# Step down voltage

Discussion in 'General Electronics Chat' started by HaPPy_BoY, Jan 7, 2011.

1. ### HaPPy_BoY Thread Starter Member

Dec 5, 2010
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I'm a noob in electronics. So, i like to know what is the key factor of circuit and hardware required to make the output voltage to be lower than the input voltage, but increase the output current to be higher than input current ? Let's say the input supply is a 11.1V 2200mAh. The output to be 6V 3A

I'm trying some components in Multisim and I found that JFET controls the current easily but not the voltage, and MOSFET controls the voltage easily but not the current.

Boosting the voltage is easy with a switching converter but I'm trying to understand how to design a step-down switching dc-dc converter.

Last edited: Jan 7, 2011
2. ### mik3 Senior Member

Feb 4, 2008
4,846
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If boosting is easy, then a buck (step down) converter is the solution you are looking for.

Dec 26, 2010
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You have made an interesting couple of statements there. Could you explain how you came to those conclusions?

4. ### retched AAC Fanatic!

Dec 5, 2009
5,201
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The most efficient way to reduce voltage is a switching regulator, or DC to DC converter.

Check out SMPS.com.

You can also use voltage drops. Using a resistor will drop voltage according to Ohms law, a silicon diode will drop about .6v per diode, an LED will drop its forward voltage, which changes color to color.

A transformer is a pretty good way to drop voltage, if you need to drop more than a few volts.

5. ### HaPPy_BoY Thread Starter Member

Dec 5, 2010
36
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Just a simple tank circuit with parallel with a JFET on low side and an inductor on its drain (if i assume that JFET pin is the same as MOSFET). Changing the inductor will increase or decrease the output current.
As for MOSFET, a high side with some tank circuit arrangements will boost the output voltage. However, the input current is quite high but very low at the output.

Though i'm not sure if i'm doing it correctly but i'm only saying what i saw from my simulation. Don't be mad if i did say it wrongly and please correct me if i'm wrong.

Last edited: Jan 8, 2011
6. ### HaPPy_BoY Thread Starter Member

Dec 5, 2010
36
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Btw, how do i measure if the MOSFET or JFET is fully turned on ?

7. ### HaPPy_BoY Thread Starter Member

Dec 5, 2010
36
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If i use resistor to drop voltage, will the resistor have higher current loss ? Also, what kind transformer will work ? Can it be a pulse transformer and is it lightweight ?

8. ### #12 Expert

Nov 30, 2010
17,897
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2200 milliamp hours is not the amps. It says you can use 2200 milliamps for 1 hour...or 1100 milliamps for 2 hours etc.

Lower voltage higher current is done with a transformer, but only with AC voltages.

Step down switching converter design can be found at National Semiconductor website. Look for Simple Switchers.