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ACT361US-T Datasheet(PDF) 6 Page - Active-Semi, Inc |
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ACT361US-T Datasheet(HTML) 6 Page - Active-Semi, Inc |
6 / 13 page ACT361 Rev 8, 14-Nov-12 Innovative Power TM - 6 - www.active-semi.com Copyright © 2012 Active-Semi, Inc. in a constant secondary side output current profile. The energy transferred to the output during each switching cycle is ½(LP × ILIM 2) × η, where LP is the transformer primary inductance, ILIM is the primary peak current, and η is the conversion efficiency. From this formula, the constant output current can be derived: where fSW is the switching frequency and VOUTCV is the nominal secondary output voltage. The constant current operation typically extends down to lower than 40% of nominal output voltage regulation. Primary Inductance Compensation The ACT361 integrates a built-in proprietary (patent-pending) primary inductance compensation circuit to maintain constant current regulation despite variations in transformer manufacturing. The compensated range is ±7%. Primary Inductor Current Limit Compensation The ACT361 integrates a primary inductor peak current limit compensation circuit to achieve constant input power over line and load ranges. Protection The ACT361 incorporates multiple protection functions including over-voltage, over-current and over-temperature. Output Short Circuit Protection When the secondary side output is short circuited, the ACT361 enters hiccup mode operation. In this condition, the VDD voltage drops below the VDDOFF threshold and the auxiliary supply voltage collapses. This turns off the ACT361 and causes it to restart. This hiccup behavior continues until the short circuit is removed. Output Over Voltage Protection The ACT361 includes output over-voltage protection circuitry, which shuts down the IC when the output voltage is 40% above the normal regulation voltage for 4 consecutive switching cycles. The ACT361 enters hiccup mode when an output over voltage fault is detected. Over Temperature Shutdown The thermal shutdown circuitry detects the ACT361 die temperature. The typical over temperature threshold is 135°C with 20°C hysteresis. When the die temperature rises above this threshold the ACT361 is disabled until the die temperature falls by 20°C, at which point the ACT361 is re-enabled. TYPICAL APPLICATION Design Example The design example below gives the procedure for a DCM flyback converter using the ACT361. Refer to Application Circuit in Figure 6, the design for a charger application starts with the following specification: The operation for the circuit shown in Figure 6 is as follows: the rectifier bridge D1−D4 and the capacitor C1/C2 convert the AC line voltage to DC. This voltage supplies the primary winding of the transformer T1 and the startup resistor R1/R2. The primary power current path is formed by the transformer’s primary winding, the NPN transistor, the ACT361 internal MOSFET and the current sense resistor R7. The network consisting of capacitor C3 and diode D5 provides a VDD supply voltage for ACT361 from the auxiliary winding of the transformer. C3 is the decoupling capacitor of the supply voltage and energy storage component for startup. The diode D7 and the capacitor C7 rectifies and filters the output voltage. The resistor divider consisting of R8 and R9 programs the output voltage. The minimum and maximum DC input voltages can be calculated: FUNCTIONAL DESCRIPTION CONT’D ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × × ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × × × = OUTCV SW 2 CS P OUTCC V f R 9 . 0 V 396 . 0 L 2 1 I η (2) V 90 F μ 7 . 4 2 % 70 ) ms 5 . 3 50 2 1 ( 5 . 3 2 85 2 C ) t f 2 1 ( P 2 V 2 V 2 IN C L OUT 2 ACMIN INDCMIN ≈ × × − × × − × = × − − = η (3) V 375 265 2 V 2 V ACMAX INDCMAX = × = × = (4) Input Voltage Range 85VAC - 265VAC, 50/60Hz Output Power, PO 3.5W Output Voltage, VOUTCV 5.0V OCP Current, IOUTMAX 0.9A Full Load Current, IOUTFL 0.7A Transformer Efficiency, ηxfm 0.9 System Efficiency CC, ηsystem 0.69 System Efficiency CV, η 0.7 |
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