SVSA2800S 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 SVSA2800S 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 SVSA2800S 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 SVSA2812S 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 SVSA2812S converters can be stacked to provide a 24 V output at 12 W.
6.2 FUNCTION DESCRIPTIONS
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6.2.1 On/Off Control (Inhibit)
28V IN
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.
10K
BIAS
5
INH
OPTIONAL
CAPACITOR
12V
IN COM
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Sales Information
Phone:(425) 353-3010
Fax: (425) 353-4030
SVSA2800S - 9.0
Page 8
E-mail: vptsales@vptpower.com
Web: www.vptpower.com
VPT [ VPT, Inc. ]
