BF1006. General Description. Features. Application. Typical Application. Constant Current Controller for AC/DC LED Driver

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1 Constant Current Controller for AC/DC LED Driver General Description is a high performance AC/DC offline LED driver which uses Pulse Frequence Modulation method to build Discontinuous Conduction Mode flyback power supplies. It operates in primary-side sensing and regulation while removing the need of secondary feedback circuitry. The device operates in PFM in CC mode and ON-OFF in CV mode. Particular inductance compensation mode without more external components can achieve a high tight output current regulation. Application LED lighting Typical Application Features Very tight LED constant current regulation at universal AC Input Eliminates Opto-coupler and all secondary CV/CC control circuit Constant frequency startup mode accelerate start-up process Perfect EMI performance, easily meets EN55022 class B without Y capacitor Build-in Leading Edge Blanking(LEB) Low Start-up Current(Max.5μA) Low Operating Current(Max.200μA) UVP(under voltage protection) Typ.16.5V start-up Typ.7 V shut-down Output Driver Ability(Typ.20 ma) Small SOT23-5 Package D2 D5 D1 1N4007 D4 + C2 + C3 4 6 C5 R6 D3 D C1 R2 V + 3 R1 L1 R12 2 R7 R5 R11 V - D7 R13 1N4007 R8 C8 4 IC1 3 2 R Q1 R9 Vsense 5 1 Isense R12 Datasheet TS-POM-PD-0042 Rev.A/0 Page 1 of 6

2 Block Diagram Package Type Isense Vsense TOP VIEW Pin Definition Pin number Pin name Pin description 1 Isense Current sense input. 2 Ground. 3 Gate drive output for the external power BJT switch. 4 Power supply. 5 Vsense It senses the forward time of secondary diode. Datasheet TS-POM-PD-0042 Rev.A/0 Page 2 of 6

3 Operation Description The regulate the output voltage in a new method of controlling off time of the external power BJT. It uses PFM with a constant factor between the de-magnetic time and the operate cycle time to regulate the output current. The controller consists of the CV/CC control module, leading edge blanking, current limited circuit, the power BJT driving circuit, feedback sense circuit, start control and the pin. Startup Current and Constant Frequency Start The is designed to have a low startup current so that can be charged up above the UVLO threshold and starts up quickly. After startup, will operate in a constant frequency (Typ. 20KHz) until the output Voltage up to a certain value, so that the output can set up quickly. CC Operation Mode(Inductance Compensation) As the output voltage ramps up, secondary diode on time (Tds) falls down. The Vsense pin sense Tds and adjust switching frequency, so the output current can be constant. Because Tds has no relationship with the primarily inductance, the CC precision can be up to ±5% without the inductance correction circuit. The output current can be calculated by the following expressions: (Np: Primary-side winding turns of the transformer; Ns: Secondary-side winding turns of the transformer.) CV Operation Mode(On-Off) Tds Np Iout = 0.5 * Ip T Ns As the pin voltage approaches Vcccv from the CC regulation mode, the power supply transitions into CV operation. The switching frequency at this point is at its maximum value, corresponding to the peak power point of the CC/CV characteristic. During CV operation, the IC adjusts the BJT switching frequency to provide a constant output voltage. The output voltage can be calculated by the following expressions: Ns Vout = [( VD6) ] VD3 Na (Ns: Secondary-side winding turns of the transformer; Na: Bias winding turns of the transformer.) Current limit and leading edge blanking The current limit circuit senses the primary current form the voltage on the sensing resistor cycle by cycle. When the voltage exceeds the internal threshold, the external BJT will turn off immediately. The leading edge blanking circuit inhibits the current limit comparator for a short time (TLEB) after the power BJT is turned on, this leading edge blanking time have been set so that current spikes caused by capacitance and rectifier reverse recovery time will not cause premature termination of the power BJT condition. Datasheet TS-POM-PD-0042 Rev.A/0 Page 3 of 6

4 Over load protection and Auto-restart When the voltage exceeds the internal threshold Von, the converter starts operate. In the event of a fault condition such as an output over loads or an output short circuit condition, the output voltage falling will cause the voltage of fall. As voltage falls to the internal threshold Voff, the enters into an auto-restart mode. During the period of voltage decreasing, the output current is in normal range because of the excellent CC mode. Electrical Characteristic (TA = 25 C, if not otherwise noted) Item Symbol Conditions Min. Typ. Max. Unit Supply Voltage Start-up Current Idd VCC=14V 3 5 µa Operation voltage Vov 19 V Operation current I oc µa Turn-on Threshold Voltage VCCON V Turn-off Threshold Voltage VCCOFF V CC/CV mode change voltage Vcccv V Oscillator Duty Cycle Tds/T VCC=19V % Current Sensing Leading Edge Blanking TLEB ns Current Sense Detection Voltage Vcs VCC=19V V Else Output Delay Time Td 150 ns Output Driver Current IDriver ma Absolute Maximum Ratings Item Symbol Value Unit pin input voltage 40 V Lead temperature TL 260 SENSE pin input voltage VSENSE ISENSE 7 V Power Dissipation PD 400 mw Operating Junction Temperature TJ -40 to +125 Storage Temperature Range TSTJ -55 to +150 Datasheet TS-POM-PD-0042 Rev.A/0 Page 4 of 6

5 Test Circuits 1) Start-up current consumption Connect circuit like test circuit 1. Set V1=14V±0.03V with 1ms delay time, The current A1 flowing into is the start-up current IS VS consumption. V1 A1 2) Hysteresis start-up Connect circuit like test circuit 1. Test circuit1 When V1 increases over Vx1 (the first threshold voltage) from 0V, the IC current consumption changes from less than 5uA to greater than 100uA; and only when V1 decreases under Vx2 (the second threshold voltage), the IC current consumption changes from greater than 100uA to less than 5uA. 3) Over current protection detection voltage Connect circuit like test circuit 2. Set V1=19V±0.03V, V2=0, make the pin floating. The over current protection detection voltage is the voltage V2 when the output voltage changes from 4V~6V to 0V. V2 IS V1 A1 VS 4) Duty Cycle of Vsense pin Test circuit2 Connect circuit like test circuit 3.Set V1=19V±0.03V, V3=5V±0.03V. The duty cycle of Vsense pin is from 41.2% to 42.8%. 5) CC/CV mode transforming voltage Connect circuit like test circuit 3.Set V1=19V±0.03V, V3=3V±0.03V. The CC/CV mode transforming voltage is voltage V1 when the frequency of Vsense pin changes from greater than 2KHz to less than 100Hz. Datasheet TS-POM-PD-0042 Rev.A/0 Page 5 of 6

6 1A 1Y 2A 2Y 3A 3Y G HD74HC04P V 6A 6Y 5A 5Y 4A 4Y 1A 1B 1Y 2A 2B 2Y G SN74HC132N V 4B 4A 4Y 3B 3A 3Y V R2 20KΩ R4 5KΩ R2 20KΩ V1 VSS 2 R4 5KΩ VS IS 5 1 Q C1 2nf Q C1 1nf Test circuit3 RESTRICTIONS ON PRODUCT USE The information contained herein is subject to change without notice. (short for BME) exerts the greatest possible effort to ensure high quality and reliability. Nevertheless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability to physical stress. It is the responsibility of the buyer, when utilizing BME products, to comply with the standards of safety in making a safe design for the entire system, including redundancy, fire-prevention measures, and malfunction prevention, to prevent any accidents, fires, or community damage that may ensue. In developing your designs, please ensure that BME products are used within specified operating ranges as set forth in the most recent BME products specifications. The BME products listed in this document are intended for usage in general electronics applications (computer, personal equipment, office equipment, measuring equipment, industrial robotics, domestic appliances, etc.). These BME products are neither intended nor warranted for usage in equipment that requires extraordinarily high quality and/or reliability or a malfunction or failure of which may cause loss of human life or bodily injury ( Unintended Usage ). Unintended Usage include atomic energy control instruments, airplane or spaceship instruments, transportation instruments, traffic signal instruments, combustion control instruments, medical instruments, all types of safety devices, etc.. Unintended Usage of BME products listed in this document shall be made at the customer s own risk. Datasheet TS-POM-PD-0042 Rev.A/0 Page 6 of 6