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Help me with this. PIC16F877 program

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mimisalt

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I JUST NEED TO MAINTAIN THE OUTPUT VOLTAGE AT 24V

Circuit diagram of the proposed system
Figure 10 shows that power stage included switch SW where it may consists of one or more parallel connected power MOSFET, a fast switching type flyback diode D, an inductor L wound onferrite core with air gap to prevent core saturation, and output capacitor C.The controlling stage consists of a PIC16F877 microcontroller with built-in analog-to-digitalconverter (ADC), a power MOSFET driver, and a voltage divider. The control strategy based on theflow chart in Figure 8 will be written and load into the microcontroller. Voltage divider resistors R1and R2 will divide the output voltage to a suitable voltage range which is acceptable by the built-inADC in the microcontroller. PIC16F877 will then perform calculation based on the control algorithmand produce a PWM signal with a set of duty cycle. The frequency of the PWM is programmable byPIC16F877. The PWM signal is then transmitted to power MOSFET in power stage through a power MOSFET driver to perform on and off state.The PIC16F877 microcontroller unit features an eight-bit, successive approximation ADC, used by the control program to measure signals required for the power flow control. The 10-bit resolution isadequate for the proposed design. Also, it features two PWM outputs with program-controlled dutycycle and 208.3 kHz maximum frequency when driven by the 20 MHz clock of the unit. The firstPWM output is used to control switch SW in boost converter while the second PWM output can beused to control switch in auxiliary circuit such as zero voltage switching circuit and zero currentswitching circuit to reduce switching losses in boost converter. This type of microcontroller waschosen because it has the necessary features for the proposed design such as built-in ADC, PWMoutputs, eight-bit architecture, high clock rate, low power consumption and low cost.In order to calculate the value for
Lmin and Cmin
, the switching frequency will be set to thelowest value of 20 kHz. The rating of the proposed converter will be 100W and 24V output. Byreferring to (3),
Lmin maximum will occur at k = 0.333 and the calculated value will be 2.1 mH. As thedesired output voltage ripple factor is below 1%, the calculated value of C min will be 687μF.PIC16F877 microcontroller uses 5V as its reference voltage for the ADC. Therefore, the ADC shouldsense less than 5V from the voltage divider. The converter switching frequency and the inductancevalue is compromised between the converter’s efficiency, cost, power capability and weight.For the control system, PIC16F877 microcontroller will produce a PWM signal pulse train withvarying duty cycle in the range of 0 to 1.0. Practically, duty cycle for boost converter is only in therange of 0 to 0.75. This is due to instability of boost converter (Mahmood et al., 2008). Therefore, therange of the input voltage for the boost converter is in the range of 6V and 24V. If the voltage detectedis not within the range, PIC16F877 microcontroller will put the whole system into sleep mode.In order to control the duty cycle, voltage divider divides the output voltage of 24V to PICreference voltage of 5V because ADC in PIC16F877 microcontroller is unable to operate under highvoltage. The resistance of R1 and R2 should be high enough in order not to produce high power losses,I2R and affect the overall converter performance. Furthermore, as the reference voltage of PIC16F877microcontroller is 5V, the PWM signal pulse train with the amplitude of 5V is unable to switch the power MOSFET on and off. Therefore, a current sink and source power MOSFET driver is needed tooperate the power MOSFET as a switch working in the active region of its I-V characteristic.
 

circuit.jpg


tHIS IS THE CIRCUIT DIAGRAM
 

Change to 8051 in assembly language
 

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