# What is the commonality between a radio, a welding power source and an induction heater?

I was reading into the basics of welding power supply (because I have taken up TIG welding) and inductive heating (because it is part of a number of applications in metal fabrication), and I noticed that the two seem to share basic concepts also found in radio circuitry, namely the idea that you adjust the frequency of an AC signal.

To my newbie eye, it seems like an inductive heater is a high power radio sans the information encoding and with a coil where the antenna was, and the welding machine seems to replace the coil with an arc, but I might well be off track there.

Now, I only have a very rudimentary understanding of electronics, yet. I have worked with sensors that measured electricity for a couple of years, so I have a basic understanding of AC power, and I have heard of inductive and capacitive loads.

If I were to draw a block diagram (with functional groups instead of the actual circuitry), what would be common elements in the three types of devices? It seems I usually have a rectifier followed by an inverter, to change grid AC to "my-frequency" AC. Then there seems to be something called a "resonant tank circuit", and I have read the Wikipedia page, but I am not exactly sure if I have really understood it already.

My immediate goal here is to have a map for learning more about these topics, i. e. I would like to understand the larger building blocks of those devices first, gain some vocabulary that I can use for further study, and then work my way down to how the details work. Pointers to learning resources are appreciated.

The basic concept here is probably "resonance", which is related to the ringing of a bell or the swinging of a pendulum at its natural frequency.

Strike a bell and it will ring. But if you play back the sound of its ringing, it will also start to ring. This is because the resonant frequency is optimal for it accepting energy.

You can keep a swing going over a large range of motion with a small push, correctly timed. Same phenomenon.

LC circuits also "ring". In the case of radios, this is used for tuning: it resonates most strongly near the desired radio frequency. So it absorbs radio waves at that frequency and turns them into an electrical signal, while absorbing waves at different frequency less strongly.

In the case of the heater and welder, it's being used to optimise the power transfer through a transformer to produce a large current.

A full theoretical understanding of AC involves calculus and complex numbers.

• Radio pretty much always envolves resonance because you are interested in a narrow band around a specific frequency. I'm not sure about welding, but inductive heating doesn't necessarily rely on resonance. A inductive heater is basically a high power transformer primary. The stuff being heated is conductive, so becomes a single-turn secondary. Resonance is not necessary, and will take some tweaking to achieve since the load characteristics can vary. – Olin Lathrop Mar 21 '13 at 12:05
• @OlinLathrop - Inductive heaters often adjust their frequency dynamically. I assume this is to achieve resonance despite changing characteristics of the object being heated. See this interesting teardown. – Rocketmagnet Mar 21 '13 at 14:35