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ARH2812SCK Datasheet(PDF) 7 Page - International Rectifier |
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ARH2812SCK Datasheet(HTML) 7 Page - International Rectifier |
7 / 12 page www.irf.com 7 ARH28XXS Series 28V Input, Single Output Circuit Operation and Application Information The ARH28XXS series of converters have been designed using a single ended forward switched mode converter topology. (Refer to Figure I.) Single ended topologies enjoy certain advantages in radiation hardened designs in that they eliminate the possibility of simultaneous turn on of both switching elements during a radiation induced upset. In addition, single ended topologies are not subject to transformer saturation problems often associated with double ended implementations. Figure I. Block Diagram The design incorporates a two-stage LC input filter to attenuate input ripple current. A low overhead linear bias regulator provides both a bias voltage for the converter primary control logic and a stable, well-regulated reference for the error amplifier. Output control is realized using a wide band discrete pulse width modulator control circuit incorporating a unique non-linear ramp generator circuit. This circuit helps stabilize loop gain over variations in line voltage for superior output transient response. Nominal conversion frequency has been selected as 250 KHz to maximize efficiency and minimize magnetic element size. Output voltages are sensed and fed back to the controller using a patented magnetic feedback circuit. This circuit is designed to be relatively insensitive to variations in temperature, aging, radiation and manufacturing tolerances making it particularly well suited to radiation hardened designs. The control logic has been designed to use only radiation tolerant components, and current paths include series resistances to limit photocurrents. Other key circuit design features include output short circuit and overload protection, input undervoltage lockout and an external synchronization input port, permitting operation at an externally set clock rate. Alternately, a synchronization output is provided to lock frequencies with another converter when using more than one converter in a system. The ARH series of converters is capable of providing relatively high output power from a package of modest volume. The power density exhibited by these devices is obtained by combining high circuit efficiency with effective methods of heat removal from the die junctions. Good design practices have effectively addressed this requirement inside the device. However when operating at maximum loads, heat generated at the die junctions depends upon minimally restricted thermal conduction from the base plate for that heat to be carried away. To maintain case temperature at or below the specified maximum of 125°C, this heat can be transferred by attachment of the ARH28XXS to an appropriate heat dissipater held in intimate contact with the converter base-plate. Thermal Considerations Effectiveness of this heat transfer is dependent on the intimacy of the baseplate to heatsink interface. It is therefore suggested that a heat-transferring medium possessing good thermal conductivity be inserted between the baseplate and heatsink. A material utilized at the factory during testing and burn-in processes is sold under the 11 13 Sample & Hold +Vout Output Return Overload & Short Circuit Pulse Width Modulator Primary Bias & Reference EMI Filter Under-Voltage Detector 1 3 4 2 +Input Enable Sync In Input Return Level Translator & Buffer Error Amp + - 10 9 +Sense -Sense 5 Sync Out 12 14 |
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