PWM circuit 555

[Paul-R]

What frequency is your 555 runinng at? 42.8Khz is favoured by most.

[Artic_Knight]

less than 1khz i believe, but i can assure you its a long ways away from the famous 42.8

i was aiming for 923 as there was some experiments that said that was a good frequency but it didnt do me any good.

i would need to reduce the capacitor to 1nf i think to reach 42.8 but i have not tried yet to be honest.

i assume by you mentioning the 42.8khz you are looking for the magic sweet spot. unfortunately that will vary from setup to setup as there is a different frequency for every plate setup electrolyte setup etc.  as the temperature changes or electrolyte concentration changes its going to bring it out of the "sweet" spot so i dont even bother trying right now. i just want to get the basics working predictably and then move forward

it must be because im sick that i missed it... adding that resistor to the VDC In or pin 8 should reduce the current flow in the chip and as consequence reduce my heat. thanks for bringing that up

[pese]

less than 1khz i believe, but i can assure you its a long ways away from the famous 42.8

i was aiming for 923 as there was some experiments that said that was a good frequency but it didnt do me any good.

i would need to reduce the capacitor to 1nf i think to reach 42.8 but i have not tried yet to be honest.

i assume by you mentioning the 42.8khz you are looking for the magic sweet spot. unfortunately that will vary from setup to setup as there is a different frequency for every plate setup electrolyte setup etc.  as the temperature changes or electrolyte concentration changes its going to bring it out of the "sweet" spot so i dont even bother trying right now. i just want to get the basics working predictably and then move forward

it must be because im sick that i missed it... adding that resistor to the VDC In or pin 8 should reduce the current flow in the chip and as consequence reduce my heat. thanks for bringing that up

Search for astable (pagg. 5-6-7) in the following datas*eet: http://www.fairchildsemi.com/ds/LM/LM555.pdf the "typical"component value is shown in the fig.6 table. You will easily be able to make the 555 generate also 50kHz frequency.
Same thing for http://focus.ti.com/lit/ds/symlink/ne555.pdf : see pagg.10-11 (fig.14).

Gustav Pese

www.alt-nrg.de/pppp

[mscoffman]

@AK

The BD243 is a silicon npn bipolar power transistor as your
schematic shows but not a p channel FET as the comment indicates.

bipolar power transistors often have low beta gain at 60. Ic = Beta * Ib
Thats called their transfer function, how they are primarily designed to
be used. Consequently they need to be driven hard with a lot base
of current. That current is overheating the output circuit in your
NE555.

The way to correct this is to form a darlington coupled pair with two npn
transistors. The first one is a small 2n2222 and has a larger base resistor
(2.2K) and it's emitter directly drives the base of the power transistor.
It's simple. The collective beta current gain will be like 600. = 60 * 100

http://en.wikipedia.org/wiki/Darlington_pair

NE555 is good for probably <1MHz. with the appropriate components
the NE555 is bad at low frequencies like <10Hz. There use a
"long range timer" component. Use an N channel MOSFET if desired.

:S:MarkSCoffman

[Artic_Knight]

thanks mark actually i do have a fet in use, this diagram was ripped from the web so it does show a transistor. if i understand it correctly the fets are not a strain on anything as they are only driven by voltage and thus require less curernt than a transistor right? thats why i chose to use fets. it should be wide open at 12v which it will have when i connect to a car battery later in life, until then 6v it is.