In Fig. 4.6 shows a diagram of a power source that maintains its performance even in case of voltage loss in the network, wherein the device switches to the battery. Step-down transformer, used in this scheme, is selected based on the maximum current, the required load. Usually a large current is consumed audio the alerter.
The AC voltage from the secondary winding of the transformer is fed to rectifier bridge made of the diodes D1-D4. Further pulsating voltage smoothed by the electrolytic capacitor C1 and serves on the stabilizer the voltage on the transistors Q1, Q2 and the Zener diode D5 In General, the majority of schemes, described in this book, are not critical to the stability of the supply voltage. So the stabilizer can be removed, not including in the circuit of the transistors Q1, Q2, a Zener diode D5 and resistor R2. The positive electrode of the electrolytic capacitors C1 and C2 connect a wire. With the help of diodes D6 and D7 spare battery. B1 all disabled when is the line voltage, and thus the capacitor. When the loss of this battery is included under load. Diodes D1-D4, D6, D7 choose based on the value of current consumption. The voltage of the Zener diode D5 12 14... V.
The Assembly of the device. For reliability, cost loopback alarm is better placed in the metal housing. It is better to take a larger than necessary to the future to be able to add anything else. The same applies to the source voltage.
To pay any suitable insulating material. It is also convenient to use foil-plated hardened paper or glass fiber. However, if you are going to place on Board only one scheme, the faster it can be done without resorting to printed installation. When assembling the power source should pay attention to reliable fixation of the transformer at the bottom of the metal case.
SCR and transistor Q2 in the power source for the best heat conductivity should set on a heat sink. For this purpose, suitable two aluminum plates on 13 cm each. In fact, the jump in energy consumption occurs only when the the audible alarm and the time is relatively short.