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The main source of power in a telecommunications system is -48 V. This source’s negative polarity and its large magnitude with respect to ground pose a challenge when designers want to use low-power ICs in the telecom system’s application circuits. Fortunately, the emergence of high-voltage ICs with operating voltages of 75 V and higher has enabled the use of simple biasing techniques in designing circuits for -48-V systems. The technique described here provides a dimming control for an LED. The circuit uses a 65-V hysteretically controlled LED driver (MAX16822A) with its ground pin connected to -48 V and its power input connected to the system ground (Fig. 1). For proper dimming, therefore, the circuit’s logic-level control signal (at Control) must be level-shifted down to –48 V and applied to the DIM input. The high-voltage pnp transistor (CMPT5551) (80 V/500 mA) enables a simple solution to that problem. Logic-Level Signals Dim -48V LED Driver Circuit Diagram The transistor circuit ...

This is a simple project of Logic-Level Signals Dim -48V LED Driver Circuit Diagram. The main source of power in a telecommunications system is -48 V. This source’s negative polarity and its large magnitude with respect to ground pose a challenge when designers want to use low-power ICs in the telecom system’s application circuits. Fortunately, the emergence of high-voltage ICs with operating voltages of 75 V and higher has enabled the use of simple biasing techniques in designing circuits for -48-V systems. The technique described here provides a dimming control for an LED. The circuit uses a 65-V hysteretically controlled LED driver (MAX16822A) with its ground pin connected to -48 V and its power input connected to the system ground (Fig. 1). For proper dimming, therefore, the circuit’s logic-level control signal (at Control) must be level-shifted down to –48 V and applied to the DIM input. The high-voltage pnp transistor (CMPT5551) (80 V/500 mA) enables a simple solution to that pro...