square wave power supply design

[imjeffd]

hey guys I need some help with a square wave ac power supply that has adjustable Hz ranging from 100khz to 250khz 12 to 20vac and 200ma+ current.
I bought this generator

http://www.ebay.com/itm/181138490860?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

and what im thinking is i need to use a op-amp with a dc filter to amplify the output of the generator but i don't now how to build this amp could someone show me what amp would work for this and what components i will need

 

[Harald Kapp]

Using a DDS sythesizer for a square wave is a bit of overkill, but. o.k., you have it and you shall use it.
For amplification of the signal into the range envisioned, an opamp is not the right device. 200mA is out of range for an opamp.
You can use a booster stage based on Linear Technology's 1010 (see here) or bild a transistor based booster stage (e.g. here).

 

[imjeffd]

thank you harald kapp one more question will Figure 3. Fed-Forward Wideband Current Booster in this link http://cds.linear.com/docs/en/application-note/an18f.pdf
work for what I wont to do I just wont to make sure before I buy the parts thanks

 

[Harald Kapp]

Figure 3 will work, but it's a bit of an overkill compared to the much simpler transistor circuit.

 

[imjeffd]

thanks I have another question the RL50Ω that's at the output I don't need that correct? I think it's just a dummy load for testing and the RL stands for return loss. well I might as well go over the parts and make sure I did not mess something up
I'm using multilayer ceramic capacitors
besides for the tantalum capacitors
1/2w Metal Film Resistors
this is the -15v power supply and I will be using inductors for added filtering
as it specifies in the data sheet
http://www.mouser.com/Search/Produc...AHvirtualkey59500000virtualkey595-PTN78000AAH
and a linear regulator for the 15v
all powered from a 24v ac to dc wall adapter
and I'm going directly from the output on the generator to the amp input
I can't think of anything more thanks for all the help I really appreciate it
I only get one shot at this I just do not won't to mess it up

 

[Harald Kapp]

RL= Rload= load resistance. This is your load, it is not part of the amplifier.
Ceramics instead of tantalum is normally o.k.
all resistor 1/2 W is o.k. too, except for the 10 Ohm series resistors in the output. These carry the output current so you need to calculate P=I^2*R to find the required rating (better add some safety margin on top of that).

You don't need an additional linear regulator for the power supply. It can be set to -15V. Adding a linear regulator would require more than 15 V output from the switching supply (there's a voltage drop across any linear regulator). Or do you mean for the +15V? That's not entirely clear. Besides, it would reduce the efficiency of the power supply. Adding some additional filtering is a good idea, though.
Reulating 15V from 24 V is not a good idea. The linear regulator will drop 9 V which translates into considerable power loss. Better use something in the range 18V (unregulated) or use a regulated 15 V supply.


If you have only one shot, I recommend you proceed in small steps:
- get the +15 V running (using the linear regulator, as I assume)
- get the -15 V running (using the switched converter).
- get the 7V-9V supply for the DDS generator running (you will need an additional regulator for that, I hope you didn't forget that?)
Once all supply voltages are up and running, build the amplifier.
- get the DDS module running
- get the amplifier running
- conect eerything for the complete generator/amplifier circuit.

At each step verify current consumption and watch out for any funny smells, noises etc.

 

[imjeffd]

thanks! that was vary helpful and you saved me on theses 10ohm resistors big time ok so I drew up some schematics with the part type and everything
and I think I should add a ptc resettable Fuses 1.5A maybe? Prior to any components just to be safe

I also went with this power supply seems perfect to me its got 18vdc output
http://www.amazon.com/Universal-Pav...k-Satellite/dp/B005EV9132/ref=pd_sim_sbs_hi_4

I realized something about the generator it's DDS frequency range is 1HZ-65534Hz
so I guess I will be using the hf output that go's to 8mhz I might not be able to adjust the Amplitude it seems to imply it will not I will quote "Amplitude and offset of DDS signal can be adjusted by two potentiometers" it seems to me it would say Amplitude and offset of DDS and hf signal can be adjusted by two potentiometers if hf had amplitude control but it probably dose not matter to my understanding witch is not much the output will be 13.5vp-p or so at the mA I'm using over a wide range of input.

thanks again for all this help you are giving me

 

[Harald Kapp]

Adding fuses is always a good idea. Put them in front of the regulators.