From the control performance point of view, power semiconductor devices can be divided into non-control devices, semi-control devices and full control devices and other three categories.
The Non-control device is represented by a diode, the so-called non-control means the device have no control pole, does not have making and breaking function of weak current control, while the non-control device performance is not perfect, however it has the simple structure, high reliability, is currently the highest reliability semiconductor devices under the same conditions (rated voltage and current).
2)Half-controlled device [thyristor, DDS (T)]
The semi-controlled device is represented by a thyristor, DDS (T) (dynamic drive device), which has a control pole, but the control pole can only control the conduction of the device, but can not control the device to cut off, the device cut off only can be realized by changing the main circuit operating conditions. Semi-control devices in the control performance, although still not perfect, however the reliability is the only device that can be compared with the non-control device, because:
- Thyristor has not the the amplification area which is between the conduction and shutdown, so it has the minimum internal resistance, the least heat, withstand current capacity is very strong, can reach 10-20 times of the rated current.
- Single tube current is large, no need multiple devices connected in parallel. The high power thyristor can easily reach rated current 3000 A-5000A, to avoid that the high current applications must be connected in parallel, resulting in uneven flow to cause the device damage.
- Only need a very narrow pulse, easy to use the transformer to achieve strong and weak isolation, so that to protect the weak control from strong electrical interference, greatly improving the reliability of the control device.
- Heat dissipation is good, the temperature is the enemy of semiconductor device reliability, theory and practice has proved that the vast majority of the reasons of, failure, damage and performance degeneration of the semiconductor devices attributed to the excessive temperature. High-power thyristor commonly used double-sides pressure mounting, the two poles of the main circuit lose the heat at the same time, has the smallest thermal resistance, the best cooling effect, when the working current is greater than 500A, the use of double-sides pressure mounting cooling is the most reliable way.
Thyristor and DDS (T): DDS (T) is a new generation of semi-control devices used to replace thyristors, which retains all the advantages of thyristors at the same time, and overcomes the thyristor problems like the high frequency characteristics is low, the driving blind area is big, the drive power consumption is high, and the drive circuit is complicated Etc.
3)Full Control Device (Transistor)
A full control device is a semiconductor device, such as an IGBT (Insulated Gate Bipolar Transistor), which is controlled by a control electrode to turn on and off. The typical advantage of transistors is amplification, but in the case of high power converter technology and as an electrical switch application, there is almost no application possibility due to the factors such as the amplification zone and the “latching effect”. Transistor can also be used for switches, is to make it work in the saturation and cut-off state, the advantage is simple technology.
- IGBT and other transistors over-current capability is very low, compared with the thyristor, IGBT over-current overcurrent amplitude is 2 times of rated value, while for thyristor it is 15 times, so it’s less than 1/10 thyristor; and withstand overcurrent time of IGBT is only 10us, for thyristor it is 10ms, the difference between the two is nearly 1000 times, the transistor over-current amplitude is low, short time is difficulty for protect, so to reduce the device reliability.
- Single tube current capacity is small, the transistor manufacturing process is very different from the thyristor, it is not possible to make single tube current capacity greater than 100A currently, if open an IGBT of rated current greater than 150A, the internal is actually a number of unit of 75A single pipe connected in parallel, due to the discreteness of the semiconductor device, the device will produce uneven voltage and current when the device is connected in series or connected in parallel. It is more difficult to realize dynamic voltage balancing and current balancing. Strictly speaking, the ideal voltage balancing and current balancing can not be realized. Based on the fact that IGBTs stated above, high current application need at least multi-tube connected in parallel, the reliability of the product is reduced.
- The module structure is poor in heat dissipation, the high-power IGBT can only be made into a module structure subject to the process. Compared with the double-side crimp thyristor structure, the module structure can only be dissipated on one side and the heat dissipation plane must be insulated from the device electrode. Single-sided heat to make heat dissipation, coupled with the thermal resistance caused by insulation, the device is very easy to failure. A more serious problem with the module structure is that the failure may cause the module to explode.
- Drive isolation is difficult, although the IGBT drive circuit and the signal circuit to achieve the optical isolation, but the drive circuit and IGBT main circuit is still an electrical connection, there is no isolation, which will lead to the drive circuit suffered the impact of the main circuit and adverse effects.
Comparison of Characteristics of IGBT, Thyristors and DDT(S)
It should not evaluate the advancement of semiconductor devices purely theoretically, should even more prevent speculation for business purposes.
Non-control devices, semi-controlled devices and full-controlled devices have their own use, we should select the device based on the actual circuit needs, can not blindly believe that the full-controlled devices can replace all other devices, especially should pay attention in the highlight reliability products.