All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 08-30-2010, 06:36 PM
jarek319 jarek319 is offline
Junior Member
 
Join Date: Jan 2010
Posts: 18
Default LM339/LM324 Voltage Controlled Oscillator Circuits

I'm looking over the datasheets for the LM339 and LM324 chips and was wondering about their Voltage Controlled Oscillator circuits.

http://www.national.com/ds/LM/LM324.pdf pg. 13
http://www.national.com/ds/LM/LM339.pdf pg. 13

First off, I heard that the LM339 is faster than the LM324, from a previous thread I posted, but that was for a different circuit. Would the speed difference be the same in this case? I am looking to generate 60Hz->10KHz square and triangle waves.

On both datasheets, there is a marker for V+/2. Am I correct in assuming this is the voltage input going through a voltage divider with R1 = R2?

The LM339 mentions that V+ = 30V. Does this mean I can only drive it with 30 Volts? I am looking to make this powered by a 9V battery; which parts would I have to change in order for it to work with a lower voltage?

On the LM324 datasheet, it mentions that the wide voltage range is 0Vdc<=Vc<=2. I understand that bit, but what does the second part mean (V+ -1.5DC)?
Reply With Quote
  #2  
Old 08-30-2010, 07:03 PM
SgtWookie's Avatar
SgtWookie SgtWookie is offline
Expert Member
 
Join Date: Jul 2007
Location: In the vast midwest of the USA; CST
Posts: 22,030
Default

Quote:
Originally Posted by jarek319 View Post
First off, I heard that the LM339 is faster than the LM324, from a previous thread I posted, but that was for a different circuit. Would the speed difference be the same in this case? I am looking to generate 60Hz->10KHz square and triangle waves.
The LM324 will "run out of gas" at around 7kHz; even at that low speed, your square wave will look closer to a triangle wave.

The LM339 will not have that problem.

Quote:
On both datasheets, there is a marker for V+/2. Am I correct in assuming this is the voltage input going through a voltage divider with R1 = R2?
Yes.

Quote:
The LM339 mentions that V+ = 30V. Does this mean I can only drive it with 30 Volts? I am looking to make this powered by a 9V battery; which parts would I have to change in order for it to work with a lower voltage?
Reduce all of the resistances by roughly 2/3; for example a 100K resistor becomes 33k, a 50k resistor becomes 16.7k.
Don't forget your input voltage range will reduce correspondingly as well.

Quote:
On the LM324 datasheet, it mentions that the wide voltage range is 0Vdc<=Vc<=2. I understand that bit, but what does the second part mean (V+ -1.5DC)?
The LM324 can't "see" within about +V-1.5v.
The actual formula reads:
0Vdc <= Vc <= 2(V+ -1.5DC)
so, if V+ is 9v, that would evaluate as 2(9v-1.5v) = 2(7.5v) = 15v; then:
0Vdc <= Vc <= 15v
__________________
General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.
Reply With Quote
  #3  
Old 08-30-2010, 07:12 PM
jarek319 jarek319 is offline
Junior Member
 
Join Date: Jan 2010
Posts: 18
Default

Wow, thank you very much for the prompt responses! I'll be putting this together right now using the LM339! The 10 ohm resistor going into the capacitor gets changed as well? I'll have trouble finding a 3 ohm resistor that's not a few watts....As for the other awkward value resistors (16.7k, 6.6k, 1.7k) would it be better to round up or down to the next closest common resistor?
Reply With Quote
  #4  
Old 08-30-2010, 07:39 PM
SgtWookie's Avatar
SgtWookie SgtWookie is offline
Expert Member
 
Join Date: Jul 2007
Location: In the vast midwest of the USA; CST
Posts: 22,030
Default

You can leave the 10-Ohm resistor as is.

Here's a calculator for generating possible combinations of resistors in series/parallel:
http://www.qsl.net/in3otd/parallr.html

You can do some rounding if you'd like. After all, you'd be hard-pressed to find a 50k Ohm resistor to begin with; they should've used 51k or 47k in the schematic.
__________________
General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.
Reply With Quote
Reply   Post New Thread

Tags
, , , , , , ,


Related Site Pages
Section Title
Worksheet Opamp oscillator circuits
Worksheet Passive integrator and differentiator circuits
Worksheet Mixed-frequency signals
Textbook The Unijunction Transistor (UJT) : Thyristors


Similar Threads
Thread Thread Starter Forum Replies Last Post
Variable Voltage Controller (Analogue controlled) ollieking60@hotmail.com The Projects Forum 7 06-03-2010 08:13 AM
Assessing an unknown transformer someonesdad General Electronics Chat 37 05-27-2010 05:22 AM
voltage controlled switch Northtexasengineer The Projects Forum 11 04-11-2010 09:21 PM
Beginners tutorials #2 designing using different transistors hobbyist General Electronics Chat 0 10-09-2009 06:50 AM
Voltage Controlled Current Source Management General Electronics Chat 0 06-04-2009 01:04 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 05:04 PM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin
Copyright ©2000 - 2014, vBulletin Solutions, Inc.