Various diagram

This handy circuit can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz.

SILICON CHIP has produced a number of DC speed controllers over the years, the most recent being our high-power 24V 40A design featured in the March & April 2008 issues. Another very popular design is our 12V/24V 20A design featured in the June 1997 issue and we have also featured a number of reversible 12V designs.Circuit looks like:
For many applications though, most of these designs are over-kill and a much simpler circuit will suffice. Which is why we are presenting this basic design which uses a 7555 timer IC, a Mosfet and not much else. Being a simple design, it does not monitor motor back-EMF to provide improved speed regulation and nor does it have any fancy overload protection apart from a fuse. However, it is a very efficient circuit and the kit cost is quite low.Parts layout:
Connection diagram:

There are many applications for this circuit which will all be based on 12V motors, fans or lamps. You can use it in cars, boats, and recreational vehicles, in model boats and model railways and so on. Want to control a 12V fan in a car, caravan or computer? This circuit will do it for you.Circuit diagram:

The circuit uses a 7555 timer (IC1) to generate variable width pulses at about 210Hz. This drives Mosfet Q3 (via transistors Q1 & Q2) to control the speed of a motor or to dim an incandescent lamp.Halogen lamps:While the circuit can dim 12V halogen lamps, we should point out that dimming halogen lamps is very wasteful. In situations where you need dimmable 12V lamps, you will be much better off substituting 12V LED lamps which are now readily available in standard bayonet, miniature Edison screw (MES) and MR16 halogen bases. Not only are these LED replacement lamps much more efficient than halogen lamps, they do not get anywhere near as hot and will also last a great deal longer.
Source: Silicon Chip 15 November 2008

Most, if not all, recent cars have an impressive amount of electronics, whether it be ABS brake systems, engine control with injection calculators, airbag activation, or other various functions, called comfort functions. Among them is one which we tend to forget because it has become so common today. It turns on the windshield wipers automatically for a few seconds after the windshield cleaner. This practice is almost indispensable because it avoids any dripping of excess rinse product right in the middle of a just-cleaned windshield.

Unfortunately, many ‘low end’ cars or some of the older cars are not equipped with this automatic function which is a very nice convenience to have. So, since all that is required is a handful of components that any electronics hobbyist worthy of the name already has in his/her drawer, we will discuss the circuit proposed here. This project is super simple and simply keeps the windshield wiper activated for a few seconds after the windshield washer control contact has been released.

While the windshield washer pump is operating, the 12 volts delivered by the battery are present at the terminals and are therefore charging capacitor C1. Once the windshield washer has stopped, this capacitor can only discharge through R2, P1, R3, and the T1 emitter-base junction, due to the presence of diode D1. It thus keeps T1 in the conductive state during a certain time, the exact period of which depends on the setting of P1. T1 in turn saturates T2, which then does the same for T3.

Circuit diagram:

The Re1 relay is therefore connected which maintains the windshield wiper in operation because its work contact is wired in parallel to the control switch. Once C1 is sufficiently discharged, T1 is blocked, which then blocks T2 and T3 and deactivates relay Re1. The type of components is not really critical, even if we indicate specific reference numbers for T3, any low-power npn transistor with a gain over 25 will work. However, considering the amount of power consumed by the windshield wiper motor, relay Re1 will imperatively be an ‘automobile’ relay.

You can find very low-priced ones at many car accessory shops (and even at some component retailers). These relays maintain contact under 12 volts and often do not have more than one work contact but they are, in general, capable of cutting off about 20 amps. Finally, the only delicate point of this project is to properly identify the control wire for the windshield pump on one hand, and the windshield wiper motor on the other. Observing what is happening at the various connections with a simple voltmeter, should get it right without too much difficulty.

This circuit of a voltage and frequency calibrator provides simultaneous voltage and frequency calibrations by generation of a precision squarewave.
The 555 timer IC is used in a slightly unusual configuration, having the advantage that an exact 50:50 mark/space ratio may be attained by trimming R1. The frequency of oscillation may be set between l0 kHz and 1 kHz by switching timing capacitors C14. C5 decouples the internal ref- erence potential-divider of the 555 from supply·transients. The squarewave output from pin 3 of the IC, while stable in frequency, is not stable in peak-to-peak voltage as this depends on the supply voltage. This is used to switch on and off a temperature compensated constant- current source O1. R2 ensures that the current·source turns off completely when pin 3 goes high. The current- source output, trimmed by R3 to be exactly 1 mA, drives a resistor ladder network so that a series of precise squarewave voltages are generated. The advantage of current drive rather  than voltage drive for this sort of net- work is that calibration is much easier. A simple ladder network is shown by way of example, and more complex ones may simply be constructed to give a wider variety of output voltages.  The non-standard component values used were obtained by paralleling standard values. For the timing capacitors several in parallel had to be used, and only the resultant value is shown on the diagram. 

Almost every electronic circuit needs a separate power supply, which may be a battery or a rectified power supply. Here we will deal with the design and making  of small transformers that are normally used in conjunction with mains-operated power supplies.
This will help electronic hobbyists to design and construct their own transformers according to their needs. In the following pages, a simplified design procedure is given so as to obtain satisfactorily designed transformers. However, the design procedure is often a matter of trial and error.

The tables provided here cut calculations short and help the designer to choose the proper size of wire or core lamination. Only relevant data and calculations are provided so that the designer is not confused by unnecessary details.

The transformer

A transformer has two or more windings of insulated copper wire over an iron core. They are: one primary winding and one or more secondary windings. Each winding is electrically isolated from the other, but they are magnetically coupled with the help of a laminated iron core. Small transforrners have a shell type construction, i.e. the windings are surrounded by the core as shown in Fig. 1. The power delivered by the secondary is actually transferred from the primary, but at a voltage level determined by the turns ratio of the two windings.

Making the Preliminary Transformer design

As the first step to the design of a transformer, the primary and secondary voltage ratings and the secondary current rating must be clearly stated. Then decide on the core material to be used: ordinary steel stampings or cold rolled grain oriented (CRGO) stampings. CRGO has a higher allowable flux density and lower losses.

Core area = 1.l52 x root of (Output voltage x output current) sq. cm.

For transformers with multiple secondaries, the sum of the output volt-amp. product of each winding is to be used. The number of tums on the primary and secondary windings is decided by the turns per volt ratio as:

Turns per volt = 1/ (4.44 X l0^-4 frequency x core area x flux density)

Here, the frequency is 50Hz for Indian domestic mains supply. The flux density can be taken as about 1.0 Weber/ sq. m. for ordinary steel stampings and about 1.3 Weber/ sq. m. for CRGO stampings.

Primary winding design

The current in the primary winding is given by:

Primary Current = Sum of (output volts x output amps)/(Primary volts x efficiency)

The efficiency of small transformers varies between 0.8 to 0.96. A value of 0.87 can be used for ordinary transformers. The proper wire size has to be selected for the winding. The wire diameter depends on the current to be supplied by the winding and the allowable current density of the wire. The current density may be as high as 233 amps/ sq. cm. in small transformers and as low as 155 amps/sq. cm. in large ones. Usually, a value of 200 amps/ sq. cm. can be taken, on whose basis Table 1 is given.

The number of tums in the primary winding is given by:

Primary turns = Turns per volt x primary volts.

The space taken up by the winding will depend on the insulation thickness, method of winding and the wire diameter. Table I gives the approximate values of the turns per square cm. from which we can estimate the window area occupied by the primary winding.

Primary Winding Area = Primary turns/Turns per sq. cm. from Table1

Secondary winding design

Since we have assumed that we know the secondary current rating, we can find out the wire size for the secondary winding by referring to Table 1 directly.

The number of turns on the secondary is calculated in the same way as for the primary, but about 3% extra turns are to be added to compensate for the internal drop of secondary voltage of the transformer, upon loading. Thus,

Secondary Turns = 1.03 (turns per volt x secondary volts)

The window area required for secondary winding is found from Table1 as

Secondary window area = Secondary Turns/Turns per sq. cm from Table1




Core size

The main criterion in selecting the core is the total window area of winding space available.

Total window area = Primary window area + sum of secondary window areas + space for former and insulation

Some extra area is required to accommodate the former and insulation between windings. The actual amount of extra area varies, although 30% may be taken to start with but may have to be modified later. The suitable core sizes having a larger window area are selected from Table ll. . Taking into account the gap between laminations while stacking them (the core stacking factor taken as 0.9), we have

Gross core area = Core Area/0.9 sq.cm.

ln general, a square central limb is preferred. For this, the width of the tongue of lamination is

Tongue width = root of Gross core area cm.

Now refer to Table ll again and finally select the proper i core size, with sufficient window area and a close value of the tongue width as calculated. Adjust the stack height as required to obtain the required core section.

Stack height = Gros core area/Actual tongue width cm.

The stack should not be much less than the tongue width but may be more. However, it should not be more than 1% times the tongue width.




How to Design and Make a Transformer finally

The windings are wound on an insulating former which .fits over the center limb of the core.The primary is usually wound first, then the secondary, with insulation between windings, A final insulating layer is provided over the windings to protect them from mechanical damage. When thin wires are used, their ends must be soldered to thicker wires for bringing the terminals outside the former. The laminations are assembled over the former with alternate laminations reversed in assembly. The laminations must be held together tightly by a suitable clamping frame or by screws (if holes are provided in the laminations).




Shield

lt is a good practice to use an electrostatic shield between the primary and secondary windings to prevent disturbances from passing through to the secondary from the primary. The shield is made out of a copper foil which is wound between the two windings for slightly over a tum. Insulation must be provided along the length of the foil and care taken so that the- two ends of the foil do not touch each other. A wire soldered to the foil is bought out and connected to the ground.





A practical design example can be witnessed below:

Guitar Amplifier Circuit Diagram

This means that conduction occurs through the complementary pairs of TR1/TR4 and TR2/TR3 on alternate marks and spaces, effectively doubling the voltage across the ultrasonic transducer, LS1. This is optimised to generate a high output at ultrasonic frequencies. This configuration was tested by decreasing the frequency of the oscillator to an audible level and replacing the ultrasonic transducer with a loudspeaker; the results were astounding. If the dog repellent circuit was fed by a bench power supply rather than a battery that restrict the available current, the output reached 110dB with 4A running through the speaker which is plenty loud enough!

The Dog and Cat repellant was activated using a normal open switch S1 to control the current consumption, but many forms of automatic switching could be used such as pressure sensitive mats, light beams or PIR sensors. Thus it could be utilise as part of a dog or cat deterrent system to help prevent unwanted damage to gardens or flowerbeds, or a battery powered version can be carried for portable use. Consider also using a lead-acid battery if desired, and a single chip version could be built using the 556 dual timer IC to save space and improve battery life.

Mag- Magnatec (Semelab Subdivision)
Semelab Plc. Coventry Road, Lutterworth, UK. Phone: +44-1455-552505
http://www..semelab.co.uk

Max- Maxim Integrated Products
120 San Gabrial Sunnyvale, CA 94086, USA. Phone: +1-800-998-8800
http://www.maxim-ic.com

Mcp- Microchip Technology Inc.
2355 West Chandler Blvd. Chandler, AZ 85224-6199, USA. Phone: 480-792-7200
http://www.microchip.com

Mit- Mitsubishi Electric Co. Ltd. (ICs manufacture is handed to Renssas Ltd.)
2-3 Marunouchi, 2-chome J 100 Chiyoda-Ku, Tokyo, Japan. Phone: +81-3-3218-2863
http://www.mitsubishichips.com

Mot- Motorola Inc. (ICs manufacture is handed to ON Semiconductor)
6501 William Cannon Drive W Austin, TX 78735 USA. Phone: +1-512-891-2000
http://www.motorola.com

Mps- Monolithic Power Systems
6409 Guadalupe Mines Road, San Jose, CA 95120, USA. Phone: 408-826-0600
http://www.monolithicpower.com

Mts- Mitsumi Electric Co. Ltd.
8-8-2, Kokuryo-cho, Chofu-chi, Tokyo 182-8557, Japan. Phone: (03)3489-5333
http://www.mitsumi.co.jp

Msk- M.S.Kennedy Corp.
4707 Dey Road Liverpool, N.Y. 13088 USA . Phone (315) 701-6751
www.mskennedy.com

Mul- Mullard LTD (Is not a current ICs manufacturer)
New Road Mitcham, Surrey England CR4 4XY. Telex: 264341
NEC Electronics Inc. (Nippon Electrical Company)
NEC Building 7-1, Shiba 5-chome, Minato-ku Tokyo, Japan. Phone: +81-3-3454-1111
http://www.ic.nec.co.jp

NJR- New Japan Radio Co., Ltd.
Arvco Tower 17F, 1-8-1, Shimomeguro, Meguro-ku, Tokyo 153, Japan.
Phone: +81-3-5434-8335
http://www.njr.com

Npc- Nippon Precision Circuits Inc.
4-3, Fukuzumi 2-chome, Koto-ku, Tokyo 135-8430, Japan. Phone:+81-3-3642-6661
http://www.npc.co.jp/453

NSC- National Semiconductor Corp.
North America PO Box 7643 Mount Prospect, IL 60056-7643, USA.
Phone: +1-800-628-7364, ext 305
http://www.national.com

NTE Electronics Inc.
44 Farrand Street, Bloomfield, NJ 07003, USA. Phone: 800-631-1250
http://www.nteinc.com

Nxp- NXP Semiconductors
PO Box 80073, 5600 KA Eindhoven, Netherlands. Phone: +31 40 27 45678
http://www.nxp.com

Oki Semiconductor Inc.
785 N Mary Avenue Sunnyvale, CA 94086, USA .Phone: +1-408-720-1900
http://www.okisemi.com

Omn- Omnirel (Acquired by International Rectifier)
 205 Crawford Street, Leominster, MA 01453 USA. Phone: (508) 534-5776
http://www.omnirel.com

Ons- ON Semiconductor (Motorola semiconductors subdivision)
Japan Customer Focus Center 4321 NishiGotanda, Shinagawaku, Tokyo, Japan
Phone: 81357402745
http://onsemi.com

Pan- Panasonic Electronics Corp.
1 Kotari-Yakemashi, Nagaokakyo, Kyoto 617, Japan. Phone: 075/921-8151
http://www.mec.panasonic.co.jp

Pch- PointChips Co. Ltd.
4FL., Dabong Tower Bldg. 890-12, Daechi-Dong, Kangnam-Gu, Seoul 135-280, Korea
Phone: 82-2-508-2443
http://www.pointchips.com

Phi- Philips GmbH (ICs manufacture is handed to NXP Semconductor)
Hammerbrookstrasszlige 69 D-20097 Hamburg, Germany. Phone: +49-40-23536-0
http://www.philips.com

Pjn- Promax-Johnton
(There is no accesible padding information)
http://www.p-johnton.com

Pls- GEC Plessey Semiconductor
(Is not a current ICs manufacturer)
Pnr- Pioneer Not the manufacturer of ICs
Will use custom IC with Pioneer type marking
Ptc- Princeton Technology Corp.
2F, No. 233-1, Baociao Road, Sindian City, Taipei 23145, Taiwan, R.O.C.
Phone: 886-2-66296288
http://www.princeton.com.tw

Rca- RCA Corporation (Is not a current ICs manufacturer)
Route 202, Sommerville, NJ 08876, USA. Phone: 201/685-6423
http://www.rca.com
Ren- Renessas Ltd.
Nippon Bldg., 2-6-2, Ohte-machi, Chiyoda-ku, Tokyo 100-0004, Japan,
Phone: 852-2424-9127
http://www.renesas.com

Switching regu­lators are available is different schema configurations in­cluding the flyback, feed-forward, push-pull, and non-iso­lated single-ended or single-polarity types. Also, the switching regulators can operate in any of three modes – step-down, step-up, or polarity inverting. rovide the active functions for step-down (back) switching regulator, capable of driving a1A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, 15V and an adjustable output version.

LM2575 Regulator Switching Circuit

LM2577 Regulator Switching Circuit

The National Semiconductor LM 1577/LM 2577 are monolithic ICs that provide all of the power and control functions for step-up (boost), fly back, and forward converter switching regulators. The device is available in three different output voltage versions: 12 V, 15 V and adjustable.

Via:[http://www.diagramtoday.com/switching-regulators-using-lm-2575-and-lm-2577]