Interference simulator for testing network filters. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The proposed device (its diagram is shown in Fig. 1) can be used for a comparative assessment of the efficiency of LC filters designed to operate in a 220 V AC network.

Fig. 1

In fact, this is a half-wave phase power regulator based on a VS1 trinistor with a control unit based on an analog of a VT1VT2 unijunction transistor. The presence of a powerful load is imitated by capacitors C1, C2, connected in series with current-limiting resistors R1, R4. Suppose that at the moment the device receives a negative half-wave of mains voltage. In this case, capacitors C1 and C2 are charged through diodes VD1, VD3 and resistors R4, R1, R2 so that the potential of their upper (according to the circuit) plates is negative, and the lower ones are positive. The diode VD3 is closed, therefore, the control unit on transistors VT1, VT2 is de-energized and the trinistor VS1 is closed. In this state, the device is until the end of the negative half-wave of the mains voltage.

With the advent of a positive half-wave, the diode VD3 opens and the capacitor C3 begins to charge through resistors R10, R11. When the voltage on it and the emitter of the transistor VT2 connected to it becomes approximately 0,6 V more than the voltage at its base, both transistors open like an avalanche and the capacitor is discharged through them, the current-limiting resistor R5 and the control electrode of the trinistor VS1. As a result, the latter opens and through the resistors R1, R4 quickly recharges the capacitors C1, C2 - the voltage on their plates changes sign, and a short pulse enters the 220 V network, the amplitude of which depends on its parameters - resistance, inductance of the wiring and the presence of closely spaced noise suppressors in the network capacitors. The supply voltage of the trinistor control unit during the action of the positive half-wave of the mains voltage is limited by the parametric stabilizer formed by the zener diode VD4, the HL1 LED (mains on indicator) and the resistor R7. Resistor R2 is used to discharge capacitors C1, C2 after disconnecting the device from the mains.

Fig. 2

The details of the device are placed on a printed circuit board (Fig. 2) made of foil fiberglass. All fixed resistors, except for R4, are MLT, OMLT, S2-33 or similar imported ones indicated in the power diagram. Resistor R4 must be wire-wound with a power dissipation of 7 ... 15 W (for example, C5-35V, C5-37 or imported). It is desirable that its inductance be minimal. If a screw is used to fasten it to the board, then it is better that it be brass. It should be noted that during operation this resistor gets very hot, and if the board is placed in a compact case, ventilation holes should be provided in its wall opposite the resistor. Trimmer resistor R11 - any small-sized, for example RP1-63Mb.

Capacitor C1 - ceramic high-voltage K15-5 or similar imported with a capacity of 4700. 10000 pF. Capacitor C2 - three-terminal K73-21g (such capacitors were used in network filters of unified domestic semiconductor TVs) or imported film with a nominal voltage of 250.280 V AC (installed in imported kinescope TVs and computer monitors at the input of the mains voltage filter 220 V). The applied capacitor during operation should not noticeably hum and heat up, if such effects take place, then such a capacitor is not suitable for operation in this device. The wire resistor R4 can also hum, but this is acceptable.

High-voltage diodes 1N4007 are interchangeable with UF4007, 1N4937GP, 1N5399, KD209G, KD243Zh, KD247D, instead of the D814D zener diode, D814D1, KS212Zh, 1N4742A, BZV55-C12, BZV85-C12 are suitable. The AL307KM LED can be replaced by any other continuous glow without a built-in resistor, for example, from the KIPD21, KIPD66, L-1513 series. We will replace the KT503E transistor with any of the KT503, KT645, KT646, KT6114, 2SC2331, 2SC2383, SS8050 series, and KT502A with any of the KT502, KT6115, 2SA931, 2SB564, SS8550 series, however, it should be noted that the pinout of the replacement transistors may differ from that shown in Fig. . 2.

The trinistor KU221G is fixed on the circuit board with two M3 screws with nuts and two metal bushings 3 mm long put on the screws (between the trinistor flange and the board). No heat sink required. A possible replacement for the trinistor is KU221A-KU221V, 2U221A-2U221G or imported, for example MCR218-10FP To connect to a 220 V network, use wires with a cross section of 1 mm² and up to 600 mm long. The appearance of the mounted board is shown in fig. 3.

Fig. 3

To test the performance of the interference simulator G1 (Fig. 4, a) and the step-down transformer T1, the secondary winding of which is connected to the input of the oscilloscope P1, are connected through the XP2XS2XS3 tee to the XS1 socket connected to the 220 V network through a known good mains filter Z1 (it is necessary for prevent interference from the simulator from entering the network). If the simulator is working, the oscilloscope screen will clearly show the short noise it creates, the polarity of which depends on the position of its plug in the tee socket. The adjustment comes down to setting the engine of the tuning resistor R11 to a position in which the trinistor opens at the peak of the amplitude of the mains voltage, in this case the level of interference generated by the device is maximum.

Fig. 4

The tested network LC filter Z1 is switched on according to the scheme shown in fig. 4b. Here, as in the previous case, Z1 is a filter that protects the network from simulator interference, a powerful wire resistor R1 imitates a "bad" network, increasing its resistance, A1 is the real load with which the filter is supposed to work, or its imitation (and the one and the other may be absent), T1 - the output transformer of the sound channel from the tube TV (you can use any low-power step-down transformer with a voltage on the secondary winding of 5.15 V). In the absence of filter Z2 and load A1, an impulse noise with an amplitude of 30 ... 40% of the voltage swing with a frequency of 50 Hz will be observed on the oscilloscope screen. By changing the resistance of the part of the tuning resistor R11 introduced into the circuit, one can observe how the interference moves along the positive or negative half-wave of the mains voltage.

The interference simulator will also be useful when testing different devices for susceptibility to interference penetrating from the network. If, for example, you have an AF power amplifier that is very sensitive to mains interference, it is connected through a surge protector and a tee to the same outlet along with the simulator, and if the interference it creates is heard in the speakers connected to the amplifier, then you can try to reduce them or completely eliminate by various circuitry or constructive methods.

When setting up and operating the described simulator, it should be remembered that all its elements are under dangerous AC voltage, therefore, it is necessary to strictly follow the rules of electrical safety.

Author: A. Butov

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