SR036DB1 Inductorless Switching Power Supply Specifications Introduction The Supertex SR036 is an inductorless, dual output off-line regulator intended for 120/240VAC line operation. The operating principle is to activate a pass element between line and load only when the input voltage is lower than a certain value. Thus conduction only occurs with a low voltage drop across the pass element, resulting in more efficient operation compared to a standard linear regulator. 24VAC to 264VAC 40Hz to 100Hz AC Input Output Voltages VUNREG VREG Output Current IUNREG + IREG The SR036DB1 demo board contains all the circuitry needed to supply a low-current (<40mA) load. Included are input protection circuitry, a full wave bridge rectifier, a pass element, and output capacitors. 18V±20% 3.3V ±10% 40mA @ 120VAC 30mA @ 240VAC Efficiency ACIN=120VAC 60Hz, IU=40mA, IR=0mA 40% typ Board Layout and Connections Q1 D1 Z1 IC1 ACIN F1 C1 C2 GND WARNING!!! Do not connect to scope ground or to the ground of other earth-grounded instruments. Doing so will short the AC line, resulting in damage to the circuit and/or instrument. Either use an isolation transformer on the AC line, use a differential probe, or use a floating, battery-powered instrument to make measurements. VREG VUNREG WARNING!!! No galvanic isolation. Dangerous voltages are present when connected to the AC mains. ACIN VUNREG Connect to the AC line. Neutral to top, hot to bottom. The unregulated output. Nominal output voltage is 18 volts. This output will have a certain amount of 120Hz ripple, depending on load. GND Circuit common. Note that since galvanic isolation is not provided, connecting this point to an earth-grounded instrument (such as an oscilloscope) will short the AC line, resulting in circuit and/or instrument damage. Also note that GND may be at a higher potential with respect to earth ground, even if the AC is switched off. Use caution! Do not connect to earth-ground. Do not connect to earth-grounded loads. VREG The regulated output. 5V nominal output voltage. Do not connect to earth-grounded loads. Fuse The AC input is fused to protect against overloads. It should be replaced with a 125mA, 250V standard 3AG fuse. 16APR02 1 SR036DB1 Inductorless Switching Power Supply SR036 Circuit F1 125mA D1 Q1 VN2460N8 ACIN Z1 P6KE400CA VUNREG C1 220µF IC1 VREG SR036 C2 1µF Parts List Desig Description Part Number F1 Fuse, 3AG, 125mA, 250V Z1 Transient voltage suppressor, 400V D1 Diode bridge, 1A, 600V IC1 HV Supply Controller Supertex SR036SG Q1 MOSFET, 600V N-channel Supertex VN2460N8 C1 Capacitor, alum, 220µF, 35V C2 Capacitor, cer, 1µF, 16V P6KE400CA Modifications The SR036DB1 may be modified to provide higher output current. Remove Q1 and replace with a D-Pak N-channel MOSFET with a voltage rating appropriate for the input voltage. The on resistance of the replacement FET is not as important as the gate threshold voltage – the lower the threshold voltage, the more efficient the converter. To reduce ripple at the higher output current, C1 may be replaced with a higher value capacitor. 16APR02 2