I would like to drop a variable DC voltage from input 30Vdc to 200Vdc to output 5Vdc with a max 200mA

Question

I am new to electronics and would like some help if possible. The incoming voltage will be variable from 30Vdc to 200Vdc coming from a bank of solar panels. The output is 5vdc at a max of 200mA. I have looked at a similar question where they are reducing from 240Vdc to 5Vdc at 5mA. Some of these solutions will work.

1. 136Vdc to 240Vdc converting to 5Vdc
2. There are many devices to reduce 34Vdc to 5Vdc.

Can you help?

Added information. Details above were modified. We are using a bank of solar panels that will generate from 0Vdc to 240Vdc. I have looked at our situation further. I would like the equipment to be controlled to work with a range of 30Vdc to 200Vdc. This voltage must run some equipment at 5Vdc, but I can control this if it is slightly higher at a fixed voltage if necessary.(eg 5Vdc to 9Vdc.)

Answer 1

Such wide range supply is not trivial. I've helped designing one professionally last year and the solution we settled at consisted of two parts. A discrete shunt regulator and an offline AC-DC buck converter, in parallel.

The offline switch converter can be made with an Renesas RAA223011 for example.

Image source: Renesas RAA223011 datasheet

Note: These are difficult circuits to develop due to high voltages and energies. And the fact that the entire chip is at the high side, and not ground referenced, meaning special isolated probes are required to perform measurements on this circuit.

Your low starting voltage poses difficulties since a chip like this won't start at all until you have 30-ish volts or higher. The linear shunt regulator is paralleled to make it work lower.

A very basic example of a linear shunt regulator. The transistor can be replaced by a N-channel mosfet. Depending on how much current and what voltages you want there will be a heat losses.

Image source: Wikipedia - Voltage regulator, Transistor regulator

You could make your entire circuit based on the shunt regulator, but that would lose about 50 Watts of heat.

I hope this gives you some more things to research.

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And above examples are not galvanically isolated, if that is also a requirement it gets another whole level more extra complication.

Answer 2

So the difficulty is that the wide voltage range appears on a single input.

Many AC-DC switching power supplies will work with a DC input since these begin with a rectifier. Here's one that is specified to work over 70-430V DC, it's pretty cheap, and it has 5-8-12-24V versions. Most of the brick style AC-DC supplies are specified to start working at 85VAC, so they will have a minimum DC input of 120V.

• option 1

Since your solar panels feed batteries, and these should offer DC above 200V, simply power the thing from the DC batteries with one of the 5V supplies listed above. This is the simplest option.

• option 2

Use a 9-12V PB0-5C AC-DC supply, which starts to run at 70VDC, to charge a small battery 9-12V pack. From that, use a buck to make 5V. This counts on the fact that your solar panels will deliver more than 70V at least once a day to recharge the small battery. It will work even if the main solar battery is offline, which would be useful if the thing's job is to monitor the battery and alert if it fails. It will also work during the night.

• option 3, what you actually asked

The same PB0-5C AC-DC supply in 5V version, to power the device directly. Before it, a boost converter to raise input voltage from 30V to 75V if it is below that. When input voltage is above 75V, the boost converter does nothing, it's just a diode. However the boost MOSFET should withstand the maximum DC voltage plus safety margin. This would have lowest efficiency when lowest input power is available, but it's not too complicated.

• option 4

High voltage buck 200V to 36V, then a readymade 36V to 5V buck which is easy to find.

The problem with this one is the first buck, which can't be bought off the shelf, so it'll have to be designed. It could be replaced with a linear regulator, which will dissipate a lot, about 6W, at max. input voltage.

• option 5

Two-way:

1. 70-430V to 24V SMPS
2. 36V to 5V buck that is powered either from the above 24V SMPS, or from a 75-200V to 36V linear regulator that is only turned on when the output of the SMPS is not available.

If you don't want to design a switching converter, that's the simplest option.

In fact, I just found a few 5V bucks with 72V maximum input voltage, so let's go with that.

When input voltage is above 75V, the "AC-DC" block in the bottom left is active and outputs 24V. This turns on Q1 which turns off M1, and the output buck receives 23.4V input and produces 5V.

When input voltage is too low for the AC-DC brick to work, Q1 turns off, with turns on M1, which limits its source voltage to say 65V to power the buck.