Hi pple,
My main supply is 12V and i have a amplifer that has 9V input.
how do i step down the voltage to 9V?
I heard before a voltage spliter is there such a thing?
Sorry i am quite new at this..

Thanks in advance..

 

You need a voltage regulator IC. The minimum voltage drop is about 2.5 to 3 V for these devices. You can use a 7809 regulator, but I suggest that you have a look at some LDO regulators (Low Drop Out), that guarantee a better regulation if the input voltage is close to the output voltage (typically 0.8 V at full current)

 

If u don't need a stabilized voltage for the amp, or the 12V imput is stabilized use 4X1N400x in series for droping the voltage to ~9.2V .

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A couple of things (assume you are talking about DC voltage):

A. Is the 12 volt source exactly that or more like 13.8? While the difference may not seem like much, an extra volt helps with what eng1 mentions. If you could stick with a 7809 or LM317 it will be easier to find one.

B. What are the current requirements? Is this a preamp for RF or some kind of audio amp with significant power output. The 7809 and 317 do have limits in terms of current handling.

C. A series resistor could be used. This is only practical if the load current is very small, fairly constant and you can tolerate the lack of stability in the 9 volt supply.
In this case, if a 50 ma load is expected then a 60 ohm resistor (1/4 watt) would do the job. If it's not 50 ma then the value is quite different.

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stevez

 

Here are a couple of schematics

Attached Images

	12 v to 9v adapt.gif (16.5 KB, 60 views)
	12v to 9v dc.gif (10.2 KB, 59 views)

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John DeRosa (Hotwaterwizard)

hotwaterwizard@aol.com

 

Thx for the reply pple,
stevez,
The input supply is for a regulated power supply. ~12V. as i measured.
Actually i need to integrate some speakers in my circuit but i only wanna use
one adaptor or power supply.. the speakers i used is some cheap PC speakers that requires 9V - 400mA. My main supply unit is 12V - 4A.
So i guess i just need to match it right?
so can use a 7809 or the circuits that "hotwaterwizard" has suggested?

Thx in advance.

 

Yes, and LM7809 or buffered zenner (like hatwater wizard's) will both work. I recommend the LM7809 as it'll give you the best regulation and short circuit protection.

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Since the power supply is already regulated the fluctuation will not be there. you could also just put a 3 volt light bulb in series with the 9 volt load to create a 12 volt load. An Incandescent bulb will take up the fluctuation as well. The bulb must be a larger current draw than the amplifier or it will simply act like a fuse.

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John DeRosa (Hotwaterwizard)

hotwaterwizard@aol.com

 

If the 12V supply is regulated why bother with 7809? Just use something like 4X1N400x diodes in series. The voltage drop acros is somewhat the same in the 50-400mA range and the circuit will generate litle heat (so no small heatsink required).

__________________
If is too complicated.....most of the times is the wrong way.