Sales Information

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SVRHF2800S - 8.0

E-mail: vptsales@vptpower.com

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Page 8

SVRHF2800S 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 SVRHF2800S Series is an isolated single-output flyback 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 SVRHF2800S 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 SVRHF2812S can

provide +12 V DC 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 SVRHF2812S converters can be stacked to provide a 24 V output at 30 W.

6.2 FUNCTION DESCRIPTIONS

6.2.1 On/Off Control (Inhibit)

The INH (Inhibit) pin is a primary-side control pin referenced to INCOM. The INH pin

must be driven using an open collector or open drain configuration. Pulling the INH

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

INH 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 INH to

INCOM may be used to delay turn-on. The INH pin should be left open if not used.

INCOM

7

INH

1

28VIN

8

OPTIONAL

CAPACITOR

BIAS

12V

10K