OVER- / UNDER-VOLTAGE PROTECTION OF ELECTRICAL APPLIANCES

C.H. VITHALANI

 This circuit protects refrigerators as well as other appliances from over and under-voltage. Operational amplifier IC LM324 (IC2) is used here as a comparator. IC LM324 consists of four operational amplifiers, of which only two operational amplifiers (N1 and N2) are used in the circuit.

The unregulated power supply is connected to the series combination of resistors R1 and R2 and potmeter VR1. The same supply is also connected to a 6.8V zener diode (ZD1) through resistor R3.Preset VR1 is adjusted such that for the normal supply of 180V to 240V, the voltage at the non-inverting terminal (pin 3) of operational amplifier N1 is less than 6.8V. Hence the output of the operational amplifier is zero and transistor T1 remains off. The relay, which is connected to the collector of transistor T1, also remains de energised. As the AC supply to the electrical appliances is given through the normally closed (N/C) terminal of the relay, the supply is not disconnected during normal operation.

When the AC voltage increases beyond  240V, the voltage at the non-inverting terminal (pin 3) of operational amplifier N1 increases. The voltage at the inverting terminal is still 6.8V because of the zener diode. Thus now if the voltage at pin 3 of the operational amplifier is higher than 6.8V, the output of the operational amplifier goes high to drive transistor T1 and hence energise relay RL. Consequently, the AC supply is disconnected and electrical appliances turn off. Thus the appliances are protected against over-voltage. Thus the appliances are protected against over-voltage.

Now let’s consider the under-voltage condition. When the line voltage is below 180V, the voltage at the inverting terminal (pin 6) of operational amplifier N2 is less than the voltage at the non-inverting terminal (6V). Thus the output of operational amplifier N2 goes high and it energises the relay through transistor T1. The AC supply is disconnected and electrical appliances turn off. Thus the appliances are protected against under-voltage. IC1 is wired for a regulated 12V supply.

Thus the relay energises in two conditions: first, if the voltage at pin 3 of IC2 is above 6.8V, and second, if the voltage at pin 6 of IC2 is below 6V. Over-voltage and under-voltage levels can be adjusted using presets VR1 and VR2, respectively.

WINDOW CHARGER

Keep away intruders with this compact electrified window charger. The charger produces non-lethal shocks that are strong enough to threaten intruders.

The circuit uses IC CD4047 as a free-running astable multivibrator. Capacitor C1 and preset VR1 are timing components. The pulse repetition rate is determined by the value of 4.4C1×VR1. The frequency can be varied with the help of preset VR1.

 

The IC generates complementary squarewave signals at pins 10 and 11. Transistors T1 and T2 serve as drivers for the following push-pull amplfier stage. A high-voltage generator, realised using step-up transformer X1 and medium-power transistors T3 and T4, follows the astable multivibrator. The stepdown transformer is used for reverse function (step-up) and its output is rectified by diode D1, filtered by capacitor C3 and then given to window (made of metal frame).

LIGHTING OF FUSED FLUORESCENT LAMP

Here, a mechanism is presented by which fused fluorescent lamp can be enlighted: 

 

 

                In this model, only healthy filament of fused fluorescent lamp can emit the sufficient electrons and collected by other one to glow up. In the circuit a DC voltage is provided across two filaments with fixed polarity through a Full Wave Bridge Rectifier. In which one port inputs are two different tube-end-pins connection. And other’s port inputs are Supply Line and Choke input point connection. Choke is connected between supply line and bridge rectifier input terminal to control the current flow through back emf process. Starter is also connected across the tube to develop striking voltage. Here Starter and Choke functions same as in a healthy fluorescent lamp.

MOBILE CHARGER WITHOUT TRANSFORMER

Here is a simple battery charger circuit diagram:

Click on the image to enlarge it:

  

You can see the values of the components used below:

R1: 56 giga ohms resistor

R2: 220 Mega ohms resistor

C1: 105 Kilo pico farad , 250 voltage capacitor

D1: IN 4007 Diode

D2: Light emitting diode indicator

D3 : IN 4007 Diode

If you use the values of the components stated above the circuit can recharge a 3 voltage rechargeable battery , You can change the value of R1 and C1 to get recharge battery of more voltage.

USB CHARGING DEVICE

Nowadays mobiles can also be charged using the USB outlet of PC. The mobile charger circuit presented in this project can give 4.7V of synchronized voltage for charging the phone. As USB outlets can give 5V DC and 100mA of current. It is sufficient for slow charging of mobile phones so they can be used to charge the mobile phones. USB stands for Universal Serial Port. It is one of the latest methods to exchange information from PC to the real world. The USB port offers power to the external devices. +5V of power is available at pin1 and -5V of it is available at pin4.

VERSATILE BATTERY CHARGER

This transformer-based battery charger circuit can be used to charge any battery, provided the transformer rating is higher than the battery rating. Normally, a linear regulator IC is used for charging. But this charger circuit uses a MOSFET switch, which effectively draws current from the transformer when its voltage is close to the desired battery charging voltage.

The full-wave bridge rectifier rectifies the transformer output and the combination of diode D5 and capacitor C1 provides gate bias voltage to the MOSFET (T2). Zener diode ZD1 maintains the gate voltage at a maximum of 12V relative to the source. The rectified AC potential is also divided by the combination of resistor R1 and 5-kilo-ohm preset VR1 to set the charging voltage. 

When the rectified AC voltage is below the threshold of IC1 (TL431), the MOSFET conducts. Filter capacitor C2 at its output charges through diode D6. As the rectified voltage decreases from peak to 0V, IC1 turns off at approximately 13.6V. Transistor T1 conducts to provide another pulse current to charge capacitor C2. Thus power drain from the transformer occurs in short pulses and the battery charges between the pulses.

To limit the charging current to the battery, the current through the battery is sensed by resistor R3. Once the voltage drop across R3 reaches the base-emitter threshold of transistor T1, it conducts to turn on IC1, which, in turn, switches off MOSFET T2. This process continues, limiting the charging current to the battery.

VOLTAGE INVERTER - II

This simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input. It is therefore extremely useful for powering opamp and other circuits that require a dual voltage from a single battery. The circuit will operate at an input voltage from around 5V to 20V and produce a output from +-2.5V to +-10V.

Parts

Part	Total Qty.	Description	Substitutions
R1	1	1M Linear Pot
C1,C2	2	15uf 25V Electrolytic Capacitor
U1	1	LM380 Audio Amp Chip
MISC	1	Heatsink For U1, Binding Posts (For Input/Output), Wire, Board

 Notes

1. U1 dissipates around 1W and will therefore require a heatsink.
2. R1 is used to equalize the outputs. The first time you use the circuit, it should be set to mid range and then adjusted with the aid of a voltmeter. Measure each output while adjusting. The circuit is calibrated when both outputs read the same voltage (either positive or negative).

VOLTAGE INVERTER - I

This simple circuit is a good solution to the powering a dual supply op amp from a single battery problem. The circuit simply takes a positive voltage and inverts it. It uses only one 555 timer and a few other passive components, so it doesn't add much in the way of size and cost to a project.

Parts

Part	Total Qty.	Description	Substitutions
R1	1	24K 1/4 Watt Resistor
R2	1	56K 1/4 Watt Resistor
C1	1	3300pF 25V Ceramic Capacitor
C2	1	47uF 25V Electrolytic Capacitor
C3	1	10uF 25V Electrolytic Capacitor
C4	1	100uF 25V Electrolytic Capacitor
D1, D2	2	1N4148 Silicon Diode
U1	1	555 Timer
MISC	1	Wire, Board

Notes

1. V+ can be anywhere from 4 to 16V. -V is one volt less than V+. So for -12V output, use +13V input. The maximum current output of the circuit is about 280mA, more than enough for a few op amps.
2. For better regulation, a 79LOxx series regulator can be used.
3. A zener diode may also be used to regualte the output voltage.

SOLID STATE TESLA COIL CIRCUIT

Similar to the two transistor solid state Tesla Coil already on this site, this solid state Tesla Coil design uses a normal flyback transformer to generate it's high voltage output. Unlike the other circuit, this one does not use two huge power transistors and high wattage resistors. Instead it uses a 555 timer to more efficiently drive a single MOSFET. It's waveform has adjustable off and on time, making for an efficient circuit with little waste heat. It can be adjusted to drive most commonly found flyback transformers and can operate from a 12V to 18V supply. HV output can reach 60KV or more depending on the transformer and supply voltage. 

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1, R5, R9	3	180 Ohm 1/4W Resistor
R2	1	10K Pot
R3, R7	2	10 Ohm 1/4W Resistor
R4	1	5K Pot
R6	1	7.5K 1/4W Resistor
R8	1	150 Ohm 1/4W Resistor
R10	1	1 Ohm 5W Resistor
C1	1	0.0047uF 50V Polyester Capacitor
C2	1	0.05uF 50V Polyester Capacitor
C3	1	220uF 25V Electrolytic Capacitor
C4	1	0.01uF 1200V Polyester Capacitor
Q1, Q2	2	2N2222 NPN Transistor	2N3904
Q3	1	SSM5N55 MOSFET
U1	1	555 Timer Integrated Circuit
U2	1	LM7809 9V Linear Regulator
L1	1	100uH Choke Coil
T1	1	Penn-Tran 1-017-5372 Flyback Transformer	See Notes
MISC	1	Board, Wire, Case, Socket for U1, Heatsink For Q3, Output Terminal (See Notes)

Notes

1. T1 as specified in the parts list is going to be almost impossible to find, but don't worry. Penn-Tran was bought by Wiltron and no longer exists. However, most any medium to large flyback transformer will work as long as it does not have an internal rectifier. Suitable units are most often found in TVs made during the 1970s and 1980s. Look for the most impressive, dangerous, menacing transformer you can find. If you need an idea, a picture of a great transformer for use in this circuit:
   
   These can be found in a small metal box generally in the corner of the TV case, complete with a very handy voltage multiplier unit and usually a nice heatsink.
   You will need to either look up the datasheet for the transformer you have, or probe it with an ohmmeter to identify the coil connections. Most flybacks have a load of taps on the HV side to provide focusing, horizontal and vertical signals. These taps are generally of no use to you. To find the primary (coil B-A on the schematic) you need to find the two lowest resistance connections that are not also connected to the HV secondary wiring. Alternately, if your flyback has an open frame like the one in the picture, you can wind on 5 or so turns of 16 gauge magnet wire as a primary. You will need to experiment with the number of turns to get maximum output. The HV ground lead (connection C on the schematic) is generally easy to locate. It will come from the HV secondary and be tied to the frame of the transformer or chassis ground.
   If by some miracle you were able to locate the Penn-Tran transformer, then connection B is the red dot on the transformer, A corresponds to the black dot, and C matches the orange dot.
2. If the TV you salvaged the transformer from has a voltage multiplier unit (visible slightly at the far right of the above picture), then take it as well. It can multiply the output of this circuit into very high (over 100KV) DC voltages.
3. When building the circuit, leave the flyback disconnected. Connect a 10 Ohm 10W resistor in place of the primary of T1 and connect a scope to the collector of Q3. Adjust R4 to produce an off time of about 10 microseconds. Adjust R2 for an on time of about 70 microseconds. Now remove the scope, 10 ohm resistor, and connect up T1. Power the circuit back on and you should have a high voltage available at the output. If you do not have a scope, just set both pots in their middle position and then adjust them by trail and error until you get the biggest spark at the output of T1.
4. Q3 will require a heatsink.
5. Needless to say, this circuit can produce dangerous voltage. At the very least you are looking at a painful shock. More then likely a decent burn will result from contact with the HV output, as well as instant and uncontrollable muscle contraction. If you have heart problems, don't build this circuit. Be careful!.

SOLID STATE TESLA COIL/HIGH VOLTAGE GENERATOR

This is a fun and useful circuit for demonstrating high frequency high voltge. It can produce up to about 30KV, depending on the transformer used. It is cheap and easy to make, thanks to the standard TV flyback transformer used. It can power LASERS (although I have never tried), demonstrate St.Elmo's fire, and even cause a fluorescent bulb to light from as much as 2 feet away.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	27 Ohm 5W Resistor	27 Ohm 10W Resistor
R2	1	240 Ohm 5W Resistor	240 Ohm 10W Resistor
BR1	1	50 Volt, 6 Amp Bridge Rectifier
C1	1	8000uf, 35 Volt Capacitor
Q1, Q2	2	2N3055 NPN Power Transistor
T1	1	24V 5A Transformer (See "Notes")
T2	1	TV Flyback Transformer (See "Notes")
S1	1	115V 3A SPST Switch
MISC	1	Case, Wire, Heatsinks, Line Cord

Notes

1. T2 is a high voltage flyback transformer salvaged from an old TV, or ordered from Fair Radio Sales (see Where To Get Parts). Look for the biggest, most intimidating transformer you can find. Old tube TV's are a good place to look. The transformer should not have a rectifier built in.
2. You will need to rewind the transformer's primary. First, remove the old primary, being careful not to damage the high voltage secondary. If the transformer is wound with all windings incased in plastic, use another transformer. Second, wind on 5 turns of 18 AWG wire, twist a loop (center tap), and then wind on 5 more turns. This becomes winding C-D. Now, wind on 2 turns of 22 AWG wire, twist a loop, and wind on 2 more turns. This becomes winding A-B.
3. Q1 and Q2 will run HOT if not used with a large heatsink. After the circuit has been running for a minute or two, you should still be able to put your finger on the transistors without being burnt. Also, R1 and R2 will run hot.
4. If you experience arcing on the exposed transformer leads, select a lower voltage for T1. If you are powering the circuit with a power supply (see Power Supply), just crank down the voltage.
5. For a real high voltage output, connect a voltage multiplier (from an old TV or computer monitor) to the output of T2.
6. If the circuit does not work, reverse connections A and B.
7. I finally got around to taking some pictures of the circuit in operation. Here they are:
   
   
   The first picture is the high voltage generator without the voltage multiplier. Notice how hot the arc looks. The second picture is the high voltage generator with a voltage multiplier installed. Notice how much brighter the arc is.
   
   
   The above pictures of myself were taken with me standing on an pie plate that was resting on the top of a plastic bucket. The pie plate was connected to the high voltage generator and charged to about 40,000V. If you do this, be sure to have someone else turn on and off the high voltage generator. Also, don't touch anything when you are charged. Have everything you are going to hold/play with already sitting on the bucket and away from grounded objects. Remember to take off your watch..

Where To Get Parts

When building electronic projects, the hardest thing can somethimes be finding parts. This is especially true if you live in a small town with no speciality electronics stores. Sometimes there is a local surplus shop, but they might not have what you need, and their inventory comes and goes, or mabe guidance systems from Sidewinder missiles are not what you are looking for......

Anyway, now it's time to use the old postal system. To help keep you from making a bad choice and buying some bad murchandice from a dealer that won't back it up, or fess up to their mistakes, I have composed a list of some of the dealers I have had a good expirience with. If they have a Web site, there is also a link to that site.

The Electronic Goldmine

The Electronic Goldmine: PO Box 5408, Scottsdale AZ, 85261. Phone: 1-800-445-0697 The Electronic Goldmine is by far the best company I have dealt with. They are helpful, well stocked and the prices are great. They carry the Yellow Inverter Transformer (part # G993) and Filtered Blacklight Tube (part # G3008) used in the Black Light on the Circuits page. Regular catalog.

All Electronics Corp

All Electronics Corp.: PO Box 567, Van Nuys CA, 91408-0567. Phone: 1-800-826-5432 All Electronics Corp is well stocked with new and surplus electronics. their prices are usually reasonable, except on some items. They stock all the standard parts and a few not so standard parts. Regular catalog.

Fair Radio Sales

Fair Radio Sales: PO Box 1105, Lima Ohio, 1016 E. Eureka St., 45802. Phone: 1-419-223-2196 Fair Radio Sales deals mostly with government and civil radio surplus. They have a selection of tubes and other goodies. They are a great place to find high voltage capacitors for Tesla Coils, etc. Reasonable prices. Regular catalog.

Jameco Electronics

Jameco Electronics: 1355 Shoreway Road, Belmont, CA, 94002-4100. Phone: 1-800-831-4242 Jameco Electronics has a large selection of parts and kits. This is one place to purchase the 8 8 bit ISA prototyping board used in the Computerize Your Room/House project. They also have a wide selection of computer parts and ICs. Free catalog.

MWK Industries

MWK Industries: 1269 W. Pomona, Corona, California 91720. Phone: 1-800-356-7714 MWK Industries is a great place to find laser and optical equipment of all types. You'll find laser tubes, heads, argon, ruby, CO2, semiconductor and even copper vapor lasers in their great, free catalog. They also have a wide selection of plans and books on building and using lasers.

Newark Electronics

(See http://www.newark.com/locate.htm for addresses) I have been told that Newark is a great source of any sort of parts, and by looking at their online catalog I have to agree. They have their entire catalog available on their site, complete with a very powerful search feature. You can search and cross reference parts from any manufacturer. Of course, ordering their 2000 page catalog through the mail could get a little expensive...

POWER SUPPLY

When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find. 

Parts

Part	Total Qty.	Description	Substitutions
C1	1	14000uF or 10000uf 40 VDC Electrolytic Capacitor
C2	1	100uF 50Vdc Electrolytic Capacitor
C3	1	0.1uF Disc Capacitor
C4	1	0.01uF Disc Capacitor
R1	1	5K Pot
R2	1	240 Ohm 1/4 W Resistor	See Notes
U1	1	LM338K 1.2 to 30 Volt 5 Amp Regulator
BR1	1	10 Amp 50 PIV Bridge Rectifier
T1	1	24 V 5 Amp Transformer
S1	1	SPST Toggle Switch
MISC	1	Wire, Line Cord, Case, Binding Posts (for output)

Notes

1. The regulator comes in a TO-3 case and MUST be used with a LARGE heatsink. You may want to mount a small fan to blow air across the regulator (I did).
2. The filter capacitor is large. It won't fit on any board so bolt it to the case.
3. You can, of course, add a volt and amp meter.
4. Since this project operates from 120 VAC, you must include a fuse and build the project in a case.
5. R2 may need to be decreased to 120 Ohm if you experience voltage drift at light loads. 240 Ohm may not load the output appropriately on some regulators. The datasheet for the LM338K does specify 120 Ohm (I suggest you use a 1/2W unit) so you may just want to use 120 Ohm and not bother with the 240 Ohm resistor showin the parts list.

PORTABLE CD PLAYER ADAPTER FOR CAR

Whenever I'm in the car listening to my favourite CD, it always happens; my batteries go dead. To solve that problem, I built this extremely simple regulator circuit. It steps down the 12V from the lighter socket to 9V which is used by the CD player. Different CD players (I have a Sony Discman) may require different voltages, so just use the correct regulator. All the 78xx series regulators have the same pin out, so the circuit is universal. 

Schematic

Parts

Part	Total Qty.	Description	Substitutions
C1	1	1000uF 25V Electrolytic Capacitor
C2	1	10uF 25V Electrolytic Capacitor
C3	1	1uF 15V Elextrolytic Capacitor
C4	1	0.1uF 15V Electrolytic Capacitor
U1	1	7809 Or Other Regulator (See "Notes")	See Notes
MISC	1	Cigarette Lighter Plug, Plug For CD Player (See "Notes"), Heat Sink For U1, Wire, Case.

Notes

1. The voltage your CD player needs will determine which regulator you use. For 9V, use the 7809. For 6V, use the 7806. For the unlikely 5V use the 7805. Remember that whatever regulator you use, you will need to heat sink it. The metal case or metal cover on the case makes a great heat sink.
2. I built the circuit in a small case with the long wire to the cigaratte lighter plug coming out one end, then another, slightly shorter wire going out the other end to the CD player.
3. Triple check your wiring. You would hate to ruin an expensive CD player because you reversed one of the connections or hooked the regulator up backwards.  

LASER POWER SUPPLY

If you have ever worked with lasers, you know how fun and interesting it can be, you also know how expensive it can be. The high voltage power supplies for the laser tubes are often more expensive then the tubes themselves. This supply can be built with commmon parts, most of which you probably already have in your junk box. The secret is the transformer used. It is a common 9V 1A unit, connected backwards for step up.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	10 Ohm 10W Or Greater Resistor
R2	1	Ballast Resistor, See "Notes"
D1, D2, D3	3	1N4007 Silicon Diode
C1, C2, C3	3	0.1 uF 2000V Capacitor
T1	1	9V 1A Transformer
S1	1	115V 2A SPST Switch
MISC	1	Case, Wire, Binding Posts (for output), Line Cord

Notes

1. T1 is an ordinary 9V 1A transformer connected backwards for step up.
2. R1 MUST be installed on a LARGE heatsink. A good heatsink is the metal case the supply is built in.
3. R2 Protects the laser tube from excess current. It should be soldered directly to the anode terminal on the tube. To find R2, start with a 500K 10W resistor and work down until the tube lights and remains stable.
4. If you have trouble with the tube not starting easily, use a longer anode lead that is wrapped around the tube.
5. Depending on the transformer you use, the circuit may or may not work. I cannot guarantee the operation of this circuit. Build at your own risk. Some transformers contain very few secondary windings which will quickly saturate the core and basically act like a direct short. The more secondary windings (that is, primary in this circuit) the better.