the simple gate drive of the low voltage drive circuit
The maximum gate-source voltage of a typical power FET is about 20V, so in a 24V application, the gate-source voltage must not exceed 20V, which increases the complexity of the circuit. But in applications with 12V or lower, the circuit can be greatly simplified.
The left picture shows one side of a 12V transaxle, and the triode part of the upper circuit is replaced by two diodes and two resistors. (Note that the logic in the above diagram is reversed.) Due to the presence of the gate capacitance of the FET, charging the gate capacitor through R3 and R4 causes the FET to delay conduction; and directly discharges the gate capacitance through the diode to effect the field effect. The tube is immediately cut off, thus avoiding common state conduction.
This circuit requires a square-wave pulse with a sharp edge at the IN input. Therefore, after the control signal is connected from a microcontroller or other open-output device, it must pass a Schmitt trigger (such as 555) or a high-speed comparator with push-pull output. Can receive the IN end. If the input edge is too slow, the diode delay circuit will lose its effect.
The selection of R3 and R4 is related to the rising and falling speed of the edge of the IN signal. The steeper the edge of the signal, the smaller the R3 and R4 can be selected, and the faster the switching speed can be. In the boost circuit used in the Robocon game (similar in principle), the 555 is used before the IN.
Third, the edge delay drive circuit
In the pre-stage logic circuit, the falling edge of the control PMOS and the rising edge of the control NMOS are deliberately delayed, and then the square wave is formed, and the common-state conduction of the FET can also be avoided. In addition, this can simplify the gate drive circuit of the latter stage, and can be a low-resistance push-pull drive gate, which does not need to consider the gate capacitance, and can be better adapted to different FETs. This drive circuit was used in the 2003 Robocon competition. The following figure is the delay circuit of two kinds of edges:
This gate drive circuit consists of a two-stage transistor: the front stage provides the correct voltage required to drive the FET gate, and the latter stage is a level one emitter follower that reduces the output impedance and eliminates the effects of gate capacitance. In order to ensure that the common state is not turned on, the input edge should be relatively steep, and the above-mentioned circuit that delays and reshapes the above can be done.
Fourth, other drive circuits
(Relay + semiconductor power device ideas)
The relay has the advantages of large current and stable operation, which can greatly simplify the design of the drive circuit. In the motor drive circuit that needs to achieve speed regulation, the relay can also be fully utilized. One solution is to use relays to control the direction of the current to change the direction of the motor. Instead of using a single extra-large current FET (such as the IRF3205, which typically has only N-type extra-current tubes), PWM speed regulation is achieved, as shown in the right figure below. This is one way to achieve particularly high current drive.
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