DN05045/D Design Note – DN05045/D 1–10 V PWM Dimming for CCR Lighting Circuits Device Application Input Voltage Output Power Topology NSI50350AD, NSI50010Y, LM2903 1-10 V LED Dimming 15 Vdc 3.45 W Comparator for PWM Schematic Figure 1: 1-10 V Comparator Dimmable PWM CCR Lighting Circuit. Circuit Description This Design Note features a dimmable LED circuit using pulse width modulation (PWM). The dimming circuitry uses two comparators to adjust the brightness of the LEDs. Comparator A (U1-A) generates a Resistor-Capacitor (RC) wave that has a minimum of 1 Vdc and a maximum of 10 Vdc. Comparator B (U1-B) takes the generated RC wave (Vcompare) and compares it with the 1-10 Vdc input (Vdim) of the analog dimmer. When the 1-10 April 2013, Rev. 0 Vdc dimming is set to 1 Vdc or less, then the LEDs are off. When it is set to 10 Vdc, the LEDs will be completely on. For this circuit, the 1 to 10 Vdc dimming is controlled with a 100 Ω to 1 kΩ potentiometer (R6) in series with a 10 mA CCR (CCR1). At 100 Ω and 10 mA, 1 Vdc will be available and at 1 kΩ and 10 mA, 10 Vdc will be available. If an existing 1 to 10 Vdc source is available, then R6 and CCR1 can be removed, and www.onsemi.com 1 DN05045/D the source can be substituted. The adjustable source is then connected to the Vs+ of U1-B. Key Features Current regulation to protect LEDs. Dimmable circuit for analog dimming of 0/1 to 10 Vdc. Single input source with dimming provided by a 0/1 to 10 Volt source. No flicker. Configurable for greater load voltages. Compatible for AC source inputs. Design Considerations Comparator Voltage Min and Max, Width Adjusting resistors R1 and R2 will adjust the minimum and the maximum of the RC wave generated from Comparator A shown in Figure 2. This will determine the range offered that controls the PWM function used to switch on and off the MOSFET to control dimming the load. For example, increasing R1 will raise the peak of the RC wave. Increasing R2 will lower the minimum of the RC wave. Adjusting resistor R4 or the capacitor C1 will change the period of the waveform generated. It is suggested that the frequency be set above 200 Hz to avoid flickering by . LED Current and Voltage With this design, a suitable Constant Current Regulator (CCR) will need to be selected depending on the LEDs chosen. This design is currently set for an input voltage of 15 V and 350 mA through the LEDs. The CCR will provide a constant current over a varying range of input voltage. The CCR Vak needs to be greater than 1.8 V to be in regulation. With a 15 V input and the three 3.3 V LEDs there will be enough overhead Vak for the current to regulate properly. If additional LEDs are needed, simply increase the input voltage allowing for sufficient voltage across the LEDs and the CCR. The Zener diode, D1, will clamp the Vcc of the LM2903 (U1-A,U1-B) comparator to 15 V to protect it. The maximum rating for VCC of the comparator is 36 V. April 2013, Rev. 0 120 - 240 VAC Compatibility This circuit can also be used with an AC source as well. By taking the original circuit and using a 15 V Zener diode in place of the 15 Vdc source, the circuit will function with an AC input. Additional components include a bridge and a smoothing capacitor rectifier to convert the voltage to DC. The load will also need to be increased. In Figure 2, the LED voltage is ~ 120 Volts for use with a 120 VAC (170 Vpeak) source. Be sure to size the load according to the provided input voltage for the particular design. Since the input voltage is much higher than the original design, a different MOSFET is recommended to accommodate for this change such as the NDD02N60Z 600 V NChannel Power MOSFET. www.onsemi.com 2 DN05045/D Figure 2: 1-10 V Comparator Dimmable Circuit with AC Source Bill of Materials Designator Manufacturer Quantity NSI50010Y 2 NSI50350AD 1 Description Value Tolerance 50 V, 10 mA 50 V, 350 mA 3.3 V, 1A 2.2 kΩ, 0.25 W 10% U1-A, U1-B ON Semiconductor LM2903 1 M1 ON Semiconductor NTD3055-150 1 D1 ON Semiconductor 1N5929B 1 D2-D4 Cree, Inc. MX6AWT 3 R1 Any - 1 Current Regulator Current Regulator Low Offset Voltage Comparator N-Channel Power MOSFET Zener Voltage Regulator High Power LEDs Resistor R2 Any - 1 Resistor 2.2 kΩ, 0.25 W 10% R3 Any - 1 Resistor 100 Ω, 0.25 W 10% R4 Any - 1 Resistor 3.6 kΩ, 0.25 W 10% R5, R7 Any - 1 Any - 1 2.2 kΩ, 0.25 W 100 Ω to 1 kΩ, 10% R6 Resistor Adjustable Resistor CCR1, CCR2 CCR3 April 2013, Rev. 0 ON Semiconductor ON Semiconductor Manufacturer Part Number www.onsemi.com 30% 10% 36 V, 20 mA N/A 60 V, 9A N/A 15 V, 3W N/A N/A 10% 3 DN05045/D 0.25 W C1 Any - 1 C2 Any - 1 C3 Any - 1 Electrolytic Capacitor Electrolytic Capacitor Ceramic Capacitor 0.22 μF, 20 V 4.7 μF, 20 V 1 μF, 20 V 20% 20% 20% Waveforms Figure 3: Voltage from Comparator A (U1-A) that will be compared with the 1-10 Vdc source. April 2013, Rev. 0 www.onsemi.com 4 DN05045/D Figure 4: Vdim at 33% of Vcompare. The LEDs will be on, but dimmed. Figure 5: Vdim at 66% of Vcompare. The LEDs will be on for a greater amount of time, but not full brightness. April 2013, Rev. 0 www.onsemi.com 5 DN05045/D Figure 6: Vdim at 100% of Vcompare. The LEDs are completely on during the whole duration. Appendix A: List of optional 1 to 10 Vdc Sources Manufacturer Lutron Philips Description Diva 1-10 V Control High Frequency 110V Dimming Ballast 1-10 V Analogue Dimming Module Eaton Serial Number DVTV HF-Regulator F8078 ________________________ 1 © 2013 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 Loren Ledgerwood, e-mail: [email protected] April 2013, Rev. 0 www.onsemi.com 6