This article will introduce the actual control (switching) of the H-bridge driven by brush DC motor driven.
H-bridge circuit: switching of output status
In the previous article I mentioned four ways to connect to the two terminals of the motor:
1 The two terminals are not connected anywhere.
2 Connect the (+) of the DC power supply to one terminal, (-) to the other terminal.
3 Connect the DC power to the electrical machine according to the opposite polarity of 2.
4 Connect between the two terminals.
If you can enter 2-bit binary values, these four states can be created through their combinations. For a simple example, if there are 2 logical input terminals, 2 * 2 = 4 combinations can be obtained. Below is an example of a brush DC motor drive of a built-in H-bridge circuit, which gives a substantially internal functional block diagram.
The logic circuit for switching the h-bridge state is inin1 and IN2 as the input, from the broken line. The true value table of the logic circuit is as follows:
It can be seen that VG status relative to IN input logic. VG is the gate voltage state of each MOSFET of Q1 to Q4. For example, the Vg of Q1 is H, which means the voltage of the H level is applied, rather than directly represents the ON / OFF of Q1.
The H bridge is a combination of PCH MOSFET (Q1, Q3) and NCH MOSFET. The high side side is the PCH, the low side side is NCH pairs (Q1 and Q2, Q3 and Q4), each drain and source are connected and become OUT1 (Q1 and Q2 pairs) and OUT2 (Q3 and Q4 pairs) output .
As can be seen from the block diagram, the Q1 and Q3 of the PCH have an active state of the active state on the gate, so the VG is L, in a state of on. Q2 and Q4 are H, thus Q2 and Q4 are h, and are in a state of turn-on (ON). From this point of view, it is the same as the CMOS inverter logic circuit, but the gate is controlled by IN1 and IN2.
OUT corresponds to the four required states. Open means that all MOSFETs are shut down and in high impedance state. L means that connects to GND through the MOSFET, H represents connected to the motor power supply Vm.
Although there is no direct relationship with the control logic of the H-bridge, the level shift displayed in the functional module and the simultaneous conductive function is the function of the hardware control.
Level conversion is a circuit that converts the low voltage logic circuit to accommodate high voltage MOSFET driven. The logic circuit portion is designed to operate under a conventional logic level of 3.3V or 2.5V, but the H bridge portion operates at a high voltage of 5V, 12V, 24V (drive voltage of the motor). Therefore, the level conversion circuit is required since the low voltage logic output is not directly driven.
At the same time, the on-to-conduct function is used to prevent both sided transistors that may occur simultaneously at the same time when switching at the high side transistor and the low-side transistor ON / OFF switch. This is a phenomenon caused by the subtle time point when switching. It is often mentioned that in the case of synchronous rectifier switching power supply cases, in an instantond conduction overlap, there is a current called "shang-through" current from the power supply to GND, there is a damaged switch transistor Or the risk of IC.
Although I talk about the content of a little seemingly related, please seize this paper: 2-bit logic input can be used to get four states through the H bridge.
Key points:
· You can achieve switching of the four connection states of the H-bridge through 2 digits.
· In addition to the H-bridge with a brush DC motor and a control logic circuit of a brush DC motor, many actual brush DC motor drive ICs also have level conversion and simultaneous conductive function.
Edit: hfy, read full text
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