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五相步進電機驅(qū)動電路開發(fā)(論文翻譯)(編輯修改稿)

2025-07-17 04:28 本頁面
 

【文章內(nèi)容簡介】 ace. The L297 generates three modes of phase sequences, namely half step mode, full step mode and wave mode depending on the input signals it receives. Fig. 1. Circuit diagram to drive a 2 phase bipolar or 4 phase unipolar stepper motor using L297 and L298N ICsA. CURRENT CONTROLSmall stepper motors generally need small DC supplies that control the winding currents and they are limited by the winding resistances. On the other hand, motors with the larger rated torque values have windings with smaller resistances. Therefore, they require a controlled current supply.The L297 provides load current control in the form of two Pulse Width Modulation (PWM) chopper circuits and each chopper circuit consists of a parator, a flipflop and an external sensing resistor.In this method, while the motor current is increasing, the control system applies the supply voltage to the motor. When the current is reached up to the threshold, the control system tries to maintain the current at the desired value by changing the duty ratio of the voltage supply as shown in . For each chopper circuit, the duty ratio (D) of the voltage supply to the motor is defined as:D = Ton / (Ton + Toff),where the Ton and Toff are switch on and off durations respectively of the H bridge.In the chopper circuit, the flipflop is set by each pulse from the oscillator, enabling the output and allowing the load current to increase. As it increases the voltage across the sensing resistor increases and when this voltage reaches Vref the flipflop is reset, disabling the output until the next oscillator pulse arrives. In this method Vref determines the peak load current.Fig. 2. Circuit containing the flipflop, the oscillator and the parator used . PWM operation of the voltage for current control for current controlling shows how the current through the motor is controlled. When the motor current goes beyond the set point, the voltage applied to the motor terminal will be grounded. Therefore the current will decay and finally the motor current can be controlled. The L298N is a monolithic circuit contains two H bridges. In addition, the emitter connections of the lower transistors are brought out to external terminals allowing the connection of current sensing resisters.B. CURRENT CONTROL IN INHIBIT CHOPPER MODE Inhibit chopper control mode and phase line chopper control mode are two of the most mon types of current control techniques available. In the latter case when the voltage across the sensing resistor reaches to Vref, only the low side switch is made off. Hence this method is not suitable and inhibit chopper control mode has to be used. The required switching sequences for this can be taken directly from L297. Inhibit chopper mode can be selected by pulling down (grounded) the CONTROL input signal of L297. Then chopper acts on INH to control the current through the motor coils. Therefore the contribution of INH signal generated from L297 is very important to create ENABLE signal for L298N. In the case when the voltage across the sensing resister reaches to Vref, the chopper flipflop is reset and INH is activated and is brought to low. Then it turns off all four switches of the bridge. The chopping frequency is determined by the internal oscillator of the L297. After switching off all transistors, the diodes provide a path to divert the winding current. The switches of the H bridge are made on in the next oscillator cycle. explains current control phenomena at an instant when phase signal A is high and B is low. These A and B signals are fed to two AND gates connected to low and high side switches in the L298N to generate excitation signal with the same INH1 signal in order to control the load current. The AND gate output will bee high only if and only if the INH1 is high.Fig. 4. Inhibit chopper waveform when CONTROL is LOWIII. LOGIC CIRCUIT DESIGNING In any mode of operations, wave patterns of A, B, C and D phases of the L297 repeat after four clock cycles as shown in . Translation of the repetition of the phase waveform after the ten clock cycles is essential to derive the drive topology
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