Newsgroups: sci.electronics.misc
Subject: Re: Function Generator Sweep option
References: <[email protected]> <[email protected]> <[email protected]>
"Dave"  writes:

> I need a function generator with 50 volts. Normal ones only have
> 9 volts. Why do they limit it to just 9 

The limit of the outpu voltage range is generally 
mostly limited by the operating voltage used in the 
function generator. That 9V output voltage can be easily generated 
with +-12V power supply. That's the operating voltage range 
the ICs used in function generally work. 
Around +-12V supply is suitbale for many operational 
amplifier ICs. So there is good selection of 
suitable output amplifier ICs for that voltage 
range available. 

If the funtion generator maker would have wanted 
higher output voltage range, he would have needed to 
use higher operating voltages inside the device 
and possibly needed much more special ICs to 
implement it. This would have made the function 
generator propably considerably more expensive. 

> and how much difficult
> to make it 50 or so.

If ou have a suitable amplifier that has this 
output voltage rating, and amplification of 6 or more, 
you will get the voltage you need by just feeding 
the function generator signal to it and get 
the suitable signal level from output. 
Make sure that the amplifier you have can 
properly work at the frequencies you need signals at, 
the bandwidth of amplifier should be considerably 
higher then your needed frequency if you want to 
avoid the amplifier to distort your triangle and 
square wave signals.

High voltage amplifier circuits that can 
operate from DC to high frequencies tend to 
be expensive. 

If you operata at normal audio frequencies (20 Hz to 20 kHz), 
a suitable hifi amplifier could be one possibility 
as the amplifier. If you want 50V output voltage, 
you would need to select a quite powerful PA amplifier.
50V to 8 ohms is 312.5W and when connected to 4 ohms 
power is 625W. If you use norma audio amplifir, you would 
be looking for amplifier in the voltage range.

Other amplifiers when working with audio frequencies 
could be propably those amplifiers designed to drive 
distributed speakers that connect to 70V or 100V line. 
Those should nicely drive 50V to output when not 
in full power.. Size the amplifier based on the 
power you need. This kind of amplifiers has 
limitations on bandwidth (no lowest bass and 
the highest audio frequencies coudl be attenuated). 

If your current needs on output are low and you 
don't need very low frequencies / DC output, then 
in some cases just a suitable step-up transformer 
connected to the output of function generator could 
work. Or at somewhat higher powers, a normal audio 
power amplifier (several watts to tens of watts) driving 
a suitable step-up transformer could be one way to do things. 
I have used the audio amplifier + transformer when I 
needed to generae quite high voltage telephone ring signals at
http://www.epanorama.net/circuits/telephone_ringer.html
 
> Another thing.
> Suppose I set the function gen to 10Hz Sine Wave.. and I use
> some coils in the output, can the coil produce magnetic fields?

A suitable coil connected to function generator will generate 
a magnetic field. 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/