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Modern digitals is vital for each huge version railroad system, and it gives a option to virtually every problem. Although ready-made merchandise are exorbitantly expensive, clever digitals hobbyists attempt to use a minimal number of parts to be triumphant in most useful results together with low prices. This strategy can be tested using the moderately atypical semiconductor power flip-flop described here. A flip-flop is a toggling circuit with two stable switching states (bistable multivibrator). It care fors its output state even in the absence of an enter pulse.

Flip-flops can simply be carried out the usage of triacs if no DC voltage is on hand. Triacs are also so inexpensive that they're often used by means of edition railway builders as semiconductor energy switches. The decisive advantage of triacs is that they're bi-directional, which implys they may be ready to be precipitated during both the positive and the bad half-cycle by means of making use of an AC voltage to the gate electrode (G). The polarity of the set off voltage is as a result irrelevant. Triggering with a DC present is additionally that you could assume of. Figure 1 presentations the circuit diagram of this type of energy flop-flop. A permanent magnet is suited to the version teach, and when it commutes from left to proper, the magnet switches the flip-flop on and off by approach of reed switches S1 and S2.

In order for this to work in each guidance of commute, every other pair of reed switches (S3 and S4) is hooked up in parallel with S1 and S2. Briefly closing S1 or S3 triggers the triac. The RC network C1/R2, which acts as a section shifter, handles the trigger current. The present thru R2, C1 and the gate electrode (G) reaches its most price when the voltage throughout the load passes thru zero. This lead tos the triac to be precipitated anew for every half-cycle, despite the very fact that no pulse is current at the gate. It remains prompted till S2 or S4 is closed, which lead tos it to return to the blocking state.The load will likely be incandescent lamps within the station space (platform lighting) or a solenoid-operated instrument, any suchs a crossing gate. The LED connected across the output (with a rectifier diode) point outs the state of the flip-flop. 

The circuit shown here is designed for use in a edition railway machine, however there will no longer be any the purpose is it may not be used for different softwares. The reed switches may additionally be changed by customary pushbutton switches. For the frequently used TIC206D triac, which has a most current rating of four A, no heat sink is vital in this software except a load present exceeding 1 A should be supplied continuously or for a long time frame. If the switch-on or switch-off pulse shows to be insufficient, the worth of electrolytic capacitor C1 need to be elevated a little.

Author: R. Edlinger - Copyright: Elektor July-August 2004