In the field of automotive electronics, MOS tubes are widely used. Most of them are used as switch tubes. From power supplies to various types of power drivers, MOS tubes are indispensable. Today we will briefly introduce the application of MOS tube in automotive electronics.
1. Power module
The power supply devices on the car are all directly powered from the battery, and the battery voltage is 24V and 12V. The voltage of electrical appliances is varied, there are high voltages of 5V, 3.3V and even 50V. Therefore, various voltage conversions are required in the power module, among which buck step-down and boost step-up are commonly used.
As shown in the figure, in the application of switching power supply, whether it is boosting or bucking, it gradually changes with the continuous opening and closing of the MOS tube. The selection of MOS tubes here should consider the current flowing through the MOS tubes and the withstand voltage. In addition, in the application, the design of switching frequency and damping, as well as the switching noise generated by the isolation MOS tubes, should be considered.
2. Power module
There are generally two types of power devices on automobiles, resistive loads and inductive loads . Driving both loads requires current
Because the on-resistance of the MOS tube is extremely low, the MOS tube is generally used as the driver.
2.1. High and low side drive
The common one is low-side drive, which uses an NMOS transistor, which corresponds to the current injected into the drive terminal, as shown in Figure 2a:
In Figure 2a, the MOS tube is close to the ground, and the current is injected into the driving end of the MOS tube from the outside. This type is called low-side drive, and whether the load is working is determined by controlling the opening and closing of the MOS tube.
The other is high-side drive. As shown in Figure 2b, the MOS tube is close to the power supply end, and the MOS tube drive end outputs current to the external load. This type is called high-side drive, which also controls the opening and closing of the MOS tube. to determine whether the load is working.
Let's take a look at the difference between these two circuits:
Because the tubes commonly used in these two circuits are NMOS tubes, the structure of the low-side circuit is simpler: the voltage at the S terminal is 0, and the MOS tube can be turned on as long as the voltage at the G terminal is controlled to reach the GS voltage threshold. The high-side application is more complicated: after the GS voltage reaches the threshold, the S terminal voltage instantly becomes the power supply voltage, so in order to maintain conduction, the G terminal voltage must rise to the power supply voltage + GS threshold voltage . Therefore, a booster module is generally added to the high-side drive, which increases the cost.
On the other hand, it is considered from the perspective of failure. In automotive applications, because there are many grounding points, the frequency of short-circuit to ground faults is high. At this time, if the low-side drive is used, it means that the load will continue to work, which obviously increases the possibility of load failure. And if it is driven by the high side, it means that the load will not be enabled and the load will stop working. This in turn has a protective effect. Therefore, many key components are driven by high side, such as oil pump.
2.2. Bridge drive
Bridge circuits generally have half bridges and full bridges. Its structure is shown in Figure 3:
The difference between the high-side drive and the bottom-side drive's response to failure has been mentioned above. Among them, the high-side drive can better respond to a short-circuit to ground fault, so it is not difficult to think that the low-side drive can better respond to a short-circuit to the power supply fault. Therefore, many loads with high safety requirements in the car will be driven by the board bridge, which is to make the two MOS tubes work in turn, no matter which tube fails, it will have better protection for the load. Common applications are fuel injection valve drive, motor drive, etc.
In the application of the motor, the half-bridge circuit can control the size of the current by controlling the opening and closing of the low-side MOS tube, so the speed regulation is more convenient, but it cannot change the forward and reverse rotation of the motor. In addition to the advantages of a half-bridge circuit, a full-bridge circuit can also convert the direction of current flow. Therefore, it is widely used in the control of the motor, because it can not only adjust the speed, but also conveniently control the forward and reverse rotation of the motor .
It can be said that MOS tubes account for nearly half of the application in automotive electronics, so the reasonable selection of driver types and MOS tube models has a great impact on cost control. I hope the content of this article can give you a reference.
Visamp Mall is a local component catalog distributor. It adopts the sales model of "small batch, spot and sample", and is committed to meeting the procurement needs of customers with multiple models, high quality and fast delivery. Visamp builds efficient and intelligent warehouses by itself, with more than 70,000 kinds of self-operated inventory, providing one-stop genuine spot procurement, personalized solutions, selection and substitution and other diversified services.