Use of Inductor/choke in Transformerless power supply

[chirag2239]

Hello,

I am in search of a circuit that can give 36V/1A output without using transformer.
I want to know why chokes and inductor is used in transformerless power supply circuits? Is this for increasing current?

I want to drive a load of 1A max. I have used the capacitor connected directly to mains with parallel resistor is of around 15uF/400V, (5 x 3.3uF/250V ). But this seems to large circuit. I am having one of the circuit which is having 1uF/400V capacitor and then after 2 inductor chokes are connected and then after bridge is there. So I am worried why they have used? Is this is for current regulation/increment?

Can anyone guide me what should I do to have an output of 36V/1A?

Thanks.

 

[KlausST]

Hi,

Can anyone guide me what should I do to have an output of 36V/1A?

At first I thought: Use 3 12 batteries.

But then I read about "mains" ....this means AC....
You never mentioned if you want 36V/1A AC or DC....

So we have to guess.
And we have to guess what is your mains frequency...and what is your mains voltage....
And I wonder why you insist in transformerless.
What's wrong with transformers?

Did you read about transformers?
That they are used for AC only, they can step up and they can step down the voltage....
And while they step down voltage ...the same time they step up current.
That they isolate the output voltage from input voltage ... and therefore they ensure safety...
They are simple, they are common , they are rugged....

Please clarify....

Klaus
Klaus

 

[FvM]

Inductors are used in buck or boost voltage converters. Although you are apparently talking specifically about power supply with capacitive voltage drop, "transformerless" only means that you don't have isolation from mains power. It can be a rectifier with an inductive buck converter as well, probably a better concept if you need more current than a few 10 milliamperes.

An example of a transformerless buck converter discussed in a recent thread https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00005174.pdf

https://www.edaboard.com/threads/362975/

Needless to say than an off-the-shelf SMPS module with safe isolation is much smaller and probably cheaper than your capacitors.

 

[schmitt trigger]

The app note to which FvM refers to, has an interesting sentence:
"There are some applications, where an off-line power supply without isolation between input and output can be tolerated and rather low output current is required."

Then it shows a circuit which will deliver a total power of 1.6 watt. Your requirement is more than 22 times as large.
In the end, you'll have a larger and more expensive circuit than a proper transformer based one. Plus you get isolation with the latter, which is not a trivial thing.

 

[c_mitra]

I am in search of a circuit that can give 36V/1A output without using transformer..

It is entirely possible that in the rare case you decide to use a transformer that some one may one day decide to thank you.

 

[schmitt trigger]

I believe that, if we were able to make a statistic of all the posts here in the analog forum, that the "transformer-less supply" request would be among the top requests for assistance.

Probably it even is the number one request.

 

[chirag2239]

Hi,

I am working on 230V/50Hz AC and main concern is size so I compulsory have to go with the transformerless power supply. I am creating the driver for LED tubelight that works on 36V/1A. So to supply the driver, I need supply in DC from AC. That'swhy I am worried a little otherwise I am already having an option of Transformer.
So I need 36V/1A DC supply for the driver.

- - - Updated - - -

Hi,

I am working on 230V/50Hz AC and main concern is size so I compulsory have to go with the transformerless power supply. I am creating the driver for LED tubelight that works on 36V/1A. So to supply the driver, I need supply in DC from AC. That'swhy I am worried a little otherwise I am already having an option of Transformer.
So I need 36V/1A DC supply for the driver.

 

[c_mitra]

I am working on 230V/50Hz AC and main concern is size so I compulsory have to go with the transformerless power supply. I am creating the driver for LED tubelight that works on 36V/1A...

Perhaps you could have provided the details in the beginning. Do you need a constant current supply? LEDs work better on const current rather than const voltage. I presume you have the LED on a series connection and the LEDs can happily run on a const current. If you need specific help, please give more details.

 

[FvM]

You should have mentioned LED power supply earlier.

State-of-the-art for high voltage LED drivers is non-isolated buck converter, preferably with PFC function. ICs like Fairchildsemi FLS0116 are made for this application.

 

[mtwieg]

I believe that, if we were able to make a statistic of all the posts here in the analog forum, that the "transformer-less supply" request would be among the top requests for assistance.

Probably it even is the number one request.

No way, the "my IR2110 isn't working" threads are definitely #1.

 

[chirag2239]

HI,

Actually I am developing a driver for LED tubelight. But first I need a source that can supply sufficient voltage and Current. Voltage and current both should be same. As you have told before, LEDs works best on const current, that's true. So I am trying to develop the source with input capacitor. I have used 6.6uF/400V X-Rated capacitor or polestar capacitor. In parallel with it, I have used 470k resistor for discharging the capacitor. Then 1.5A bridge, and then after I have some problems. I can not decide which resistor and capacitor value should be there. I have tried with 330k/2W resistor after placing 10uF/400V capacitor parallel to the bridge output. That means, across + and - of bridge, capacitor is attached that will filter the DC output. Then a resistor is attached in series with the zener diode. At last, I have attached a return resistor for inrush current.

When I switch ON the supply, the inrush resistor which connected to the N of the line, burns out. I am not getting feasible current. And the circuit fails to run.

Please guide me. I will be thankful to you.

Please have a look on this attached file.

Thanks.
Chirag

 

[sac1991]

Inductor is used so that any sudden change in the current is not possible and it will give time to the control circuit to adjust duty cycle to maintain the current across load. What LM3402 is doing is limiting the current as per your design requirement(Rsense) and switching the mosfet. In the datasheet of LM4302 design procedure is given for inductor and output capacitor(if you need).

 

[c_mitra]

When I switch ON the supply, the inrush resistor which connected to the N of the line, burns out. I am not getting feasible current. And the circuit fails to run.

The capacitor in parallel to the resistor serves no purpose. If your target current is approx 1A, you need to use a capacitor (resistor will dissipate lots of power) with reactance of approx 220 Ohms.

It is not going to work in the present form.

 

[FvM]

It's stated in the text that the capacitor has 6.6 µF, good for about 450 mA DC output current. The resistor is probably a high ohmic discharge resistor. In so far it's a common "transformerless" capacitive power supply.

But there are many design faults that will likely cause device failure. Particularly:

- missing voltage limit means for the "40V DC" node. If the voltage rises above 40V, it will burn all connected voltage regulators.
- wrong LM3402 circuit, missing rectifier diode
- input current too low to source the intended 36 W
- less problematic, some useless components like R16, D5. D3 and D4 unless they are meaned as power zener diodes (different symbol and diode type).

Furthermore the whole design concept seems flawed to me. See previous comments about useful LED power supply topology.