Author Topic: 0-1V DC-DC Step down Converter?  (Read 2947 times)

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Offline eevblognube

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0-1V DC-DC Step down Converter?
« on: February 18, 2016, 06:57:29 pm »
Please let me know if I should post this is a different subforum.

I am seeking an off-the-shelf, adjustable DC-DC Step down converter with the following specs.
Input Voltage: 12-16VDC
Output current: 50mA minimum
Output Voltage: 0V-1VDC

Ideally, the adjustable output voltage range would be 0mV-1000mV, although an acceptable range would likely be 500mV-1000mV.

Most of the DC-DC converters I have found have a much greater output voltage.  Exceeding 1000mV will likely damage the equipment connected to the converter's output.

Alternatively, I could likely get away with having a fixed output voltage, but I'd have to experiment with voltages between 500mV to 1000mV in 100mV increments.  An adjustable unit would be preferred for this reason.

If anyone has seen a product like this, I'd sure like to check it out!


*EDIT*
It appears the B3603 unit on ebay would suffice.  I would be worried that this thing would lose its memory and output some voltage greater than 1V that will damage the equipment on the output, though.  This unit will be powered by an ignition wire on a car, so power will be completely cut every time the vehicle is shut off.
« Last Edit: February 18, 2016, 07:08:31 pm by eevblognube »
 

Offline AmmoJammo

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Re: 0-1V DC-DC Step down Converter?
« Reply #1 on: February 18, 2016, 07:07:14 pm »
You just need to have a voltage divider on the feedback line set up such that you can't adjust it above 1volt output.
 

Offline eevblognube

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Re: 0-1V DC-DC Step down Converter?
« Reply #2 on: February 18, 2016, 07:16:56 pm »
You just need to have a voltage divider on the feedback line set up such that you can't adjust it above 1volt output.

Agreed, although I don't actually have any electronics materials.  I just have some basic tools and a multimeter.  I figure a voltage divider will also sap energy and produce heat.  I'm not opposed to purchasing a resistor kit and soldering iron, I was just hoping to find an off-the-shelf product first.  I will likely need to fabricate an enclosure for the device, but I'm trying to stay away from protoboards at this time.
 

Offline eevblognube

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Re: 0-1V DC-DC Step down Converter?
« Reply #3 on: February 19, 2016, 05:20:01 pm »
Here is a unit that seems to fit the bill:
http://www.ebay.com/itm/Digital-controlled-4-5-23V-to-0-20V-2A-Converter-Step-down-Power-Supply-Module-R-/330940929785?hash=item4d0d9dd6f9:g:X58AAOxyqOxRvbEe

Also this unit:
http://www.amazon.com/5-32-0V-0-30-0V-Adjustable-Regulator-Converters/dp/B00ZF9ROKU/ref=sr_1_21?ie=UTF8&qid=1455899270&sr=8-21&keywords=smakn+converter+adjustable

Anybody have experience with these converters? 
The unit must be able to store and restore the stored output voltage automatically after the input power is cycled off/on.
 

Offline exe

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Re: 0-1V DC-DC Step down Converter?
« Reply #4 on: February 19, 2016, 08:00:40 pm »
Anybody have experience with these converters? 
The unit must be able to store and restore the stored output voltage automatically after the input power is cycled off/on.

Ask sellers what IC they are based on.  Then it's a matter of comparing claimed specs with datasheets. Do not take for granted that the devices can meet the claimed specs.
 

Offline eevblognube

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Re: 0-1V DC-DC Step down Converter?
« Reply #5 on: February 19, 2016, 08:05:25 pm »
Anybody have experience with these converters? 
The unit must be able to store and restore the stored output voltage automatically after the input power is cycled off/on.

Ask sellers what IC they are based on.  Then it's a matter of comparing claimed specs with datasheets. Do not take for granted that the devices can meet the claimed specs.

I think I'm going to go ahead and test out this unit:
http://www.amazon.com/DROK-Regulator-Converter-Switching-Stabilizers/dp/B00Q48BRFO/ref=sr_1_38?ie=UTF8&qid=1455903164&sr=8-38&keywords=drok+converter

Most of the units I've looked at use the LM2596.  This unit seems to be able to power up when power is applied (ideal for my usage), since there does not seem to be an on/off button.  Also, they claim that the issue where the voltage spiking at first power-up has been fixed.  I'm willing to give this thing a try, since its under $10 and is available with free 2-day shipping with Amazon Prime.

 

Offline exe

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Re: 0-1V DC-DC Step down Converter?
« Reply #6 on: February 19, 2016, 09:20:20 pm »

Most of the units I've looked at use the LM2596.

Yeah, and its clones. The problem is they cannot go below 1.2V (reference voltage). Anyway, good luck :)
 

Offline eevblognube

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Re: 0-1V DC-DC Step down Converter?
« Reply #7 on: February 20, 2016, 06:58:03 am »

Most of the units I've looked at use the LM2596.

Yeah, and its clones. The problem is they cannot go below 1.2V (reference voltage). Anyway, good luck :)
Check the link, it seems pretty convincing that they go to 0V.  There are a lot of answered questions and reviews. Worth a shot.

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Offline mariush

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Re: 0-1V DC-DC Step down Converter?
« Reply #8 on: February 20, 2016, 07:42:13 am »
The problem with those switching dc-dc converters would be the noise on the output, it wouldn't suprise me to see +/- 10-40mV on the output, especially at the low currents the thread author mentions (50mA and up) ... some of those regulators even need a minimum of 1-5mA to function properly (and often those cheap eBay boards don't have "built in" minimum load)

I can't think of anything off the shelf that would do your requirements (0..1v with a relatively decent amount of control, and at low currents like 50mA).

Seems like small linear regulators with very low voltage drop would be ideal for this though and you could probably protect the output using some sort of zener diode or optionally disabling the regulator by setting the regulator's enable (if it has any) line high/low if the voltage goes above 1v.
If you don't really need 0v but you could settle for a minimum of 0.25v or something like that, there are small linear regulators that have internal voltage references smaller than the typical 1.25v

For example a 3$ LT3020 has an internal voltage reference of 0.2v so you can output 0.2...1v but at maximum 100mA and maximum 10v input voltage (you can just use a 2.5v or 3.3v fixed linear regulator in front of this chip or a cheap mc34063 solution or another dc-dc converter to make sure the voltage is always low enough for this chip)

A 4.5$ LT3021 can do up to around 550mA and it's easier to solder (SOIC, 8 easy to solder leads) but otherwise has the same pros (0.2v minimum) but also same limitations.

A <1$ Microchip (former Micrel)  MIC47053 will do 0.4..1v at up to 500mA  but it's even pickier about the input voltage (shouldn't use more than 3.6v) and it would be somewhat difficult to solder. Maybe you can find it in other packages at other stores, I only checked Digikey.

MIC59300 is more expensive at around 3$ but it's quite easy to solder and would allow you to go for high currents (up to 3A) and has internal voltage reference of 0.5v so it gives you directly 0.5 .. 1v . It also works with low input voltages (up to 3.8v) so you'd have to use a regulator before it to give it the low voltage it needs.

Digikey is quite good at this, you can go on the linear regulators page, filter by "positive" and "adjustable" and combinations of these words, then filter by minimum output voltage to see the regulators that can output much lower than 1v without messing around.
« Last Edit: February 20, 2016, 07:53:55 am by mariush »
 

Offline eevblognube

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Re: 0-1V DC-DC Step down Converter?
« Reply #9 on: February 24, 2016, 07:07:46 am »
The problem with those switching dc-dc converters would be the noise on the output, it wouldn't suprise me to see +/- 10-40mV on the output, especially at the low currents the thread author mentions (50mA and up) ... some of those regulators even need a minimum of 1-5mA to function properly (and often those cheap eBay boards don't have "built in" minimum load)

I can't think of anything off the shelf that would do your requirements (0..1v with a relatively decent amount of control, and at low currents like 50mA).

Seems like small linear regulators with very low voltage drop would be ideal for this though and you could probably protect the output using some sort of zener diode or optionally disabling the regulator by setting the regulator's enable (if it has any) line high/low if the voltage goes above 1v.
If you don't really need 0v but you could settle for a minimum of 0.25v or something like that, there are small linear regulators that have internal voltage references smaller than the typical 1.25v

For example a 3$ LT3020 has an internal voltage reference of 0.2v so you can output 0.2...1v but at maximum 100mA and maximum 10v input voltage (you can just use a 2.5v or 3.3v fixed linear regulator in front of this chip or a cheap mc34063 solution or another dc-dc converter to make sure the voltage is always low enough for this chip)

A 4.5$ LT3021 can do up to around 550mA and it's easier to solder (SOIC, 8 easy to solder leads) but otherwise has the same pros (0.2v minimum) but also same limitations.

A <1$ Microchip (former Micrel)  MIC47053 will do 0.4..1v at up to 500mA  but it's even pickier about the input voltage (shouldn't use more than 3.6v) and it would be somewhat difficult to solder. Maybe you can find it in other packages at other stores, I only checked Digikey.

MIC59300 is more expensive at around 3$ but it's quite easy to solder and would allow you to go for high currents (up to 3A) and has internal voltage reference of 0.5v so it gives you directly 0.5 .. 1v . It also works with low input voltages (up to 3.8v) so you'd have to use a regulator before it to give it the low voltage it needs.

Digikey is quite good at this, you can go on the linear regulators page, filter by "positive" and "adjustable" and combinations of these words, then filter by minimum output voltage to see the regulators that can output much lower than 1v without messing around.
Excellent info. I agree that linear converters are a good way to go. I did purchase that buck converter from Amazon because I need to do some testing to see what voltage range will work properly.  I will use a 12V to 5V phone charger to supply 5V to the converter so the step down is less sharp.
I think there is decent tolerance for ripple for my application, but I'm not really sure.
Once I determine a proper range, I'll likely pursue a linear solution. 
Thanks!

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