Switching power supply, 220/29x2 volts 8 amps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Powering high-power audio frequency amplifiers requires a power supply, usually having either a bipolar output with a midpoint, or two galvanically uncoupled outputs. The output voltage should practically not change with sudden changes in the load current in the range from minimum to maximum, as well as when the mains voltage changes, the efficiency of the source should be maximum. The source must be protected against short circuit and overload.

All these requirements are met by the switching power supply (SMPS) presented in the article. It is made on a widespread element base and does not contain expensive or scarce components.

(click to enlarge)

Purpose of SMPS components:

SA1 - power switch;

FU1 - fuse that protects the power supply in case of an accident at the source;

RK1 - a thermistor that limits the initial charge current of capacitors C1.C4 to a safe value for diodes VD1 and VD2;

RU1 - varistor shunting overvoltage impulses penetrating from the network;

C5-C6-L1 - network filter that suppresses high-frequency oscillations generated by the converter;

VD1-VD2-C1, C4-R1-R2 - mains rectifier with capacitive divider.

Resistors R1 and R2 discharge capacitors C1 ... C4 when the source is turned off from the network. The capacitances of capacitors C1, C3 and C2, C4 are generally not the same, and the middle point of the divider is shifted relative to half of the supply voltage. However, due to the capacitor C8 in steady state, the bias current does not flow through the power transformer T1;

C7-C10-C11-L2-VD3-VD5-VD6 and C13...C15-L2-VD9-VD10-VD16 - output rectifiers with smoothing LC filters, made according to the McLeaman scheme. The installation of electrolytic capacitors immediately after the output rectifiers is unacceptable, since these capacitors will quickly overheat due to large voltage ripples and fail;

C9-C12-DA1-R3-R4-VD4-VD7 and C16-C17-DA2-R9-R11-VD17-VD22 are compensation voltage regulators (Low Drop type) that provide protection against overload and short circuit. At the moment the source is turned off, diodes VD4 and VD22 protect the DA1 and DA2 microcircuits from reverse voltage from capacitors C9 and C16, and diodes VD7 and VD17 from reverse voltage from capacitors C12 and C17. Stabilized output voltages can be changed by selecting resistances R3, R4 and R9, R11;

R5-HL1-VD8 and R8-HL2-VD13 - circuits for indicating the operation of the stabilizer protection;

T1 - pulse power transformer, galvanically separating the input and output of the power supply;

R6, R7, VD11, VD12 are components that prevent the flow of through currents through key transistors. Until the excess carriers in the base circuit of one transistor resolve, the other transistor will not be able to open;

VD14, VD15, VD18, VD19 - damping diodes;

VD20-VD21 - voltage pulse limiter EMF self-induction reactor L3;

L3 - a reactor that provides a delay in opening transistors due to the limitation of collector currents. Due to the safe switching of transistors, there is no secondary breakdown of the semiconductor structure;

VT1, VT2 - switching transistors. The voltages supplied to their bases from the T2 transformer and from the circuits that prevent through current should be approximately the same. In this case, when the polarity of the voltage taken from T2 is changed, these voltages are compensated, and the base currents do not flow through the closed transistors;

R15-HL3-VD23 - elements of light indication of switching on the SMPS;

C19-R10-R16-T1-T2 - a positive feedback circuit that provides self-excitation of the converter. With an increase in power consumption, the conversion frequency increases, and the voltage on all windings of the transformer T1 decreases. But almost the same voltage is applied to the base-emitter junctions of the key transistors, since the voltage on the windings of the switching transformer T2 almost does not decrease due to a decrease in the capacitance of the capacitor C19. Thanks to the capacitor C19, transistors VT1 and VT2 do not work in the active region, in which the power dissipated by them would increase many times over and the efficiency of the converter would decrease. The direct connection of the capacitor C19 with the winding IV of the transformer T1 is unacceptable, since then the key transistors will fail;

C18-R14-VS1 - a trigger circuit that generates a pulse after turning on the source, which opens the transistor VT2, causing the auto-generation to start.

T2 is a saturable switching transformer. The parameters of the magnetic circuit and the number of turns in the windings set the generation frequency of the converter. The smaller the overall dimensions and the fewer turns in the windings, the higher the conversion frequency.

Integrated voltage regulators DA1, DA2 type KR142EN22A can be replaced by LT1083. Each microchip is mounted on a heat sink with a cooling surface area of ​​350 cm2. Switching transistors VT1 and VT2 (KT839A) are replaced by KT838A KT846A, BU208A or similar ones with a reverse voltage of at least 1000 V and a collector current of at least 4 A. Each of the transistors is mounted on a heat sink with an area of ​​60 cm2.

Dinistor VS1 (KN102D) can be replaced by DB-3, DB-4 or any dinistor from the series. KN102. Diodes VD1 and VD2 - type KD203G. they can be replaced with KD203D, HFA06TB120 or similar ones with a reverse voltage of at least 1000 V and a forward current of at least 8 A.

Diodes VD3, VD5, VD9, VD16 (KD2997V) are replaced by KD213A, 30CTQ100, SFA1604G or similar with a reverse voltage of at least 100 V, direct current of at least 10 A and a frequency of at least 100 kHz. Each diode is fixed on a heat sink with a cooling surface area of ​​at least 50 cm2. Installation of diodes on heat sinks is mandatory. Instead of diodes VD4, VD6, VD7, VD10, VD17, VD20, VD22 (KDl212A), you can use KD226B, KD243B (V), KD247B (V), KD528A, MUR120, SF34 or similar with a reverse voltage of at least 100 V and direct current not less than 1 A. Diodes VD11, VD12 (KD2997A) can be replaced with any diodes from the KD2997, KD213 series, with diodes KD527A, 1N5822, 31DQ10, 50SQ080, 50SQ100 or similar ones with a direct current of at least 3 A. Damper diodes VD14, VD15, VD18 19 , VD228 (BY243) are replaced by KD247Zh KD527Zh KD528D, KD1D, 7A1, 7F1, 4007N1. 5408N1, 5399N150, 02EBU208, HER26, BYM26E, BYV157E, FR207, FR207, RL1000 or similar with a reverse voltage of at least 1 V and a direct current of at least 23 A. Diode VD102 (KD103A) can be replaced by KD221A, KD509A, KD510 518A, KD522A, KDXNUMXA or KDXNUMXB.

Instead of zener diodes VD8, VD13 (KS515A), D814D, KS509A (B), KS518A or similar ones with a stabilization voltage of 14 to 20 V and a maximum current of at least 10 mA are suitable. instead of VD21 (D816A), D816B or similar with a stabilization voltage of 22 V to 30 V and a maximum current of at least 150 mA.

LEDs HL1 and HL2 (L5013SGD) can be replaced with L5013SGD-B, L5013UEBC-B, HL3 (AL307GM) - with any LED of the AL102, AL307 series.

Capacitors C1, C2, C12, C17 - type K50-27, K50-35; C3 ... C7, C10, C13, C14 C18, C19 - K73-16, K73-17; C8 - K75-10, K75-12, K75-24; C9 C11, C15, C16 - KEA-II, K50-6, K50-27, K50-35. Capacitor C8 must have a power of at least 550 VAR and can have a capacitance of 0,47 to 1,5 microfarads. The capacitance of the capacitor C19 can be from 0,022 to 0,047 uF. Capacitors can be replaced with any similar ones designed for the same voltages.

Resistors R1, R9, R11, R15 can be of the type MLT, OMLT C2-22 C2-23, and R10 and R16 - C5-16MV, C5-37 or PEV-5. Resistors can be replaced with any similar ones designed for the same power. Varistor RU1 (VCR391) can be replaced by JVR-10N361K, JVR-14N361K, JVR-20N361K, JVR-10N391K, JVR-14N391K,

JVR-20N391K, JVR-10N431K, JVR-14N431K, JVR-20N431K or similar, RK1 thermistor (SCK-103NTC) - on MZ92-P220RM, MZ92-R220RM, MZ92-P330RM, MZ92-R330RM or similar.

Choke L1 is made on a ring made of alsifer TCHK55 or TCH60 of size K24x14x7. Windings I and II contain 20 turns of MGTF, PELSHO or PEV-2 01 mm wire each and are wound in two wires. Additionally, it is recommended to put a ferrite ring M2000NM K10x6x3 on one of the terminals of each winding, it is not recommended to use the ferrite rod of the receiver’s magnetic antenna as L1, since the stray field of the inductor will increase significantly, and shielding the high-voltage inductor is quite problematic.

Choke L2 is wound on a magnetic circuit. Ш7х8 from ferrite 2000НМ. Windings I and II contain 75 turns of PETV, PEPSHO or PEV-2 wire 01,7 mm each and are wound in two wires. The core core has a non-magnetic gap of 0,3...0,5 mm made of textolite or getinaks. To reduce the stray field, the choke is shielded by wrapping all three rods outside with one turn of a brass tape 0,05 ... 0,1 mm thick. The ends of the tape are soldered to each other.

The L3 reactor is made on a ferrite ring M2000NM or Micrometals K20x10x6. Each of the half-windings has one turn of wire. MGTF PETV, PEV-2 or conventional mounting wire 0,6 mm.

Transformer T1 is made on three ferrite rings folded together from ferrite M2000NM1, M2000NM-A or M2000NM1-17 of size K45x28x8. Windings I and III contain 15 + 15 turns of wire 01,7 mm each; winding II - 264 turns 0,9 mm; winding IV - 7 turns 0,41 mm; windings V and VI - 1 turn 0,25 mm each. Wire - MGTF, PELSHO or PEV-2. Winding II is wound first and contains 4 layers of insulation: after winding every 66 turns, a layer of PTFE or Mylar film is laid.

Transformer T2 is made on a ferrite ring M2000NM-A K10x6x8. All windings (I, II and III) contain 0,3 turns of wire. MGTF, PELSHO or installation wire in reliable insulation. In windings I and II, the wire is 0,42 mm, and in III - XNUMX mm.

Design. The mutual arrangement of the conductors and parts of the source is not critical. At me the source is executed by hinged installation. The diameter of the wires that connect parts operating under high voltage must be 1 mm or more, the wires connecting the source to the load must be at least 1,7 mm. All wires must be securely insulated.

Establishment. Attention! Some of the source elements are under high voltage, life-threatening. Observe the safety regulations!

Before turning on the source, you should carefully check the installation for compliance with the SMPS circuit, assembled from serviceable parts, usually starts working immediately. If, after turning on the source, auto-generation does not occur (the HL3 LED is off), then it is necessary to change the phasing (swap the ends) of either the windings IV of the transformer T1 or the windings III of the transformer T2.

If, at a mains voltage of 220 V, the no-load current of the source is more than 40 mA (measured after the mains filter), it is necessary to proportionally increase the number of turns of all windings of the transformer T1. If the output voltages differ from 29 V, they can be set by selecting the resistances R3 and R11.

Author: E. Mokatov, Taganrog, Rostov region.

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