Linear power supply is a power conversion device that reduces the voltage amplitude by passing the AC through the transformer, and then obtains the pulsed DC after being rectified by the internal rectifier circuit, and then obtains the DC voltage with small ripple voltage through filtering.
Working principle of linear power supply:
The linear power supply is actually a high-power triode connected in series at the output end of the transformer. As long as the control circuit outputs a small current to the base of the triode, it can control the output high current of the triode, so that the power supply system can stabilize the voltage again on the basis of the transformer. Therefore, the voltage stabilizing performance of this linear regulated power supply is 1-3 orders of magnitude better than that of switching power supply or transformer. However, the power triode (also known as the regulator) generally occupies a voltage of 10 volts. For every output current of 1 ampere, an additional 10 watts of power will be consumed inside the power supply. For example, the loss of 500V 5A power supply on the power tube is 50 watts, accounting for 2% of the total output power. Therefore, the efficiency of linear power supply is slightly lower than that of voltage converter.
Advantages of linear power supply: stable performance, no interference such as high-frequency ripple. Disadvantages of linear power supply: heating and low energy utilization. There is no super power supply to choose from.
The voltage feedback circuit of linear power supply works in linear (amplified) state, and the voltage of switching power supply is regulated by voltage. The tube works in saturation and cut-off zone, that is, in switching state. The linear power supply samples the output voltage and then sends it to the comparison voltage amplifier with the reference voltage. The output of the voltage amplifier is used as the input of the voltage regulator to control the regulator to change its junction voltage with the change of input, so as to adjust its output voltage. However, the switching power supply changes the output voltage by changing the on and off time of the regulator, that is, changing the duty cycle. From its main characteristics: Although the linear power supply technology is mature, its production cost is not low, and it has lost too much advantage compared with the switching power supply in terms of price. However, the linear power supply can achieve high stability, small ripple, and its own interference and noise ratio are small. However, because it works at power frequency (50Hz), the transformer has large volume, low efficiency, large overall volume and appears bulky And the input voltage range is required to be high; The switching power supply is in the high-frequency state of operation. The volume of the transformer is relatively small and relatively light, but the output ripple is larger than that of the linear power supply. However, due to its simple structure, low cost and high efficiency (the efficiency of the switching power supply on the market can also reach more than 90%), it has replaced the linear power supply in many occasions, which is the development trend of the power supply in the future.
