Sales Information

Phone:(425) 353-3010

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SVRFL2800S - 11.0

E-mail: vptsales@vptpower.com

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Page 8

SVRFL2800S Series

6.0 TECHNICAL NOTES

Please note that many of these

functions are also

demonstrated in detail on the VPT website in the form of technical video labs.

6.1 GENERAL INFORMATION

6.1.1 Topology Description

The SVRFL2800S Series is an isolated, single output, forward converter. It operates over a wide input voltage range and provides a

tightly regulated positive output voltage with respect to the OUTCOM pin. Feedback isolation is accomplished using VPT’s proprietary

magnetic feedback technology. The converter regulates with zero load, and no minimum load is required.

6.1.2 External Components

The SVRFL2800S Series is designed to operate stand-alone in most applications. It does not require any external components for

proper operation or to meet the datasheet specifications. Input and output L-C filters are provided internally for low ripple and noise. To

further reduce output ripple and noise, a small ceramic capacitor, 1 µF to 10 µF, can be added at the output. Most application specific

ripple requirements can be met with the addition of output capacitors alone. External output capacitance can be added up to the

maximum listed in

Section 3.2.

6.1.3 Source Impedance

The impedance of the 28 V input source can interact with the DC-DC converter and can affect performance. High source impedance is

often caused by a long input cable or components added in series with the input. Source resistance will cause a DC voltage drop as the

converter draws DC input current. This voltage drop is simply the cable resistance multiplied by the input current at low line. The

voltage drop and the actual voltage at the input to the converter will determine the minimum source voltage at which the converter will

operate. A high source inductance can interact with the feedback control loop of the converter. VPT’s EMI filters will usually isolate the

source and eliminate this problem. In some cases, additional input capacitance will be needed to stabilize the system.

6.1.4 Output Configurations

Since the converter is isolated, the output can be configured as a positive or negative voltage. For example, the SVRFL2812S model

can provide +12 V referenced to OUTCOM or -12 V referenced to +VOUT.

The outputs of multiple converters can be stacked in series to provide higher voltages. When outputs of multiple modules are stacked,

they naturally share the load. For example, two SVRFL2812S converters can be stacked to provide a 24 V output at 200 W.

6.2 FUNCTION DESCRIPTIONS

6.2.1 On/Off Control (INH1 and INH2)

The INH1 (Inhibit 1) pin is a primary-side control pin referenced to

IN COM. The INH1 pin must be driven using an open collector or

open drain configuration. Pulling the INH1 pin low disables the

converter output, removes bias voltage from internal control

circuitry, and puts the converter in a state of minimum input

current draw. Leaving INH1 open enables the output, allowing the

converter to operate normally. The pin must be pulled below

1.5 V to disable the output. An optional capacitor from INH1 to

INCOM may be used to delay turn-on. The INH1 pin should be

left open if not used.

The INH2 (Inhibit 2) pin is a secondary-side control pin referenced to OUTCOM. The INH2 pin must also be driven in an open collector

or open drain configuration. Pulling INH2 low to OUTCOM disables the converter output. Internal control circuits, however, remain

active. The pin must be pulled below 1.0 V to disable the output. The INH2 pin should be left open if not used.