Use a multimeter to measure the output voltage of LED light driving power supply: 319V
The LED power supply belongs to the constant current driving power supply, with an output voltage range of 125V~140V, an output current of 360mA ± 3%, and a power consumption of about 60W. Its meaning is that within the voltage range of 125V~140V, the output current is 360mA. Taking 3V/2W LED beads as an example, it can be inferred from 125/3 ≈ 41.7140/3 ≈ 46.7 that the LED driving power supply can connect 42-47 LED beads in series.
Why is the voltage value measured at no load 319V? According to U=IR, regardless of the resistance, when the current I=0, its voltage value is also 0. So in a constant current source, when the load current is 0 (no-load), the series connected current limiting resistor or capacitor voltage reducing circuit does not reduce the voltage. The actual measured voltage value is the DC voltage after rectification and filtering of 220V AC power. The output voltage of 220V rectification and filtering under no-load is 220V * 1.414=311V, and there will be a deviation of 5% above and below the mains power of 220V. Therefore, the no-load measurement of 319V is normal. The following figure shows an LED constant current driving power supply designed using PT4207 high-voltage step-down LED driving control chip. PT4207 has a built-in 350mA switch and is equipped with an external MOS switch driving port. For applications below 350mA, an external MOS switch is not required. When the driving current is greater than 350mA, it can be expanded through an external MOS switch.
