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Jan 23 2018

The Working Principle of High-Power Adjustable Switching Power Supply

Warm hints: The word in this article is about 3500 and reading time is about 18 minutes.

Summary

This paper presents a new design of high-power adjustable switching power supply. Using Buck-type switching power supply topology, with a single PWM output, MC33060 as a control IC, and dual output IR2110 driver chip, We can design a high-voltage high-power switching power supply as an effective solution to adjustable high-voltage Switching power supply circuit. Which can solve the problem effectively that in the non-isolated topology, the common switching power supply can not reach high limits, and attached with over-current protection usage. In this paper, based on the application of MC33060, I present the design method of adjustable switching power supply, then the composition of the system and the function of each part are explained in detail. Finally, the characteristics of the system are summarized.

Article coreThe Working Principle of High-Power Adjustable Switching Power SupplyCategoryPower
English nameHigh-Power Adjustable Switching Power Supply

Feature

High power,adjustable and etc.



Catalogs

Catalogs
I.Swithching Power Supply Introduction2.2 DC / DC power supply topology3.3 Reverse delay drive circuit
1.1 High-power power supply characteristicsb2.3 Typical circuit and parameter design3.4 Main circuit and output sampling
1.2 DC power supply characteristics of indicatorsIII.The System Design3.5 Over-current protection circuit
II.Typical Switching Power Supply Design3.1 Rectifier filter circuitIV.Conclusion
2.1 Control IC3.2 Control IC and input circuit



Introduction

I.Swithching Power Supply Introduction

As an alternative to linear regulated power supplies, switching power supplies have become increasingly sophisticated in use and implementation. The integrated technology has driven electronic devices to be smaller and more intelligent. the new electronic devices require switching power supply with smaller size and lower noise interference in order to achieve integration and integration. For small and medium-power switching power supply is monolithic integration, but in the field of high-power applications, because of its power loss is too large, it is difficult to make monolithic integration, had to be based on its topology to ensure that the power of the various parameters Try to reduce the system size.

Here is some information about high-power switching power supply’s technical indicators. High-power switching power supply is mainly used in high-frequency power system switching power supply, the technical indicators must be very high and accurate.

Determine the technical indicators are as follows, here attached an example model of High-power adjustable switching power supply technical characteristics diagram.

  • 1. Input voltage: 380_ + 20%;

  • 2. Grid frequency: 50Hz_ + 10%;

  • 3 power factor: 0.93 above;

  • 4. Input over-voltage alarm: 437V_ + 5V;

  • 5. Enter the brown-out alarm: 320V_ + 5V;

  •  6. Output nominal voltage: 220V;

  • 7. Output voltage range: 176-286V;

  • 8. Output ripple voltage: 10mV;

  • 9. Output rated current: 5A;

  • 10. Output over-voltage protection: 325V + _5V;

  • 11. Output under-voltage protection: 195V + _5V;

Model


ANSXYD(X-voltage Y-current)

Input

voltage

Single-phase:AC220V±15% or AC110V±15%

Three-phase:AC380V±10%(more than 8KW)

frequency

AC380V±10%(8KW以上)

voltage

0-1000V

Output

current

0-100000A

power

Voltage value × current value

Diapaly


LED digital tube

Source effect

voltage

≤0.2% effective value

current

≤0.2% effective value

Temperature drift

voltage

≤ 0.03% rms / ℃

current

≤ 0.03% rms / ℃

Time drift

voltage

≤ 0.5% effective value

current

≤ 0.5% effective value

Ripple


≤0.3% 10mV(rms)

Noise


≤65db

Efficiency


≥0.85

Protection ability


Input over/under voltage, output voltage limit, current limit, over current, over voltage, over temperature and so on

Communication Interface


4-20mA, 0-10V analog RS-232 / RS485 communication interface

Cooling method


Smart air / forced air cooling

Temperature


﹣10℃~40℃

Humidity


10%~90% RH

1.1 High-power power supply characteristics

Regulated power supply technical indicators can be divided into two categories: one is the characteristic indicators, such as output voltage, output current and voltage regulation range; the other is the quality indicators, reflecting the pros and cons of a regulated power supply, including stability, Equivalent internal resistance (output resistance), ripple voltage and temperature coefficient.

1.2 DC power supply characteristics of indicators

  • (1) the maximum output current. It depends on the main regulation of the maximum allowable working current and the transformer capacity and the maximum diode rectifier current.

  • (2) Output voltage and voltage adjustment range. This can be determined according to the requirements of the user. For a device that needs a constant power supply, the regulation range of the regulated power supply is preferably smaller. And once the voltage value is adjusted, it’s better not to be changed any more. For the djustable output voltage power supply, the output ranges from the most of the zero-volt adjustment, usually requiring a wider range of voltage regulator, and continuously adjustable.

  • (3) protection features. In the DC power supply, when the load current overload or short circuit, the regulator will be damaged. Therefore, fast response overcurrent protection circuits must be used. In addition, when the regulator current fails, the output will appear the phenomenon of voltage is too high, which will be harmful to the load. Therefore, it also requires over-voltage protection circuit.

  • (4) Efficiency. Regulated power supply is a transducer, therefore, there are also energy conversion efficiency issues. Improve efficiency is mainly to reduce the power consumption adjustment tube.

Here is a specific explanation about adjustable switching power supply:

This is a tutorial on feedback resistors in DC-DC converters and how to build a high current adjustable power supply using an LM2678

II.Typical Switching Power Supply Design

The switching power supply generally consists of Pulse Width Modulation (PWM) control IC (Integrated Circuit) and power devices (power MOSFET or IGBT)。 It meets three conditions: the switch (the device works in the switch non-linear state), the high frequency (The device operates at high frequency non-close to the upper frequency of the low frequency) and DC (power output is the DC instead of AC).

2.1 Control IC

Take MC33060 as an example to introduce control IC.

The MC33060 is a high performance, voltage-driven pulse-width modulator manufactured by ON Semiconductor and operates from -40 ° C to 85 ° C with a single-ended fixed-frequency output. Its internal structure shown in Figure 1 [1], the main features are as follows:

  • 1) Integrated pulse width modulation circuit

  • 2) Built-in linear sawtooth oscillator, the external components only one resistor a capacitor;

  • 3) Built-in error amplifier;

  • 4) Built-in 5V reference voltage, 1.5% accuracy;

  • 5) adjustable dead zone control;

  • 6) Built-in transistor provides 200mA drive capability;

  • 7) undervoltage lockout protection

MC33060 internal structure

Figure 1 MC33060 internal structure

Its operating principle is described briefly: MC33060 is a fixed frequency pulse width modulation circuit, built-in linear sawtooth oscillator.Tthe oscillation frequency can be adjusted by an external resisto r and a capacitor, the oscillation frequency as (2-1) type:

oscillation frequency

The width of the output pulse is achieved by comparing the positive-polarity sawtooth voltage on capacitor CT with the other two control signals. The output of the power transistor Q1 is controlled by a NOR gate, that is when the sawtooth voltage is greater than the control signal.

When the control signal increases, the width of the output pulse will be reduced, the specific timing see the following figure

MC33060 timing diagram

Figure 2 MC33060 timing diagram

Control signals inputs from the outside of the integrated circuit, along the way to the dead time comparator, then to the error amplifier input. The dead-time comparator has an input offset voltage of 120mV which limits the minimum output dead time to approximately 4% of the sawtooth period, ie, the maximum output-driven duty cycle is 96%. When the dead-time control input is terminated The fixed voltage (in the range of 0-3.3V) can generate additional dead time on the output pulse. Pulse Width Modulation The comparator provides a means for the error amplifier to regulate the output pulse width: when the feedback voltage changes from 0.5V to 3.5V, the pulse width of the output drops from zero to the maximum on percentage determined by the dead band. The two error amplifiers have a common-mode input range from -0.3V to (Vcc-2.0), as perceived by the power supply's output voltage and current. The output of the error amplifier, which is often high, is OR'ed with the inverting input of the pulse width modulator. It is this type of circuit configuration that allows the amplifier to dominate the control loop with minimal output.

2.2 DC / DC power supply topology

DC / DC power topologies are generally divided into three categories: buck, boost and buck-boost. Here to step-down topology, simplified renderings as shown in Figure 3 below. Output and input with the same polarity, the input current ripple, the output current ripple small, simple structure.

Bulk step-down chopper circuit

Figure 3 Bulk step-down chopper circuit

In the switch turn-on time, the input power supply to the load and inductor; switch off, inductor energy stored in the freewheeling circuit through the diode to ensure continuous output. The load voltage satisfies the following relation (2-2):

load voltage satisfies the following relation

2.3 Typical circuit and parameter design

Typical circuit as shown in Figure 4

MC33060 step-down chopper circuit

Figure 4 MC33060 step-down chopper circuit

MC33060 as the main control chip switch on and off, from the internal structure of the function we can see that within the MC33060 has a +5 V reference voltage is usually used as two inverting comparator reference voltage. The design of comparator of pin 1 and pin 2 is used as feedback of the output voltage, the comparator of 13 feet and 14 feet is used for detecting whether the electric current of the switch tube is overcurrent. 2 feet in the circuit is connected to the reference voltage through an anti-phase circuit. And step-down output feedback flows through a phase connected to the MC33060 1 foot. When the circuit is in working condition, 1 foot and 2 feet voltage will be compared with each other, according to the difference between the two to adjust the output waveform pulse width, to achieve the purpose of control and stable output.

Overcurrent protection circuit 0.1 ohm rated power of 1W power resistor as a sampling resistor, the current flow point, the sampling resistor voltage of 0.1V.14 feet as a sampling point, so the 13-pin reference voltage by the Vref points Pressure set to 0.15V, compared to 0.1V leave some room. When the sampling voltage is higher than the set value, MC33060 will automatically protect and turn off the PWM output. The protection point is also related to the control signal of the 3-pin. According to the functional analysis of this pin, the integration feedback circuit is selected so that the voltage of the Comparator pin is always within the normal range (0.5V-3.5V) when the buck circuit is under no- within.

The frequency of the output PWM waveform is determined by the capacitance of pin 5 and the resistance value of pin 6. The step-down circuit adopts the waveform frequency of 25KHz, selects the 1nF capacitor with CT value, and the common resistor with RT of 47K meets the design requirements.

III.The System Design

The design uses a DC (Direct Current) / DC converter circuit buck topology. Input is 220VAC and 0-10V adjustable DC voltage, the output is adjustable 0-180V, the maximum output current up to 8A. The system block diagram shown in Figure 5 below. In the design of high-power switching power supply, in order to prevent the surge current surge at start-up, soft-start circuit is generally used, but this article doesn’t focus on the type.

system block diagram

Figure 5 system block diagram     

3.1 Rectifier filter circuit

Full-bridge rectifier circuit, shown in Figure 6 below. Output current requirements up to 8A. Considering the power loss and a certain margin, we can choose 10A square bridge KBPC3510 and 10A fuse. Rectified voltage rises up to 310V, using two 250V / 100uF capacitor for filtering. In figure below, switch S1 and resistor R1 in parallel act as a "soft-start" part, which will not explained in detail here. a detailed soft-start design can be seen in another article named a variety of soft-start switching power supply design.

rectifier circuit

Figure 6 rectifier circuit

3.2 Control IC and input circuit

MC33060 control circuit and the input regulation circuit are shown in Figure 7-1 and Figure 7-2, the selected MC33060 is used as the control IC, the peripheral device selection will not repeat them here. Refer to the typical circuit design parameter selection section. Comparator 1 is used for voltage sampling, comparator 2 is used for current sampling. Input adjustable voltage followed by the partial pressure into the negative side of the comparator usually used as a reference voltage control power output size.

MC33060 Control circuit

Figure 7-1 MC33060 Control circuit

input adjustment circuit

Figure 7-2 input adjustment circuit

3.3 Reverse delay drive circuit

Inverting delay drive circuit is shown in Figure 8 below. The driver chip in the circuit adopts the IR2110 from International Rectifier (IR) Company of the United States, which includes not only the basic switch unit and drive circuit, but also the protection control function combined with the external circuit. The floating channel design makes it possible to drive the switch in the bus voltage is not higher than 600V. Its internal is equipped with undervoltage protection. Combined with the external circuit, you can easily design over-current, over-voltage protection, so do not need Additional over-voltage, under-voltage, over-current protection circuit simplifies the circuit design.

inverted delay drive circuit

Figure 8 inverted delay drive circuit

The chip is output high-voltage gate driver, with 14-pin dual in-line. The drive signal delay is ns level, and the switching frequency is from tens of hertz to hundreds of kilohertz. The IR2110 has two input signals and two output signals. One of the two output signals has a level shifting function that directly drives the power devices on the high-voltage side. The driver can be run in common with the main circuit, and only need to control the power all the way to overcome the shortcomings that the conventional driver needs multiple isolated power supplies, greatly simplifying the hardware design. IR2110 simple truth map as shown in Figure 9 below.

IR2110 simple truth map

Figure 9 IR2110 simple truth map

IR2110 has two output drivers, the signal is taken from the input signal generator, the generator provides two outputs, the low side of the drive signal directly from the signal generator LO, and the high side of the drive signal HO must be through the level of conversion For high-side output driver. The system driven double need an IR2110 can be.

Due to driving the double tube, and the double tube can not be turned on at the same time, the control IC outputs have only one signal. In the control IC output and drive, an anti-phase delay circuit needs to be added. The PWM output by the control IC is in-phase and in-phase After the device, the resistor R29 and R30 pull-up capacitor C12, C13 were charged delay, making the two PWM symmetrical complementarity and has a certain dead zone, to ensure that the two main switch circuit will not turn on . The waveform of HIN and LIN in the circuit is shown in Figure 10 below.

inverted drive waveform

Figure 10 inverted drive waveform

3.4 Main circuit and output sampling

The main circuit shown in Figure 11, the use of half-bridge switching circuit. 

main circuit

Figure 11 main circuit

According to the rectified voltage and input current parameters, the IRF840 is selected as the high-frequency switch. The maximum withstand voltage VDS is 500V and the maximum withstand current ID is 8A, which meets the design requirements. Freewheeling diodes working in the high-frequency state of the general selects fast recovery diodes. Here I choose HFA25TB60, which can withstand 600V reverse voltage drop, the maximum on-current 25A, and the recovery time is only 35ns. The output part of the two The resistor divides the voltage sampling circuit, as shown in Figure 12 below.

Voltage Sampling Circuit

Figure 12 Voltage Sampling Circuit

3.5 Over-current protection circuit

Overcurrent protection circuit as shown in Figure 13 below.

overcurrent detection circuit

Figure 13 overcurrent detection circuit

In the upper end of the main circuit in series with a 0.33 ohm 10W power resistor as a sampling resistor, when the current is too large, the optocoupler phototransistor conduction, the detection circuit outputs a high level to IR2110 SD terminal, SD is low because the effective , High off point, so the current is too large to protect the circuit. And as mentioned earlier, IR2110 itself has a variety of protection circuits, so the external current and voltage protection circuit can be greatly simplified.



Analysis

IV.Conclusion

This design gives a non-isolated topology design of high-power switching power supply method, the circuit structure is simple. In the main circuit, the half-bridge circuit is used instead of the traditional single-tube switch circuit. When the upper tube is closed, the opening of the lower tube can better ensure the stability of the output freewheeling and ensure the output of the power. The article does not give the calculation method of inductance, because it is not the focus of discussion, according to the circuit output current, voltage and switching tube RDS (MOSFET tube drain and source resistance) and other parameters to calculate the actual should stay Have some margin value. System operation is basically stable, which can be considered for industrial power supply design.



Book Recommendation

  • Switching Power Supply Design and Optimization, Second Edition

Extensively revised throughout, Switching Power Supply Design & Optimization, Second Edition, explains how to design reliable, high-performance switching power supplies for today's cutting-edge electronics. The book covers modern topologies and converters and features new information on designing or selecting bandgap references, transformer design using detailed new design charts for proximity effects, Buck efficiency loss teardown diagrams, active reset techniques, topology morphology, and a meticulous AC-DC front-end design procedure.This updated resource contains design charts and numerical examples for comprehensive feedback loop design, including TL431, plus the world’s first top-down simplified design methodology for wide-input resonant (LLC) converters. A step-by-step comparative design procedure for Forward and Flyback converters is also included in this practical guide.

--Sanjaya Maniktala  (Author)

  • Switching Power Supply Design, 3rd Ed.

Recognized worldwide as the definitive guide to power supply design for over 25 years, Switching Power Supply Design has been updated to cover the latest innovations in technology, materials, and components. This Third Edition presents the basic principles of the most commonly used topologies, providing you with the essential information required to design cutting-edge power supplies. Using a tutorial, how-and-why approach, this expert resource is filled with design examples, equations, and charts. Get Everything You Need to Design a Complete Switching Power Supply: Fundamental Switching Regulators * Push-Pull and Forward Converter Topologies * Half- and Full-Bridge Converter Topologies * Flyback Converter Topologies * Current-Mode and Current-Fed Topologies * Miscellaneous Topologies * Transformer and Magnetics Design * High-Frequency Choke Design * Optimum Drive Conditions for Bipolar Power Transistors, MOSFETs, Power Transistors, and IGBTs * Drive Circuits for Magnetic Amplifiers * Postregulators * Turn-on, Turn-off Switching Losses and Low Loss Snubbers * Feedback-Loop Stabilization * Resonant Converter Waveforms * Power Factor and Power Factor Correction * High-Frequency Power Sources for Fluorescent Lamps, and Low-Input-Voltage Regulators for Laptop Computers and Portable Equipment

--Abraham I. Pressman (Author),‎ Keith Billings (Author),‎ Taylor Morey (Author)

  • Simplified Design of Switching Power Supplies (EDN Series for Design Engineers)

Simplified Design of Switching Power Supplies is an all-inclusive, one-stop guide to switching power-supply design. Step-by-step instructions and diagrams render this book essential for the student and the experimenter, as well as the design professional.Simplified Design of Switching Power Supplies concentrates on the use of IC regulators. All popular forms of switching supplies, including DC-DC converters, inverters, buck, boost, buck-boost, pulse frequency modulation, pulse width modulation, current-mode control and pulse skipping, are described in detail. The design examples may be put to immediate use or may be modified to meet a specific design goal. As an instructional text for those unfamiliar with switching supplies, or as a reference for those in need of a refresher, this unique book is essential for those involved in switching power-supply design.

  1. Describes the operation of each circuit in detail

  2. Examines a wide selection of external components that modify the IC package characteristics

  3. Provides hands-on, essential information for designing a switching power supply

--John Lenk (Author)



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