University of Santo Tomas Faculty of EngineeringElectronics Engineering Department

Design of a Buck Converter for a Solar ChargerJaphet Alfeo Niño D. Ang 1, Jasper T. Chua2, Ronchester Sigfrid S. Mendoza3, Katrina Ysabel M. Soriano4

Electronics Engineering Department, Faculty of Engineering, University of Santo Tomas, Manilajaphet.alfeoang@yahoo.com1, jasperchua57@yahoo.com2, ronchester.mendoza@gmail.com3 , katrinaysabelsoriano@gmail.com4

INTRODUCTION

DESIGN OF POWER COMPONENTS

RESULTS

CONCLUSIONIn this study, the design of an open loop and closed loop buck converter is constructed

and simulated using SIMetrix-SIMPLIS software. From the simulations conducted, it is observed that the open loop buck converter can produce an output of 4.8 volts when the input of the converter is between the values of 20 to 25 volts at a 46.60% value of duty cycle and at a switching frequency of 54.6795. In the simulation of the hardware or the output, the buck converter system gives out an output of 5.5V. The voltage is also regulated at the said voltage.

Furthermore, it is perceived that implementing a closed loop buck converter with the use of a current mode control can improve the system’s output and stability. The closed loop buck converter also generates an output of 5.5 volts when the input is between the values of 20 to 25 volts, almost similar to the value gathered from the open loop buck converter. Through utilizing the current mode control, the output voltage ripple became smaller, the system became faster in responding to the variations in the input voltages, and can compensate to the error rapidly.

[1] Buck DC/DC Converters. (n.d.). Retrieved May 08, 2016, from http://www.mouser.ph/applications/power-supply-topology-buck/[2] Midya, P., Greuel, M., & Krein, P.T. (1997). Sensorless current mode control-an observer-based technique for DC-DC converters, Power Electronics Specialists Conference, PESC'97 Record., 28th Annual IEEE, 197-202.[3] S. Keeping, "Voltage- and Current-Mode Control for PWM Signal Generation in DC-to-DC Switching Regulators DigiKey", Digikey.com, 2014. [Online]. Available: http://www.digikey.com/en/articles/techzone/2014/oct/voltage-and-current-mode-control-for-pwm-signal-generation-in-dc-to-dc-switching-regulators. [Accessed: 20- Apr- 2016][4] Trescases, O., Lukic, Z., Wai-Tung, N., & Prodic, A. (2006). A low-power mixed-signal current-mode DC-DC converter using a one-bit and Delta; and Sigma; DAC in Applied Power Electronics Conference and Exposition, APEC '06. Twenty-First Annual IEEE, 5.

The buck converter is a very simple type of DC-DC converter that produces an output voltage that is less than its input. The Current Mode Control technique is used to regulate the output voltage. This control technique involves a current feedback and control signal that is used to regulate the peak of the inductor current and maintain the inductor equal to a preset current. It creates a voltage-controlled ideal current source which is programmed to produce a regulated voltage at the output of the converter. converters are well-known for converting high voltage to a low voltage with high efficiency. There are lots of products built to charge a battery from a solar panel with a higher voltage. Solar cells have outputs whose current-voltage curves are non-linear. Thus, solar chargers make use of the current mode control buck converter to draw the maximum amount of power by varying the load current to charge batteries in the shortest time possible. Figure 1. Shown above are the voltage at the output (left) and the bode plot (right) of an open loop buck

onverter.

Figure 2. The images above displays the PWM and the output voltage of a closed loop buck converter that implements the current mode control technique.

The voltage regulates at an output voltage of 5V while the phase margin is at 45º and the gain margin is at -10 dB at a 10kHz crossover frequency. Voltage also oscillates before it regulates. Comparing this to the closed loop buck converter system, the output oscillates faster and regulates faster. The output voltage is also almost similar to that of the open loop, only having a difference in decimal values. In the actual circuit testing, the voltage at the output is also almost equal to that of the open loop and closed loop simulation.