1、 Starting circuit loss
The general startup circuit is R+C startup, as shown on the left in Figure 1. The resistance in the startup circuit will have a certain loss, which may not seem significant, but still accounts for a certain proportion during standby. How can we reduce this loss? While ensuring compatibility with product startup and short-circuit capabilities, the larger the value of R, the smaller the loss. Another method is to let R not work after the product is started, and the loss will naturally decrease.
2、 Transformer losses
The losses of a transformer include iron loss and copper loss. The iron loss of a transformer is affected by the operating frequency and inductance value. Low frequency results in less loss, while high inductance results in less loss. Therefore, when designing a transformer, it is important to consider both the operating frequency and inductance value. A suitable value will result in less loss; When in standby mode, the copper loss of the transformer is very small and has little impact on the overall loss. When designing the transformer, choose the appropriate wire diameter and number of turns.
3、 IC loss
ICs all have a working current to enable them to function properly, and this loss is unavoidable. When selecting an IC, try to choose one with a lower working current.
4、 Loss of switch tube
The MOS transistor Q1 at the input end mainly exhibits switching losses during standby, so it is necessary to reduce the losses of the MOS transistor during standby, and the operating frequency of standby needs to be lowered. When selecting chips, choosing chips that operate under light and no-load conditions will cause frequency hopping (i.e. reducing the operating frequency of no-load and light load), and MOS transistors should be selected with low gate loads to reduce losses.
The losses of rectifier D1 include switch losses, reverse recovery losses, and conduction losses. When selecting rectifier tubes, choosing diodes with low conduction voltage drop and short reverse recovery time can reduce losses.
5、 Absorption circuit losses
A small capacitor is usually added between the DS poles of the switch MOS transistor, as shown on the left in Figure 2, to absorb voltage spikes on the transistor. The absorption capacitor C5 on the MOS transistor will consume energy, and the smaller the capacitance value of the absorption capacitor, the smaller the loss, while ensuring sufficient residual stress on the transistor.
The RC absorption circuit on the output rectifier tube is shown in Figure 2. To reduce the loss of RC absorption, if the circuit allows, reduce the capacitance of capacitor C12 and the resistance of resistor R6 to reduce the loss.
6、 False load resistance loss
Most module power products will add a dummy load at the output end to ensure the stability of the module under no-load or light load conditions. This dummy load will cause losses. Under the condition of ensuring stable module performance, the larger the choice of dummy load resistance, the smaller the loss. When the circuit can operate stably without the need for false loads, it is possible to choose not to add false loads, so that the losses caused by false loads do not exist.
