MOS (metal oxide semiconductor) tube diode is based on MOSFET (metal oxide semiconductor field effect transistor) structure BAS70-06W Diode. It has the advantages of MOSFET, such as high input impedance, low power consumption and fast switching speed, and can also realize diode rectification function. It is formed by the source, body and drain of MOS transistor, and is generally considered as an inherent characteristic of MOS transistor.
The operating principle of MOS tube diode is similar to that of MOSFET, which is formed by a surface doped P-type or N-type substrate covered with insulation layer, gate and source drain electrode. When the gate voltage is negative, an inverted junction is formed between the gate and the substrate, causing the diode to cut off. When the gate voltage is positive, a positive junction is formed between the gate and the substrate, causing the diode to turn on. Therefore, MOS diode can switch the working state according to the positive and negative gate voltage.
MOS diode has two main functions: first, it can provide a reverse voltage protection. When the voltage between the source and drain of MOS transistor is negative, the body diode will be turned on, so that the current can flow from the source to the drain, avoiding MOS transistor being damaged by reverse voltage. Secondly, it can also provide a bootstrap voltage supply. When the MOS transistor works in the switching power supply, the conduction of the body diode can increase the gate voltage of the MOS transistor, so that the MOS transistor can be turned on.
However, MOS diode may also have some problems, mainly as follows:
1. On loss: because the on voltage of the body diode is usually high (about 0.7V), it will produce large on loss when it is on, which is unacceptable for power systems that need high efficiency.
2. Switching speed: the speed of making and turning off the body diode is usually slow, which will affect the switching speed of MOS transistors, thus affecting the dynamic response speed of the power supply system.
3. Thermal stability: because the conduction current of the body diode needs to flow through the body electrode of the MOS tube, when the conduction current is large, the body electrode of the MOS tube will generate greater heat, thus affecting the thermal stability of the MOS tube.
In order to solve the above problems, engineers usually adopt some methods, such as using a body diode with lower conduction voltage, optimizing the structure of MOS tubes to improve the switching speed, and increasing heat sinks to improve thermal stability.
In general, MOS diode is an important feature of MOS transistor, which plays an important role in providing reverse voltage protection and bootstrap voltage supply. However, there are also some problems, which require engineers to take corresponding solutions according to the specific situation.
