The project report describes 43 (nominal) V, 150 W reference design for power supplies for 90-265 VAC LED street lights and other high-power lighting applications. The power supply is designed with a constant current output to drive the 150 W LED panel directly at a 43 V voltage.
This design is based on PFS7326H for the PFC front end and LCS702HG for the LLC output stage.
Assembled circuit board photo, top view.
Street light power application circuit - input filter, PFC power level, bias power supply, and LLC level.
Circuit description
Enter the filter / boost converter / bias power supply - Schematic shows the input EMI filter, PFC level, and primary bias power / boot circuit. Power factor corrector utilizes PFS7326H. The primary and secondary biasing power supplies from the windings on the PFC inductor (L2).
EMI filter / surge restrictions - capacitors C1 and C2 are used to control differential mode noise. Resistance R1 is used to damn, improve power factor and reduce EMI. After disconnecting the AC power, the resistors R2-4 make C1 and C2 discharge. The inductor L1 controls the common mode EMI. The radiator of U1, U3 and BR1 is connected to the main circuit to eliminate the source of the radiation as radiation / capacitance coupling noise. Thermistor RT1 provides surge limit. Capacitor C33 filter common mode EMI. Inductor L4 filter difference EMI.
PFC primary - components R17-19 and R23 provide output voltage feedback. Capacitor C15 provides fast DV / DT feedback to the U1 FB pin to achieve a fast downstrap and overshoot response of the PFC circuit. Frequency compensation is provided by C19, C20 and R21, R22, and R24. The resistor R10-12 (filtered by C10) provides input voltage information to U1. Resistor R13 (filtered from C11) programs U1 as "efficiency" mode.
The main bias power / start-component R5-7, R8-R9, Q1, and VR3 provide startup bias to U1. Once U1 starts, components D1, D3, and C3-5 generate a baseline bias power source through the winding PFC choke L2. This is used to power the PFC and LLC phase of the power supply. Once the primary bias supply voltage is established, it is used to turn off the MOSFET Q1 through diode D6, thereby reducing power consumption. If the power cannot start, resistors R8 and R9 protect Q1 from excessive power consumption.
The LLC converter-schematic depicts ~ 43 V, 150 W LLC DC-DC converter with constant current output using LCS702HG.
The primary-integrated circuit U3 includes the control circuitry, drive, and output MOSFET required for the LLC resonant semi-bridge (HB) converter. The HB output of the U3 drives the output transformer T1 by a blocking / resonant capacitor (C30). The rated working ripple current of the capacitor can withstand the high voltage that appears under fault conditions.
The output of the output rectifier-transformer T1 is rectified and filtered through D11 and C34-35. These capacitors have a polyester dielectric that selects the output ripple current rating. The output rectifier D11 is a 150 V Schottky rectifier selected for high efficiency. Two semi-windings of the transformers are intertwined together (see Transformer Structure Details in Section 8) to reduce the leakage between the two half windings, reduce the peak reverse voltage of the worst case, and allow usage The 150V Schottky diode has higher efficiency. L3 and C36 provide additional output filtering. Capacitor C36 can also suppress LLC output impedance peaks caused by LLC "virtual" output series RL and output capacitors C34-35 at ~30 kHz.
Output current and voltage control - output current sensing through resistors R52 and R53. These resistors are clamped by diode D13 to avoid damaging the current control circuit during output short-circuit. Components R45 and U2 provide a reference voltage for the current detection amplifier U5. The reference voltage is divided by R46-47 and R50 and filtered by C39. The voltage from the current detecting resistor is filtered through R51 and C41 and applied to the in-phase input of U5. The operational amplifier U5 drives the optical coupler U4 via D12 and R25.
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