I have a 240v-5v transformer for recharging, and it makes an annoying very high-pitched squeaking noise. What causes the noise?
Normal transformers with iron laminated cores operate at 50-60Hz (50-60 times a second), but transformers in modern cell-phone chargers and PC power supplies require a higher power than would be possible for the given size restraints. A 240v to 5V @ 1A 50-60hz transformer would be the size of a deck of cards and would weigh several kilograms, but if you replace the core of the transformer with a ferrite material (powdered iron) and switch the primary winding at high frequency, say 20Khz or more (20 thousand times a second) the size of the transformer shrinks to the size of a small coin. The ringing sound you are hearing could be caused by several things: 1. It's operated at a near-audible frequency, like 19Khz (not very likely) 2. It's under very high load condition and it's struggling to meet the power requirements and as a consequence the duty cycle of the PWM has increased which can make a chirping sound. 3. It's defective or dying, and it's having a hard time regulating the output voltage and it's excessively modulating the PWM. 4. You are young and young people have better than normal hearing in the higher end of the frequency range and you might be hearing a harmonic of the higher than audible drive frequency. Hope that answers your question :)
SQUEEK? That sounds like a high (audio) frequency oscillator. So this sounds like a pulsed regulator, not like a transformer-type power supply. I would guess that your unit is measuring the battery voltage, then applying a pulse of power to charge the battery, then checking the voltage again in a continuous sequence. This would be a switching type charger. 5 Volts - sounds like a personal electronics unit, for instance a cell phone or personal entertainment. Right? 240 Volts - Sounds like Europe. Right? (In America it would either be 120 Volts or some switching supplies are designed to operate from 90 to 250 Volts.)
