Transistor DC Motor Driver

1. Input level conversion section:

Introduced by the DATA input signal line, a pin is ground, the other is the signal line. Note 1 foot on the ground to connect a 2K resistor Europe. When the driver board and the MCU power supply, respectively, this resistance can provide the signal current return path. When the driver board and share a single chip power supply, this resistor can be connected to prevent large current flows along the ground MCU board disruption. In other words, the equivalent of the driver board ground and the MCU ground separated, thus enabling "grounding."

High-speed op amp KF347 (can also use the TL084) is the role of the comparator, the input logic signal from the light and with a 2.7V reference voltage diode compared to convert the power supply voltage range close to the square wave signal. KF347's input voltage range can not be close to the negative supply voltage, otherwise it will go wrong. Therefore, an increase in the op amp input voltage range to prevent overflow of the diode. One of the two input resistors to limit one to the input floating pulled low when the input side.

Can not open with LM339 or any other place of the comparator output op amp, because the open state of the output of the high output impedance over Europe in a thousand, pressure drop, the transistor will not be behind a cut-off.

2. Gate drive components:

Behind the transistor and resistor, voltage regulator tubes, signal amplification circuit to further drive the FET gate and the use of FET gate capacitance itself (about 1000pF) to delay, under the arms to prevent the H bridge FET At the same time turn ("turn-of state") caused by power short circuit.

When the op amp output is low (approximately 1V to 2V, can not reach zero), the following cut-off transistor, FET. Above the transistor conduction, FET cutoff, the output is high. When the op amp output is high (approximately VCC-(1V to 2V), can not fully meet the VCC), the following transistor conduction and field effect transistor cut-off. Above cut-off transistor, FET, the output is low.

The above analysis is static, the following discussion of the dynamic process of switching converter: transistor resistance is much less than two thousand in Europe, the transistor switch to turn from the end when the FET gate capacitance of the charge can be rapidly released, field-effect tube rapidly closing. But by the turn transistor switch to close when the FET gate charge by two 1000 ohm it takes some time. Accordingly, the FET switch to cut-off from the conduction rate than the cut-off switch to turn faster. If the two transistors are switching simultaneously, this circuit allows the upper and lower arms FET Break-Before the elimination of state conduction phenomena.

In fact, the op amp output voltage change takes time, this time in the op-amp output voltage between positive and negative power supply voltage of the median. Then turn the two transistors at the same time, FET on the same end of the. Therefore, this ideal than the actual situation of the circuit even safer.

FET gate 12V Zener diode is used to prevent over-voltage FET gate breakdown. Normal FET gate voltage is 18V or 20V, 24V voltage will be directly coupled with the breakdown, so the Zener diode can not be replaced by an ordinary diode, but you can use two resistors instead of thousands of Europe, the same can be 12V partial pressure.

3. MOSFET output section:

Internal power FET source and drain in reverse parallel between a diode, connected as H bridge use, the equivalent output has been in parallel with the elimination of the four diode voltage spikes, so there is no external diodes. Parallel a small output capacitor (out1 and out2 between) to reduce the voltage spike generated by the motor has some advantages, but when using the PWM peak current produced side effects, so that the capacity should not be too large. When using low-power motor of this capacitor can be omitted. If you add the capacitor, then, must use high-pressure, common porcelain capacitor breakdown may occur short-circuit fault.

Parallel output from the resistor and the light-emitting diode, capacitor circuit composed of the motor direction of rotation direction.