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TPS54061: TPS54061 Operating Under Voltage

Part Number: TPS54061
Other Parts Discussed in Thread: TEST

I need your help here regarding one of the switching regulator used in the design. We are using TPS54061 and need to regulate 24VDC output, although this is used just to provide power to 24V relays.

The schematics we are using is standard circuit as per the online design calculator.

We have the requirement of operating between 18VAC to 30VAC.

So at 18VAC

18 * 1.414 = 25.425V

Measured Voltage VDC =  Approx. 22VDC to 23VDC, considering drop across the bridge and series diode which we have in the design.

At 18VAC/22VDC, we see ripple is about 0.4V peak to peak , that should be fine for driving the relays.

Also at 14VAC we confirmed we get about 0.4V ripple.

At about 19.5VAC this is not the issue as input of the switcher goes beyond 24VDC and we get stable no ripple output. Basically at 18VAC/22VDC, switch is not regulating anymore which is the reason we see the ripple.

The concern we have here is that what worst can happen especially at 18VAC? Will there be any case that it work at all? We think 0.4V ripple shouldn’t be problem for relay.

Can you please review this information and share your thoughts?