DN05087/D Design Note – DN05087/D Low Cost Universal AC Input LED Circuit Application Input Voltage Topology Output Power Input Power LED Lighting, AC 80 to 280 VAC Chopper 0.74 to 0.85 W 1.5 to 1.8 W Figure 1 – Universal Input Chopper Circuit Top/ Bottom View Key Features Operates from 80 to 280 VAC with just one 48 V LED required The LED receives a constant current independent of input voltage Extremely low BOM cost Schematic Figure 2 – Universal Input Chopper Schematic. Circuit Operation April 2016, Rev. 0 www.onsemi.com 1 DN05087/D This circuit is a simple, low parts count, chopper topology. It is designed to safely operate with input voltages varying from 80 VAC to 280 VAC. ON Semiconductor CCRs are used to provide constant LED current and to protect LEDs from over-voltage conditions. This circuit uses active switching to change how the load is being driven. The LED load will either be driven from the capacitor, C1, discharging, or directly from the AC source. The CCR ensures a constant current through the LED throughout all modes of operation. The switching point of the circuit may be changed by varying the resistor, R1. Changing this switching point will change the amount of time the capacitor is charging. If a higher power output is desired a higher current CCR can be used and the switching point will need to be changed. A metal oxide varistor and fuse are designed into the circuit for surge protection purposes. Universal Input Chopper Attributes vs. Input Voltages We created the following plots in order to show how the universal input chopper circuit performs over a wide range of input voltages. We varied the input voltage from 80 VAC up to 280 VAC. Figure 3 shows that the output current and the output power being supplied to the LED remains very constant. This leads to a constant and predictable light output of the LED. Figure 4 plots the power factor and efficiency of the driver vs. input voltage. Again, we varied the input voltage from 80 VAC to 280 VAC. The efficiency remains fairly constant at 50%. This is because our input and output power levels do not vary that much, as seen in figure 3. The power factor, however, does decrease at the higher input voltages. This decrease in power factor arises from a decrease in the amount of time we are conducting from the AC source at the higher voltages. Our LED driver meets all of the power factor requirements in the U.S. because it draws less than 5 W of power. UIC Characteristics vs. Input Voltage 10 70.0 Input Current 60.0 Power (W) 40.0 Output Power 1 30.0 Output Current Current (mA) 50.0 Input Power 20.0 10.0 0.1 0.0 80 100 120 140 160 180 200 220 240 260 280 Input Voltage (VAC) Figure 3 – The plot above shows the constant current, power nature of the LED driver. April 2016, Rev. 0 www.onsemi.com 2 DN05087/D UIC Characteristics vs. Input Voltage 1 100.0 90.0 80.0 70.0 60.0 0.1 50.0 Efficiency 40.0 Efficiency (%) Power Factor Power Factor 30.0 20.0 10.0 0.01 0.0 80 100 120 140 160 180 200 220 240 260 280 Input Voltage (VAC) Figure 4 – The plot above shows how the power factor and the efficiency of the driver varies with the input voltage. Universal Input Chopper Thermal Considerations When it comes to designing circuits and PCB’s one must take into account the amount of power that will be dissipating on each part. With an excessive amount of power on a part we will observe an excessive amount of heat on that part. The biggest challenge is creating an aesthetically pleasing PCB that embodies a small form factor, all while allowing proper heat dissipation. Because of our expertise in circuit design we know that the majority of the power in this circuit will be dissipated over the CCR at low input voltages and over Q3 at higher input voltages. It is critical to add heat sinking to the cathode of the CCR and also the collector of Q3. By using a FLIR camera we are able to study how our circuit/PCB performs thermally over different input voltages. We are also able to verify our logic of where the heat should be dissipating for the given input voltage. Figure 5 shows the universal input chopper operating with an input voltage of 120 VAC. The hot spot in the image is the CCR, peaking at approximately 90˚C. At the lower input voltages the CCR and LED are being driven by C1 discharging for a longer period of time. There is a large voltage across the CCR, causing it to heat up. Our thermal images verify to us that the CCR is still safely operating. April 2016, Rev. 0 www.onsemi.com 3 DN05087/D Figure 5 – The image above shows the heat dissipation of the driver operating at 120 VAC. We next moved on to a higher input voltage, 240 VAC. Figure 6 below shows the thermal characteristics of the universal input chopper now. Please notice how the CCR has now cooled off and the majority of the heat dissipation is now across Q3. The capacitor C1 is not driving the CCR and LED for an extended period of time. We get a voltage built up across the emitter-collector junction of Q3, causing this BJT to dissipate heat, peaking at approximately 80˚C. These thermal images again assure us that the circuit/PCB are operating in a safe region. Figure 6 – The image above shows the heat dissipation of the driver operating at 240 VAC. Circuit Performance Data Input Voltage (VAC) PF 80 100 120 140 160 180 200 220 240 260 280 0.447 0.320 0.252 0.208 0.177 0.153 0.135 0.119 0.108 0.099 0.090 April 2016, Rev. 0 Input Current (mA) Input Power (W) Output Power (W) Output Current (mA) Efficiency (%) 49.8 53.7 55.7 57.3 58.2 59.1 59.6 59.9 60.0 59.9 58.9 1.79 1.68 1.70 1.66 1.66 1.58 1.62 1.60 1.56 1.59 1.50 www.onsemi.com 0.846 0.845 0.843 0.839 0.836 0.830 0.822 0.808 0.792 0.776 0.742 18.3 18.3 18.3 18.2 18.1 18.0 17.8 17.5 17.2 16.9 16.2 47.3 50.3 49.6 50.5 50.4 52.5 50.7 50.5 50.8 48.8 49.5 4 DN05087/D Bill of Materials Designator Quantity Description R1 1 Resistor SMD R2-R6 5 Resistor SMD Capacitor Aluminum TH PNP Bipolar Transistor SMD PNP Bipolar Transistor SMD NPN Bipolar Transistor SMD Zener Diode SMD Constant Current Regulator SMD Bridge Rectifier C1 1 Q1 1 Q2 1 Q3 1 ZD1 1 CCR1 1 BD1 1 F1 1 Fuse MOV1 1 Varistor LED1 1 SMD LED Value 33kΩ, 1/8th W 510kΩ, 1/8th W 10µF, 160 V Tolerance Footprint Manufacturer Manufacturer Part Number Substitution Allowed 1% 0805 Any Any Yes 1% 0805 Any Any Yes Yes 20% TH Chemi-Con EKXE161ELL100MH B5D N/A N/A SOT-23 ON Semiconductor MMBT3906LT1G No N/A N/A SOT-23 ON Semiconductor MMBT6520LT1G No N/A N/A SOT-223 ON Semiconductor PZTA96S No 91 Vz N/A SOD-123 ON Semiconductor MMSZ5270B No 120V, 20mA 15% SMB ON Semiconductor NSIC2020JB No N/A N/A DIP4 ON Semiconductor DBB08G Yes N/A TH Bel Fuse Inc. 3JQ 1-R Yes N/A TH Bourns Inc. MOV-07D471KTR Yes Phillips Lumileds L13550800CHV00001 No 1A, 350 VAC 423V, 1.2kA 48V N/A 2-SMD © 2016 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 Andrew Niles and Andrew Stemple April 2016, Rev. 0 www.onsemi.com 5