PWM circuit 555

[Artic_Knight]

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]

What are you trying to do with the secondary output?

[Artic_Knight]

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]

@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]

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