Design Of Hall Signal Detection Amplifying Circuit And PWM Frequency Conversion Circuit In BLDCM Driven IC

As one of the motor driven products,brushless DC motor(BLDCM)drives have been widely developed and applied.This paper first introduces two drive methods of Brushless DC motor,including sensor drive: using Hall sensor for commutation control and sensorless drive: using back EMF for commutation control,and describes their respective principles and control technology.For the single-phase motor used for notebook cooling applications,this paper will introduce the design method of single-phase motor driving IC integrated with Hall sensor and power transistor.Two key modules are described in detail: the design of Hall detection amplifying circuit and PWM frequency conversion circuit.The circuit design is based on the Maxchip 0.18 ? m BCD process,and the feasibility of the circuit design is verified through the Hspice simulation.The purpose of designing Hall detection amplifying circuit is to amplify the Hall signal which changes with the magnetic field and switch it to switch signal,which drives the motor to commutate.In order to eliminate the influence of Offset Voltage of Amplifier on the circuit,the chopper zero adjustment technology is applied on the traditional Instrumentation amplifier,the Offset Voltage is collected in the first half cycle,and the latter half cycle is eliminated.According to the simulation results,the gain of the amplifying circuit is about 34.3 times.In order to ensure that the circuit has the proper magnetic reversal characteristic,a trimming circuit is designed,which can repair the circuit when the chip is tested.The maladjustment can be adjusted at step 2.08 mV in ± 263.5mV.A hysteresis comparator is used to transform the amplified analog signal into a switching signal,which can suppress the noise signal interference.Finally,the overall verification of the circuit shows that the Hall signal with a range from several m V to dozens of mV and a frequency less than 3KHz can be accurately amplified and converted to a switching signal.The purpose of designing the PWM frequency conversion circuit is to convert the PWM signal of the external 5KHz~100KHz to the internal PWM signal of about 44 KHz,and the internal signal is the same as the duty ratio of the external signal.In order to produce a fixed frequency PWM signal,a triangle wave with fixed frequency must be generated.This paper uses a reference voltage source to clamp the high and low levels of the triangular wave,and produces a near zero temperature coefficient current to charge or discharge the capacitor to ensure the constant temperature characteristic of the triangular wave frequency.The temperature coefficient of the reference voltage is 12.30 ppm under the typical simulation conditions.Under the condition of 3.3V,the absolute value of the reference voltage varies in the range of 1.220V~1.245 V,and the output current varies with the temperature within ±0.015 ? A.The rail comparator is designed to replace the traditional comparator,which can meet the requirement of the minimum 2V supply voltage and the triangle wave height.Finally,for the designed triangular wave generator,the output triangle wave frequency is typically 43.5KHz,and the frequency of triangular wave varies within 42.4KHz~44.4KHz in the whole temperature range.In the range of 2V~6V power supply,considering the change of process and temperature,the triangle wave frequency falls in the range of 20KHz~90KHz,the amplitude is about 0.89 V.At the same time,the design of the Unit gain follower,the two order Low pass filter and the Schmidt trigger was completed according to the requirements.Finally,the verification of the whole circuit shows that in typical cases,for 5KHz~100KHz input PWM signal,the output PWM signal frequency is about 41.9KHz,and the duty cycle of output signal is consistent with the input signal,and varies with the input signal.