Is there voltage between the positive pole and the neutral line of the 24V switching power supply?
Whether it is a switching power supply or a linear power supply, the low-voltage DC part is generally completely isolated from the AC high-voltage input part, so there is no voltage between the positive pole and the neutral line (N) of a 24V switching power supply!
The design concept of a linear power supply is to first convert high voltage AC into low voltage AC through a power frequency transformer, such as a 220VAC/24VAC transformer, which first transforms 220V high voltage AC into 24V low voltage AC. As the transformer is a coupled transformer, the high voltage side and low voltage side are completely isolated. Then, through rectification, filtering, and voltage stabilization, low-voltage DC power is obtained. It can be seen that the negative pole of low-voltage DC is only grounded with the low-voltage AC on the secondary side of the transformer, and is completely isolated from the live and neutral wires of the 220V input terminal.
The design concept of a switching power supply is to first rectify 220V AC power into a high-voltage DC voltage of around 300V through a rectifier bridge (it can be seen that the high-voltage part of 300V is not isolated from 220V AC power), and then convert the high-voltage DC power into a constantly changing current signal through pulse width modulation technology (PWM) or pulse frequency modulation technology (PFM), and output low-voltage AC power through high-frequency transformer coupling, and then rectify and filter to obtain low-voltage DC voltage. From this, it can be seen that the high-frequency transformer completely isolates the high voltage part from the low voltage part. If there is a feedback circuit, it is isolated through an optocoupler, as shown in the circuit diagram of the 24V switch power supply. The high-frequency transformer and optocoupler completely isolate the left high voltage part from the right low voltage part, so neither the positive nor negative pole of 24V can form a circuit with the live or neutral wire of 220V AC power.
