need help!

[srcmt80]

i,ve been doing lot of internet searches on whats out there and all the low hz, units seem to be stationary, as for the high frenquancy units are adjustable. light dimmers and stoves have adjustable PWM with low frenquancy's, but there AC not DC, How hard would it be to set one up to control on/off curcuit for the timing, whats your thoughts on building one with an adjustable digital loop to control the frequancy pulse?

 

[(*steve*)]

If you google "555 PWM" you should be able to find plenty of circuits

 

[Puno]

I agree to what Steve said. Using a 555 timer to generate a variable frequency and you might need some amplification driver at the output to increase the voltage but maintaining the frequency. Look up on MOSFETS as drivers.

By the way I have been tattooing just over a year now wish had more time to tattoo. But can't leave work yet.

 

[poor mystic]

...and if you need to change the mark:space ratio it can be done using a comparator measuring a DC voltage against the sawtooth wave on the capacitor.
A sketch of the idea is attached, without values for the resistors and capacitors.
The load, which is inductive, is shown as inductor L1. The Mosfet for the job depends on the load.

 

[srcmt80]

right on thanks i will start checking into it, and puno if you havent gone through the blood borne pathogen training you should do that before you continue tattooing! always remember safety first, it not just skin your tattooing. lifes are at steak!

 

[srcmt80]

oh and puno if you have any questions, that i can help you with feel free to contact me on FB shawn cowan is my name im in montana usa, so to be in Williston ND.

 

[Puno]

thanks shawn of course safety first you don't want to put your life and others at risk no.1 priority. if you have spare time you could check my page out at inkedunderground.com (uno) you may have to open up an account its free but.

 

[srcmt80]

right on ill be there!

 

[duke37]

I will try to upload a diagram of a simple circuit which will give rectangular pulses with equal on/off times where the voltage and frequency can be controlled I suggest using a primitive battery charger as the power source to give the required voltage and mains isolation. The TIP3055 will dissipate quite a lot of heat and will need a heat sink.
A transistor audio amplifier could provide a box, power supply with large reservoir capacitor and driver and output transistors with heat sink.
The cmos 4093 contains 4 gates, only one is needed, the others need their inputs connected to something, I suggest ground. If they are left open, the chip can go bananas.
If the load is inductive it will need a catching diode across it to protect the fet. You can add a resistor in series to reduce the switch off time, I suggest a value of twice the load resistance (10 ohms?).
Let us know if this works.

 

[srcmt80]

thats awesome, so i can set up a retrostat to control voltage anf frenquency. or just link this unit to control timing from my supply?

 

[(*steve*)]

Only 2 problems with that circuit. Firstly the regulation will be poor, and secondly the switching times for the mosfet will be large.

I suggested a 555 because it can drive 200mA or thereabouts to the gate of the mosfet.

 

[srcmt80]

the heat issue didnt sound fun any way!

 

[duke37]

Hi Steve,
On your comments.
1. I have used 4093 gates to drive mosfets in low frequency inverters. The fets don't get warm so the switching speed is fast enough. The repetition rate here is quite low. The simple 4093 oscillator circuit gives equal on/off times, not so easy with the 555 but this may not be necessary.
2. No specification was given for the voltage regulation and the voltage is set by a twiddle pot, regulation problems may become serious if the load is changed. The load has not been specified.

The heat problem and regulation could be solved using a controlled switch mode power supply - not a job for a novice or me! I tried to describe the simplest possible circuit.
Audio amplifiers still use a lossy method of voltage control.

 

[srcmt80]

the load will change do to different sized coils! im not sure if what i want to do will even be possable, i just got the idea a couple weeks ago and am just trying to figure out the best way to go about it! thanks guys

 

[(*steve*)]

Hi Steve,
On your comments.
1. I have used 4093 gates to drive mosfets in low frequency inverters. The fets don't get warm so the switching speed is fast enough. The repetition rate here is quite low. The simple 4093 oscillator circuit gives equal on/off times, not so easy with the 555 but this may not be necessary.

Possibly, but it does depend to some extent on the load. Also in this case the load is inductive, so the rate of rise of current will be relatively low and that does permit one to get away with somewhat slower turn on.

You have three other gates there not doing anything. At the very least, I'd connect them in parallel and use them to buffer the output and to increase the available current to the gate.

2. No specification was given for the voltage regulation and the voltage is set by a twiddle pot, regulation problems may become serious if the load is changed. The load has not been specified.

Yeah, but I think we can assume that when he says he wants to vary the voltage from 0 to 12V that he expects the voltage to stay approximately the same under load. In your case, the reference voltage is unregulated. Even placing a 13V zener across the pot would make a significant difference.

The heat problem and regulation could be solved using a controlled switch mode power supply - not a job for a novice or me!

true

I tried to describe the simplest possible circuit.
Audio amplifiers still use a lossy method of voltage control.

Audio amplifiers have feedback (and other design considerations) which allows the output to be relatively unaffected by changes in power supply voltage.

 

[srcmt80]

that clears up that the timed 555 is probably the way to go! the less comlicated curuitry the better! it does need to very 1-20 V and at the same time as holding steady voltage, the frenquency needs to be adjustable between 80- 160 would be the precise range, and i know you guys aint stupid. so i will answer the question i im trying to reinvent the wheel! and it has to do with tattooing. i plan on building custom machines once i can afford equipment. and i have a few ideas! Will any of them fly, i hope so, cause i spend to much energy on trying to better myself to keep getting craped on. you guys are awesome and have helped more than you will ever know. THANKS!

 

[srcmt80]

And if i ever do make it rich, Yes we will ALL GET SOME! cause thats the only way to suceed! sharing!

 

[(*steve*)]

that clears up that the timed 555 is probably the way to go! the less comlicated curuitry the better! it does need to very 1-20 V and at the same time as holding steady voltage, the frenquency needs to be adjustable between 80- 160 would be the precise range, and i know you guys aint stupid. so i will answer the question i im trying to reinvent the wheel! and it has to do with tattooing. i plan on building custom machines once i can afford equipment. and i have a few ideas! Will any of them fly, i hope so, cause i spend to much energy on trying to better myself to keep getting craped on. you guys are awesome and have helped more than you will ever know. THANKS!

Regardless of my criticisms, the other solution offered here is not too bad. As long as the mosfet remains cool (and with the combination of low frequencies, moderate current, and an inductive load it almost certainly will) you would have little to worry about. If it does get warm, there are numerous easy steps that could be taken to improve things.

The difference in complexity between this and using a 555 is not significant.

With the addition of a zener diode and maybe the tweaking of some resistances it would be fine I expect.