Switching power supply based on its own small size and high conversion efficiency has been widely used in electronic products, especially in the United States TOPSwitch company PI series of high frequency switching power supply integrated chip, the circuit design is more mature, simple and convenient.
But the TOPSwitch series integrated chip of the typical input voltage design for not more than 275v work, in the industrial field, the voltage of the power grid often benefit from electric load changes and changes, especially load larger when the situation is particularly serious, also the field peak interference will superimposed on the input voltage together into the power supply circuit, resulting in the harsh environment of normal power supply power supply chips or other elements of extremely easy to damage. Over wide range of input power supply can be in the range of 80 ~ 400V range, but also for the use of 220V phase voltage or 380V line voltage, or a high-voltage transformer out of the 100V voltage, can be directly used to provide a convenient.
Design of multi channel practical switching power supply based on TOP242N
In this paper, we use TOP242N to design a practical switching power supply, which is 5V / 0.15A, 5V / 0.6A, 15V / 0.1A, and the circuit diagram is shown in Figure 1. The input voltage range is from 80 to 400V, and the total output power is about 6W.
Front end circuit design
When the input voltage is AC400V, the maximum input voltage is about 800V, the highest input voltage reaches about 460V, and the output voltage is 650V. The maximum voltage of Uor is 700V, and the MOS can be used to guarantee the normal work. In order to guarantee the TOP242, the MOS tube is connected with TOP242. This design uses the MOS pipe is IRFBC20 600V, its pressure is IR, the clearance of the guide clearance of dozens of NS, which can greatly reduce the switching losses. The MOS control of the tube is controlled by the TOP242N, which can make the switch tube in the MOS tube and the TOP242N be consistent.
Peripheral control circuit design
The circuit is set to the maximum value of the TOP242N, the TOP242N is set to the full frequency operation mode, the switching frequency is 132kHz, and the S is short.
Regulator feedback circuit design
The feedback loop in the form determined by the accuracy of output voltage, this design uses the “feedback optocoupler plus TL431”, see figure 1. The output voltage can be controlled within 1%, and the feedback voltage is sampled by the 5V output. Voltage feedback signal through the resistance divided voltage divider R10, R11 obtained voltage sampling, and TL431 2.5V reference voltage were comparison and output voltage error, then through the optocoupler change TOP242N control side current LC, then by changing the duty ratio to regulate output voltage to keep the change. Another function is to cool and optocoupler isolation raidi. After the R8 and C4 filter, the peak voltage can be adjusted to keep the bias voltage stable, and the R10 and R11 can be adjusted to change the output voltage.
High frequency transformer design
Should generally be selected to meet the high frequency switch of Mn Zn ferrite core, for winding and core shape can choose EI or EE type, the transformer primary winding and the secondary winding should be phase winding. Because of the large number of interrelated variables, the design of high frequency transformer is complicated, which is designed to reduce the workload of the designer. The design software of the high frequency transformer for TOPSwitch switching power supply is designed. The software is designed to be easy to use.
Secondary output circuit design
The output rectifier filter circuit is composed of a rectifier diode and a filter capacitor. Rectifier diodes can be used to reduce the loss and eliminate the output voltage ripple, but Schottky diode should be coupled with the larger power of the radiator; capacitor should choose the low ESR equivalent series impedance of the capacitor. In order to improve the filtering effect of the output voltage, the voltage noise and voltage spike caused by high frequency switching are filtered out, and the LC filter is usually used in the rectification filter.
Protection circuit design
In order to protect the power supply under the instantaneous high voltage, the input of the power supply has been designed with the additional over-voltage protection measures, see Figure 1, that is, the input terminal and the power of the high power, and the common mode inductance and the negative temperature coefficient of the thermal resistance, can effectively inhibit the power of the voltage surge. In order to prevent the switching period, TOP242N fault leakage to produce a sense of voltage spikes on the TOP242N damage, circuit in design by Zener clamp tube vd5, blocking protection network composed of diode VD6. The network in normal operation, the loss of the VD5 is very small; and in the boot or overload, VD5 will limit the drain voltage.
Power performance test and result analysis
According to the design method, the performance of multi output switching power supply with TOP242N design is tested. The experimental results show that the power supply can work reliably and stably under the condition of 60 ~ 500V, and the power supply is more than 85%, the stability of the ripple voltage and the output voltage is within the specified range. In the EMC test, the 4000V of the fast pulse group 4000V can work normally, and all the performance indexes are satisfied with the test.
As mentioned in this paper, the synchronous switch of a series of field effect tube is added to the front end of the design, so that the working voltage range of the integrated chip TOP242 is greatly expanded, which effectively improves the reliability and convenience of the switching power supply in the industrial field. The design principle of this paper can be used in the TOPSwitch series or other series of power supply integrated chip of the pressure expansion, has a good application effect.
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