Transistor voltage converter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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Transistors connected in series can open themselves in turn. Such an autogenerator (Fig. 1) is designed to transmit electricity in portions that accumulate in the capacitor of a series oscillatory circuit.
The input voltage for it is the mains rectified by the VD1 bridge.
The operating point of the transistor VT2 is brought out by resistors R4 and R5 to the cutoff mode boundary in such a way that the transistor is still closed, but its collector-emitter conductivity is increased. The slightest increase in voltage at the base of VT2 leads to its opening. To create the conditions for auto-generation, the conductivity of the VT1 key is increased due to the parallel connection of the resistor R1.
When the input of the converter is connected to the network, the smoothing capacitor C1 is smoothly charged through the resistor R2, designed to protect the diode bridge VD1 from overload and reduce interference penetrating the network. The voltage from C1 through the resistor R1 is applied to the oscillatory circuit formed by the transformer T1 and the capacitor C2. A voltage pulse arises in the winding II T1, the power of which is sufficient to open the transistor VT1 (at the initial time, the current does not flow through the transistor due to the self-induction of the transformer T1).
After opening VT1, the current from the winding II T1 increases, which keeps the transistor VT1 in the open state. Transistor VT2 during this half-cycle of the oscillatory process is closed due to the EMF induced in the winding III T1. At the end of the charge of the capacitor C2, the current through VT1 stops, and it closes.
In the second half-cycle of the oscillatory process in the circuit T1-C2, the current at the initial moment of time, when the transistors are closed, passes through the divider R5-R4. As a result, the transistor VT2 opens and is held open. After the discharge of the capacitor C2, the current through the transistor VT2 stops and it closes. Thus, the current passes through the transistors at those moments when they are fully open and have a minimum collector-emitter resistance. The operating conversion frequency is about 20 kHz. The power transmitted to the output is determined by the bandwidth of the oscillatory circuit and the frequency. Any of its points can serve as the output of the converter. In the above diagram, the output is the additional winding IV of the transformer T1.
Figure 2 shows the dependence of the output voltage on the resistance of the load connected to the winding IV.
Transformer T1 is made on a ferrite ring 2000NM1, size K32x16x12. Windings I, II, III and IV are wound turn to turn and contain, respectively, 70, 6, 6 and 5 turns of PEV-2 wire 00,3 mm. Capacitors C1, C2 - any type with an operating voltage of at least 400 V.
This converter is the basis of ballasts of modern energy-saving lamps.
Attention! When working with the device, taking into account the galvanic connection with the network, the safety regulations must be observed.
Author: V.Solonin, Konotop, Ukraine
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