500W switching power supply for car amplifier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The switching power supply considered in the article has a high efficiency and high output power with a small number of cheap and common radio components used. The bipolar output of the device has a galvanic isolation from the mains. The schematic diagram of the power supply is shown in the figure:

(click to enlarge)

Main Specifications

• AC supply voltage, V ........... 220 +10% -20%
• Constant output voltage, V ............... 75 + 75
• Maximum output power, W ................... 750
• Auto-generation frequency, kHz .................................... 8
• Maximum efficiency of the device, % .............................. 92

The prototype of the apparatus is the device described in the article [1]. The price for extreme simplicity is the lack of output voltage stabilization and overcurrent protection, as well as a rather low conversion frequency, which lies in the frequency range audible to the human ear. Due to these shortcomings, our power supply is recommended for specific applications outside of residential areas, such as in a garage.

The power that a switching power supply is capable of delivering to a load is approximately equal to one horsepower. In Belarus, the Russian Federation and other countries of Europe, horsepower is such a power that allows you to lift a body weighing 1 kg by 75 meter within 1 second. This horsepower, called metric horsepower, is strictly 735,49875 watts. In the US, horsepower is considered to be 745,6999 watts. And electric horsepower means 746 watts. Due to the ambiguous definition of horsepower, the term is not often used.

Purpose and possible replacement of components

The SA1 power switch can be used with a keyboard type brand B127B (250 V, 8 A), B127A (250 V, 16 A) or B1024, SWR74 (250 V, 16 A). In the author's version, a backlit switch was used. Thermistor RK1 reduces the amplitude of the current pulse consumed by capacitors C5, C6, C9 and CU during their charge when the power source is connected to the network. The brand of the NTC thermistor is B57364-S 100-M (7,5 A, 10 Ohm). Fuse FU1 protects the power supply from overload in case of failure of the device components. The brand of the fusible insert is VP2B-1 V, VPZB-1V, VPZT-2Sh, or VPB6-40. Varistor RU1 protects the input components of the power supply from surges. Varistor brand - CNR10D431, CNR14D431, CNR20D431, CNR10D471, CNR14D471, CNR20D471, TVR10431, TVR14431, TVR20431, TVR10471, TVR14471, TVR20471 or S14K275. Capacitor C2 and two-winding inductor L1 form an L-shaped mains filter that prevents the penetration of high-frequency interference from the pulse converter into the mains.

The dual choke L1 was selected brand B82725-A2602-N1 manufactured by Epcos. This choke has an inductance of 2x3,9 mH and is designed to operate at a voltage of 250 V at an alternating current of up to 6A. allowing the flow of current up to 82725 A at an alternating voltage of 2103 V. A two-winding inductor L1 can be made independently. To do this, winding wires of the PELSHO brand with a diameter of 2 mm are laid on two semicircular magnetic circuits made of MO-permalloy MP1,8 or MP10 with a standard size of KP250x1x250, 160 mm in diameter, until the core window is filled. Before laying the windings, the magnetic circuit is covered with a layer of insulation, for example, varnished cloth or Teflon. This is also done in the manufacture of pulse transformers TV36 and TV25. It is important to ensure that the winding wire does not push through or cut through the insulation layer. The windings are placed simultaneously in two wires.

Capacitor C2, designed to operate at an alternating voltage of up to 300 V, can be taken from brands B32923-A2474-M or B81131-C1474-M manufactured by Epcos. Fixed resistors R2, R3 and bipolar transistors VT1, VT2 form an analogue of a dinistor. Instead of an analogue of a dinistor, you can use a KH102A or DB3 dinistor from ST Microelectronics. Capacitor C1 at the moment of charging when the device is turned on consumes a current, which, flowing through the winding I of the matching transformer TV1, creates the initial control signal for the key transistors. Capacitor C1, as well as capacitors C3 ... C6, you can take the brand K73-17. The current of the charge of the capacitor C1 limits the constant resistor R1.

Diode assembly VD1 and capacitors C5, C6, C9 and SU represent a mains rectifier with a capacitive filter that forms a voltage divider. Fixed resistors R11 and R12 remove charges from capacitors C5, C9 and C6, SU, respectively. Electrolytic capacitors C7 ... C10 can be used brand K50-35 or similar. It is permissible to change the VD1 diode assembly to devices СР1008, KVRS1008, KBU10К, BR1010, PBU1007, KBU10M, KBU1010, RS1007nnn KVRS1510.

The matching transformer TV1 is made on one toroidal magnetic circuit with a size K20x10x5 made of M2000NM-17 ferrite. All three windings, which are laid on the magnetic core at the same time, contain 8 turns of PELSHO wire with a diameter of 0,5 mm.

Fixed resistors R4 and R5 limit the base currents of bipolar transistors VT3, VT5 and VT4, VT6, respectively.

Powerful bipolar transistors VT3.. .VT6 serve as switching components of the converter. Transistors of the 2T812A brand can be changed to KT812A, KT840A or, worse, to KT828A. Transistors VT3 ... VT6 should be installed on four independent coolers with a useful area of ​​​​each about 140 cm2. Fixed resistors R6...R9 equalize the emitter currents of bipolar transistors VT3...VT6 and serve as elements of local feedback circuits that speed up the switching of transistors. Without these resistors, the key transistors will fail due to current overload. Resistors R6 ... R9 must have as little parasitic inductance as possible, otherwise the key transistors will be disabled.

Each of the indicated equalizing resistors can be made up of ten constant MLT resistors connected in parallel with a resistance of 1 ohm and a power of 0,25 watts. Diodes VD2...VD5 brand HER508 damping. They can be changed to 8ETX06S, BYC10-600, HFA04TB60, HFA08TB60 or similar diodes. The current limiting resistor R10, winding I of transformer TV1 and winding I of transformer TV2 form a positive feedback circuit, thanks to which auto-generation is maintained in the converter. Resistor R10 can be made up of five 2 W resistors, which are connected in parallel.

The impulse transformer TV2 is made on four ring magnetic cores folded together with a standard size K45x28x8 from M2000NM-A or M2000NM-17 ferrite. Winding I consists of 10 turns of wire with a diameter of 0,5 mm, winding II of 103 turns of 1,00 mm diameter, and winding III of 51 + 51 turns of 1,6 mm diameter. It is permissible to use winding wires with enamel insulation grades PET-200-1, PET-200-2, PETD-180, PETV-1, PETV-2, PEE1-130-MEK, PEE2-130-MEK, PEEI1-200, PEEI2- 200 or PEF-155. Interwinding and cover insulation is carried out with varnished cloth tapes. Diodes VD6 ... VD9 rectify the impulse voltage that occurs on the winding III of the TV2 transformer, and smoothing capacitors C3, C4, C7 and C8 filter it from the variable component. These diodes can be taken from the brands 15ETH06, 15ETX06S or DSEI12-06A. Diodes should be mounted on four separate coolers with a total surface area of ​​approximately 50 cm2 each.

Setting

Before connecting the device to the network, remember that some of the components are under life-threatening voltage. Follow the safety regulations.

Usually, a power source, if assembled from serviceable parts and exactly according to the scheme, does not need to be configured and starts working immediately, without adjustment. However, if auto-generation does not occur, you should try to change the phasing of turning on the I winding of the TV2 transformer. You can try to increase the conversion frequency to about 25 kHz if you use a smaller-diameter toroidal core made of ferrite with high magnetic permeability (at least 1 ... 2000) as the magnetic core of the matching transformer TV3000. From this, unfortunately, the losses in the key transistors VT3 ... VT6 will increase, and the efficiency of the power supply will become less. This will happen due to the fact that the pulses on the windings II and III of the matching transformer TV1 will have more gentle fronts.

Literature

1. Gaino E., Moskatov E. Powerful switching power supply. - Radio, No. 9, 2004, p. 31,32.

Author: E.Moskatov, Taganrog, moskatov.narod.ru

See other articles Section Power Supplies.

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