Many power provide alarm alerts, similar to AC Fail, DC Good, and so on., make the most of optocouplers or optical isolators as a way of transferring alarm alerts from the power provide to the end-users tools with out direct connections. The primary goal of an optocoupler is to stop noise, floor loops, and/or high voltages from the power provide from damaging the end-equipment to which the alerts join. Under is a typical schematic diagram of an optocoupler that consists of an LED on the enter aspect and a phototransistor on the output aspect. Alerts from power provide activate the LED, which in flip prompts the electrically remoted phototransistor.
Typical power provide alarm alerts might embody AC Fail, DC Good, Over-Temp, and Inverter OK.
Pull-Up Resistors - When utilizing open-collector alarm alerts an external pull-up resistor is required. This pull-up resistor must be chosen and linked between the alarm output (collector) and an external voltage source (+VCC). The aim of the resistor is to restrict the quantity of present that flows via the open-collector transistor. For instance, in some functions the present mustn't exceed 10mA, nonetheless, all the time examine your power provide guide to substantiate the utmost allowable present and most +VCC voltage.
Exterior +VCC – The +VCC voltage that's linked to the pull-up resistor(s) for the alarm sign(s) ought to come from an external voltage source if most isolation is desired. Nevertheless, in some instances power provides include an Auxiliary DC Output, which is all the time current so long as the AC enter voltage is current. In some functions, this Auxiliary DC Output can be used because the +VCC for the alarm alerts apart from “AC Fail.”
Logic Floor – If an remoted logic floor is current, it often must be tied to both the (-) Vout of the power provide or to the bottom of the end-equipment system.
Alarm Sign Ranges - Generally, when an alarm situation is Not current the open-collector transistor output(s) will likely be On (or logic Low). If an alarm situation ought to happen, the open-collector output(s) will flip Off (or logic Excessive). However, totally different provides can have totally different alarm logic ranges, so you need to all the time examine your power supply’s instruction guide to find out the supply’s alarm logic ranges, with and with out alarm circumstances.
Combining Alarm Alerts – The diagram beneath reveals an instance of how “DC-OK” alerts from 3 totally different power provides which can be mounted in a power system rack can be mixed (OR’d) to kind a single sign On this instance, the +VCC comes from the Aux DC Output of the power system is linked to 3 separate pull-up resistors. These pull-up resistors (10Ok ohm) hook up with an open-collector “DC-OK” output from every of the 3 power provides. And, all open-collector transistors have a standard floor connection (just like Fig A above).
Usually, if all provides are OK, their DC-OK alerts will likely be within the low state (approx. +0.6Vdc or decrease). Ought to one of many power supply’s output’s fail, its “DC-OK” open-collector transistor will flip off and that output will go high through the pull-up resistor to the +12 to +15Vdc aux provide output. This optimistic “high” sign will ahead bias the diode and trigger the mixed “DC-OK” alarm output to go high (relative to the Return or Floor line), which signifies that one of many 3 provides have failed “DC Not OK”. The indicator mild on the failed provide will present which provide has failed.
Alternatively, every of the “DC-OK” alerts from the person provides on this power system may have been linked individually to a monitoring system (with out combining them). The benefit of doing that is that the particular failed provide could possibly be recognized remotely with out viewing the front panel mounted indicators.
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