The US plug 12W AC DC adapter is a common item in daily life, familiar to everyone. However, when it comes to the US plug 12W AC DC adapter, most people probably still don't have a clear understanding. So today, let's take a look at the advantages and disadvantages of the five classic structures of the US plug 12W AC DC adapter.

1. Single-pole positive-negative type

Single-ended: Drives the pulse transformer in a single direction through a single switching device.

Forward mode: The phase relationship between the primary and secondary sides of the pulse transformer ensures that when the switching transistor is conducting and the primary side of the transformer is being driven, the secondary side of the transformer simultaneously supplies power to the load.

The problem with this circuit is that the switching transistor T operates in both on/off states. The stored magnetic energy will be accumulated in the next cycle until the inductor saturates, causing the switching device to burn out.

2. Single-ended flyback converter

The flyback circuit is the opposite of the forward circuit. The problem of magnetic energy accumulation in the pulse transformer is easier to solve. However, due to the leakage inductance of the transformer, a voltage spike will be formed on the primary side, which may cause the switching device to be broken down. Therefore, a voltage clamping circuit needs to be set up for protection. The circuit composed of D3 and N3.

3. Push-pull type

The characteristic of this circuit structure is: symmetrical structure. The primary side of the pulse transformer consists of two symmetrical coils. The two switching tubes are connected in a symmetrical manner. The current is continuously on and off, and the working process is similar to the Class B push-pull power amplifier in a linear amplification circuit.

Main advantages: High utilization rate of the transformer core (compared with single-ended circuits), high utilization rate of the power supply voltage (compared with the half-bridge circuit to be described later), large output power, both base electrodes of the two tubes are at low levels, and the driving circuit is simple.

Main drawbacks: The utilization rate of the transformer windings is low, and the withstand voltage requirement for the switching tubes is relatively high (at least twice the power supply voltage).

4. Full Bridge Type

The characteristic of this circuit structure is that four identical switching tubes are connected in an electric bridge configuration to drive the primary winding of the pulse transformer.

Main advantages: Compared with the push-pull structure, the primary winding is reduced by half, and the withstand voltage of the switching tubes is halved.

Main drawbacks: A large number of switching tubes are used, and strict parameter consistency is required. The driving circuit is complex, and achieving synchronization is difficult. This circuit structure is typically employed in ultra-high power US plug 12W AC DC adapter circuits with power exceeding 1KW.

5. Half-bridge configuration

Main advantages: It has a certain ability to resist imbalance, and does not have very strict requirements for circuit symmetry; The power range it can adapt to is quite wide, ranging from several watts to kilowatts; The withstand voltage requirement for the switching tubes is relatively low; The circuit cost is lower than that of full-bridge circuits. This type of circuit is often used in various DC converters with non-stabilized output, such as in the driving circuits of electronic fluorescent lamps.

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