Suggestions for Very-Low-Cost DC Supply

[abicash]

Hi,
I have a requirement which demands use of a very low cost DC power supply for a stationed unit.I have a 12V with not more than 200mA max current requirement.
I could use a standard Transformer-rectifier-filter-regulator(7812/317) but the catch is "VERY LOW COST"
I am thinking of using DC-DC converters..but will it keep the costs down?
Is it really possible to keep costs very-very low (maybe<20cents)
I want some suggestion here,if it can really be done?
Thanks for any pointers in advance

 

[dknguyen]

Hi,
I have a requirement which demands use of a very low cost DC power supply for a stationed unit.I have a 12V with not more than 200mA max current requirement.
I could use a standard Transformer-rectifier-filter-regulator(7812/317) but the catch is "VERY LOW COST"
I am thinking of using DC-DC converters..but will it keep the costs down?
Is it really possible to keep costs very-very low (maybe<20cents)
I want some suggestion here,if it can really be done?
Thanks for any pointers in advance

No, DC-DC converters tend to cost cost more than a transformer-rectifier-capacitor solution. BUt they also do different things (one is DC-DC the other is AC-DC).

 

[abicash]

Hi thanks for that .But i know that.I want to know of a very cheap option.I know of such circuits where i can eliminate the transformer and insert a RC and then a rectifier.People use this for small load currents but without isolation.Can this be used for higher currents as well?

 

[dknguyen]

You probably could, but the capacitor and resistor would have to be big and at some point the transformer just becomes a better choice.

 

[mvs sarma]

if the newton's laws are still valid, we may not expect 12V200mA at such low cost like <20cents. if the demand is for few seconds only , perhaps 3V lithium cells like MAXEL2032 ( a bundle of 4 will make 12V) may serve. But still these components are equally costly in my pat of the world. perhaps the spec is too conservative, unless designed and manufactured in millions.-- anyway if there are some cell chargers at 12V (older designs), one could aim at them. how ever you may try Simple OFF line power supply using TL431 and it can deliver up to perhaps 100mA, and beware, it will NOT be isolated. you may find it here.
https://www.electro-tech-online.com/threads/transformerless-240v-12v.35192/#post272064

It is again cautioned about the Life Risk involved.

 

[bunghole]

if it's possible to link two 7812 CZ's in parallel to add current, then you can use two of those, and power those by a suitable 12v plug-pack you may find at a 'trash and treasure market'

 

[abicash]

Hi thanks all for the tips,I would be using a design this week

 

[abicash]

Hi all,
So working more on my project,I have cut down on most resources and peripherals.
I require now
5V@50-60mA
(or even lesser)
My actual load is a 5V relay,a small Freescale microcontroller and a Vishay IR detector.So really the most power consuming part would be the relay,which I am still looking for a better volume price.

I was looking at Sarma's document using TL431 which says that the Line will see the i/p capacitor as an impedance and as such dissipate reactive power.
My customer requires power dissipation <0.5W,and I cant see TL431 ckt taking me anywhere with substantial Power dissipation.

I cannot use a transformer too..
So anymore help would be appreciated.
Thanks and regards

 

[mvs sarma]

Hi all,
So working more on my project,I have cut down on most resources and peripherals.
I require now
5V@50-60mA
(or even lesser)
My actual load is a 5V relay,a small Freescale microcontroller and a Vishay IR detector.So really the most power consuming part would be the relay,which I am still looking for a better volume price.

I was looking at Sarma's document using TL431 which says that the Line will see the i/p capacitor as an impedance and as such dissipate reactive power.
My customer requires power dissipation <0.5W,and I cant see TL431 ckt taking me anywhere with substantial Power dissipation.

I cannot use a transformer too..
So anymore help would be appreciated.
Thanks and regards

I fear that you are having day dreams, if you don't offend.
you know Newtons laws. Enrgy can nether....
without anything how do you get some thing?
Perhaps we can donate a PSU. even then it would be costly as you pay for courier charges.
please settle for three alkaline cells like duracel or two maxwell 2032 lithum cells and be happy.

 

[abicash]

I fear that you are having day dreams,

No I am not having day dreams.The Microchip Application note 954 says that Pd can be kept to as low as 0.23W for a 10mA load.I was considering a relay as load which I can very well change to a TRIAC with a MOC3021 like opto-isolator.Even with this I would need around 15mA for the LED ,another 2-3mA for the controller device,and 10mA for the detector.
So its less than 30mA.

Perhaps we can donate a PSU. even then it would be costly as you pay for courier charges.

Thanks for the generous offer and your kind heart.

please settle for three alkaline cells like duracel or two maxwell 2032 lithum cells and be happy.

Its not a question of I being happy.Its the customer who should be happy.If you cannot provide a solution please do not mock at the learning process.Who knows, someone might come with an invention of sorts or a better solution/option!

 

[Boncuk]

You might take a look at the TEA152X-family (ranging from TEA1520 (250mA) to TEA1523 (2A) , Philips --> see nxp.com)

They can work with input voltages rectified directly from mains in the range from 80 to 265V. They require very few external parts.

 

[abicash]

Thanks Boncuk,
I will take a look.

 

[erosennin]

The Microchip Application note 954 says that Pd can be kept to as low as 0.23W for a 10mA load.

Keep in mind that power dissipation isn't linear... i.e. it wont be 0.69W for 30mA.
I assume that, that value is instantaneous, and hence will build up over time.

I think you should talk to your customer and explain that although they want low cost, it may not be the best option for the product.
I also realise that linear regulators will lose about half of the power as heat.

What boncuk suggested will also work but will end up rising in cost as it is a Switchmode Power Supply IC. You'd need a choke, transformer, resistors and capacitors... It will be small and efficient though...

National claims on their site, a cost of $0.19c for 1000 LM78L05 linear regulators, and then you'd need to consider your other components on top of that...

I believe you're in a bit of a pickle...

 

[Torben]

I have no idea how you'd even try to meet the requirement of < 20 cents with this.

You haven't stated what the available input voltage and current is. Is this thing supposed to run from the mains, or from a low-voltage supply?

Also, how many of these do you need to build? Is this something which will be manufactured, or are you just doing a one-off for a client?


Torben

 

[mvs sarma]

No I am not having day dreams.The Microchip Application note 954 says that Pd can be kept to as low as 0.23W for a 10mA load.I was considering a relay as load which I can very well change to a TRIAC with a MOC3021 like opto-isolator.Even with this I would need around 15mA for the LED ,another 2-3mA for the controller device,and 10mA for the detector.So its less than 30mA.

Here you have perhaps accepted that the design has to spend forMOC3020 and the relevant Triac. It wont stop there . The Triac will need a Heat sink. These things will cost little over a relay cost.

Thanks for the generous offer and your kind heart.


[QUOTE Its not a question of I being happy.Its the customer who should be happy.If you cannot provide a solution please do not mock at the learning process.Who knows, someone might come with an invention of sorts or a better solution/option![/QUOTE]
I get confused as to whether the site is used for business as the word 'Customer' is used.If so what the person who offers the suggestion gained helping business person to improve his lot? (Sorry don't mis-understand me. ) or whether the site helps a learning process where technical knowledge of the seeker is elevated on the process of discussion. I sincerely feel I am not for any Mockery as claimed.

Let the Site administration debate, moderate and decide.

 

[abicash]

Keep in mind that power dissipation isn't linear... i.e. it wont be 0.69W for 30mA.

The calculation was based for a 110Vrms/60 Hz.Putting a value of 230Vrms/50 Hz with the same R & C values,I get 22mA@0.542W.I can increase the current to 33mA with a sacrifice of output voltage(5.1Vdc),that it drops to around 4.5V,but thats okay since my microcontroller operates from 1.8V and so do the other peripherals.And Power Dissipation comes to be 0.67W.So its a bit up than my limit of 0.5W,this seems explainable/acceptable at the moment-to me as well as my client.

What boncuk suggested will also work but will end up rising in cost

So I guessed after looking at the app note of TEA152X-family.So this cant work

You haven't stated what the available input voltage and current is. Is this thing supposed to run from the mains, or from a low-voltage supply?

Sorry for not providing that earlier.
Vin=230Vrms@50Hz
This is supposed to run from Mains(230V).
I am not allowed to use a transformer.So I have to generate the 5Vdc for all my devices.

Also, how many of these do you need to build? Is this something which will be manufactured, or are you just doing a one-off for a client?

There will be a big volume manufacturing done by the client,so the effort!

The Triac will need a Heat sink. These things will cost little over a relay cost.

If I were to use a BTA12600 which costs quite low,it wont need a heatsink.Since the load to be switched is <4A@230V.Yes this Opto+TRIAC costs little over a relay,but again I may not have a choice since using a relay will need a sturdy PS and that eats money.So this may be a trade-off,where I save on the PS and waste on the Output switch.

I get confused as to whether the site is used for business as the word 'Customer' is used.If so what the person who offers the suggestion gained helping business person to improve his lot? (Sorry don't mis-understand me. ) or whether the site helps a learning process where technical knowledge of the seeker is elevated on the process of discussion.

I dont see how I use this wonderful site for business with my posts?
If I were promoting a product then it would be so!
I have been using this forum for one year now and learned a lot of things and tried to contribute wherever possible.So how does it matter when I learn something on open,free forums for either business purpose or my education purpose which I may or may not utilise in future for some commercial use unless of course its bound by a NDA(Non Disclosure Agreement).Even since its an open forum,people either students or professionals are definitely aided by the thoughts generated on a topic.
I also take back my words about the mockery and apologise for any discomfort.For a moment I forgot that everybody here is to help.

 

[Papabravo]

45 years of engineering experience says that this cannot be done. You're just wasting your time trying to satisfy the requirement by going through normal purchasing channels. The only way to meet the requirement is to have what you need stolen by a criminal gang.

 

[abicash]

The only way to meet the requirement is to have what you need stolen by a criminal gang.

that sounds interesting.

 

[abicash]

Hi
I almost forgot to mention all these days about a wonderful device which I have used for my xmerless power supply from Power Integration which has substantially reduced my power dissipation and cost.
Check this **broken link removed**

I can get good currents (up to 300mA @5V).Although its not isolated but its the same thing I needed!

 

[mvs sarma]

Hi
I almost forgot to mention all these days about a wonderful device which I have used for my xmerless power supply from Power Integration which has substantially reduced my power dissipation and cost.
Check this **broken link removed**

I can get good currents (up to 300mA @5V).Although its not isolated but its the same thing I needed!

Considering the cost of the chip and the transformer, i feel that it has NOT practically met your goal of VERY LOW COST..... . You are satisfied with what you got is another issue.