Author Topic: PWM circuit 555 (Read 52876 times)

Artic_Knight · « **on:** March 17, 2010, 05:18:09 PM »

so im using a simple 555 setup like the one listed except the cap is 100nf, the resister leading to the mosfet is 2.2k and im using a p-chan mosfet instead of a transistor.

ive noticed my 555 chip gets hot. im using a powersupply of 5 1.2v nickel metal hydride batteries for 6v.

has anyone experienced this issue and how can you resolve it? i can touch the chip but not for prolonged periods of time and if im going to run this for any length of time (10 minutes it gets hot!) im going to need to resolve this issue.

i like this circuit as its simple and works really well! the frequency and duty cycles are easy to modify for the most part (sometimes requires a little play) and the cap can be reduced for higher frequencies.

i googled the issue and only a couple people report this and not much is said except the circuit is fried but i dont think it is as its currently working provided i dont leave it on over night :-p

thanks for any comments or assistance.

Paul-R · « **Reply #1 on:** March 17, 2010, 05:31:21 PM »

What are you trying to do with the secondary output?

Artic_Knight · « **Reply #2 on:** March 17, 2010, 05:35:22 PM »

well eventually i will use a A setup like that for water experiments but for now im not using the transformer. just a 11.3k resistor in place of the 1k (but i changed that to make sure it wasnt causing the heat) and the 2.2k where it is.

right now im just passing the strait output through the mosftet to my hho cell, i have the one output line to the base of the mos and i have the source to pos on batt and the drain to pos of the hho cell neg of hho cell to neg of batt.

just a strait pass through circuit using the 555 to control pwm

i expect the mos to run hot but its staying cool while the 555 gets hot. if im right it should be running about 900hz to 1khz according to simulators anyways.

attatched is my accurate setup.

gyulasun · « **Reply #3 on:** March 17, 2010, 05:55:17 PM »

@Artic_Knight

Probably voltage spikes come back from the transformer and sit onto the battery voltage, this may heat up the 555.

To remedy this, separate the positive supply feed point to the 555 from the transformer primary. USe a 1kOHM series resistor in the supply wire of the 555 that leads to the + battery and use also at least 220 - 470nF capacitor directly between the supply pins of the 555.

The series 2.2 kOhm is also helpful at the base you did.

Gyula

Artic_Knight · « **Reply #4 on:** March 17, 2010, 06:22:27 PM »

so your saying at a 1k resistor where i did in series with the vdc feed for the 555? now where is this cap supposed to go?

you know, this chip is only rated for 200mah, i wonder if that resistor on "vdc in" that i added on the diagram will resolve the issue..

thanks for your input, just so i understand your full statement where are you suggesting to add the cap? connected to pins 8 and 4 but still allowing pins 8 and 4 to connect to the positive feed directly? pin 4 if i remember correctly is the reset (either it or 8 one.)

thanks

Paul-R · « **Reply #5 on:** March 17, 2010, 06:25:36 PM »

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

Artic_Knight · « **Reply #6 on:** March 17, 2010, 06:41:56 PM »

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 · « **Reply #7 on:** March 17, 2010, 06:52:53 PM »

Quote from: Artic_Knight on March 17, 2010, 06:41:56 PM

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 · « **Reply #8 on:** March 17, 2010, 07:51:07 PM »

@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 · « **Reply #9 on:** March 17, 2010, 08:38:19 PM »

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.

mscoffman · « **Reply #10 on:** March 17, 2010, 09:35:40 PM »

Yes that should be ok, If you disconnect the fet. Does the ne555
still run hot? If so the high vcc is at fault. My tendency would have
been to use the orignal circuit with the load moved from the collector
to the emitter of the power transistor. If the signal is not a square
wave then load will see the opposite polarity inverted signal. But the
current drive should be correct. If the ne555 runs hot with the load
disconnected though the bipolar transistor won't help that.

:S:MarkSCoffman

gyulasun · « **Reply #11 on:** March 17, 2010, 11:00:50 PM »

Quote from: Artic_Knight on March 17, 2010, 06:22:27 PM

so your saying at a 1k resistor where i did in series with the vdc feed for the 555? now where is this cap supposed to go?

you know, this chip is only rated for 200mah, i wonder if that resistor on "vdc in" that i added on the diagram will resolve the issue..

thanks for your input, just so i understand your full statement where are you suggesting to add the cap? connected to pins 8 and 4 but still allowing pins 8 and 4 to connect to the positive feed directly? pin 4 if i remember correctly is the reset (either it or 8 one.)

thanks

Hi, I attached what I thought may clean up the supply input to the 555 if nasty pulses may appear on the battery fed back from the transformer, such already happened with me.
IF you use MOSFET instead of the bipolar transistor it can also happen that the drain-source side high voltage pulse (if any) may leak through to the 55 output via the FET self capacitances that may be several hundred pF to some nF too and you would need to protect the 555 output from it, mainly with series resistor like in the bipolar transistor case.

rgds, Gyula

Paul-R · « **Reply #12 on:** March 18, 2010, 06:13:34 PM »

Quote from: Artic_Knight on March 17, 2010, 06:41:56 PM

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.

It won't.

If you want to split water, you should first try using 42.8khz, as used by
Bob Boyce (along with an octave down, and another an octave down on that).
Stan Meyer and Dave Lawton. Also as used by John Worrell Keely before them.

Artic_Knight · « **Reply #13 on:** March 18, 2010, 07:11:16 PM »

yes the famous 42.8 is good but as previously stated the frequency changes a lot with different conditions (temp, electrolyte, plate size, etc) and i didnt want to sit down and commit to a frequency anyways. 923 was convienient so i started with that but mearly needed a pwm for testing.

i figure when i get good and ready to play with frequencies and see if they are useful i will need to know more about the resonant fracturing of water as im going to want to keep resonance despite changes in the cell temp and water contaminants.

first things first, im working this weekend with the circuit again to make sure its running cool, then im finishing my dry cell and testing its production

after that if i feel lucky ill try some resonance.

as with many members of this forum i feel the need to take it one step at a time, but i am glad i have many knowledgable people here who are willing to lend some advice! thanks to everyone for their kindness!

Paul-R · « **Reply #14 on:** March 18, 2010, 09:38:15 PM »

Quote from: Artic_Knight on March 18, 2010, 07:11:16 PM

yes the famous 42.8 is good but as previously stated the frequency changes a lot with different conditions (temp, electrolyte, plate size, etc)...

No, with respect, I think you are wrong. You start with 42.8khz.
That is a given. Everything else can be changed. Achieving this
number is not difficult. It is a matter of using the 555 spreadsheet
and getting the right values for the resistance and capacitance.

News:

User Menu

Author Topic: PWM circuit 555 (Read 52876 times)

Artic_Knight

PWM circuit 555

Paul-R

Re: PWM circuit 555

Artic_Knight

Re: PWM circuit 555

gyulasun

Re: PWM circuit 555

Artic_Knight

Re: PWM circuit 555

Paul-R

Re: PWM circuit 555

Artic_Knight

Re: PWM circuit 555

pese

Re: PWM circuit 555

mscoffman

Re: PWM circuit 555

Artic_Knight

Re: PWM circuit 555

mscoffman

Re: PWM circuit 555

gyulasun

Re: PWM circuit 555

Paul-R

Re: PWM circuit 555

Artic_Knight

Re: PWM circuit 555

Paul-R

Re: PWM circuit 555