Hi,
I have created simple oscilloscope circuit taken from magazine, when I
use 6V battery (4 pcs AA type), the input voltage is 6V, but when I am
using regulator circuit 7806, the input voltage will drop.
Why this happen?, my electrics basic is not  so good, sorry.
TIA
Yanto

yanto wrote:
> Hi,
> I have created simple oscilloscope circuit taken from magazine, when I
> use 6V battery (4 pcs AA type), the input voltage is 6V, but when I am
> using regulator circuit 7806, the input voltage will drop.
> Why this happen?, my electrics basic is not  so good, sorry.
> TIA
> Yanto

Assuming you are powering the 7806 from the batteries, the output will
be Vbatt - V dropout (typically 2V for the 78xx series). So if you
power it with 6V, you'll get about 4V out, and not regulated properly
either.

Datasheet available at:

http://www.onsemi.com/PowerSolutions/product.do?id=MC7806A

Cheers

PeteS

PeteS wrote:
> yanto wrote:
> > Hi,
> > I have created simple oscilloscope circuit taken from magazine, when I
> > use 6V battery (4 pcs AA type), the input voltage is 6V, but when I am
> > using regulator circuit 7806, the input voltage will drop.
> > Why this happen?, my electrics basic is not  so good, sorry.
> > TIA
> > Yanto
>
> Assuming you are powering the 7806 from the batteries, the output will
> be Vbatt - V dropout (typically 2V for the 78xx series). So if you
> power it with 6V, you'll get about 4V out, and not regulated properly
> either.
>
> Datasheet available at:
>
> http://www.onsemi.com/PowerSolutions/product.do?id=MC7806A
>
> Cheers
>
> PeteS

In case you are confused about dropout, it is the minimum voltage
difference between input and output of a regulator for it to function.

In this case, if you want to provide a regulated 6V from the 7806,
power it from a 9V battery and you'll be fine, but keep in mind the
power dissipation of the regulator:

P = (Vi - Vo) * Io where Vi = Vin, Vo = Vout and Io = output current.

Cheers

PeteS

Thanks PeteS
So better I use higher regulator ICs like 7809 as solution?
Any suggestion?
TIA
Yanto


PeteS wrote:
> yanto wrote:
> > Hi,
> > I have created simple oscilloscope circuit taken from magazine, when I
> > use 6V battery (4 pcs AA type), the input voltage is 6V, but when I am
> > using regulator circuit 7806, the input voltage will drop.
> > Why this happen?, my electrics basic is not  so good, sorry.
> > TIA
> > Yanto
>
> Assuming you are powering the 7806 from the batteries, the output will
> be Vbatt - V dropout (typically 2V for the 78xx series). So if you
> power it with 6V, you'll get about 4V out, and not regulated properly
> either.
>
> Datasheet available at:
>
> http://www.onsemi.com/PowerSolutions/product.do?id=MC7806A
> 
> Cheers
> 
> PeteS

yanto wrote:

> So better I use higher regulator ICs like 7809 as solution?

No. Use a voltage source with higher voltage than 8V, then your 7806 will 
provide a regulated 6V-output.


-- 
Rikard.

On 15 Dec 2006 01:47:16 -0800, "yanto" <y...@gmail.com> wrote:

>Thanks PeteS
>So better I use higher regulator ICs like 7809 as solution?
>Any suggestion?
>TIA
>Yanto

The regulator requires a "head room" of 4 volts to stay in regulation
- the input voltage needs to be 4 volts higher than the output or 10
volts if you use the 7806 and want 6 volts out.  It will be in the
datasheet on the part you have and you can look it up on-line easily.

Search:  7806 datasheet

Low dropout regulators require less differential to stay in regulation
(different part number)  LDO's work well but are more prone to
oscillate if the output or input isn't bypassed with a cap - read the
application notes to find out how to use the parts - any parts.

And don't forget the ripple if you are using a transformer for mains
power - A rule of thumb is 1,000 microfarads per 1/2 amp of current,
for about 10% ripple at 60 HZ.  If the "valley of the ripple" drops
lower than the differential the regulator requires - ripple shows up
on the output.

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"yanto" <y...@gmail.com> wrote in message
news:1...@16g2000cwy.googlegroups.com...
> Hi,
> I have created simple oscilloscope circuit taken from magazine, when I
> use 6V battery (4 pcs AA type), the input voltage is 6V, but when I am
> using regulator circuit 7806, the input voltage will drop.
> Why this happen?, my electrics basic is not  so good, sorry.
> TIA
> Yanto

Simply put, the input voltage has to be a couple of volts higher than the
output voltage. The output of the 7806 is 6 volts when regulating properly.
This means the input must be 8 volts or higher for proper operation. For
this regulator, use a 9 volt battery. Or, don't use any regulator at all,
just hook your circuit to the 6 volt battery stack.