Abstract: The paper mainly analyzes the problems of the conventional stabilized power supply, with increasing defects in various tests. Such problems can be reduced and even solved by the ITECH IT6722 (A) programmable DC power supply with the novel circuit design.

I. DC Stabilized Power Supply

The DC stabilized power supply is an electronic device to supply stable DC power to the load. Various stabilized power supplies are needed in research development in the automobile, industry, medicine, military and other fields. With test types increasing, the conventional stabilized power supply cannot meet the needs of testers.

II. Defects of Conventional DC Stabilized Power Supply

The circuit design of the conventional general stabilized power supply is simple to reduce the costs, and the output is unstable as a result of a series of problems.

The first problem is power grid pollution. The switching power supply maintains the stable output voltage by controlling the ON/OFF time ratio of the switch tube. It works in the power tube conduction and cutoff zone, where high-frequency switching will cause high-order harmonic current, and conduction interference and radiation interference will be generated along the power transmission line of the power grid, thereby causing pollution of the power supply system and affecting normal operation of other devices.

The second problem is the limit effect of the auxiliary power supply. The switching power supply generally consists of the main power circuit, auxiliary power supply and control circuit. The non-independent design, using the independent winding separated from the transformer of the power circuit as the auxiliary power supply to energize the chip of the control circuit, is applied in most of general switching power supplies to save costs. However, the working states of the auxiliary power supply and main transformer are constrained by each other. If the auxiliary power supply fails to supply power to the control circuit, the main transformer will fail to work, and the auxiliary circuit will be cut off. Thus the output voltage of the auxiliary power supply will decrease or increase when the output of the power supply is too low or high. The unstable power supply voltage will result in unstable output of equipment.

The third problem is large ripple. The output of the switching power supply is not purely DC voltage, but contains AC components caused by ripple and noise which are related to frequent ON/OFF actions of the switching power supply. Therefore, the peak value of the ripple is generally measured within 20MHZ and the effective value within 1MHZ. For the general switching power supply, the peak value of 400W ripples is up to 200mVpp. Excessive ripples will result in interference to external equipment; therefore, the general switching power supply is not applied to high-end fields such as communication.

The fourth problem is the wide range design. The switching power supply with PWM pulse width modulation is not generally used in the wide range design. If any, the price is relatively high, and the performance and budget cannot be balanced.

III. ITECH IT6722 (A) Programmable DC Power Supply

ITECH Electronics launched the IT6722 (A) programmable DC power supply of 80V/20A/400W. In addition to the previous features such as small size, built-in RS232, USB and GPIB (IT6722) interfaces and programming function, the wider novel circuit design is used, which reduces and even solves some problems of conventional stabilized power supplies.

To solve the problem of power grid pollution caused by the conventional stabilized power supply, the 220V AC input end of the IT6722 (A) programmable DC power supply is provided with the additional APFC circuit, so that the input current waveform can completely match the voltage waveform to reduce the harmonic distortion of input current and reduce the power grid pollution. Moreover, the corrective part of additional active power factor can help to achieve higher working efficiency in the subsequent circuit. The overall efficiency is up to 85%.

Meanwhile, the independent auxiliary power supply design is used in IT6722 (A), so that the stable voltage can be supplied to the chip of the control circuit while the main transformer is not working, thereby ensuring the stable output of the power supply. Due to the delicate circuit structure design, the size of IT6722A is not enlarged in spite of use of the auxiliary power supply, which is a perfect solution to the technical problem of incompatibility between the size and performance.

The current ripple of the IT6722 (A) programmable DC power supply is only 50mVp due to the reasonable layout, wiring and grounding, and basically close to the indicator of the linear power supply. Therefore, the problem of large ripple of the conventional stabilized power supply is solved. With the wide-range circuit design, the maximum voltage of the IT6722 (A) programmable DC power supply is 80V and the maximum current is 20A under the power 400W. One IT6722 (A) programmable DC power supply is equivalent to the combination of multiple single-model power supplies, such as 20V/20A, 40V/10A and 50V/8A, thus, the costs are greatly reduced. The price of the IT6722 (A) programmable DC power supply is also a wide-range switching power supply solution with the performance and price balanced.

Conclusion:

In sum, with the novel circuit design, the IT6722 (A) programmable DC power supply has the perfect integration of a series of advantages such as small ripple, good isolation performance and wide-range output, in addition to small size and high efficiency. Therefore, the perfect and novel experience can be provided to medium/high-end users of small power.