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PR45-24S300 v1Many DC/DC converters come with remote ON/OFF functionality to give designers a means to control the unit externally. This elementary function ordinarily appears as a bullet point on manufacturer product pages, but it helps to review this feature before checking off this requirement and moving on. Here’s a quick overview of what you should know about remote ON/OFF as you make your selection.

Some designs may not require remote control of the DC/DC converter. However, many designs require the converter to be enabled or disabled intermittently, such as in devices that only run on standby. Or, the function can turn the converter off to protect against damaging inrush currents, to name just two examples.

The Highs and Lows of Logic

When ordering, you’ll need to know the type of logic required.

  • Positive logic. Control pin logic 1 (a “high” signal) turns the converter ON, and a 0 (“low” signal) turns it OFF. If the DC/DC converter does not need outside control, a converter with positive logic uses the high signal to operate as default.
  • Negative Logic. Control pin logic is 0 (a “low” signal) turns the converter ON, and 1 (a “high” signal), turns the converter OFF. If the DC/DC converter does not need outside control, a converter with positive logic disables the converter by default.

The way you implement remote ON/OFF will vary depending on the converter and its logic. For both isolated and non-isolated converters with positive logic, the converter will operate by default with an open control pin or if the pin is connected to a high signal. If negative logic, the converter is enabled if the control pin is connected to a low level or to the negative input.

Things You’ll See On a Datasheet

Datasheets typically indicate whether remote ON/OFF control is available under the “Input” section along with the control pin’s orientation. Polytron Devices will state whether positive or negative turn-on is available, either as standard or as an option. Depending on the converter, Polytron may also show how and where ON/OFF control is referenced (for example, which secondary pin is used and if it is referenced to GND, or whether the control voltage reference is TTL- or CMOS-compatible). Other information on the datasheet may include the voltage required to enable or disable the converter as well as the input current the converter is rated to when ON and OFF. Keep in mind that some DC/DC converter implementations may need an external component to provide isolation, so be sure to check with the manufacturer when ordering.

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