What does +24v and -24v mean on the output of a switching power supply?
This labelling indicates that this is two 24V power supplies connected in series with zero volts at the connection, which is also the ground terminal in the circuit. This power mode is based on circuit requirements
This power mode is based on the circuit requirements. For example, some operational amplifiers and OCL power amplifiers operate on positive and negative power supplies.
Electricity is also sometimes artificially determined to be positive or negative, just like temperature. For example, the Celsius -24 ° C and 24 ° C above zero, is to use "Celsius" the old man established the Celsius temperature scale
to divide. In fact, there is a temperature difference of 48°C between these two temperatures. According to the standard of Mr Kelvin, it becomes 249.15K and 297.15K, but they describe the same two temperatures.
But they describe the same two temperatures, and the temperature difference is 48°C, so of course they can be called 48K.
We put two sets of 24V batteries in series according to Figure 1, is ± 24V power supply, and between point A and point C is 48V, just in line with the principle of series voltage addition. It is also very similar to the way the Celsius temperature is labelled.
The formula to get ± 24V, here between the AC is also 48V. finished ± 24V switching power supply is also the same!
How to change the output voltage of the switching power supply?
Switching power supply output voltage is high or low, the main PWN chip to adjust the duty cycle, that is, to change the length of the switching tube conduction time, switching tube conduction time is long, then the transformer stores more energy, the secondary induced voltage is high, switching tube conduction time is short relative to the secondary output voltage is low. Under normal circumstances, the output voltage of the power supply will be divided by several resistors in series to the ground, resulting in a reference voltage feedback to the PWM chip, if the output voltage is low, then the reference voltage obtained from the series voltage divider
If the output voltage is low, then the series voltage divider to get the reference voltage is low, feedback to the chip with the reference voltage to compare the amplification, it is open to adjust the duty cycle to make the voltage higher, on the contrary, the output voltage series voltage divider to get the voltage is high, will reduce the duty cycle to make the output voltage lower. So we want to change the output voltage, as long as we find the voltage divider resistor to change its resistance value can be, such as If we change the voltage divider resistor to a bigger one, then the voltage of series voltage divider will be low, and the feedback chip will think that the output voltage is low, and it will increase the duty cycle to improve the output voltage. On the contrary, if the resistor is small, the feedback chip will think that the output voltage is high and will reduce the duty cycle to make the output voltage lower.
