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 TE Connectivity

  • Headlamp Power Supply with Fuse Tripped Indicator

  • Created: Sep 20, 2015

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This reference design is a single-ended primary-inductor converter (SEPIC) - based headlamp power supply with fuse-tripped indicator. The SEPIC is a DC/DC converter that provides a positive regulated output voltage regardless of whether the input voltage is above, or below the the input. These converters offer wide input voltage ranges, internal Schottky diodes and external synchronization. This design also uses a virtual remote sense controller that provides a tight load regulation. Furthermore, this design features a fuse-tripped indicator. This circuitry is composed of TE Connectivity’s resettable PTC fuse, P-channel MOSFET, LED indicator, and parallel resistors.

The implementation of this design starts at the PFET fuse-tripped indicator wherein the P-channel MOSFET source is on the near side of the PTC, and the gate is on the far side of the PTC, pulled down to ground. The current through the PTC is less than the trip current of the PTC (550mA), the voltage drop across the PTC is negligible, and therefore the voltage at the gate is high with respect to the drain, and so the PFET does not conduct. When the current through the PTC exceeds the trip current, the resistance increases and the voltage drops across the PTC. Then the pull down brings the gate voltage closer to the drain voltage, and the PFET conducts, lighting up the LED. The voltage regulation circuitry follows the fuse-tripped indicator. In this design, the low dropout voltage regulator (LDO) is configured as SEPIC. This LDO drives a low external N-channel power MOSFET (Q2) from an internal regulated supply. The undervoltage detect pin (UVL0) detects when power is adequate to enable switching. On the other hand, the positive and negative feedback pin (FBX) receives the feedback voltage from the external resistor divider (R10 and R11) across the output. Frequency synchronization is done by connecting the SYNC pin of the LDO to the OSC pin of the virtual remote sense controller. The resistor and capacitor, connected to ROSC and COSC respectively, determines the oscillator frequency. The current sense resistor (RSENSE) is connected to the current sense input (SENSE) and main supply (VIN) of the virtual remote sense controller to minimize interconnection resistance.

This design can be used effectively in automotive industries, telecom power supplies, and portable electronic equipment. It is also useful to applications that require 12V high intensity lamps. The purpose of the virtual remote sense is to maintain the right amount of voltage and current to the load is supplied to the load. This ensures precise lighting control, more predictable color temperature and better efficiency of the automotive halogen headlight lamps. This improves bulb reliability while ensuring optimum illumination.



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