Power supplies provide power required by electronic devices. Depending on the circuit structure, there are linear power supplies and switching power supplies. Power supplies are extensively applied to various fields such as mobile communication devices, personal digital assistants, computer and peripheral equipment, servers, and network equipment. Thereby, power supplies power supplier play a crucial role in electronic devices.
The protection mechanism in the control circuit of a power supply provides very important functions, such as over-voltage, over-current, over-power, and low-voltage protection, for normal operations and preventing damages. Once the situation of overload, short circuit, or low voltage occurs, the power supply with complete protection mechanism will stop supplying the output power for avoiding damages on internal devices or relevant equipment. In other words, the protection mechanism is used for limiting the output power of the power supply. In general, there is a protection level inside the power supply. When the voltage or current exceeds the protection level, it is regarded that the situation of over voltage, over current, or over power occurs. At this time, the power supply is shut off for protecting the power supply and the other relevant equipment.
Nonetheless, the protection levels among different batches of power supplies differ due to the accumulation of production errors in circuit devices such as resistors, inductors, or capacitors. As a result, there are differences in the output power among different batches of power supplies. For solving this problem, generally, a variable resistor is further disposed in the power supply. By adjusting the resistance of the variable resistor manually, the protection level is adjusted. Consequently, the labor cost is increased. Besides, after long-term usage, the variable resistor will chap or fall off and varying the protection level, which, in turn, leads to inaccuracy in the limiting level of the output power. At worst, the power supply might be even damaged.
FIG. 1 shows a production flowchart of the power supply according to the prior art. Because a variable resistor is required in the power supply according to the prior art for adjusting the protection level, in the production process, the step S1 is first performed for disposing the variable resistor in the circuit by manual insertion. Afterwards, the step S2 is performed for soldering the variable resistor on the circuit by using a tin furnace. Then, the step S3 is performed for initializing the power supply, which includes testing and tuning on the stability of the power supply and adjustment for over voltage and over current. The adjustment described above is to adjust the resistance of the variable resistor manually. Next, the steps S4 is executed for performing burn-in. afterwards, the step S5 is performed for the hi-pot test. Then, the step S6 is performed for the protection test. Next, the step S7 is performed for the function test. Finally, the step S8 is performed for the power test.
It is known form the above that in the power supply according to the prior art, a variable resistor is required. By adjusting the resistance of the variable resistor, the protection level is adjusted, which, in turn, adjusts the output power of the power supply. This method is extremely labor intensive and thus leading to increase in cost. In addition, because the variable resistor in the circuit is vulnerable to damages or aging due to external factors such as humidity and temperature, the resistance may vary and thereby altering the protection level. Consequently, errors in the protection level from the initial setup may occur, and hence influencing the output power of the power supply.
Accordingly, the present invention provides an automatic adjusting device for solving the problems described above. According to the present invention, the protection level can be adjusted automatically and thus fixing the level of the output power to the expected limits without using the variable resistor and adjusting the protection level manually. Thereby, the problems in the prior art as described above can be solved.