# Step down variable high voltage DC input to low voltage DC output

I'm looking to find a system that will help me step down a high voltage DC input to a low voltage output. The problem is that the DC input in question is not very stable in terms of voltage and varies depending a number of situations out of my control.

The DC input could be from anywhere to 150V to 230V but is, for the most case going to be in the range of 200V-230V.

We need a safe way to convert the power to a stable 6V-12V DC, after this we can employ other systems to get a stable low voltage. I've had a look at existing systems but am having trouble finding anything within the correct range.The power requirements are low, no more than 1A at the specified output voltage, so a absolute max of 12 watts but usually much less.

Any recommendations or processes that combine new or existing systems would be helpful. We are currently looking at options so are not set on anything in particular.

• @Mattman944 good point, forgot to include power requirements, the requirements are low, no more than 1A of current at 6V-12V DC this will be powering a small system, I'll include this in the question. Mar 25, 2021 at 0:52
• For high step down ratio the flyback topology is often used. There are plenty of AC/DC converters available (led sources, etc..) with similar input/output levels, just remove the input rectification part and connect your source to converter DC link capacitor. The 150-230V range should not be a problem for most of converters made todays.
– user208862
Mar 25, 2021 at 1:19

Take a look at how off-the-line switch mode power supplies work. The very first thing they do is rectify the AC input to DC, using a bridge rectifier. You could literally use such a supply that's rated for 230V AC and connect it to your DC source, bearing in mind that two out of the four diodes in the bridge will be carrying the load. With your modest current / power requirements this should not be an issue.

Using an existing AC-DC switchmode power supply with DC input not only solves your step-down problem, it also isolates your low-voltage side from the dangerously high DC.

• Thanks for your anwer, looking into it I found this product, which seems to be appropriate for the use case: TML 20105C. Posting it here for anyone else who needs something with similar specifications. Mar 25, 2021 at 1:14
• Another way is just UC3845 with custom flyback tranformer Mar 25, 2021 at 7:24

Basically just a +1 to hacktastical answer, this is copied from Mean Well FAQ:

Q32: In MEAN WELL's catalog, we see AC and DC at input, what is it all about?

Ans: Due to different circuit designs, MEAN WELL power supply's input consists of three types as below: (VAC≒VDC) a.85~264VAC;120~370VDC b.176~264VAC;250~370VDC c.85~132VAC/176~264VAC by Switch; 250~370VDC

In a and b inputs models, power supply can work properly no matter under AC or DC input. Some models need correct connection of input poles, positive pole connects to AC/L; negative pole connects to AC/N. Others may require opposite connection, positive pole to AC/N; negative pole to AC/L. If customers make a wrong connection, the power supply will not be broken. You can just reverse the input poles and power supply will still work. In c input models, please make sure that you switch the 115/230V input correctly. If the switch is on the 115V side and the real input is 230V, the power supply will be damaged.

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