The SR087 is an inductorless switching regulator designed to operate directly from a rectified AC supply. The operating principle is to turn on a pass transistor when the rectified AC is below the output voltage, and to turn it off when the output voltage reaches a specific level. A linear regulator supplied by VOUT provides an additional fixed 5.0-V output. Efficiencies of around 55% may be achieved for loads up to 1.0 W in 120-V-AC applications, with around 50% efficiencies for loads up to 800 mW in 230-V-AC applications. A logic-level enable input allows the SR087 to be disabled – useful when it is employed as a keep-alive power supply. WARNING! Galvanic isolation is not provided. Dangerous voltages are present when connected to the AC supply. It is the responsibility of the designer employing the SR087 to ensure that adequate safeguards are in place to protect the end user from electrical shock. The circuits shown in this data sheet are not guaranteed to meet surge and conducted EMI requirements. The effectiveness of these circuits may vary with a particular application. The designer should conduct tests to ascertain compliance with the applicable standards and regulations.
• Efficient operation without magnetics
• No high-voltage capacitors
• Adjustable main output voltage (9–50 V)
• Additional internal 5-V regulator
• Up to 100 mA combined output current
• Single BOM for 120 V AC / 230 V AC
• Built-in soft start
• Less than 200 mW standby power
Technical data:
• Input voltage: 80–285 V
• Output voltage (adj.): 9 - 50 V
• Output voltage (fixed): 5 V
• Iout max.: 100 mA
• Load regulation: 0.017 (%/mA)
