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Question about start up current

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ArthurDent:
Electro Fan –
--- Quote ---”… On the other hand it seems like both example PS's (15V and 24V) can handle 4.5 Amps, so why should the GPSDO operate differently with 15V vs 24V?”
--- End quote ---

 The simple answer is-it doesn’t. Almost anything designed to operate over a wide voltage range today uses a SMPS. If you look at the back of your computer, or on your laptop power supply, it will probably say ‘100-240 VAC input’. This does not mean that either device will draw twice as much power at 240 VAC as 120 VAC.
 
This explanation may be overly simplified but by using pulse width modulation, switching mode power supplies transfers only enough power from the input to the output to maintain the required output. In math that is integrating the area under the curve. That means as the input voltage goes up, the input current goes down and the input power remains constant and the output voltage remains constant, controlled through a feedback loop.

 Most Telco and a lot of other battery operated equipment have to operate over a wide voltage range to compensate for the charge state of the batteries. If you have a frequency standard it must operate from a regulated source to insure it is as stable as possible.

Here is a photo of the DC-DC power module inside a Telco 24VDC GPSDO device to deliver the various regulated voltages it needs. You can see that this supply is designed to operate from 18-36 VDC which would be supplied by the Telco backup batteries during a power failure. 

Electro Fan:

--- Quote from: ArthurDent on June 03, 2019, 12:52:20 pm ---Electro Fan –
--- Quote ---”… On the other hand it seems like both example PS's (15V and 24V) can handle 4.5 Amps, so why should the GPSDO operate differently with 15V vs 24V?”
--- End quote ---

 The simple answer is-it doesn’t. Almost anything designed to operate over a wide voltage range today uses a SMPS. If you look at the back of your computer, or on your laptop power supply, it will probably say ‘100-240 VAC input’. This does not mean that either device will draw twice as much power at 240 VAC as 120 VAC.
 
This explanation may be overly simplified but by using pulse width modulation, switching mode power supplies transfers only enough power from the input to the output to maintain the required output. In math that is integrating the area under the curve. That means as the input voltage goes up, the input current goes down and the input power remains constant and the output voltage remains constant, controlled through a feedback loop.

 Most Telco and a lot of other battery operated equipment have to operate over a wide voltage range to compensate for the charge state of the batteries. If you have a frequency standard it must operate from a regulated source to insure it is as stable as possible.

Here is a photo of the DC-DC power module inside a Telco 24VDC GPSDO device to deliver the various regulated voltages it needs. You can see that this supply is designed to operate from 18-36 VDC which would be supplied by the Telco backup batteries during a power failure.

--- End quote ---

Ok, that explains a lot

- SMPS can determine the area under the curve to balance out voltage and current.
- telco equipment is designed to work with a range of battery voltages for power failure.

Thanks!

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