# Regulated Power Supply with High Power Factor for Hyperspectral Imaging Applications
## 3 Proposed Circuit Configuration  
The main objective of this work can be summarized as follows:  
Figure 2: Block diagrams of the two types of power supplies. (**a**) Linear. (**b**) Switched-mode.  
* To develop a switched-mode power supply (SMPS) with automatic PF correction and 25 VDC/20 A as output;
* To provide, at the output, two step-down converters with variable output voltage depending on the needs of the required illumination of the scene. This output should be adjustable from 7 to 21 V. The maximum power of each output should be 150 W;
* To comply with the UNE-EN IEC 61000-3-2:2019 standard [20];
* Two commercial power supplies will be used to compare the PF and performance with respect to the proposed system.  
In this work, we propose an SMPS with PFC (Power Factor Correction) and double output from two independent buck converters, shown in Figure 3. The detailed block diagram of the power supply with PFC is shown in Figure 4. As shown in Figure 5, we decided to use a two-stage DC/DC converter, which consists of adding a second stage to the single-stage converter. In the first converter, the PF correction and voltage regulation functions are performed at a fixed value, while the second stage regulates the output voltage and provides a fast dynamic response through a control loop. This structure overcomes the shortcomings of the previous structure and improves its performance by achieving more effective control of the output voltage, reducing its ripple and the sensitivity of the input current to output disturbances [21].  
Figure 4: Breakdown of the switching power supply with PFC. (**A**) Uncontrolled rectifier bridge with capacitor filter (**B**) Automatic PF and THD correction using a DC-DC boost converter. (**C**) DC-DC converter with galvanic isolation and automatic output voltage control using forward topology.  
Figure 3: Switching power supply with PFC and double output from two independent buck converters.  
The integration of automatic PFC is a crucial component of this design, as it adjusts the current drawn from the electrical grid to more closely resemble a pure sine wave signal. This modification enhances the efficiency of the equipment and reduces distortion in the power supply. The control of the PF is located just after the diode bridge. Regarding the type of control employed, currently, there is a wide variety of methods devoted to correcting the PF. Generally, two basic control loops are required for any control strategy, as shown in Figure 6. An external voltage loop is used to keep the bus voltage level at a fixed value. An internal current loop controls the current through the coil and forces it to adopt the most similar waveform to the rectified voltage input signal, thus achieving a PF close to the maximum. This integrated circuit is not a simple addition to the PF corrector but integrates the functions of the modulator, the multiplier, and the operational amplifiers of the internal and external loop regulators. For this purpose, the UC3854 contains an analogue voltage amplifier, a multiplier/splitter, a current amplifier, and a fixed frequency PWM (Pulse-Width Modulation) modulator.  
The implementation of such control loops makes the system stable with a tolerable dynamic behavior regardless of the system load conditions. The power supply developed in this work is part of the lighting equipment and will demand an active input power higher than 500 W. For this reason, it belongs to Class C, and the harmonic currents must not exceed the relative limits indicated in Table 1.  
Figure 5: Forward DC/DC converter.  
Figure 6: Control scheme of a boost converter.