Universal Input, 20 W, LED Ballast

Transcription

1 Design Note DN06040/D # Universal Input, 0 W, LED Ballast Device Application Input Voltage Output Power Topology I/O Isolation NCP35 Solid State Lighting Vac 0 W Flyback Yes Maximum Output Voltage Ripple Nominal Current Other Specifications Output 33 V Not Given 700 ma PFC (Yes/No) Target Efficiency Max Size Operating Temp Range Cooling Method/Supply Orientation Signal Level Control No 80 % at nominal load 5 x 37 x 35 mm 0 to +70 C Convection No Other Requirements Circuit Description The NCP35 controller provides for a low cost, variable frequency, flyback converter. It incorporates a very low quiescent current allowing for high value resistors to be used as a start-up circuit direct from the HV rail. The design comprises and input filter, bridge rectifier (using low cost N4007 diodes), bulk capacitors and line inductor in -filter arrangement, the power stage, rectifier diode and smoothing capacitors. Feedback is CVCC, constant current drive for the LED s with a constant voltage in the event of an open circuit output. In order not to need PFC the input power is capped at 5 W, so assuming 80% efficiency the maximum output power is ~0 W. In cooperation with Key Features Wide input voltage range 85 Vac to 65 Vac Small size, and low cost Good line regulation High efficiency Overload and short circuit protection. Number of LED s in series LUXEON I LED Current 350 ma 700 ma A.5 A #NOTE LUXEON III LUXEON V 5 3 #NOTE #NOTE LUXEON K 6 4 LUXEON K with TFFC #NOTE LUXEON Rebel #NOTE V Z (D0) 47 V 33 V V V R & R3 3R6 R8 R 0R8 #NOTE Out of LED specification. #NOTE Recommended for use above A. Feb 008, Rev. 0

2 Schematic Feb 008, Rev. 0

3 LED Current The light output of an LED is determined by the forward current so the control loop will be constant current, with a simple Zener to limit the maximum output voltage. For a white LUXEON K the VI characteristics are: I F V F 350 ma 3.4 V 700 ma 3.60 V 000 ma 3.7 V 500 ma 3.85 V Driving eight LED s at 700mA thus gives an output power of 0. W at 8.8 V. DN06040/D The output current is sensed by a series resistance, once the voltage drop across this reaches the baseemitter threshold of the PNP transistor current flows in the opto-coupler diode and thus in the FB pin of the NCP0x. The LED current is thus set by: 0.6V ILED...(Eq.) R SENSE Total sense resistor power dissipation is: P I 0. V...(Eq.) D LED 6 So for 700 ma we need a 0.9 sense resistor capable of dissipating 40 mw, two 330 mw surface mount resistors,.8 each in parallel, are used. Inductor selection In a flyback converter the inductance required in the transformer primary is dependant on the mode of operation and the output power. Discontinuous operation requires lower inductance but results in higher peak to average current waveforms, and thus higher losses. For low power designs, such as this ballast, the inductance is designed to be just continuous (or just discontinuous) under worst case conditions, that is minimum line and maximum load. The specification for this ballast is as follows: Universal input 85 Vac to 65 Vac 5 W maximum input power PFC limit Assuming 80% efficiency 0 W output power 700 ma output current 00 khz operation at full load This gives us a minimum DC input voltage of 0 V, there will be some sag on the DC bulk capacitors so an allowance will be made for this by using 80 V as the minimum input voltage, including MOSFET drop etc. First we need to calculate the turn s ratio, this is set by the MOSFET drain rating, line voltage and reflected secondary voltage. Since this is a constant current circuit we are designing, with a varying output voltage, we need the maximum output voltage. V IN(max) is the maximum rectified input = 375 V. V IN(min) is the minimum rectified input = 80 V. V OUT is 35 V (0 700 ma is 9 V plus a margin for safety). With a 600 V MOSFET and derating of 80%, our maximum allowable drain voltage is: V Dmax V...(Eq.3) Good results are obtained if we set V CLAMP, at ~50% of the reflected secondary: VCLAMP N k C.5...(Eq.5) V V OUT f V f = 0.7 V as we will need a high voltage diode. Re-arranging for N: N S N N 05 P (Eq.6) We will use a ratio of 0.5 or :, this will give a good transformer construction. We can now calculate the maximum duty cycle running in CCM: VOUT MAX VOUT VIN min N (Eq.7) And thus headroom, V CLAMP for the reflected secondary voltage and leakage spike of: VCLAMP VDmax VIN max (Eq.4) 05 V Feb 008, Rev

4 I DN06040/D PIN 5 I AVE 33 ma...(eq.) V 80 IN (min) I PK I I VALLEY I L The average pulse current, I, is: I AVE 0.33 I 66 ma...(eq.3) 0.47 max I AVE T SW T SW Looking at the waveform of the current flowing in the primary of the inductor (above) if we define a term k equal to; I L k...(eq.8) I And use the equation: V IN (min) MAX L...(Eq.9) f SW kpin Then we can determine the inductance we require. If k = then we are in boundary conduction mode as the ripple current equals twice the average pulse current, so setting k to : L 83 H...(Eq.0) Thus we can now find the primary ripple current assuming operation in boundary conduction mode: VIN (min) TON VIN (min) max I L L Lf SW...(Eq.) A The average input current, I AVE, is: t Demonstrating that I L does equal twice I and that the peak primary current is.3 A. We can calculate the RMS current in the MOSFET and sense resistor for dissipation purposes. For a steppedsawtooth waveform of this type the equation is: I L 3 I RMS I...(Eq.4) I Thus:.3 I RMS ma...(eq.5) We can also determine the current sense resistor, allowing for a drop across the resistor of 0.8 V: VDROP 0.8 R SENSE (Eq.6) I.3 PK The total power dissipation is: P D( sense) I RMS R 70 mw SENSE (Eq.7) Two. resistors in parallel will be used as sub resistors typically cost more. The threshold voltage for the current sense is set by an offset resistor; this has a bias current of 70 µa in it so we can determine the resistor value: VSENSE 0.8 R OFFSET 3.0 k...(eq.8) 6 I 700 BIAS Feb 008, Rev

5 Rectifier snubber 6.50 Testing demonstrated the need for snubbing on the R s 37...(Eq.3) rectifier as there was a large amount of ringing present 800 after the rectifier turns off. The snubber consists of a resistor and capacitor in series, and knowing the junction capacitance and ringing frequency we can determine the necessary values: L Rs...(Eq.9) C C s j LC j...(eq.0) R s Knowing that: f...(eq.) LC j We can determine L, the stray inductance which then allows us to calculate the necessary snubber resistor. f = 4.5 MHz (measured on oscilloscope) C j = 80 pf (datasheet figure for MUR840 at 6 V) L 4C j 6 f H...(Eq.) C s 504 pf 37...(Eq.4) The nearest standard values are 470 pf and 40, inserting these into the circuit eliminated the ringing due to the rectifier. Auxiliary winding Normally in a flyback converter the auxiliary winding would be in the form of a flyback winding, i.e. in phase with the output winding, and thus provide a semi-regulated voltage to supply the controller. As this ballast is current controlled and the output voltage can vary over a considerable range depending on the number of LED s connected, a forward phased winding is used. The auxiliary will therefore vary with line rather than output voltage. Since neither option could supply sufficient volts at low input/output voltage whilst still staying below the maximum V CC figure of 8 V, a voltage regulator is used formed by Q and D6. Below ~0 V the regulator does nothing other than act as a small volt drop, however as the voltage rises it clamps the voltage to around 0.7 V, since the current is very low into the V CC pin there is very little loss. Feb 008, Rev

6 MAGNETICS DESIGN DATA SHEET Project / Customer: Part Description: Schematic ID: Core Type: Core Gap: Inductance: Bobbin Type: ON Semiconductor/Future Lighting Solution 5 W Transformer - EE5 Gap for 50 µh 50 µh NIC 0-pin vertical Windings (in order): Winding # / type Turns / Material / Gauge / Insulation Data N, Primary Start on pin and wind 0 turns, of 0.8 mm triple insulated wire (e.g. Tex-E), in one neat layer across the entire bobbin width. Finish on pin. N, Secondary Start on pins 9&0 and wind 0 turns, of 0.8 mm Grade II ECW, distributed evenly across the entire bobbin width. Finish on pins 6&7. N3, Primary Start on pin and wind 0 turns, of 0.8 mm triple insulated wire (e.g. Tex-E), in one neat layer across the entire bobbin width. Finish on pin 3. N4, Primary (Aux) Start on pin 4 and wind 5 turns, of 0.8 mm triple insulated wire, in one neat layer spread evenly across the entire bobbin width. Finish on pin 5. Sleeving and insulation between primary and secondary as required to meet requirements of double insulation. Primary leakage inductance (pins 6&7 and 9&0 shorted together) to be < 6 µh NIC part number: NLT84W3P400S5P0F Hipot: 3 kv between pins,, 3, 4 & 5 and pins 6, 7,8, 9 & 0 for 60 seconds. Schematic Lead Breakout / Pinout N 6, mm N 4 7 N3 9, N mm Feb 008, Rev

7 Ref Part Type / Value DN06040/D Bill of Materials Comment Footprint Description Manufacturer Part Number C 0nF X 75VAC 8X0mm, 5mm pitch X-class EMI suppression capacitor NIC NPX4M75VXMTBF C 47uF 400V Ø6mm, 7.5mm pitch General purpose high voltage electrolytic NIC NREH470M4006X3F C3 470pF 00V X7R 06 Ceramic chip capacitor NIC NMC06X7R47K00TPRF C4 00nF 50V X7R 0603 Ceramic chip capacitor NIC NMC0603X7R04K50TRPF C5 0nF 50V X7R 0603 Ceramic chip capacitor NIC NMC0603X7R4K50TRPF C6 4.7uF 35V Ø5mm, mm pitch General purpose low voltage electrolytic NIC NRWA4R7M50V5XTRF C7 80pF 50V NP Ceramic chip capacitor NIC NMC0603NP08J50TRPF C8 47nF 50V X7R 0603 Ceramic chip capacitor NIC NMC0603X7R473K50TRPF C9 0nF 50V X7R 0603 Ceramic chip capacitor NIC NMC0805X7R4K50 C0 0nF kv NP0 0 Ceramic chip capacitor NIC NMC-H0NP0KKVTRPF C uf 50V Ø5mm, mm pitch General purpose low voltage electrolytic NIC NRWAR0M50V5XTRF C nf Y Radial, pitch 0mm Ceramic Y-class capacitor Murata DEE3KX0MN4AL0 C3 470uF 6V Ø.5mm, 5mm pitch Miniature low impedance electrolytic NIC NRSZ47M63V.5X5F C4 470uF 6V Ø.5mm, 5mm pitch Miniature low impedance electrolytic NIC NRSZ47M63V.5X5F C5 0nF 00V X7R 06 Ceramic chip capacitor NIC NMC06X7R4K00 C6 uf 50V 06 Ceramic chip capacitor NIC NMC06X7R05Z50TRPF D N4007 A, 000V Axial Axial Lead, Standard Recovery ON Semiconductor N4007RLG D N4007 A, 000V Axial Axial Lead, Standard Recovery ON Semiconductor N4007RLG D3 N4007 A, 000V Axial Axial Lead, Standard Recovery ON Semiconductor N4007RLG D4 N4007 A, 000V Axial Axial Lead, Standard Recovery ON Semiconductor N4007RLG D5 MMSD448 00mA, 00V SOD-3 Switching diode ON Semiconductor MMSD448TG D6 0V.5W SMA Zener Diode ON Semiconductor SMA593BT3G D7 MURA60 A, 600V SMA Ultrafast rectifier ON Semiconductor MURA60T3G D8 MMSD448 00mA, 00V SOD-3 Switching diode ON Semiconductor MMSD448TG D9 MUR840 8A, 400V DO-0 Ultrafast Power Rectifier ON Semiconductor MUR840G D0 33V 5%, 00mW SOD33 Zener diode ON Semiconductor MM3Z33VTG IC NCP35 - SOIC8 Variable Off-Time PWM Controller ON Semiconductor NCP35BDRG IC HCPL-87 Wide pitch HCPL E Opto-coupler HCPL-87 Agilent HCPL-87-W0AE L RN-0.5/0 - RN Common Mode Choke Schaffner RN-0.5/0 AC -Way 5mm pitch - Screw Terminal - - LED -Way 5mm pitch - Screw Terminal - - M 5.9 C/W - - Heatsink Aavid 5770B00000G M 5.9 C/W - - Heatsink Aavid 5770B00000G Q BC847 45V SOT-3 General purpose NPN ON Semiconductor BC847ALTG Q IRFBC40A 600V TO-0 MOSFET IR IRFBC40A Q3 BC857-45V SOT-3 General purpose PNP ON Semiconductor BC857ALTG R 50R 0.33W 0 Resistor thick film NRC NIC NRC5J5TRF R k 0.W 0603 Resistor thick film NRC NIC NRC06JTRF R3 3k0 0.W 0603 Resistor thick film NRC NIC NRC06J30TRF R4a R W 5 Resistor thick film NRC NIC NRC00JRTRF R4b R W 5 Resistor thick film NRC NIC NRC00JRTRF R5 M W Axial Carbon film resistor NIC NCF00J05TRF R6 M W Axial Carbon film resistor NIC NCF00J05TRF R7 k 0.5W 0805 Resistor thick film NRC NIC NRC0JTRF R8 0R 0.5W 06 Resistor thick film NRC NIC NRCJ00TRF R9 6k8 0.W 0603 Resistor thick film NRC NIC NRC06J68TRF R0 k W Axial Carbon film resistor NIC NRC00J3TRF R 00R 0.5W 0805 Resistor thick film NRC NIC NRC0J0TR R R8 0.33W 0 Resistor thick film NRC NIC NRC5JR8TRF R3 R8 0.33W 0 Resistor thick film NRC NIC NRC5JR8TRF R4 00R 0.5W 0805 Resistor thick film NRC NIC NRC0J0TRF R5 4k3 0.5W 0805 Resistor thick film NRC NIC NRC0J43TRF R6 00R 0.5W 0805 Resistor thick film NRC NIC NRC0J0TRF Tx FUTURE 4W LED TRANSFORMER - NIC 0 pin vertical 4W Flyback transformer NIC NLT84W3P400S5P0F All parts can be ordered from Future Electronics Feb 008, Rev

8 Component Locations Top view. Bottom view. Feb 008, Rev

9 PCB Tracks Results 5 µs 500 ns 00 V 00 V V IN = 65 V AC V PK = 46 V V IN = 30 V V IN = 30 V AC V PK = 44 V V IN = 0 V AC V PK = 56 V V IN = 0 V AC Drain waveform at 0 Vac and 30 Vac Turn-off in detail at 0 Vac, 30 Vac and 65 Vac Iout vs Vout Efficiency vs Vout % % 76% % Iout (A) VAC 30 VAC Efficiency (%) 7% 70% 68% 66% 0 VAC 30 VAC % 6% V out (V) 60% V out (V) Feb 008, Rev

10 On-Semiconductor is a Certified LUXEON Solution Partner 008 ON Semiconductor. Disclaimer: ON Semiconductor is providing this design note AS IS and does not assume any liability arising from its use; nor does ON Semiconductor convey any license to its or any third party s intellectual property rights. This document is provided only to assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its products at any time, without notice. Design note created by Anthony Middleton, Anthony.Middleton@onsemi.com Feb 008, Rev