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I am trying to use this UPS design (max 500mA), but I want to use a switching regulator instead of a linear regulator to keep regulated Vout as constant as possible even when the battery drops below Vout.

Ex: 6 V battery and 9 V power supply -> Vout needs to be 4.7 V -> I would like to get a Vout of 4.7 V even when the battery voltage is 4.7 V. (Note: D3 is reducing battery voltage by 0.7 V)

What kind of switching regulator can I use and how can I design it so that it can step down when the voltage is above 4.7 V and step down when below?

This UPS circuit need to pass intrinsic safety requirements.

enter image description here

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  • \$\begingroup\$ Is it possible? Yes, it is possible. How? Well assuming you aren't planning to build your own switching regulator since you don't know anything about them, step 1 would be to find a switching regulator module that does what you want. \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Aug 20, 2018 at 1:51
  • \$\begingroup\$ My problem is I don't know what kind of switching regulator I need to use (maybe that better question) since I have the main power supply and battery. how do adjust the regulator to step down (power above 4.7)and then step up when power drops \$\endgroup\$
    – amir
    Commented Aug 20, 2018 at 2:03
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    \$\begingroup\$ Most regulators automatically do that. It will probably have a little knob you can turn to adjust the output voltage, then it will keep the output voltage the same automatically. As for the type of regulator, look for a buck-boost one (or boost-buck). Buck converters can only step down and boost converters can only step up, but a buck-boost one can do both. \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Aug 20, 2018 at 2:28

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That is a horrible UPS design.

4.7V? What kind of battery is that?

UPS is best done with sealed lead acid which is least affected by over charging.

A constant voltage source does not make a charger.
It's much more complicated than that.
You use a smart charger chip and a micro-controller to monitor the process and make adjustments when things go wrong.

Charging is a 3 stage process. Stage 3 is extremely important for a UPS. A hysteresis charge can be used in place of the float charge.

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The you have maintenance events like adding a topping charge to reduce sulfation and replenishing energy lost to self discharge. You need to always know the state of charge. You need to monitor the battery temperature.

It is not simple to prolong battery life for 5+ years.
A UPS charger design is not trivial.

You are in way over your head.

Need a UPS? Buy one from APC. Why APC? Because they have been doing it so many years they know all the tricks and they are not telling anyone else their trade secrets.



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  • \$\begingroup\$ Thanks for the feedback the battery is 6v and power supply is 9v the regulated output is 4.7v. Regarding using chip to monitor the charging state I only found one chip that can do this which is expensive. \$\endgroup\$
    – amir
    Commented Aug 21, 2018 at 0:35

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