Table of Contents
1: What is a linear series regulated power supply?
Answer: Linear regulated power supply means that the adjusting power tube in the regulated power supply circuit works in the linear amplification area; series switching regulated power supply circuit means that its energy storage inductor is connected in series between the input and output voltages.
It consists of transformer, rectifier, filter circuit and linear voltage stabilizing circuit.
2:What is a switching regulated power supply?
Answer: It consists of a full-wave rectifier, switching power tube V, PWM control and driver, freewheeling diode VD, energy storage inductor L, output filter capacitor C and sampling feedback circuit. In fact, the core part of the switching regulated power supply is a tributary transformer.
3: What types of switching regulated power supplies?
1. According to the excitation method: separately excited~ and self-excited~
2. According to the modulation method: pulse width modulation type~, frequency modulation type~ and hybrid type~
3. According to the working mode of switching power tube current, it can be divided into: switching type ~ and resonant type ~
4. According to the type of power switch: transistor type~silicon controlled type~MOSFET type~and IGBT type
5. According to the connection method of the energy storage inductor: series type~ and parallel type~
6. According to the connection mode of the power switch: single-ended forward ~ single-ended flyback ~ push-pull ~ half-bridge ~ full-bridge ~
7. According to the input and output voltages: boost type ~ buck type ~ output polarity reversal type ~
8. According to the working mode: controllable rectifier type ~ chopper type ~ isolation type ~
9. According to circuit structure: component type ~ integrated circuit type ~
4: How does the step-down switching regulated power supply work?
Answer: Add the driving square wave signal to the base of the power development V, so that the power switch will periodically turn on and off according to the frequency of the driving square wave signal. The working process can be based on the conduction of the power switch and the stability of the switch. Explain the process of realizing dynamic balance of piezoelectric power source.
1. During Ton=t1-t0, the power switch is turned on, and the freewheeling diode is cut off due to reverse bias. Although the input voltage is a DC voltage, the current in the inductor cannot change suddenly, and the current in the inductor will rise linearly, and Energy is stored in the energy storage inductor in the form of magnetic energy. At time t1, the current in the energy storage inductor rises to the maximum value.
2. During the period of Toff=t2-t1, the power switch is turned off, but at time t1, since the power tube has just turned off and the current in the energy storage inductor cannot change suddenly, a voltage with opposite polarity to the voltage at both ends of L is generated. Self-induced electromotive force. At this time, the freewheeling diode begins to conduct forward, and the magnetic energy stored in the energy storage inductor will begin to be discharged in the form of electrical energy through the freewheeling diode and the load resistor. The waveform of the discharged current is the current that decreases with time in the sawtooth wave. At time t2, the current in the energy storage inductor reaches the minimum value.
3. Dynamic balance can only be achieved when the current increased by the energy storage inductor in Ton during the turn-on period of the power switch is equal to the decreased current during the turn-off period of the power switch. It can be concluded that U0=Ton/T*Ui
5: Design of step-down switching regulated power supply?
1. Selection of power switch V: When the output power is above tens of kilowatts, choose IGBT; when the output power is between several kilowatts, choose MOSFET; when the output power is below several kilowatts, choose GTR. Once the type of power switch V is selected, the selection of specific device models should follow the following principles: ① The smaller the conduction saturation voltage Uces of the power switch V ② The smaller the reverse leakage current Ico when V is turned off, the better ③ The V The high frequency characteristics should be good, ④V’s switching time should be short, that is, the conversion speed should be fast, ⑤V’s base drive power should be small, ⑥V’s reverse breakdown voltage should satisfy: Uc=2*1.3*Ui=2.26*Ui.
2. Selection of freewheeling diode VD: ① The forward rated current of VD must be equal to or greater than the maximum collector current of the power switch V, that is, it should be greater than the current on the load resistor R1 ② The direction withstand voltage value of VD must be greater than the input voltage Ui value ③ In order to reduce the output ripple voltage caused by switching switching, VD should choose a Schottky diode or a fast recovery diode with very fast reverse recovery speed and conduction speed. ④ In order to improve the conversion efficiency of the whole machine and reduce internal losses, it must be To choose a Schottky diode with a lower voltage on the forward conductor
3. Selection of energy storage inductor L: ① Critical value of L Lc=R1*(1-D)/2F ②L=R1max*(1-D)/1.5F
4. Selection of output filter capacitor C: C=U0*(1-U0/Ui)(8L*F*F*deltaUo)
6: How does the boost switching regulated power supply work?
Answer: When the power switch is on, the input voltage is applied to both ends of the energy storage inductor, and the diode is reversely biased and cut off. The current flowing through the energy storage inductor is an approximately linearly rising sawtooth wave current, and It is stored in the energy storage inductor in the form of magnetic energy. When the power switch is turned off, the polarity of the voltage across the energy storage inductor is opposite. At this time, the diode is forward biased and conducts. The energy stored in the energy storage inductor is transmitted to the load resistor and filter capacitor through the diode. The bleeder current is the linear falling part of the sawtooth current. During the saturated conduction period of the power switch, the current value increased in the energy storage inductor should be equal to the current value decreased in the energy storage inductor during the power switch cut-off period. Only in this way can dynamic balance be achieved, and U0=Ui*D/(1 -D).
7: How does the polarity reversal switching regulated power supply work?
Answer: When the power switch in the polarity reversal type switching regulated power supply circuit is turned on, the diode is turned off due to reverse bias. When the power switch is turned off, the diode is turned on due to competing bias. At this time, the energy storage inductor The stored energy will be transferred to the load through the diode, and the relationship between the output voltage and the input voltage is U0=—Uin*D/(1-D)
8: What is the difference between a boost switching power supply and a polarity reversal switching power supply?
Answer: The boost switching power supply circuit is actually an emitter output parallel switching power supply circuit, while the polarity reversal switching power supply circuit is actually a collector output parallel switching power supply circuit. . From a formal point of view, the only difference between them is that the positions of the power switch and energy storage resistor are exchanged. From the output characteristics, their output voltage polarity is exactly opposite.
9: Common control circuits?
Answer: Circuits such as sampling, comparison, reference source, oscillator, pulse width modulator (PWM) or pulse frequency modulator (PFM).
10: What are the common instability factors at the output end of switching regulated power supply?
Answer: Overcurrent, overvoltage, undervoltage, overheating
11:What is the driving circuit of switching regulated power supply? Its kind?
Answer: Definition: The drive circuit is a drive signal that can quickly turn off when turned off and maintain the leakage current of the turn-off device approximately equal to zero; quickly turn on when turned on and maintain the tube voltage drop during the conduction period approximately equal to zero. circuit.
Type: single-ended pulse transformer~, anti-saturation~, fixed reverse bias~, proportional~, complementary~, open emitter~
12: What are the requirements for protection circuits in switching regulated power supplies? Its kind?
Answer: Requirements: ① The delay time of the soft-start automatic protection circuit must be greater than the recovery time of the primary rectification and filter circuit in the switching regulated power supply circuit. The recovery time mainly refers to the charging time of the filter capacitor after primary rectification. ② The total time used for sampling processing, feedback control and power switch shutdown in protection circuits such as overcurrent, overvoltage, undervoltage and overheating is longer than the power conversion cycle time, that is to say, the control shutdown of these protection circuits The speed must be fast. Only in this way can we protect both the load system and the regulated power supply circuit itself from damage. ③For the overcurrent protection circuit, when the fault that caused the overcurrent phenomenon is eliminated or the overcurrent phenomenon is restored, the regulated power supply circuit must be able to automatically resume normal operation. In addition, the power supply systems in some more advanced electronic equipment and electromechanical products are not only required to have various protection circuits, but also are required to have various protection status displays and self-diagnosis functions.
Types of protection circuits: overvoltage~, overcurrent~, undervoltage~, overheating~, overload~, switch soft start~
13:What is primary breakdown and secondary breakdown? What’s the difference between the two?
Answer: Primary breakdown: When the reverse voltage increases to a certain value, the carrier multiplication effect is like an avalanche, increasing rapidly and much, and the reverse current suddenly increases. This is the phenomenon of avalanche breakdown, also called primary breakdown. breakdown. Secondary breakdown: After avalanche breakdown, when the current increases to a certain value, the voltage between the collector and the emitter suddenly drops, while the collector current increases sharply. This phenomenon is called secondary breakdown. Difference: ① Judging from the secondary breakdown characteristic curve of the power switch, after the second breakdown, the collector voltage is much lower than the collector voltage after the primary breakdown; ② The primary breakdown is reversible, but the secondary breakdown is irreversible. . ③The primary breakdown depends on the voltage applied to the power switch, while the secondary breakdown depends on the amount of energy applied to the power switch and the length of accumulation time. ④The reason for primary breakdown is clear, but the reason for secondary breakdown has not yet been fully grasped by us.
14: What is primary rectification and filtering, and what is secondary rectification and filtering?
Answer: Primary rectification circuit: The power frequency rectification circuit of the input circuit part of the switching regulated power supply circuit is called the primary rectification circuit of the switching regulated power supply. It directly introduces the power frequency grid voltage or other forms of AC input voltage. , perform full-wave rectification, and then send it to the primary filter circuit of the next stage for filtering, and finally become a DC output voltage to supply power to the power converter of the subsequent stage. Primary filtering: The primary filter circuit in the switching regulated power supply circuit is the L-shaped filter circuit composed of inductors and capacitors behind the primary rectifier circuit. Its main function is to filter the DC fluctuation voltage output from the primary full-wave rectification circuit or to ensure that the ripple voltage meets the design requirements. Secondary rectification: The secondary current circuit is a rectification circuit that appears in the secondary circuit of the switching transformer. It is generally a high-frequency rectification circuit. The rectifier diode often uses a high-frequency fast switching diode, that is, a Schottky diode. In a switching regulated power supply circuit without a power frequency transformer, the switching diode or freewheeling diode is the rectifier diode of the secondary rectification part. Secondary filtering: The high-frequency filter circuit part of the switching regulated power supply circuit is called the secondary filter circuit. The value of the filter capacitor is closely related to the level of the DC voltage ripple voltage output by the switching regulated power supply. Generally, a passive filter circuit composed of passive components such as resistors, inductors, and capacitors is used.
15: Isolation technology
In a switching regulated power supply circuit, a technology that solves the problem of how to isolate two independent units that do not share a common ground.
Classification of coupling technology: photoelectric coupling technology, transformer magnetic coupling technology, photoelectric and magnetic hybrid coupling technology and direct coupling technology
16: What are the classifications of single-ended switching regulated power supplies?
According to the excitation mode: self-excited single-tube DC converter; other-excited single-tube DC converter; self-excited two-tube DC converter; other-excited two-tube DC converter; other-excited full-bridge DC converter .
According to the polarity of the power switching transformer: single-tube forward DC converter; single-tube flyback DC converter
According to the type of power switch: GTR (transistor) type DC converter; MOSFET (insulated gate field effect transistor) type DC converter; IGBT (composite power module) type DC converter
17: What is the shielding technology of switching regulated power supply? Its classification?
Answer: Shielding technology has two meanings: First, it blocks stray electromagnetic waves and other interference signals in the environment (including stray electromagnetic waves on the power frequency grid) outside the shielded power system to prevent and avoid these stray electromagnetic waves. Dispersed electromagnetic waves and other interference signals interfere with and damage the electrical system. Second, the electromagnetic waves radiated or propagated by the oscillating signal source or alternating power radiation source in the power system through various links and various channels in the circuit are blocked inside the power system to prevent and avoid the propagation and Radiation pollutes the environment and interferes with other surrounding electrical systems.
Category: Soft shielding technology: Designers of switching regulated power supply circuits adopt effective circuit technologies (such as common mode filter technology, differential mode filter technology, bidirectional filter technology, low-pass filter technology, etc.) when designing circuits Various filter technologies) on the one hand suppress and filter the external propagation and radiation of high-frequency electromagnetic waves inside the switching regulated power supply circuit to a minimum, so as not to affect the normal operation of other surrounding electronic equipment, electronic instruments and electronic instruments. At the same time, it does not pollute the industrial frequency power grid; on the other hand, the stray electromagnetic waves input to the industrial frequency power grid are also suppressed and filtered to the minimum level, so as not to affect the normal operation of the switching regulated power supply circuit; hard shielding technology: shielding technology for electric fields , shielding technology for magnetic fields and shielding technology for electromagnetic fields.
18: Working principle of single-ended self-excited positive polarity DC conversion circuit:
Answer: Input I-frequency power grid 220V/50Hz or 110V/60Hz → bidirectional common mode filter to filter out clutter and interference signals → full-wave rectifier → filter circuit to get 300V/150V DC voltage as its power supply voltage, which passes through the primary winding Resistor Np is added to V. At the same time, the C pole of this power switch is stepped down and divided, and supplies the positive white bias voltage and common pole current to the b pole of V1. V1 is turned on, and the C-pole current of the power switch V1 flows through the primary winding Np, inducing an alternating voltage on the secondary winding Np through magnetic coupling, inducing a positive feedback voltage relative to the base of V1, injecting further current into the V1b stage. increases, so that the induced voltage on Np further increases, and the cycle becomes a strong positive feedback process. V1 enters the saturated conduction state, and the C pole current of v1 increases to β times of the B pole, reaching the maximum value, making V1 The growth rate of the C pole decreases, causing the Np induced current to decrease, and the currents of the base and C pole of V1 decrease. After that, the current and voltage conversion rate of the C pole of V1 becomes a complex power, causing the polarity of the induced voltage on Np to be opposite to the original one. , after reducing the voltage through coupling, V1 enters the reverse bias cut-off state, that is, a complete oscillation cycle from on to off is completed, and the cycle is repeated to form a single-tube self-excited multivibrator working process.
19: Why is there a damping circuit?
Answer: When the power circuit is powered on, an instantaneous rectangular wave oscillation pulse signal will be obtained at the collector of the power switch. This signal has a positive peak value and a negative peak value. Sometimes the peak voltage of this positive and negative surge can be about 2-3 times higher than the input voltage directly applied to the collector of the power switch. Such a high overshoot peak voltage is particularly likely to damage the power switch due to secondary breakdown, so two damping and attenuation circuits are introduced. One is to eliminate the overshoot peak voltage caused by the magnetic leakage of the power switch transformer, and the other is to eliminate the overshoot peak voltage caused by the voltage and current stress of the power switch.
20:What is a high frequency rectifier circuit?
Answer: Under normal rectification conditions, all rectifier diodes in the secondary circuit of high-frequency power switching transformers use switching diodes with fast recovery characteristics. Especially for those requiring larger output current, Schottky diodes need to be used. This application has special requirements. A rectifier circuit that works at high frequency, that is, a high-frequency rectifier circuit
21: Three working states of single-ended self-excited flyback DC conversion circuit:
Answer: The secondary winding current is in a critical state; the secondary winding current is in a discontinuous state; the secondary winding current is in a continuous state.
22: What is the difference between a single-ended direct-excited forward DC conversion circuit and a single-ended self-excited forward DC conversion circuit?
Answer: ①The former power switching transformer and It has nothing to do with the PWM oscillator, and the latter’s power switching transformer must participate in the oscillation work as an important component in the PWM oscillation circuit. ② The power switch V of the former has an independent PWM oscillator, driver, controller, etc., and is served by an integrated circuit, while the latter does not have an independent PWM oscillator, driver, controller, etc. circuit. ③The former power switch V has nothing to do with the PWM oscillator, while the latter power switch V, like the switching transformer, must participate in the oscillation work as an important component in the PWM oscillation circuit. ④The former does not have strict requirements on the oscillation circuit, while the latter has very strict requirements on the oscillation circuit.
23: Three working states of single-ended self-excited flyback DC conversion circuit:
Answer: The secondary winding current is in a critical state; the secondary winding current is in a discontinuous state; the secondary winding current is in a continuous state.
24 What is the difference between a single-ended direct-excited forward DC conversion circuit and a single-ended self-excited forward DC conversion circuit?
Answer: ① The former power switching transformer has nothing to do with the PWM oscillator, while the latter power switching transformer must participate in the oscillation work as an important component in the PWM oscillation circuit. ② The power switch V of the former has an independent PWM oscillator, driver, controller, etc., and is served by an integrated circuit, while the latter does not have an independent PWM oscillator, driver, controller, etc. circuit. ③The former power switch V has nothing to do with the PWM oscillator, while the latter power switch V, like the switching transformer, must participate in the oscillation work as an important component in the PWM oscillation circuit. ④The former does not have strict requirements on the oscillation circuit, while the latter has very strict requirements on the oscillation circuit.
25: What are the classifications of bridge DC circuits? Features?
Answer: It is divided into half-bridge DC circuit and full-bridge DC circuit.
1. High output power;
2. Power switching transformer core utilization rate;
3. The power switching transformer does not have a center tap, and the actual processing is relatively simple.
4. The withstand voltage of the power switch used in the circuit is twice that of the power switch in the push-pull DC circuit. Therefore, when the power switch is selected, the rated voltage value of the collector is the power of the push-pull DC converter circuit. 1\2 of the switch; so that under the same cost and input conditions, the output power of the half-bridge DC converter is twice that of the push-pull DC converter and four times that of the full-bridge DC converter;
5. In the half-bridge DC converter circuit, the voltage amplitude applied to the primary winding of the power switch transformer is only half of the input voltage. Compared with the push-pull DC converter circuit, when the same power is output, the power switch and power Twice the current must flow through the primary winding of the switching transformer. Therefore, the bridge DC converter circuit adopts the method of step-down and current expansion to achieve the same power output.
