Curved rectifier. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Curved rectifier. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / welding equipment

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As practice shows, the arc burning process is more stable in welding devices with a soft (falling) current-voltage characteristic. Among such "welders" one can, in particular, include a home-made device with a rectifier, the circuit diagram of which is made with a hitch, the essence of which is a quick change in the operating modes of diodes, switched on either through a typical valve bridge (VCM), or through the so-called voltage doubling circuit (VSU).

Curved rectifier
Rice. 1. Schematic diagram (a) and current-voltage characteristics (b) of a home-made apparatus for welding with direct current.

A special role in the technical solution under consideration is played by the X2X1 jumper. By inserting it, they get from the very usual diode bridge VD4-VD1 with a low-frequency filter C2C1L1 a rectifier, at the output of which in idle mode is doubled (compared to the first version of operation) voltage. In this case, a positive, say, half-wave of the voltage coming from the beginning of the secondary winding of the welding transformer T1 passes the semiconductor power valve VD1 unhindered and, having charged the capacitor CXNUMX almost to the maximum, returns to the end of the named winding.

With the onset of another half-cycle, the chain of passage of positive electric charges will be somewhat different: from the end of the winding II of the welding transformer T1 to C2, and from it - through the valve VD2 - to the beginning of the same secondary winding. But the capacitors C1 and C2 are connected to each other so that the resulting voltage is equal to the total, which is supplied through the inductor L1 to the gap "electrode - part", facilitating the occurrence of a welding arc.

Semiconductor diodes VD3 and VD4 with a closed jumper and the absence of a welding arc, as it were, do not participate in the operation of the circuit due to their reverse connection to the rectifier circuits. In addition, each of them turns out to be locked by voltage from the corresponding capacitor.

The disadvantage of typical doubling schemes is, according to the theory, a steeply falling external characteristic, that is, a sharp decrease in the rectified voltage with increasing load current. This forces the use of high-capacity charging capacitors (in the device under consideration, "electrolytes" of 15000 microfarads each). In addition, typical doubling circuits are explosive: when one of the power valves breaks down, the alternating voltage is directly applied to the electrolytic (oxide) capacitor, which is unacceptable. This is where the previously inactive VD3, VD4 are called upon to play their saving role (the specific contribution of these diodes, as well as the operation of the circuit directly during welding, is beyond the scope of this material, and therefore is not considered).

The graph shows the areas of existence of the welding arc fed from the HSM and from the APU.

Now about homemade nodes and radio components used in the proposed technical solution. The power of transformer T1, which has a magnetic circuit PL45x80, is 2,5 kV * A. The primary winding of the "welder" contains 156 turns of PEV2 wire with a diameter of 2,5 mm. Of course, it can also be made thinner, but folded in half, PEV2-1.7 mm. For the secondary (lowering) winding, a BPVL with a cross section of 16 mm2 was used. The required number of turns here is 22.

Choke L1 contains 33 turns of BPVL wire with a cross section of 10 mm2. They are wound on an insulating frame, which is put on the SHL 50x50 magnetic core, assembled with a non-magnetic 2 mm gap, where 2 mm thick spacers made of heat-resistant dielectric are installed. As the latter, getinax or textolite is quite suitable.

Capacitors C1 and C2 - oxide K50-18 or another type, designed for use in circuits with a voltage of 50 V or more. Diodes D161 recommended for use in the circuit can have any combination of numbers and letters at the end of the name. The use of powerful "electric locomotive" B200s is also quite acceptable here. Each of the diodes is mounted on a 80x80x45 mm duralumin heatsink with vertical fins (for better cooling due to convection). Terminals X2-X5 are M10 brass or copper bolts with washers and nuts, brought to the front panel from textolite or getinaks. Jumper with a section of 30 mm2 - made of copper or aluminum.

Author: A. Trifonov, St. Petersburg

See other articles Section welding equipment.

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ICL5102 - Efficient half-bridge AC-DC converter controller with PFC 27.08.2018

Infineon's ICL5102 is a new combined power supply controller that controls two stages at once: a power factor corrector (PFC) stage and a resonant half-bridge LLC converter stage (optionally LCC).

The high level of integration of this solution ensures a low number of components and is well suited for compact and low profile power supplies. The configuration of the parameters of the ICL5102 chip is made by selecting the resistor values. With a starting current of about 100 μA, the controller allows you to start the power supply in no more than 300 ms.

The PFC stage is implemented on the basis of a digital core and operates in the choke current limit (CrM) mode or switches to discontinuous current mode (DCM) at light load. This stage operates in the frequency range from 22 to 500 kHz and allows you to achieve a power factor of more than 95% and an input current harmonic distortion (THD) of less than 10%.

The half-bridge stage contains a built-in low and high side driver for controlling an external transistor with a maximum voltage of up to 650 V. This microcircuit implements an adaptive dead time adjustment algorithm in the range of 500-1000 ns.

The ICL5102 controller implements an algorithm for exiting the capacitive operation mode of the LLC converter. The capacitive mode can occur either with a short circuit in the load, or with a sharp increase in load (surge) or when starting the converter. The controller attempts to smoothly bring the converter out of capacitive mode by increasing the conversion frequency. If this does not help, then the controller is restarted.

Technical advantages:

Range of effective values of input voltages 85...305 V;
The operating frequency range of the PFC cascade is 22...500 kHz;
Built-in isolated coreless transformer technology high-side driver of the output stage;
High converter efficiency up to 95% is possible (both stages - KKM + LLC);
External NTC resistor for overheating protection;
Short soft start time up to 300 ms;
Algorithm of regulation in the capacitive mode of the LLC-cascade;
Run at 1,3 MHz;
Stable operation under light load;
Housing DSO-16;
Operating temperature range -40...125°C.

Typical applications:

Industrial power supplies;
Power supplies for consumer electronics;
LED drivers.