Pwm circuit

[tecker]

As is the case with me I 've gone through the mass of circuits pertaining to Pwms at least the strip down elcheapos . I was looking to make a unit with the least amount of parts and good stability with out regulation That  can fit in with circuits both ac and dc . I think I got one that's ready for prime time . This circuit uses two ne 555 s . I tried SG3524  , 556 ,discreet transistors etc but with a total component list of 11 to 15 available radioshack components this circuit is the best I found and can easilly fit in with pic or picax platforms with a switch or two .The circuit is a common one not complex at  all . Today I 'll post a booster for gray days that works well as long as you can output 1 to 1.5 amps . Panel output of less is usable if you have a SLA or the like to power the circuit . If you want to run it with larger panel outputs a 7812 is necessary and is probably a good I idea so I patched in to the circuit along with a 5kUF 50 volt to help maintain duty cycle this morning . Look it over .I ,ll post a layout and the circuit etching data later but the one in the pics uses a proto board and jumpers .AI it's solid I've packed  around quite a few of it's predecessors that I  have ripped up and rebuilt  without problem .

The torus is 180 turns 14 on a core of tie wire ( homey 6bucks for 500feet)





 The signal off the torus unloaded 115volts with the duty cyle of .5 us 12.05volts holding





The voltage into a 850 cca car batt after 1 miniute it floats there and rises to 14.53 WITH 1.1AMP





The circuit

[tecker]

The torus is 180 turns bifilar looped scap wire plenty of seperation teflon tape between single wire coarses and masking tape to start each coarse .a tape at 90 turns.

[tecker]

The sw cad file is here it if you want to hack on it

http://www.otherpower.com/images/scimages/1431/boost.asc

[RobC]

Hi tecker

I was thinking about building the same thing but I was going to use a single 555 setup for a 0-100% duty cycle and then just change the timing cap to alter the frequency. I don't know why but never could get a dual 555 pwm to work right. If I have time I might try your setup. Thanks for the info. RobC                  

[tecker]

 The ti and fairchild 555 top out at 50 %duty as a rule. By injecting the the frequency in to trigger (pin two )the second stage you can see 90 to 98 % out easily That's good for 1k and below but when boosting the 5 k and above will run the voltage up with low current in ( that  gets the wire to react). Keep the duty down and the frequency up .Digikey posts duty cycle max in some of its pages .

[RobC]

2 diodes and single 555 will do 0 to 100% Duty its one of my favorite ways of using them but to change frequency you have to change timing caps. RobC

[tecker]

 This is the circuit using the diodes to clip between discharge and threshold .You Will get the pulse to close up to full on that way no doubt. It gets flaky when you drive from the output . Refering to the circuit you can add r3 and r4 from the catode d1 to the discharge to adjust frequency a bit that way .I ran thru several mosfets using a single 555 because they ran away in a charging circuit . R1 and R3 can be trim pots for coarse adjusment  to prevent run away  this circuit works fine . As you say your frequency limited .

 With the two 555s you can get a wide range of adjusment with two more dollars of parts and it's very stable .  Input current can adjust  with either frequency or duty cycle (ie mark space) that's why I like both chips. You can have sloww speed for current control  resistive and  motor drive or high speed for charging. Same circuit. One real pisser is to be driving down the road and see smoke because your load impedance changed radically or  the sun comes  out or wind picks up steedy and the added current changes the frequency resulting in Fry ware.

 

[tecker]

 The circuit is not clear .Linked here

http://www.otherpower.com/images/scimages/1431/single_5.jpg

[RobC]

Thanks tecker

I will definitely be giving the dual 555 set up another try as I need a variable frequency and duty cycle pwm to test some of my projects. RobC  

[scorman]

Rob,

This one had been posted on board elsewhere:

http://www.otherpower.com/images/scimages/2965/TL494.pdf

it costs $0.25 ...am I missing something basic here??

Stew Corman from sunny Endicott

[tecker]

Rt and Ct you pretty much closly interrelated as with sg 3524 and the 3525 they're known as fixed frequency chips good for things like  SMPS and floresent drivers and motor speed . If you have more info linkit I'd like to look at it again. I am working with the sg 3524 it almost identical you need and external circuit to adjust frequency The duty cyle can be adjusted at pin 3 .If you adjust rt alone the output gets flakey fast.Good chips though .Regulators ,two  outputs that invert all kinda good stuff .