Power Supply Rise and Fall Output Characteristics

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A typical query requested by our prospects is “what are the power provide’s rise and fall output traits?” Our ordinary reply “it relies upon” generally raises an eyebrow. Let’s take a look at why.
As you realize, there are two methods a power provide will be turned-on and off. One technique is to use or take away the AC enter power through a swap or circuit breaker to the provision. One other technique is use the Distant On/Off management of the provision, if the unit has this feature. Let’s look at each strategies.

The curves under (Fig. 1) present the everyday delay between when the AC enter power (Vin) is utilized and the power provide’s output reaches its rated voltage of 12V underneath full load situations. As will be seen (on this instance) with a low AC enter of 85VAC the output turn-on delay is barely greater than with greater enter voltages. Nevertheless, on this instance, the everyday turn-on delay is about 250ms and the output rise time is about 25ms.


Vin : 85VAC (A)
: 115VAC (B)
: 230VAC (C)
: 264VAC (D)
lout : 100%
Ta : 25°C

Fig. 1

The subsequent curves (Fig. 2) present the identical power provide’s output (with 100% load) when the AC enter is eliminated. The time delay from when the AC power is eliminated (or misplaced) is known as the Maintain-Up time spec. For this provide, the desired minimal hold-up time is 16ms. As proven under, the measured hold-up time is about 30ms, which meets the spec. The output fall time is roughly 10ms, when measured from 90% to 10%. Be aware that the vitality is pulled from the power provide in a short time as a result of heavy load on its output.

Fig. 2

By comparability, and not using a load (zero load), the curves under (Fig. 3) present that the Maintain-Up time of the power provide will increase considerably to about 1.8 seconds, and the output drops to zero in about 6 seconds!

Fig. 3

Beneath is a graph (Fig. 4) for this power provide that reveals how minimal Maintain-Up time varies because the load modifications between 10% and 100% (most load).

Fig. 4

Subsequent, we will review how the distant on/off management (if used) can have an effect on the power provide’s output rise/fall, and delay occasions.


Vin : 115VAC (A)
lout : 100%
Ta : 25°C
Fig. 5

Within the above curves (Fig. 5), the distant On/Off management is the underside hint and above that's the power provide’s DC OK sign degree. This example assumes the AC enter in all the time on. As will be seen, from the time the Distant On is activated (goes from high to low logic degree); it takes the output about 150ms to achieve its full rated voltage. And, the DC OK sign modifications state when the output degree is about 75% of its rated voltage, which on this case is about 125ms after the Distant On sign is activated.

The subsequent set of curves (Fig. 6) present the reverse scenario, the place the Distant On/Off sign is used to show the power provide off.

Fig. 6

There may be about 25ms delay after the Distant On/Off modifications state to when the Vout reduces to roughly 75% its nominal. As well as, at the moment the DC OK sign modifications state. The output fall time, from 90% to 10% of nominal, is roughly 15ms.

From the above curves and explanations, I imagine the reader can see why our reply in the beginning was "it relies upon." In all these measurements, delay occasions are in lots of instances extra necessary than rise and fall occasions. Different issues embody the AC enter voltage, the load, working temperatures, measurement standards and the design specifications for the power provide.