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.
Switching power supply is the essence of an oscillation circuit, the conversion of electrical energy method is used not only in the power circuit, circuit in other applications are very broad, such as liquid crystal display backlight circuit, the fluorescent lamp. Switching power supply with a transformer with high rate, good stability, small size and other advantages compared. The disadvantage is that the power is relatively small, and the circuit to generate high frequency interference, transformer feedback oscillator circuit, can be bred occurred discipline of pulse current or voltage of the circuit called oscillation circuit, transformer feedback oscillator circuit is the circuitry that satisfied the conditions.
Switching power supply is divided into two forms, which are isolated and non isolated. According to the layout of the distribution of power distribution differences, can be divided into: positive and anti shock type two major categories. Flyback type means that the side of the original side of the transformer is stopped and the transformer can be stored. At the end of the primary side, secondary side conduction, energy is released to the load state of affairs, usual groovy flyback power supply tube, double tube not common. Is the original edge of the transformer in the original side of the side of the original side of the side of the side of the output voltage output to the load, energy through the transformer directly informed. According to the specification can be divided into general forward, including single forward, two transistorforward. Half bridge, bridge circuit belongs to forward circuit.
The forward and flyback circuits have their own characteristics. In the course of the planned circuit, it can be used to reach the optimal price ratio. As often as in small power can choose to use the anti shock. Slightly larger single acceptance is excitation circuit, medium power can accept double positive excitation circuit and half bridge circuit, low voltage acceptance push-pull circuit, and half bridge state of affairs similar. High power output, as usually adopt bridge circuit, low voltage may accept a push-pull circuit.
Flyback power supply because of its simple structure, saves a transformer and large volume of the inductor, and in the middle and small power supply get extensive application. Flyback power supply transformer leakage inductance is a very crucial parameters, due to the energy storage, the necessary transformer of flyback switching power supply, to get full use of the transformer core, usually to open air gap in the magnetic circuit, the target is transformation hysteresis curve of the core of the slope, the transformer to probably suffer large pulse current strike without as core into saturation nonlinear state, air gap in the magnetic circuit in high magnetoresistance state and in the magnetic circuit bred leakage magnetic far outweigh completely closed magnetic circuit.
As far as possible short pulse voltage connection, the input switch to the transformer line output transformer, rectifier to the adjacent line. The pulse current loop is small as small as the input filter capacitor is positive to the transformer to the switch tube to return the capacitor negative. Output unit of transformer output to rectifying tube to output inductance to the output capacitor return circuit transformer x capacitors to although even close to the switch power supply input end, the input line should stop and other circuit parallel, should be avoided. The Y capacitor should be arranged in the chassis grounding terminal or FG connection terminal. A total of inductance to be connected with the transformer to prevent magnetic coupling.
Output capacitor as usually accept two a near rectifier tube and the other should be close to the output terminal, can affect power output ripple index, two small capacitance and results should be better than a large capacity capacitor. Heating device to electrolytic capacitor and maintain a certain interval, in order to extend the service life of the whole machine, electrolytic capacitor is switch power life of the bottle neck, such as transformers, power tube, high power resistance and electrolytic link interval, between electrolysis is also required to set aside space for heat dissipation, conditional capacity allowed to install a fan or increase the exhaust hole.
Switching power supply electromagnetic interference filter is a passive network, which has two way suppression performance. Insert it in the AC grid
Between the power supply, the equivalent of the EMI noise between the two plus a blocking barrier, such a simple no
The source filter has been used to suppress the noise, so that it is widely used in various electronic devices.
Due to high power consumption, low power consumption, small size, light weight, wide voltage range, flexible circuit and other characteristics, wide
Widely used in computer, communications and other electronic equipment. But with the switching power supply of small, switch to high frequency
By this high frequency, the fundamental wave itself is a source of interference.
By improving the components to achieve high frequency of the same,
Also because of the radiation interference wave and lead to a super standard value of the
Signal. These signals form an electromagnetic interference
, the object is the radio communication. In order to make the radio wave
Electromagnetic interference, it is to take measures to limit the electromagnetic interference, so that the electromagnetic compatibility
Or specification, which has become an increasingly concerned problem for electronic product designers.
Characteristics of electromagnetic interference (EMI) for switching power supply
Switching frequency of the power semiconductor device in the switching power converter is usually high,
Power switch device is inevitable to produce powerful electromagnetic interference in the process of high frequency and high frequency. Compared with the digital circuit, switching power supply EMI presents a distinct characteristic:
A. switching power supply EMI interference source location is clear, mainly in the power switch device,
Diodes, and the heat sink and high frequency transformer connected to it.
B. as working in the switch state of energy conversion device, switching power supply voltage and current change rate is very high, its EMI noise signal has both a wide frequency range, and have a certain strength.
C. printed circuit board wiring is the main reason for the electromagnetic interference. These disturbances are caused by the interference of conduction and radiation to other electronic devices.
Any power line interference signal, which can be expressed by differential mode and common mode signal. In general, differential mode interference
Small amplitude, low frequency, caused by small interference; common mode interference amplitude is large, high frequency, but also can be generated through the lead
Radiation, caused by large interference. Therefore, to weaken the conduction interference, the EMI signal control in the
The most effective method is to install an electromagnetic interference filter in the input and output circuit of the switching power supply input and output circuit of the EMC standard.
A power inverter is a device that converts DC power (also known as direct current), to standard AC power (alternating current). Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone.
What is the purpose of an inverter?
An inverter converts direct voltage from batteries or direct bus to alternating voltage, normally 220 Vca with output stabilization and in the form of a 50 Hz sinusoidal wave. This wave is often cleaner that the one obtained from the electrical network. The sinusoidal inverters are used to supply all kinds of load, whereas the “square”, “pseudo sinusoidal” or “modified sinusoidal” wave shape has certain limitations given its effect on inductive or capacitative loads. It is also important to mention that the noise or interference that can cause equipment such as precision instrumentation, telecommunication, etc. to function incorrectly. The main advantage is the price as it is often less than half what a sinusoidal device would cost for similar power.
To measure a large DC current, such as tens of AMPS, and even greater, hundreds of AMPS, there is no such a large range of current meter for the measurement of current, how to do? It is necessary to use shunt. Is a short piece of conductor, can be all kinds of metal or alloy, connecting terminal; the DC resistance is strictly a good tune; connected in series in the DC circuit, the DC current excessive flow device, both ends of the shunt produced DC millivolt voltage signals, and then in the measurement of the shunt at both ends of the table pointer swing, the reading is the current in a DC circuit values. The so-called triage, a small current to drive indicator, in the small current (MA) and loop current (1a dozens of a) the proportion of smaller, the current table indicating readings of linear better and more accurate. This is the electric circuit of the common products, lightning protection and diversion measures.
The current meter has a variety of different specifications, but the actual meter is standard millivolt meter. For example, a full scale voltage meter for 75mv. So with this voltage meter measurement such as 20A current, you need to give it a 75mV voltage drop of the shunt resistance in the current flowing through the 20A when, also known as 75mV shunt.
Shunt is a to the resistance of the current through the general common 15a and 20a and 35A current meter are the need for a shunt, shunt impedance = header logo full voltage / header full scale current. Such as 20a of the ammeter shunt resistance =75mv/20A=0.00375 Omega, constant impedance according to Ohm’s law U=IR, voltage and current into a proportional, current is linear voltage is linear, so we can use a full 75mV to the voltage of the table shows the current. Therefore, the use of the current meter is actually a voltage meter.