First, H bridge principle
Figure 1 shows a typical DC motor control circuit. The circuit has been named "H Bridge Drive Circuit" because its shape is like a letter H. 4 triodes constitute the 4 vertical legs of H, while the motor is the horizontal bar (Note: Figure 1 and the subsequent figures are only schematic, not a complete circuit diagram, where the drive circuit of the triode is not drawn).
As shown, the H-bridge motor drive circuit includes four triodes and a motor. To operate the motor, you must turn on a pair of triodes on the diagonal. According to the conduction of different triode pairs, the current may flow from left to right or from right to left to left the motor to control the steering of the motor.
Figure 1 H Bridge Motor Drive Circuit To make the motor to turn on a pair of triodes on the diagonal line. For example, as shown in FIG. 2, when the Q1 tube and the Q4 tube are turned on, the current passes from the left to the left to the right from the left to right from the power supply positive electrode, and then returns to the power supply negative electrode. According to the current arrow in the figure, the flow of the flow direction will drive the motor clockwise. When the triodes Q1 and Q4 are turned on, the current will flow from the left to right, so that the drive motor is rotated in a specific direction (the arrow around the motor indicates the clockwise direction).
Figure 2 H-bridge circuit drive motor clockwise transferred to Figure 3 as shown by another pair of triodes Q2 and Q3, and current flows from right to left through the motor. When the triodes Q2 and Q3 are turned on, the current flows from the right to left through the motor, so that the motor is rotated in the other direction (the arrow around the motor is expressed as a counterclockwise direction).
Figure 3 H-bridge circuit drive motor counterclockwise rotation
Second, when the control and direction logic drive the motor, it is important to ensure that the three triodes on the H-bridge will not be at the same time. If the triodes Q1 and Q2 are turned on simultaneously, the current will be directly returned to the negative electrode from the positive electrode through the two triodes. At this time, there is no other load in the circuit except for the triode, the current on the circuit may reach the maximum (this current is only limited by power supply performance), even burn-critical triodes. Based on the above reasons, the switch of the triode is usually controlled in the actual drive circuit. Figure 4 shows the improved circuit based on this consideration, which increases four and two non-doors based on the basic H-bridge circuit. 4 with a "enable" on the door, so that the switch of the entire circuit can be controlled with this signal. Two non-gates can provide one-to-side legs on the h-bridge to be turned on. (Like the schematic shown in the previous section, Figure 4 is not a complete circuit diagram, especially in the figure, and the direct connection to the door and triode is not working properly.)
Figure 4 has an H-bridge circuit that enables control and direction logic
With the above method, the operation of the motor requires only three signal controls: two direction signals and a enable signal. If the DIR-L signal is 0, the DIR-R signal is 1, and the enable signal is 1, then the triodes Q1 and Q4 are turned on, and the current flows from the left to right (as shown in Figure 4.16); if Dir-L The signal becomes 1, and the DIR-R signal becomes 0, and the Q2 and Q3 will turn on, and the current flows through the motor.
Figure 5 enables the use of signals and directional signals
When actually use, it is very troublesome to make H bridges with discrete parts. It is good to have many packaging H-bridge integrated circuits on the market, which can be used on the power supply, motor and control signals, in the rated voltage and It is very convenient and reliable in the current. For example, common L293D, L298N, TA7257P, SN754410, and the like.
Third, the MOS Tube H Bridge 1, the upper arm PMOS, the lower arm NMOS is composed of 2 P-type field effectors Q1, Q2 and 2 N-type field effect tubes Q3, Q3, so it is called the P-NMOS tube H bridge. The four field effects on the bridge arm correspond to four switches, and the p-type tube is turned on when the gate is low, and the high level is turned off; the n-tube is turned on when the gate is high, and the low level is turned off. The field effect tube is a voltage control type element, and the current passed by the gate is almost "zero". Because of this feature, after connecting the circuit, the control arm 1 high level (U = Vcc), the control arm 2 low level (u = 0), Q1, Q4 turn off, Q2, Q3 The left end of the motor is low, the right end is high, so the current flows in the direction of the arrow. Set to the motor forward.
Figure 6 Control arm 1 high, control arm 2 low, forward
The control arm 1 sets low level, when the control arm 2 is high, Q2, Q3 are closed, Q1, Q4 are turned on, the left end is high, the right end is low, so the current flows in the direction of the arrow. Set to the motor reverse.
Figure 7 control arm 1 low, control arm 2 high, reverse
When the control arm 1, 2 is low, Q1, Q2 turn, Q3, Q4 are closed, both ends of the motor are high, the motor is not turned; when the control arm 1, 2 is high, Q1, Q2 is closed, Q3, Q4 is turned on, both ends of the motor are low, the motor does not turn, so this circuit has an advantage that the H bridge will not appear regardless of the control arm state (never allowed to hang up). "Tutant on" (short circuit).
2, 4 N-type field effect tube H bridge
There is also a H-bridge of the N-type field effect tube, the internal resistance is smaller, with "ruthenating" phenomenon, the gate drive circuit is more complicated, or the special drive chip, such as the MC33883, the principle is basically similar, no longer Given it. The following is a gate driving circuit composed of non-door CD4011, because the single-chip output voltage is 0 to 5V, and the control arm of the H-bridge used in our trolley requires 0V or 7.2V voltage to completely turn on the field effect, PWM input When 0V or 5V, the gate drive circuit output voltage is 0V or 7.2V, provided that the CD4011 power supply voltage is 7.2V. Remember! ! Therefore, the CD4011 only uses "voltage amplification". The reason why two levels and non-door are compatible with MC33886.
The combination of both is the following circuit: two PWM inputs one of the two PWM inputs, and the other is floating (pull 1), the motor is turned normally. Monitor the MOS tube temperature, such as fever, cut off the power check circuit immediately. The 14-pin feet of the CD4011 are connected to 7.2V, and 7-pin ground.
When using the single-chip PWM output signal: 1 is a PWM square wave signal, and the other is high (set 1). Inversion is also. , Read full text, original title: H-bridge circuit principle
Article Source: [Micro Signal: FCSDE-SH, WeChat Public Number: Semiconductor PDSA] Welcome to add attention! Please indicate the source of the article.
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