APPLICATION NOTE TS19721

Transcription

1 APPLICATION NOTE TS19721 Single-Stage PFC Buck Current Control LED Driver With High Voltage MOSFET Integrated Description The TS19721 is a high power factor and high accuracy constant current PWM controller. It integrates high voltage MOSFET to reduce system component.it is able to control total harmonic distortion (THD) and efficiency optimization by an external resistor. TS19721 achieves high power factor and high efficiency by boundary conduction mode (BCM). The line and load regulation of LED current are within ±2.5%. TS19721 also provides gate driving voltage clamping, V CC over-voltage protection, and system output open/short circuit protection to increase IC performance. Features Constant Current Accuracy within ±2.5% Integrated 700V MOSFET (TS19721A) Integrated 600V MOSFET (TS19721D) Efficiency > 90% High Power Factor > 0.9 Low THD <15% ~ 20% (By spec. condition) Boundary Conduction Mode Control Gate Output Voltage Clamp LED Open Protection LED Short Protection Over Current Protection (OCP) Over Thermal Protection (OTP) Design Case of Demo Board Basic Specification of Demo Board Parameter Output Power Input Voltage Output Voltage Output Current Specification 10Watt 90 ~ 264V RMS, 60/50Hz 50V 200mA Efficiency 90% LED Specification 200mA based on 17 LEDs 19.8mmm mm LED Tolerance 15 ~ 20 LEDs Ambient Temperature 25 C Board Size Dimension L 37mm, W 19.8mm 37mm

2 Operation Principle The TS19721 is a single stage Buck PFC controller. It adopts the proprietary control architecture to achieve an accurate regulation of LED current, unity power factor, and quasi-resonant valley turn-on high efficiency operation. High power factor is achieved by constant on-time operation mode, which the control scheme and the circuit structure are both simple. According to the following formula, assume Switch-on time (t ON) is a constant, inductor peak current (IL pk) and the AC input voltage (VAC) will become a linear relationship in half sine wave shape. Thus we can estimate "I IN_pk" will also be a sine wave shape to achieve high power factor and high efficiency in BCM mode. V Where : V : Voltage L : Inductor di : Differential to current dt : Differential to time IL pk : Peak of current and inductance t ON : Constant On-time TS19721 operates in boundary conduction mode (BCM) as shown in Figure 1. Switching point is controlled by RT resistor, and the frequency is changing with the input instantaneous line voltage. General suggestion is used 40kHz ~150kHz by switching frequency in system that obtain better performances. The max on time is 13μs ~ 14μs.CS pin detect MOSFET current from CS Pin. TS19721 can control the output average current accurately regardless of any changes about AC input voltage and output voltage (LED Vf). V AC Time Figure 1: Constant on-time diagram Where : : Input Voltage Waveform : Peak Current Waveform for Inductor : Charging Current Waveform for Inductor : Flywheel Diode Waveform : Output Current Waveform : MOSFET Gate Waveform

3 Pin Configurations (Top View) Pin Operation Description CS pin CS pin provides the LED current feedback function, I OUT and RS formula as below: Where : R S is the resistance 0.2 is a V reference for electric potential I OUT is the current output Also, CS pin provides over-current protection (OCP), over-current I CS (Limit) and R S formula as below: Where : I CS(Limit) is a current sense 1.4 is a voltage value for OCP R S is the resistance COM pin The most important design is compensation circuit for PFC control loop. It achieves high PFC and low total harmonic distortion (THD) function. In order to remain V COM is a constant value in every cycle we usually set the bandwidth under 10Hz. We recommend using 1μF capacitor in typ. design. If the system specification comes with higher output voltage or large output capacitor, ensure the V CC voltage above UVL(off).If not the system will fail to start or blinking or flickering. V COM level determine Switch-on time (t ON). In order to avoid malfunction that recommend operating range between 1μs ~ 14μs. N/C pin Leave it floating. DRIAN pin Drain of the internal power MOSFET.

4 RT pin RT pin can be adjusted to change the boundary point. Add RT value make the boundary point backward and increase turn-off time (t OFF), the system is set into dis-continuous conduction mode (DCM). In contrast, reduce RT value will make the boundary point forward and decrease turn-off time (t OFF), the system is set into continuous conduction mode (CCM). GND pin GND is the reference node of internal circuit. V CC pin V CC pin has built-in three levels. Such as : Start voltage level (V CC_ON), Cutoff voltage level (V CC_OFF), Over-voltage protection level (V OVP). When V CC voltage over V CC_ON level, IC will work in the system. When V CC voltage over OVP level (31.5V Typ.), IC will shut down and goes into Hiccup mode. The IC operating between UVLO (ON) and UVLO (OFF), 8 times per cycle until the OVP condition is removed. Applications Information Start up After AC supply or DC BUS is powered on, the capacitor CV CC across V CC and GND pin is charged up by DC BUS voltage through a start-up resistor Rs. Once V CC rises up to UVL (ON), the internal blocks start to work. The whole start up procedure is divided into two sections shown in Fig.2. T ST1 is the CV CC charged up section, and Tst2 is the output voltage built-up section. The start-up time T ST composes of T ST1 and T ST2, and usually T ST1 is much larger than T ST2. Figure 2 The start-up resistor R S and CV CC are designed by rules below: (a) Preset start-up resistor R S, make sure that the current through R S is larger than I ST Where I ST is the Start-up Current. _

5 (b) Select CV CC to obtain an ideal start up time T ST, and ensure the output voltage is built up. UVL (ON) = V DCBUS* #1%e - Tst1 /(Rs*CVcc) ) (c) If the CV CC is not big enough to build up the output Increase CV CC and decrease R S, go back to step (a) and redo such design flow until the ideal start up procedure is obtained. Constant Current Control Figure 3 The switching waveforms are shown in Fig.3. The output current I OUT can be represented by, 1 #()(!!* #1* 2 Where I PK is the peak current of the inductor; T S is the effective time of inductor current rising and falling; T S+T d is the switching period. In static state, the positive and negative inputs are equal. 1 + #()(!!* "! 2 According to (1)! " Where V REF is the internal reference voltage, R CS is the current sense resistor, I OUT can be programmed by R CS.

6 Protection Function OVP (Over Voltage Protection) on V CC When the V CC voltage higher than OVP voltage (31.5V Typ.), the output gate driver circuit will shut down immediately. Then switching is shut down and V CC goes into Hiccup mode, V CC voltage will gradually be released to V CC_OFF (8V Typ.). In this condition the IC operating between UVLO (ON) and UVLO (OFF) with eight times per cycle until the OVP condition is removed. The TS19721 is working in an auto-recovery mode as shown in Fig.4 Formula: DZ1 = V LED - 18V Where : DZ1 : OVP setting V LED : Series Voltage of LED 18V : Constant setting by IC Figure 4. OCP (Over Current Protection) TS19721 detects the MOSFET current from CS pin, which is for the cycle-by-cycle current limit and output feedback. The current limit threshold of CS pin is set at 1.4V (Typ.). OTP (Over Temperature Protection) When the IC internal temperature is over 150 C (Thermal Shutdown Typ.), the IC will stop and shut-down output signal which means into OTP status. While the IC internal temperature drops until to 120 C (Thermal Shutdown Release Typ.), the IC will be re-set automatically. SCP (Short Circuit Protection) When the output is shorted, the IC will be automatically shut down. Because of the V CC power is lost from power supply.

7 Power Device Design MOSFET and Diode When the operation condition is with maximum input voltage and full load, the voltage stress of MOSFET and output power diode is maximized; V MOS_ dsmax = 2 Vac_ max, Vdiode_ rmax = 2 Vac_ max Where V AC_ max is maximum input AC RMS voltage. When the operation condition is with minimum input voltage and full load, the current stress of MOSFET and power diode is maximized. Inductor (L) Figure.5 In Buck converter when the input voltage is larger than output voltage, the power is transferred from AC input to output The input voltage and inductor current waveforms are shown in Fig. 5, where θ1 and θ2 are the time that input voltage is equal to output. In boundary mode, each switching period cycle TS consists of three parts: current rising time Ton, falling time Toff and quasi-resonant time Td shown in Fig.5. The system operates in the constant on time mode to achieve high power factor. The on time increases with the input AC rms voltage decreasing and the load increasing. When the operation condition is with minimum input AC rms voltage and full load, the on time is maximized. On the other hand when the input voltage is at the peak value, the off time is maximized. Thus, the minimum switching frequency FS_min happens at the peak value of input voltage Once the minimum frequency Fs_min is set, the inductance of the transformer could be calculated. The design flow is shown as below: (a) Preset minimum frequency FS_min (b) Compute relative Ts, Ton Ts = 2 34_567, Ton = 89:;<8= Ts, Toff = Ts-Ton >8?@_567 θ1 = ascsin# >DE_FGH ),θ2 π%θ1 (c) Compute inductor maximum peak current current Where η is the efficiency; IL_pk = 2 * ILED * π * >L MNO P89 >L QRS #>T94UP VW#XYZ[* ZV\] MNO * * (d) Design inductance L #Vout)VD* Toff L _

8 (e) Compute RMS current of the inductor I is Inductor RMS current of whole AC period with minimum input AC RMS voltage and maximum load condition meanwhile, the maximum peak current through MOSFET and the transformer happens. IL_RMS = dh e f g+"_h> ) > % i >L_FGH j (f) compute RMS current of the MOSFET IL_RMS=g dh dh ed f g+"_h> ) > % i >L_FGH j Output capacitor COUT Preset the output current ripple ΔI OUT, C OUT is induced by C OUT = g#zkwlm nkwlm *Z P2 ijolpfq Where I OUT is the rated output current; ΔI OUT is the demanded current ripple; f AC is the input AC supply frequency; R LED is the equivalent series resistor of the LED load. Layout

9 Application Circuit Reference Bill of Material No. Reference Part Number Package Quantity Provider 1 U1 Driver IC TS19721CX6 SOT-8 1 TSC 2 R3,R4 SMD kΩ 1% 2 3 R5 SMD Ω 1% 1 4 R6 SMD KΩ 1% 1 5 R1 SMD KΩ 1% 1 6 CO1 Capacitor-MPP 104/400V 105 C 10% 1 7 C3 SMD 08051μF/25V 10% X7R 1 8 BD Bridge Diode 0.8A/600V TMBR6S TMBR6S08 1 TSC 9 D1 Super Fast Diode ES1JA 1A/600V SMA SMA(DO-214AC) 1 TSC 10 DZ1 Zener Diode 33V/0.8W BZD27C33P (DZ1 = V LED - 18V) SMA 1 TSC 11 D2 Super Fast Diode RS1M 1A/1000V SMA SMA 1 TSC 12 C1 Capacitor-MPP 104/450V 105 C 10% 1 13 C5 10μF 50V SMD 1 14 C4 Capacitor-EC 100μF/100V 1 15 F1 FUSE 1.25A/250V 1 16 L1 CHOKE 3mH DR6* CS1 SMD 12062Ω 1% 1 18 CS2 SMD 12062Ω 1% 1 19 L2 EE * uH 1 20 C2 SMD PF/1kV 1 21 MOV DNR7D471K NC 1 22 R8 SMD kΩ 1% 1 Board Board size 37 x 19.8 mm, board designed by 23 N/A 1 TSC Material TSC

10 Design Example A design example of typical application is shown below step by step. #1. Identify design specification V AC : 90V~264V, V OUT : 50V, I OUT : 200mA, η : 90% (a) FS_min is preset FS_min =50kHz (b) Compute the switching period T S and on time T ON at the peak of input voltage. T S = 2 rstuv rs<2 = 20μs, Ton = 20μs = μs, TOFF = 20μs μs = μs > ws θ1 = arcsin# rs<2 ) 23.62,θ2 π%23.62 = > ws (c) Compute inductor maximum peak current IL_pk = 2 * 200mA * π * (d) Design inductance L #rs<2* 22.w : L = 665μH s.w2 w > wsprs * 2 #XY.Z ZX* > ws #>T94>e.>P * s.w Z ƒ = A (e) compute RMS current of the inductor IL_RMS =.s2e : e r: g90> )50 > % i > ws rs j = 0.347A (f) Select power MOSFET and power diode (1) Compute RMS current of the MOSFET IL_RMS =g.s2e.s2e e >s r g90> )50 > % i > ws rs = 0.221A j (2) V MOS_ dsmax = 2 *264=373, V DIODE_ rmax = 2 *264 = 373V (g) Select the output capacitor C OUT C OUT = g# Z Z M. Z M *Z P2 i e.2i s 2 2.i = 347uF (h) Select Rs and CVIN UVL(on) : 18V, Ist : 45uA, ˆ"" : 2.4h, Tst1:500mS (1) RST is preset ws 2.i2i >.i5d ws 2.i2i 155.4KΩ< Rs Ω Set Rs 220KΩ *2 = 440kΩ ird (2) Design CVIN 18= 90*1.414 * #1%e - 1 / (440K*CVcc) ) = 7.44uF Set CVIN = 10uF (i) Set current sense resistor to achieve ideal output current 200h s.> p Rcs = 1Ω

11 Demo Board Data and Function Performance for Test Note 1/2 Input Voltage : 90V AC ~ 264V AC Output : 50V DC 200mA Load : 16 LEDs V AC _V P IN _W V OUT _V I OUT _A P OUT _W Efficiency % PFC THD % Curve Diagram for Test Note 1/2: Diagram 1 : Average Current Mode Accuracy ±< 2.5% within universal V AC range. Diagram 2 : Efficiency > 90% within universal VAC range.

12 Curve Diagram for Test Note 1/2: Diagram 3 : PFC > 95% within universal VAC range. Diagram 4 : THD < 15% ~ 20% within universal VAC range.

13 Demo Board Data and Function Performance for Test Note 2/2 The TS19721 can provide the high performance function for average current mode by different LED lamp series connection is based on the same of demo board. Also, the inductor can cover related power application and there is Zener diode (ZD1) must be changed according to conditions as below. Conditions for testing : Input Voltage : 90V AC ~ 264V AC Output Voltage : 21V DC ~ 80V DC I OUT : 200mA based on 6 ~ 25 LEDs 6 LEDs V AC (V) P OUT (W) I OUT (ma) Variation % V DC (V) Eff. % PF LEDs 25 LEDs V AC (V) P OUT (W) I OUT (ma) Variation % V DC (V) Eff. % PF V AC (V) P OUT (W) I OUT (ma) Variation % V DC (V) Eff. % PF * * : Test condition has more than the IC maximum duty, which the current output (I OUT) has dropped.

14 Curve Digram for Test Note 2/2 Current Output v.s. V AC Line Diagram 1 : ILED average current mode can be controlled within < ±2.5% by different LED series. Variation v.s. V AC Line Diagram 2 : The current variance performance shows the constant current accuracy by universal V AC Change.

15 Curve Diagram for Test Note 2/2 Efficiency v.s. V AC Line Diagram 3 : The efficiency will be better based on the LED lamp serieses more. Power Factor v.s. V AC Line Diagram 4 : High PF performance is better which 25 LEDs is remarkable.