Download 3.1 Battery charger based on scr

SCR UYGULAMA ORNEKLERİ
Dimer devreleri
Representative Image:
Şekil 2.20.(a) da iki ayrı diyak sembolü gösterilmiştir. Genel olarak diyaklar geniş oranda SCR ve triyak tetikleme
devrelerinde yardımcı eleman olarak kullanılmaktadırlar. Örnek bir diyak için bazı öz değerler;
3.1 Battery charger based on scr
Figure 21: battery charger
3.1.1Principle of work
A simple battery charger based on SCR is shown in figure21 .Here the SCR rectifies the AC mains voltage to charge
the battery. When the battery connected to the charger gets discharged the battery voltage gets dropped. This inhibits
the forward biasing voltage from reaching the base of the transistor Q1 through R4 and D2.This switches off the
transistor. When the transistor is turned OFF, the gate of SCR (H1) gets the triggering voltage via R1 & D3.This
makes the SCR to conduct and it starts to rectify the AC input voltage. The rectified voltage is given to the battery
through the resistor R6(5W). This starts charging of the battery.
When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit
made of R3,R4,R5 and D2.This turns the transistor ON. When the Q1 is turned ON the trigger voltage at the gate of
SCR is cut off and the SCR is turned OFF. In this condition a very small amount of charge reaches the battery via R2
and D4 for trickle charging. Since the charging voltage is only half wave rectified, this type of charger is suitable only
for slow charging. For fast charging full wave rectified charging voltage is needed.
3.1.2 Our steps to build the circuit
We build this circuit on welding plate, we used step down transformer 230V primary, 18V /3A secondary, tic116c scr,
we control the voltage of the battery by varying potentiometer (R4) and we connect the battery to the circuit by using
crocodile clips as you can see in figure22.
Figure 22: battery charger
When we run the circuit it gives a voltage up to 15v before we connect the battery, this voltage was enough to charge
our battery (ratings 12V, 7AH )
3.2 5v dc power supply
Figure 23: 5v dc power supply circuit
This circuit include the over voltage protection application by using power electronic devices.
3.2.1 Principle of work
For circuits using TTL ICs the supply voltage is a great concern and a slight increase in supply from the rated 5V may
damage the IC. Using fuses alone does not solve the problem because a fuse may take several milliseconds to blow
off and that?s enough time for the IC to get damaged.
In this circuit a crowbar scheme is used in which a triac short circuits the power supply and burns the fuse. The
burning time of the fuse is not a concern because the power supply is already shorted by the triac and the output
voltage will be zero. When the output voltage exceeds 5.6 volts the zener diode D2 conducts and switches ON the
triac T1.Now T1 acts as a closed switch, shorting the circuit. The output voltage drops to zero and fuse gets burned
off. Since the switching of triac takes place within few micro seconds there will be no damage to the TTL ICs or any
other such voltage sensitive components in the load circuit.
3.2.2 Our steps to build the circuit
We build this circuit on welding plate, we used step down transformer 230V primary, 12V/2A secondary, BT136 triac,
we build the bridge rectifier using four 1N4007 diodes and we put a thermal resistance (22 ohm, 15 watt) in series with
the triac in order when high current pass through it could handle and dissipated the energy as heat as you can see in
the figure24.
Figure 26: light dimmer circuit
3.3.2 Principle of work
This is the circuit diagram of the simplest lamp dimmer or fan regulator. The circuit is based on the principle of power
control using a Triac. The circuit works by varying the firing angle of the Triac. Resistors R1, R2 and capacitor C2 are
associated with this. The firing angle can be varied by varying the value of any of these components. Here R1 is
selected as the variable element. By varying the value of R1 the firing angle of Triac changes (in simple words, how
much time should Triac conduct) changes. This directly varies the load power, since load is driven by Triac. The firing
pulses are given to the gate of Triac T1 using Diac D1. In addition a snubber circuit consisting of resistor R4 and
capacitor C3 is included to improve the performance of the triac T1. A fuse is also included for better safety.