# dc-dc step up transformer

Discussion in 'The Projects Forum' started by RISHI HAZRA, Apr 16, 2015.

1. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
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I need to make a transformer to step up 0.3 V to around 3 V to light LEDs . My power source is dc . This transformer has to produce a dc stepped up voltage. That is why I am using it with this circuit which I came across recently.

Can anyone please help me with the size and the frequency of the transformer. This is the rough estimate I have prepared but frequency of operation still confuses me.

frequency = 50 Hz (assumed)
N1 = 10 turns (primary)
N2 = 1000 turns (secondary)
dimensions of core = 1.5 * 1.5 sq cm
flux density for normal steel core = 1 Wb/ sq m

2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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Welcome to AAC
0.3V DC to a 3VDC using just transformer.
Not possible.

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3. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
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its not just tranformer................. just check the link I posted above. Acc to it, it is absolutely possible

4. ### DickCappels Moderator

Aug 21, 2008
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Careful you don't destroy your FET -the ratio of 3:0.3 is 10. Your primary to secondary turns ratio is 100, which means that you are likely to exceed the allowable reverse gate voltage.

Is there any special reason to design this for 50 Hz? This sort of thing is often done at tens of KHz or higher. It could save you a lot of money on copper and ferrite.

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5. ### Papabravo Expert

Feb 24, 2006
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It says right in the abstract that it is a stepped up AC voltage. See, here's the thing. Transformers don't work with DC, they only work with AC. Here's another thing. when you step up the voltage you step down the current. This happens in such a way that you always get less power out than you put in. What is the source of the 0.3VDC and how much current can it supply?

6. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
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yeah you are probably right but the patent requires me to have 1:100 turns ratio. I was thinking of making a 1:10 first. I have no idea about the frequency of operation. I guess, since its dc, the frequency will depend on the FET which is as you say thousands of Hz. I assumed 50 Hz in order to make my dimensions pragmatic

E= 4.44 B*f*N*A

7. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
15
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Its more than 100 mW but in order to light the leds, I require about 0.5 mW. So, power's not a matter. Its the voltage that bothers me. My project restricts me form using any external source. Hence op-amps are out of question.

8. ### DickCappels Moderator

Aug 21, 2008
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Do you have a diagram of your circuit? For example, will you take power from the circuit while the JFET is conducting or when it is off, or both? Are you going to pass the voltage through a rectifier and filter it or just let the LED clamp the voltage?

Have you selected a JFET yet?

Do you really only 170 microamps?

And a key question: Do you already have some ferrite cores on hand?

Let me just add that in a blocking oscillator, the frequency of operation is defined by everything in the circuit, and it turns out (as far as I know) to be the best frequency for that combination of parts.

9. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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It would be interesting to know what type of LED you are planning to use with 0.5mW.?

10. ### Papabravo Expert

Feb 24, 2006
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1,800

If your input power is 0.5 mW @ 0.3 VDC that means the current you can draw from this supply is 1.667 Amperes
If the conversion process is 80 % efficient then your output power will be 0.4 mW
For an output power of 0.4 mW at 3 VDC you current will be 133 mA

Is this what you have in mind?

One other point. Just because a patent is granted does not imply that the claims are true, or that a device described within can be made operational by someone skilled in the art. It just means that the patent office was too busy to verify any of the claims. Taking their claims on faith is IMHO the road to perdition.

Last edited: Apr 16, 2015
11. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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Does any of you think it is possible with a 0.3V DC input

12. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
15
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The FET if J110. I do not have ferrite cores as of now. Since I haven't finalized my core dimensions yet. The circuit diagram can be found in the link posted above.

The frequency of oscillation is determined by the speed of the feedback loop. For this particular oscillator, the speed of the feedback is determined primarly by the inductance of the transformer T1 primary 15, the gate to source capacitance C3 of the field effect transistor Q1, and to a lesser extent the drain to source capacitance C2 of the field effect transistor Q1.

Yeah I am gonna pass the ouptput voltage of the secondary through a rectifier in order to light the leds

Last edited by a moderator: Apr 16, 2015
13. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
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The normal 3v leds

14. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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I am assuming when you state 0.5 mW you mean 0.5 milli-Watts ie: 0.0005W.?

E

15. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
15
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So this is what I am trying to do.

I have a 0.3 V input which I need to step up to about 3 V. As I already mentioned, the power requirements are being met even after stepping up the input for LEDs require about 0.5mW to light up but at 3 V. I have tried using many other options before I came across this. The input is DC. Can you please help me with any other option. Kind of desperate about making this project, you know

Jan 16, 2014
15
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Yep, why?

17. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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Have you calculated the current in a 3V LED at 5mW and compared that result with the datasheet for a regular 3V LED.?

18. ### Tesla23 Active Member

May 10, 2009
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I'd be surprised if you can get much efficiency or power, but you can probably make an oscillator. Some time ago in response to some questions here, I made a FET oscillator that operated down to 43mV, so who knows what you could do with 300mV!

With a J310 FET and a 70turn:1turn transformer wound on an old Amidon toroid (so only 2 components), it reliably oscillated at 3.2MHz from 43mV drawing 1.6mA. It needed 43mV to start and dropped out below 41mV.

At 43mV it happily allowed a 1m 50 ohm coax connected to the drain to a 1Meg input impedance on a scope to observe a reasonable looking sinusoid of about 15mV p-p. Connecting the coax only changed the frequency about 3kHz.

Placing a 10:1 scope probe on the gate reduced the frequency to 2.4MHz and increased the supply voltage needed to 66mV, but then showed a 1.13V p-p reasonable sinusoidal waveform.

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May 10, 2009
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20. ### RISHI HAZRA Thread Starter New Member

Jan 16, 2014
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thanks for the answer. Since you have made it, can you kindly guide me with the dimensions of the transformer used in your circuit