MultipurposePowerSupply
Here we intended build a multi-purpose regulated power supply that will serve as a very useful alternative too our multiple needs of different battery eliminators to operate gadgets like Transistor sets, Audio Casette Recorders and so on and so forth. The circuit shown in Fig. 7.1 produces regulated output DC voltages of 3V, 6V, 9V and 12V that are selectable one at a time with the help of a rotary switch. Each one of the outputs is capable of delivering a load current of 500mA and can take care of wide fluctuations in the input AC. Intact, the output voltage remains at its nominal value for an input of 230AC 60 volts.It may be mentioned here that almost all battery eliminators available in the market for the purpose produce an unregulated output i.e., the output voltage varies with fluctuations in the mains
CIRCUIT DESCRIPTION
The circuit shown comprises of all the necessary circuit components needed for a conventional regulated power supply. The transformer T-l is a mains transformer with a multiple secondary. The secondary winding has taps at 4.5V, 7.5, 12V and 15V. Switch SWI is a dipole, throw rotary switch and it has been shown as split up into three parts in the circuit diagram, the three parts being SW-IA, SW-IB and SW-IC. This switch can be used to select the desired output voltage. It basically selects the appropriate secondary tap. Diodes D1 to D4 constitute full wave bridge rectifier and capacitor C1 is the filter capacitor. IC-1, IC-2 and IC-3 are three terminal regulators of 78XX series. These regulators produce a fixed regulated output depending upon the type number chosen provided that the input to the regulator is at least 2.5V more than the expected output voltage. The requirement of minimum input-output voltage differential explains why we have chosen higher secondary voltages to get a certain DC output. C2toc4 are decoupling capacitors. It may mentioned once again that SW-IA, SW-IB and SW-IC are the parts of the same switch. When SW-IA is on position-l, SW-IB and SW-IC are also on position1.When the switch is on position-1, the input to the bridge rectifier is from 4.5V tap of the secondary winding. The filtered waveform across the filter capacitor has therefore an amplitude of 4.5 x 1.414 =6.36voIts. SW-IB routes this Dc voltage to R1-Vz1 combination and SW-IC routes the regulated DC voltage to the output. The operation is similar for the remaining positions of the rotary switch.
PARTS LIST
Resistors and capacitors
R1 : 3.9 ohms, 2 watt
C1 : 1000gF, Rev (electrolytic)
C2, C3, C4 : (ceramic disc)
Semiconductor devices and ICs
Diodes
D1 to D4 : 1N4001 or equivalent
Zener diode , Vzl : 3V, 2 watt
IC-1: 7812
1C-2: 7809
IC-3: 7806
Miscellaneous
Transformer T-1 : 0-4.5-7.5-1 2-15, 500mA
Mains Transformer
Fuse F1 : Tubular type 500mA fuse with Holder .
SW2 : Mains Power ON/OFF switch
SW1 : 3 pole 4-THROW Rotary switch (Fig. 7.2)
Power supply terminals, solder wire, mains cord etc.
The PCB layout and the components layout are respectively shown in Figs. 6.3 and 6.4.
NOTE : In case ICQ and IC-3 are not easily available, ICQ (7809) can be replaceable 7805 with two series connected silicon diodes of IN 4001 type wired between the uncommon terminal and circuit GND. 1C-3(7809) can also be replaced by a 7805 with a 3.9V zener diode wired from the IC’s common terminal to circuit GND.
TESTING GUIDELINES
The testing part of this project should ensure that the output voltages have correct nominal values, have the desired load current delivering capability and are nicely regulated. These things can be checked as per following guidelines:
- Measure the output voltage in case of each of the rotary switch positions. The measured voltages should tally with the expected values in each one of the cases.
- Repeat step: 1 this time connecting a resistive load across the output so as to deliver a current of 500mA. Remember you will have to change the resistance for each of the rotary switch positions. These resistances will be 6 ohms/2 watt, 12 ohms/5watt| and 24 ohms/10 watt respectively for Positions 1 ,2,3 and 4 of the rotary switch SW-1.
- The regulation part can be checked by varying the AC input to the power supply and monitoring the output voltage. Determine the input voltage range for which the output voltages maintain their values as constant,
LED IDENTIFICATION
Refer to Fig.7.5 for lead identification of IC-1,IC-2,IC3(all will have same pin configuration)and diode 1N4001.
Written by kannan on January 3rd, 2010 with
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