Sales Information

Phone:(425) 353-3010

Fax: (425) 353-4030

SVRHF2800D – 9.0

E-mail: vptsales@vptpower.com

Web: www.vptpower.com

Page 10

SVRHF2800D Series

6.3 PROTECTION FEATURES

6.3.1 Input Undervoltage Lockout

The SVRHF2800D Series provides input undervoltage lockout protection. For input voltages below the turn-on voltage, the converter

will remain off, drawing minimal current from the source. When the input voltage exceeds the turn-on voltage, the converter will start.

The lockout circuit is designed to tolerate slow ramping input voltage waveforms. VPT’s proprietary magnetic feedback technology

provides bias voltage to all secondary control circuits and control amplifiers before the output starts, ensuring a well-controlled start up

sequence.

6.3.2 Output Soft Start

The SVRHF2800D Series utilizes an output soft-start function to ramp the output in a controlled manner, eliminating output voltage

overshoot and limiting inrush current at turn on. A voltage-mode soft-start ensures the output waveform remains consistent regardless

of changes in the load current. The output rise time is approximately 8 ms. The soft-start function is active whether the module is turned

on with an application of input voltage or from release of the inhibit pin. Under normal conditions, current drawn from the source during

turn on will not exceed the full load input current. The turn-on delay time is specified from the application of input voltage (or release of

the inhibit pin) until the output reaches 90% of its final value.

6.3.3 Output Overcurrent Protection

The SVRHF2800D Series provides output overcurrent and output short circuit protection. During a load fault condition, a constant

output current control circuit reduces the converter duty cycle to limit the total output current to approximately 125% its rated value. The

current limit protection circuit limits the sum of output currents in both +Vout and -Vout. It does not distinguish if the current is on the

positive or negative output. The converter will continue to provide constant current into any overload or short circuit condition. This

feature allows the converter to start into any capacitive load. Recovery is automatic and immediate upon removal of the fault condition.

Sustained short circuit or overload operation can cause excessive power dissipation. Care should be taken to control the operating

temperature of the converter in this condition.

6.4 THERMAL CONSIDERATIONS

The SVRHF2800D Series is rated for full power operation at 125 °C. Operation above 125 °C is allowed at reduced power. Specifically,

the output power should be derated linearly from full power at 125 °C to half power at 130 °C and to zero power at 135 °C. The

operating temperature of the converter is specified on the baseplate of the converter. The converter is designed to be conduction-

cooled, with the baseplate mounted to a heat sink, chassis, PCB or other thermal surface. The internal power dissipating components

are mounted to the baseplate of the converter and all heat flow is through the baseplate and mounting flanges. The lid of the converter

does not provide a good thermal path.

The hybrid DC-DC converter contains many semiconductor components. The maximum temperature rise from junction to case is

14 °C at full load.