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The post discusses a small induction heater circuit for school project and exhibitions, using a very ordinary IC 555 astable PWM circuit. The idea was requested by Mr. Anthony


The Request

Hi,
for a school project i need to construct an AC induction cooktop and was wondering if you could help me put together a part list for a much weaker induction cooktop than yours, it only has to warm up a few MLs of water. is this something that is possible?


The Design

An induction heater is considered as an amazing circuit which is capable of converting electricity into heat with utmost efficiency and without much losses.

However a little contemplation will make you realize that actually its just the opposite. An induction heater circuit is an extremely inefficient circuit which converts all the electricity into heat.

This opinion is with regards to the general view about electrical and electronic circuits where the emission of heat is considered to be inefficient and undesirable.

But for an induction heater, this inefficiency attribute becomes its positive aspect, and the more inefficiently it is designed, the more beneficial it becomes for the user.

To be precise, an induction heater is an inefficient transformer which is purposely mismatched with its frequency and the core material specifications.

In this concept the core is normally a ferromagnetic material such as iron having a copper coil wound over it. The copper winding around this iron core is oscillated at a relatively higher frequency which may be not suited for the iron material.

The bad conductor nature of iron finds it difficult to resonate at the high winding frequency resulting in the generation of high back emf eddy currents which in turn causes high temperatures on the core material.

This feature is exploited in induction heaters for the intended purpose of achieving high temperatures

Although massive induction heater units can be built for generating extremely high temperatures using the same concept, a small induction heater circuit for school exhibition project can also be implemented easily using ordinary parts such as a IC 555 and some other inexpensive passive components.




A simple IC 555 induction heater circuit for school project is shown in the above figure.

Here the IC is configured as a PWM generator circuit, which is adjusted using the 5 K pot. The frequency is adjusted by tweaking the 1M pot or the 1uF capacitor specifically for achieving the optimized heating effect on the work coil.

The working coil here is made by winding around 50 turns (not critical) of 1mm super enameled copper wire over a fabricated iron pipe whose dimensions may be selected as per individual preference, and could be anywhere between 10 to 20 cm in diameter and 30 to 40 cms long.

Once the above set up is built and switched ON, the coil and the iron pipe could be seen developing heat gradually, and anything placed inside the pipe could be witnessed getting heated up.

If its water inside the pipe, then it could begin warming up and even reach the boiling point if the coil is optimized correctly through the frequency and PWM adjustments.

The idea behind this small induction heater circuit is simple, it is to force the iron pipe atoms to electromagnetically oscillate at an incompatible frequency resulting in the production of huge amounts of opposing eddy currents and a proportionate amount of heat due to this opposing current in the metal.

 If you have more questions regarding this induction heater circuit for school science project, do feel free to ask them through comments, below.

The post explains a simple amplifier circuit which can be quickly made using a couple of transistors )BJTs) and a few resistors. The idea was requested by Mr. Raveesh.



 The Request

Sir,

I am working in LIC of India and electronics is my hobby since so many years.  Often I will be browsing your website and found many useful projects.  I require a favour from you.

I have a FM transmitter module which works on 5 volts DC with provision to connect from Computer through USB or from audio out from any other device through 3.5 mm audio jack.  The module works great in computer USB mode with great signal strength, quality and coverage.  But when I connect the same through audio input jack from DTH set top box the signal strength becomes weak even with full volume in both set top box and FM module.  I think the audio signal level from set top box is not sufficient for the FM module. 

Please suggest me a good quality stereo audio small signal amplifier circuit which can work from 5 or 6 volts single supply, that would not load the set top box, preferably using good low noise op-amp with detailed circuit and parts label.

Sincerely hope you will help

With regards

Raveesh 

The Design

A simple amplifier circuit can be very easily built by assembling a couple of transistors and some resistors as shown in the following figure:



The circuit is a simple two transistor amplifier using a feedback loop for enhancing the amplification.

Any music as we know is in the form of a consistently varying frequency, therefore when such a varying input is applied across the indicated C1 end terminals, the same is delivered across the base T1 and ground.

The higher amplitudes are processed normally and is reproduced with a potential thats approximately equal to the supply voltage, however for the lower misc amplitudes T2 is allowed to conduct at the higher ratio which is allowed to pass to its emitter, and this is when the actual enhancement of the music is implemented by transferring this accumulated higher potential back to the base of T1 which correspondingly saturates at a much optimal rate.

This push pull action ultimately results in an overall amplification of an insignificantly small music or data input into a significantly larger output.

This simple amplifier circuit enables boosting extremely small or minimal frequencies to an appreciably bigger outputs which can be then used for feeding lager amplifiers.

The discussed circuit was actually popularly used in old cassette type playback recorders in their preamp stages for boosting the minute signals from the tape head so that the output from this small amplifier became compatible for the attached high power amplifier.

Parts List

R1 = 22K
R2 = 220 ohms
R3 =100k
R4 = 4K7
R5 = 1K
C1 = 1uF/25V
C2 = 10uF/25V
T1/T2 = BC547