555 pwm

Thread Starter

cowboy303

Joined Jan 30, 2012
10
This is my first post so hear it goes.

I was trying to design a PWM using a 555 timer chip with a separate frequency adjust using a pot.
any body know the best way to do this.

And what is the difference between the LM555N LM555CN NE555N and every other one. And witch one would I want.

Thank you all for your time
And please tell me if I'm doing anything wrong thank you again
 

wayneh

Joined Sep 9, 2010
16,384
Welcome to the forums. It would help if you could provide more details about your application. That's how you might choose between different specs for the 555 timer. Things like power supply type, voltage and current specs, target operating frequency of the PWM, anticipated load on the output, are all factors.

The devil is in the details. ;)
 

Thread Starter

cowboy303

Joined Jan 30, 2012
10
Power supply 12volt battery now 12volt wal-wart later
not sure what you mean by current
load just a 2n3055 transistor
frequency 500 to a few thousand (as high as posible)
thank you
 

wayneh

Joined Sep 9, 2010
16,384
The base current of the 2n3055 may be 10% of the collector current, which can be quite high. In other words you might be putting a bigger load onto the 555 than it can handle. What is the 2n3055 controlling?

Your "low" frequencies shouldn't be a problem.

A wall wart is unregulated, which means the voltage will vary with the load. With little load, it might be over 16v. Under increasing load, the voltage will come down and the ripple will increase. A big ripple may cause timing problems. Is your main load - the one being controlled by the 2n3055 - also powered by the wall wart?
 

Brownout

Joined Jan 10, 2012
2,390
Hi Cowboy. There is a very good method I've used that takes the output pin through a couple doides which are in turn connected to opposite ends of a center-tapped variable resistor, which then feed the timing network. I have a schematic at home, if nobody else posts it by the time I get there, I'll put it up.
 

Bernard

Joined Aug 7, 2008
5,482
Not all wall warts are unregulated, find one rated around 70 V AC to 240 V AC input & fairly light, will be switch mode & regulated.
 

Thread Starter

cowboy303

Joined Jan 30, 2012
10
The base current of the 2n3055 may be 10% of the collector current, which can be quite high. In other words you might be putting a bigger load onto the 555 than it can handle. What is the 2n3055 controlling?

Your "low" frequencies shouldn't be a problem.

A wall wart is unregulated, which means the voltage will vary with the load. With little load, it might be over 16v. Under increasing load, the voltage will come down and the ripple will increase. A big ripple may cause timing problems. Is your main load - the one being controlled by the 2n3055 - also powered by the wall wart?
The 2n3055 would be controlling 500ma MAX

The wal wart I would use with no load is 14volts (Tested) and is rated for 1.2 amps and if I put a 2200uf cap across the leads would that take out the ripple
 

Brownout

Joined Jan 10, 2012
2,390
Honestly, I wouldn't buy from e-bay, no matter how cheap they may be. I'd buy from Digi-key. That way you know you're getting good parts.
 

wayneh

Joined Sep 9, 2010
16,384
FWIW, I've had good luck on e-bay so far. But most here will say I'm just that - lucky.

Anyway, look at datasheets for the meaning of the suffix letters. If one manufacturer doesn't address it, try another.
 
Top