Bi-phase generator with adjustable pause

Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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The output signals of the proposed generator (Fig. 1) are in the form of rectangular pulses with a constant phase shift of 180°. The duration of one of the half-cycles of each phase can be changed (reduced). In this case, a gap (pause) t appears between the "shortened" phase pulses_n, in which the phase of the signals of both outputs is the same (Fig. 2). Such signals are used, for example, in master generators of switching power supplies, stepper motors, etc.

Fig.1. Schematic diagram of the generator

The generator consists of a clock generator on DD1.1, DD1.2, a repeater DD2.1, a shaper of antiphase pulses DD2.2 and coincidence elements DD1.3, DD1.4.

Fig.2. Generator output voltage diagrams

The minimum resistance of the limiting resistor R2 is selected to exclude self-excitation in the extreme positions of the variable resistor R1 engine. The variable resistor R1 together with the diodes VD1 and VD2 provide the circuit for charging and discharging the frequency-setting capacitor C1 [1]. When moving the resistor slider to the extreme terminals, either the charging time or the discharge time of the capacitor changes, which leads to a change in the duration of the half-cycles of the generated pulses. In this case, the pulse frequency changes within small limits. It depends on the switching voltage DD1.1, the total resistance of the charging and discharging circuit of the capacitor C1, its capacitance and mounting capacitance. By changing any parameter, you can set the required frequency at the generator output. Since the clock generator is assembled on two-input elements, the second input, for example, the first element DD1.1 is convenient to use to block the operation of the generator. To do this, the lower input DD1.1 according to the diagram is connected to a common wire through a resistor. To block the operation of the generator, a high logic level must be applied to it. In this case, a logical "1.2" will appear at the output of DD1.

A repeater is connected to the output of the clock generator, made on a D-trigger DD2.1, which improves the shape of the pulses arriving at it, which is especially important for the accurate operation of the counting trigger DD2.2. At the outputs of the trigger DD2.2, antiphase pulses of the meander type are formed (with a duty cycle of 2). To the direct and inverse outputs DD2.2 connected to the inputs of the matching elements DD1.3 and DD1.4. The other inputs of these elements receive a signal from the output of the clock generator.

For NOR elements, the active level is high, therefore, during a logical "1" at the trigger outputs, outputs A and B of the biphase generator are set low. It does not depend on the state of the second inputs of the match elements.

At a low level at one of the outputs of the trigger DD2.2, the duration of the half-cycle of the clock generator pulse with a high level determines a pause at the output A or B, the duration of which can be changed by changing the duty cycle of the clock generator. In this case, the frequency of the output signals is 2 times less than the frequency of the clock generator.

In devices that require low-level pulses with an adjustable pause to control, the OR-NOT elements are replaced by the AND-NOT elements (K561LA7). In this case, to block the operation of the clock generator and establish a high level at the outputs A and B, it is necessary to apply a logic "1.1" voltage to the lower input DD0 according to the circuit.

Figure 3 shows a diagram of the machine for the incubator. In this circuit, the output signals of the bi-phase generator A1 control the operation of the collector motor through the DA1 servo amplifier chip. This chip - the driver for refilling the VCR cassette - is included according to the standard scheme. The operation of the machine is simple - a high level at output A leads to the rotation of the motor shaft in one direction, and "1" at output B - in the opposite direction (Fig. 2, diagram 3). During the pause (t_n) the engine is stopped. Temporary shutdown of the machine is carried out by the switch SA1 "Block". At the same time, both outputs of the biphase generator have a low logic level.

Fig.3. Scheme of the machine for the incubator

If in the above diagram of the machine the frequency of the clock generator is increased (up to several tens or hundreds of hertz), and instead of the electric motor, the transformer winding is turned on, we get a circuit of a simple DC-to-AC converter. The form of voltage on the secondary winding of the transformer is shown in Fig. 2, diagram 4 (with a minimum pause). By changing the duration of the pause, you can adjust the output power of the converter. For the applied microcircuit, the maximum current should not exceed 1,6 A, and the maximum voltage should not exceed 18 V [2].

The following details are applicable in the generator: R1 - any variable (tuner) of group A; R2 - type MLT-0,125; C1 - K73P-3 (the best result in terms of frequency and pulse duration stability) or others from the K73, PM, FT series. C2 - blocking in the power circuit, any ceramic, the capacitance is not critical. Diodes VD1 and VD2 - any silicon, small-sized (KD522, KD503, KD102, etc.). Microcircuits are replaced by analogues from the K176, 564, K1561, K1554 series with the appropriate supply voltage.

Literature

1. V. Ageev. Generator with adjustable duty cycle. - Radio, 1989, N3, p.32.
2. Reference manual. Integrated circuits of foreign household video equipment. - St. Petersburg: VICTORIA LAN, 1996, p.149.

Author: A.Romanchuk, p.Novikovo; Publication: radioradar.net

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