What is the difference between linear DC power supply and switching power supply?
Regarding the circuit structure, whether it is a linear power supply or a switching power supply depends on the specific situation and should be adopted reasonably. These two circuits are widely used at home and abroad, and each has its own characteristics. Linear power supply is widely used for its high precision and superior performance. Switching power supply has been widely used in many situations where the output voltage and current are relatively stable, because it saves the bulky power frequency transformer and reduces its volume and weight to varying degrees.
linear power supply
The main circuit of linear power supply is as follows:
That is to say, only a part of the ~220V commercial power is added to the primary of the main transformer after being controlled by SCR. When the output voltage Uo is higher, the conduction angle of the thyristor is larger, and most of the mains voltage is "let go" by the thyristor (as shown in the above figure), so the voltage applied to the primary of the transformer, that is, Ui, is higher, which of course leads to higher output voltage after rectification and filtering.
However, when the output voltage Uo is very low, the conduction angle of the thyristor is very small, and most of the mains voltage is "blocked" by the thyristor (as shown in the following figure), so only a very low voltage is added to the primary of the transformer, that is, the Ui is very low, which is of course very low after rectification and filtering.
At present, all kinds of PWM integrated chips used to make switching power supply are mainly designed from the perspective of small output voltage variation range and relatively stable output current.
But the so-called PWM chip is a kind of pulse width modulator. When the output voltage is high and the output current is large, the switching tube inside the power supply has a long on time and a short off time:
If the output voltage and current continue to drop, it is required that the control pulse continue to narrow, but the PWM circuit can no longer meet it. At this time, the circuit becomes intermittent, as follows:
Pulses are intermittent, intermittent, noise will be emitted in the power supply, ripple will become larger, and electrical performance will deteriorate. The so-called "low-end instability" has actually become a nonconforming product. In order to solve this problem, our company adopts new technical measures to solve it better (not detailed).
Comparison between linear power supply and switching power supply
1. Linear power supply has good accuracy (1-3 orders of magnitude better than switching power supply), small ripple, good adjustment rate and small external interference, and is suitable for many occasions.
2. The power device of linear power supply works in linear state, so the loss is higher than that of switching power supply, and the efficiency of switching power supply is better.
3. The size of switching power supply is smaller than that of linear power supply, but switching power supply has the problems of power grid pollution and radiation interference.
4. Switching power supply is not suitable for continuous zero-voltage start-up when outputting high voltage and high current.
Adjust the occasion, but it is suitable for fixed output or relatively fixed output where there is no great requirement for radiation interference.
5. The linear power supply is relatively easy to maintain. However, switching power supply is difficult to maintain because of its dense components. In addition, because the circuit is completely different from the linear power supply, the technical quality of the maintenance personnel is high, and the working state of each point of the circuit can only be observed with an oscilloscope.
