basic working process is as follows:
- Signal transmission mechanism: The PWM pulse signal generated by the control circuit passes through the primary winding of the pulse transformer and is coupled to the secondary winding through magnetic induction.
- Electrical isolation characteristics: The primary and secondary windings of the transformer achieve electrical isolation through the magnetic core material, and can withstand voltages of several kV.
- Signal restoration process: The pulse signal sensed by the secondary winding passes through a shaping circuit and directly drives the gate of the IGBT.
SHYSEMI's engineer pointed out that this drive method does not require an independent isolation power supply, simplifying the circuit structure and suitable for medium and low-frequency application scenarios.
1) Passive method:
The passive method is to directly drive the IGBT device with the output of the secondary winding of the transformer. This method is very simple and does not require a separate drive power supply. However, due to the large gate-emitter capacitance CGs of the IGBT device, the waveform VGE between the gate and the emitter will have obvious distortion unless the input signal of the primary winding is changed to a certain power signal.
2) Active method:
In the active method, the transformer only provides isolated signals, and an additional shaping and amplification circuit is provided in the secondary winding to drive the IGBT device. Although the drive waveform is good, an additional isolated auxiliary power supply is required to supply the amplifier. If the auxiliary power supply is not handled properly, parasitic interference may be introduced.
3) Self-powered method:
The self-powered method has existing technology of high-frequency (above several MHz) modulation of the PWM drive signal. This signal is applied to the primary of the isolated pulse transformer, and direct rectification is obtained in the secondary to obtain a self-powered source, while the original PWM modulation signal needs to be demodulated to obtain it. Obviously, this method is complex and expensive.
The pulse transformer isolated drive scheme has the following prominent advantages:
- High reliability: The magnetic isolation method naturally has strong anti-interference ability and is suitable for harsh industrial environments.
- Fast response speed: The transmission delay is at the nanosecond level, meeting the requirements of most switching power supplies.
- High cost-effectiveness: It eliminates optocouplers or dedicated drive chips, reducing system costs.
- Simple and compact: The circuit structure is simple, easy to layout and manufacture.
SHYSEMI summarized several major application fields of pulse transformer isolated drive:
1) Industrial motor drive
In applications such as frequency converters and servo drives, pulse transformer drive provides reliable isolation guarantee. The solutions provided by SHYSEMI for industrial customers show that this method performs well in the field of motor control, especially in cases requiring multiple drive signals.
2) New energy power generation systems
In photovoltaic inverters and wind turbine converters, SHYSEMI adopts an optimized pulse transformer design to ensure stable operation of the system in high-temperature and high-humidity environments, while reducing system costs.
3) Uninterruptible Power Supply (UPS)
For medium and large power UPS systems that need to drive multiple IGBT modules, pulse transformer drive provides an economical and reliable solution. SHYSEMI has developed dedicated drive modules for such applications, improving system integration.
4) Induction heating equipment
Pulse transformer drive can handle high-frequency switching applications and has good suppression ability for electromagnetic interference.
Conclusion
From the above text, it can be seen that the design of the pulse transformer drive circuit cannot be simply based on a single formula. Different application scenarios require consideration of multiple parameters. By comparing the above three schemes, it can be observed that each structure has its own advantages and disadvantages. Therefore, one should flexibly choose based on the specific project goals.