Request expert opinion on this wireless cellphone charger circuit

it's a transformer

Notice how the center-tap is connected to +ve supply. It is also a Hartley oscillator (look it up if you want) tuned by the self-capacitance of the spiral inductors and the reflected capacitance of whatever receiver coil and attached circuitry is nearby. The frequency of oscillation will vary as the whole setup is moved.

It creates electro-magnetic pollution and will seriously annoy anyone nearby using AM BC or SW receivers.

piglet

Most respondents seem to be having issues (burnt switches), and the blogger admits that he hasn't actually done it himself with the described hardware. Oscillators operating on the principal of bipolar transistor base current starvation will be inefficient, and are best reserved for small-signal applications, where the losses are not signifigant.

References in the blog are made to a you-tube video, which shows a much larger heatsunk switch, and a maximum power transmission efficiency of less than 50%, based on the actual DC load measurements made there.

'Examining Wireless Power Transfer' TI SEM1200 topic3 slup321:

RL

its a dangerous circuit...

The 2222 is rated for 800mA last time I looked, and that should be attached to a sink. Wattage is a factor.

There should be a regulator in there to supply the phone, I would not be putting wild voltages to the phone.

Jamie

The phone's battery is a simple shunt regulator to the impedance-limited source.

RL

Good luck getting it through Part 15 as an intentional radiator.

Yeah? what about the circuits you need to go through before getting to that battery?

Think.

Jamie

I think you might mean "unintentional" radiator for external battery chargers. See: Note that for a "Class B external switching power supplies", the tests are only for "verification", which means the FCC trusts the manufacturer to be honest, competent, and trustworthy. Right.

I think the external battery chargers referred to here are just line powered switching supply bricks. It could be covered under "any other device" though. But it does intentionally radiate a RF field. And it's anybody's guess as to the frequency.

"honest, competent, and trustworthy" especially in China.

Intentional radiators are those that are intentionally designed to communicate with some other device. Unintentional radiators are those that belch RFI/EMI without a designated receiving device. I'm quite sure that a switching power supply is not intended to send useful voice, video, or data to a receiver, and is therefore an unintentional radiator.

You'll find the definitions under:

(o) Intentional radiator. A device that intentionally generates and emits radio frequency energy by radiation or induction.

(z) Unintentional radiator. A device that intentionally generates radio frequency energy for use within the device, or that sends radio frequency signals by conduction to associated equipment via connecting wiring, but which is not intended to emit RF energy by radiation or induction.

Ummm.... I was trying to be diplomatic and subtle.

On Wednesday, November 25, 2015 at 11:06:36 PM UTC-5, snipped-for-privacy@gmail.com wro te:

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It's not an oscillator, it's a short circuit on the 12V source, limited onl y by transistor beta. The DC path through the transformer to the base locks the circuit up (with 60mA base drive which is a LOT), it will not oscillat e. This type of circuit requires ac-coupled feedback to work.