Many electrical appliances are not high in power polarity, such as lighting, and pressing them can work, and the phenomenon is almost, and some electrical appliances are sensitive to power supply, and they will not work, such as most semiconductor devices, LEDs. Waiting; but there are also electrical appliances to sensitive to power supply, but is in opposition to work, difference is different, such as normal DC electromagnetic motors, because of the current direction, the magnetic pole direction generated by the coil is different. Thus the direction of rotation is different. Such characteristics make electric vehicles, remote control toy cars can be forwarded, reverse.
To achieve a polarity change, it is complicated than the normal case / opening, because the normal switch is turned off, as long as the interworking on a line can achieve, the transmission of the entire circuit current can be realized, and the polarity needs At the same time, the change in supply of two lines (the original polarity negative electrode, the negative electrode is turned ", to achieve this, the ordinary single-knife double throw switch can also be implemented, the double-knife double throw switch is required.
The direction of the rotation of the DC motor can be changed as shown in the drawing.
However, if I only have a single knife double-throw switch, but I also want to control the motor is reversing, this can be, it is actually possible, but the complexity increases, because the single knife double throw switch can only open a line, for example : I use a single knife double-throw switch to open the circuit of the positive electrode to the motor, and need to indirectly open the other terminal of the motor to the negative line through some parts, and the function is the triode:
However, the efficiency does not use double-knife double-throw switch, because the circuit needs to use a small portion of the current to turn on the motor and the negative electrode, the triode will have a certain pressure drop, but for convenience, this point efficiency loss is tolerant .
A single knife double throw switch can also be replaced by two single-knife single throws in some sense, so that the circuit has become:
This circuit seems to be the same as the single-knife double throw switch, but actually a little difference: single-knife double-throw switch can only Unicom a contact at the same time, so the motor is either transmitted, or flip, and this circuit may be two switches Closed, in fact, in the introduction of danger: two switches closed at the same time, both triode bases plus positive voltages, two triiod are turned on, the two ends of the motor will not work, the triode shorts the power supply, It may eventually cause power or triodes to be burned.
Although this circuit brings a short circuit's danger, it can completely turn off the circuit compared to single-cut switch, and as long as it is used, do not open two switches at the same time, it is still possible.
In many cases, we don't apply the switch to achieve the adjustment of the motor rotation, but through the digital circuit to control the direction of rotation of the motor, even implement the PWM speed control, and the IO of the MCU can be easily achieved with the positive electrode. The function of the single-knife single throw switch is controlled to the MCU corresponding IO output 1;
However, the MCU drive capacity is generally weak, so a triode is required to improve the driving ability of the MCU, so the circuit has become:
At this time, the circuit is already a complete H bridge. If we don't look at the baseline of the triode, the H bridge is actually four triodes plus a DC motor. It is for PNP or NPN trioint, which is completely dependent on the application. Toward, H bridge generally has the following four types:
Two triodes:
Use only one triode:
The resistor is saved in the circuit, and the base is generally mainly electrified and limited flow flow in the actual application.
Since the MCU drive capacity is different, the current is different after the triode is large. In order to reduce the difference, Dalinton tube, that is, two triode connections to improve the driving capability:
Many MCU power drive chips have been integrated with Dalin Tubes, such as ULN2003, ULN2308, etc., can provide 500mA drive current to drive normal 5VTT motors or may. At this time, the peripheral circuit is very simple:
However, no matter what, short-circuit issues still have no resolution, once the program is wrong, the circuit will face short circuit issues, the solution is to use some logical gate circuits, so that the two IO will output 1 when the triode does not work:
In theory, I have solved the problem with two non-gates:
Because there is an inverter, no matter what IO input is, two triodes on the vertical line can never work at the same time.
In order to prevent parking, the motor will continue to rotate due to inertia to generate a reverse electric shidder bridge, often use four triiod to rectify the reverse electromotive rectifier circuit to be rectified into the power supply.
However, if there is an output diode on the power supply, this circuit is no effect.
Commonly used L298N is an integrated circuit integrating H-bridge:
Can be used to drive two DC motors to prevent short circuits;
Internal equivalent circuit:
X treasure uses the module made by L298N, to the hand, joined the diode anti-reverse electric potential:
L298N power is large but not cheap, if the motor is small, there is no need to use it, you will take a h bridge.
In addition, the small power H bridge eight-foot chip LG9110H is also very common, it can provide 750mA drive current, which can prevent double high-level short circuits, and generally small motor can be driven, but the disadvantage is that a chip can only drive one motor, and MCU A 200ua current is required to drive the chip, if the MCU drive capacity is insufficient, it needs to be used.
Application circuit, read full article, original title: [Hand] About H-bridge understanding and application
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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