1. Part of the input level shift:
DATA introduced by the input signal line, a pin is ground, the other is the signal line. Note that a pin connected on a 2K ohm resistor. When the driver board and the MCU power supply, respectively, this resistance can provide the return signal current path. When the driver board and a set of shared power microcontroller, this resistance can be connected to prevent large current flows along the ground interfere with MCU board. Or, the equivalent of the driver board ground and ground separate microcontroller, to achieve "a little ground."
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 the power supply voltage into a range close to a square wave signal. KF347’s input voltage range is not 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 circuit output impedance of the output of the high state of Europe in a thousand or more, a larger drop, followed by a transistor will not be closed.
2. Gate drive section:
behind the transistor and resistor, the regulator circuit consisting of the further amplified signal, FET gate drive and use FET gate capacitance itself (about 1000pF) to delay and prevent H under the bridge both arms of the FET turn-on ("common mode conduction") 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 conduction. Turn above the transistor, 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 turn-on transistor, FET cutoff. Above the cut-off transistor, FET conduction, the output is low.
The above analysis is static, the following discussion of the dynamic process of switching converters: the transistor on-resistance is far less than 2 thousand in Europe, so the transistor from the cut-off switch to turn on when the MOSFET gate capacitance can quickly release the charge, field Effect of pipe quickly closed. But by the turn-on transistor switch to close when the FET gate charge by 2 thousand ohm it takes some time. Accordingly, FET switch to end the turn faster than the cut-off switch to turn faster. If the two transistor switching action occur simultaneously, this circuit will allow up and down his arms before break through the FET, to eliminate common-mode conduction phenomenon.
In fact, the op amp output voltage change takes time, this time the op amp output voltage is midway between the positive and negative power supply voltage value. Then turn the two transistors at the same time, FET on the same time closing the. Therefore, this ideal than the actual situation of the circuit but also safer.
12V Voltage Regulator FET gate FET gate diode is used to prevent over-voltage breakdown. General FET gate voltage is 18V or 20V, 24V voltage will be directly coupled with the breakdown, so the Zener diode can not be replaced with an ordinary diode, but can be replaced by the resistance of 2 kilohms, the same can be 12V partial pressure.
3. MOSFET output section:
Within the high-power FET between the source and drain are reverse parallel diode connected in H bridge use, the equivalent output voltage spikes have been used in parallel to eliminate the four diodes, so there is no external diode . A small capacitor in parallel output (out1 and out2 between) to reduce voltage spikes generated by the motor has some advantages, but in the use of PWM peak current produced when the side effects, so capacity should not be too large. In the use of small power motors the capacitor can be omitted. If you add the capacitor, it must use high-pressure, common ceramic capacitor breakdown may occur short-circuit fault.
Parallel output from the resistor and light emitting diode, capacitor circuit composed of the motor direction of rotation direction.
1. Part of the input level shift: