Hi voltage step down options to around 7.5V

Other Hardware General Electronics
1

Hi Everyone.

The current I need is very low around 100mA.
Step down from 24v and also 48V.
The application is a Voltage meter with IOT monitor.

1.The LM7805 regulators Input is 35V max and gets very hot when 24V as Input is used , so need a good heatsink.

2.Buck convertors (from hobby shops) is mainly around 24V to 35V max Input.
Works very good on 24V to 28V(charged batt).

3.What other options is available for higher Voltages like 48V from a Batt bank to step down?
With relation to SPACE , COST , HEAT DISSAPATION.

Thanks in advance.

2

@mikedb
What voltage do you need?
The title says 7.5V but you used a 7805 which is 5V.

3
  • For low current, use a simple zener diode to burn off some voltage.
    Example: add a 5 watt, 15 volt zener to 48V you get down to 33V
    Feed the 33V to a SMPS supply.
4

Ok , sorry for that what I mean is I can either use 5V to the 5V pin Nano clasic old bootloader.

or

7.5V to Vin Nano clasic old bootloader.

5

I will try that again.

I do have a x100 5V Zeners (orderd the wrong part).
The Zeners is bigger than a 1N4007 but smaller than a 1N5408.
I dont have the Part number with me now.

I did try using (a few years back) 1 or 2 or 5 in parallel but they got very hot , (reducing the series Voltage).

I will re do the experiment , might just work this time.

6

Or 9V or 12V.
I recommend you use 9V, since it is a standard voltage.
Can you solder together components on a protoboard, such as transistors, diodes, resistors etc.?

For maximum efficiency I would use two different designs
One for 24->9V
One for 48->9V

7

Yes , building Vero board circuits for over 40 years.

8

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9

Hi,
I have seen in many industrial applications a pre regulator.
A LM317HV will take the 48V input voltage, it is rated to 60V input, regulate it down to a suitable intermediate level for the lower voltage regulator.

Some current and voltage drop calculations would have to be done to balance out the linear regulator losses.
lm317hv.pdf (2.1 MB)

Tom.... :smiley: :+1: :coffee: :australia:

10

Thanks.
I am aware of that regulators , just don't have any ,never needed it.

The Buck convertors is ideal but not for high voltage inputs.

11

What is the battery bank composed of? four 12V batts in series?
Why not tap 12V off the first batt and buck it down to 5V?

12

So if we are limited to what you have, then please provide a list of parts that you have and we will see if it is even possible to do.

13

Been there done it with 12V Two Way Radios on a 24V system , one batt drains more and does not charge.

So we ended up with 1 flat batt after about 2 weeks.

1 Like
14

Must be small batts.

15

Not easy do able.
I have what most other electronic hobby Guy have .. boxes full of resistors , Logic ic's ,op amps dual and quad , mosfets , transistors , diodes , regulators .. 7805 , 7809, 7812 , 7824 , LM317 ,LM337 , LM388 , 10nF , 100nF, various uF .
Buck and Boost convertors and a hand full of Pic Micro controllers.

I can get 15V 5W Zeners or LM317HV no problem.
The Zener and 317HV option is a minimum approach that I could use

16

100AH Truck Batts 2 in series.

Each and every installation fail with 1 flat Batt after a couple of weeks.

17

Which ones?

18

With an extra 100mA drawn off of one? How often are they recharged?

19

They are all around 30Vmax Input.

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20

You can certainly use the LM2596 to go from 24V to 9V. However those adjustable regulators are designed so that they work over a broad range of voltages and currents and probably have poor regulation performance at low currents like 100mA but if it's all you have.

So now you just need something to drop the 48V to 24V.