I. Comparison of Control Methods for Programmable Switchgear Regulated Power Supplies
A switching power supply consists of multiple electronic components, but essentially, its core is a DC transformer. Therefore, analyzing a switching power supply is not difficult. In this article, we will introduce the selection of control methods and power improvement schemes for process-controlled switching power supplies.
1. Selection of control methods
Plan 1: Use a microcontroller to generate a PWM wave to control the switching on and off of the switch. The duty cycle is programmed to adjust based on the feedback voltage sampled by the on-chip AD converter, stabilizing the output voltage at a set value. The load current is sampled on the constantan wire, input to the microcontroller via the on-chip AD converter, and when this voltage reaches a certain value, the switch is turned off, providing overcurrent protection. This plan is primarily implemented in software, resulting in a complex control algorithm, slow speed, and poor output voltage stability. Achieving automatic recovery would be even more complex.
Plan Two: Select the TL494 constant frequency pulse width modulation controller. This chip can be push-pull or single-ended output, operates at a frequency of 1kHz~300kHz, has an output voltage of up to 40V, an internal 5V voltage reference, adjustable dead time, and an output stage pull-in/pull-out current of up to 200mA, providing strong drive capability. The chip internally contains two error comparators: a voltage comparator and a current comparator. The current comparator can be used for overcurrent protection, and the voltage comparator can be configured for closed-loop control with fast adjustment speed.
Therefore, based on the above analysis, we recommend choosing the second plan.
2. Selection of Current Working Mode
Plan 1: Current Connection Method
In continuous operation, when the current arrives in the next cycle, the current in the inductor has not yet decreased to zero, and the current in the capacitor can be replenished in time, resulting in a smaller peak output current and a smaller output ripple voltage.
Plan Two: Discontinuous Current Mode
In intermittent operation, when the inductor's energy is exhausted before the next cycle begins, the capacitor's energy cannot be replenished in time. This results in a very high peak current for the diode, placing extremely high demands on both the switching transistor and the diode. The diode's losses are also very high. Furthermore, because the current is discontinuous, the output current has a significant AC component, increasing losses in the output capacitor. For the same power output, the peak current in intermittent operation is much higher, and the output DC voltage ripple also increases, leading to greater losses.
Based on the above analysis, this plan adopts Plan 1.
3. Selection of plans to improve power
The main factors affecting power consumption include the power consumption of the microcontroller and peripheral circuits, the power supply circuitry of the microcontroller and peripheral circuits, and the power of the DC-DC converter. This design uses the ultra-low power microcontroller MSP430F169, a high-efficiency chip to power the peripheral circuits, and employs low-loss components and excellent control strategies.
II. Advantages and Disadvantages of Switching Power Supplies
1. Strengths:
Compared with series-regulated power supplies, switching power supplies are widely used because they offer many advantages, such as high efficiency and energy saving; strong adaptability to changes in mains power; wide adjustable output voltage range; the ability to easily obtain multiple power supplies with different voltage levels from a single switching transistor; and small size and light weight.
(1) Low power consumption and high power
(2) Small size and light weight
(3) Wide voltage stabilization range
(4) The power of filtering has been greatly improved, which has greatly reduced the capacitance and size of the filter capacitor.
(5) Flexible and diverse circuit configurations
2. Defects:
A drawback of switching power supplies is the presence of significant switching interference. In a switching power supply, the power regulating transistor operates under conditions where the AC voltage and current it generates cause spikes and oscillations through other components in the circuit. If these interferences are not suppressed, eliminated, or shielded, they will severely affect the normal operation of the entire unit. Furthermore, because the oscillator in a switching power supply lacks the isolation of a power frequency transformer, these interferences can be introduced into the power grid, causing severe interference to nearby electronic instruments, equipment, and household appliances.
