Taiwanese chip maker Holtek has launched an LED driver to control current on the primary side of the transformer in LED lighting applications such as LED bulb and LED tube. LED lamp designers can achieve power efficiency of around 86 to 88% using Holtek' HT7L5600 and a power factor of 0.9 with a wide operating voltage range of 85 current regulation accuracy offered by HT7L5600is less than +/-3%.
The advantage of having primary side control is not only higher efficiency but also elimination of external components including optocoupler.
The protection features offered in HT7L5600 includes VCC Under Voltage Lockout (UVLO), Over Current Protection (OCP), Output LED String Open Protection, Output LED String Short Protection, VCC Over Voltage Protection (OVP) and Leading-Edge Blanking (LEB) for current sensing. HT7L5600 also offers fully integrated thermal protection function where the external MOSFET is safeguarded against overvoltage.
The application circuit diagram provided in the datasheet has around 15 resistors, 7 capacitors, 4 diodes, bridge rectifier, MOSFET and high-frequency power transformer.
The datasheet can be downloaded from
Holtek says "By operating in the boundary conduction mode with its high power factor characteristic, the device can operate with minimum system switching losses thus offering enhanced EMI characteristics."
HT7L5600 consumes low operating current and also low start-up current of 10μA.
HT7L5600 is packaged in SOT-23-6.