When I started learning the trioint, I value its working principle. Later, I came to the actual application, and I used the triode or MOSFET directly as a switch device. Until these days, when exposed to the H-bridge drive circuit consisting of MOSFET, it was found that there will be many problems in pure as a switching device. Take some problems here and do some analysis on some causes of problems. Personal knowledge is limited, many places are inevitable, hoping to learn to communicate with the Internet.
At present, we generally drive the H-bridge as a motor or stepper motor, as shown in Figure 1, to do a well-driven circuit, you must understand some of the principles of MOSFET, will not be wrong.
Figure 1 H bridge full bridge drive motor
1, single MOSFET is driven #
Let's take a look at MOSFET and triodes, and they differ, but the principles and application scope still have a big difference. Here mainly discusses some MOSFET applications, which are more shallow. MOSFET's door (GAT, GATE), as the name suggests to turn the MOSFET, play a switch MOSFET, the base (B) of the triode, is almost this role. When the voltage of the VGS is at a range (typically 2 ~ 5V), VDS ≈ 0, that is, MOSFET is turned on. Therefore, we only need to switch the MOSFET by controlling the voltage of the VGS, so that the role of the electronic switch.
Figure 2 MOSFET and triodes
The drive load of the MOSFET should be connected to the drain (D), as shown in Figure 3 below. In the left circuit in the figure, the G electrode potential is 4V, and the S is grounded, that is, the potential is 0V, so the VGS = 4V, so the MOSFET is turned on, and the VD = 0.075V can be seen from the figure, approximately 0 . The circuit connected to the right in the figure is unable to drive the load (that is, the MOSFET cannot be turned on). Its reasons are as follows: If the MOSFET in the figure below is turned on, then vs≈vd = 24V, at this time, VGS = VG-VS = -20V, this does not turn on this MOSFET. And when MOSFET is closed, then ids≈0, at this time, VS = 0, MOSFET is turned on, and after the turn is also shown above, it will be closed.
Figure 3 MOSFET load connection method
2, H bridge full bridge drive #
With the analysis of a single MOSFET driver circuit above, it is easy to understand H-bridge drive. As shown in Figure 4 (green represents MOSFET energy, red expands), if the motor is turned forward, simply turn on Q1 and Q4, if it is necessary to reverse, to turn on Q2 and Q3. The direction of current in each case is already clear in the figure.
Figure 4 H bridge drive motor circuit
When turning on each MOSFET, must pay attention to: MOSFET's conduction conditions are VGS "3V (generally this value), not VG" 3V, that is, it can not simply think that as long as VG "3V can be turned on MOSFET to drive the circuit. Normally, VG is far more than 3V. The circuit forwarded circuit in Figure 4 as an example, when Q1 is turned on, at this time, at this time, to ensure VGS "3V, there is VG" (3 + 24 = 27) V, how Do VG has 27V, even higher voltages, this time there is a drive circuit to drive MOSFET, that is to use the MOSFET drive chip.
Experience summary #
This is also a small problem in the project. I used to understand the working principle of MOSFET. I have made mistakes here, let me remember deep. In the process of learning, we must master the theoretical knowledge and practice more, so you can understand more. Although I often listen to the elders to learn, but really doing, less. First, we generally do not have conditions to use our knowledge. Second, our understanding of knowledge is shallow, think it is difficult or too easy, so that we can't use or don't have to pay more attention to it.
After familiar with the use of MOSFET, I want to have a deeper understanding of the working principle of PN knots, and I plan to summarize it. Finally, I hope this summary can give you the students who are learning H bridges to solve doubts. At the same time, personal knowledge is limited, if there is any incorrect place in the text, please also advise yourself.
Author: This article is a CSDN blogger endlessCoding original article, here is special thanks.
Source: https://www.cnblogs.com/endlessCoding/p/6760348.html, Read more
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