Variable duty cycle and frequency with a 555

control the frequency and duty cycle(1% to 99%).

but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates

2.5us while the lm393 starts about at 100us

Actually I have been working on a pic version of this. I get much faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the

555 is in the microseconds. Unless I am mistaken... which happened before :()

Ken

Reply to
captoro
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control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

fast enough. I can see on the scope that the 555 pulse starts to deteriorates

2.5us while the lm393 starts about at 100us

time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the

555 is in the microseconds. Unless I am mistaken... which happened before :()

Just to clear up a few things. I am looking to obtain dutycycle from 1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

K
Reply to
captoro

I

is > > > not fast enough. I can see on the scope that the 555 pulse starts to

r

..

to

That was in the context of an all-digital solution. If you read that post m ore carefully, you'd realise that what you need is (for a 2kHz maximum freq uency) a 2MHz clock oscillator and a pair of 14-bit counters. The MC100EP19

5 doesn't make sense if you don't want frequencies above 2MHz. For a 2kHz m aximum they'd be ridiculous.

As before, I'd recommend buying the 2MHz oscillator off the shelf, and real ising the two 14-bit counters in a programmable logic device. I've got a we akness for the Xilinx CoolRunner parts, and they are quite big enough and f ast enough for the job.

You might want to use Binary-Coded Decimal thumb switches to set up the two dividers. That's four pins per decade, and you'd have to think about how f inely you;d want to be able to program the frequency and the mark-to-space ratio - you'd need 16-bits (4 4-bit decade counters) to cover your range if you wanted 0.5usec resolution on both periods, and 32 input pins to tell t he programmable logic part what you wanted.

A PIC might be a bit easier. One with an A/D converter might decode your se ttings from a pair of potentiometers, which might offer a tidier and more i ntuitive user interface. Ten-turn pots and turns-counting dials have gotten rare and expensive in recent years, but they are tidier than direct digita l inputs.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

control the frequency and duty cycle(1% to 99%).

You have obviously never built this circuit. It "remains the same" only very roughly. ie - you don't have to be a musician to hear a change in frequency as the mark space ratio is altered away from 50%.

I have wondered if it was possible to design a more complex network to get something closer to idealised behaviour. Obviously increasing the operating voltage and using Schottky diodes helps a bit.

The lazy way I found was a pair of 555s with a regulated supply one to set frequency and the other as a triggered monostable - the purpose being for a demonstration on sound waveforms to show how the character of a sound at constant pitch changed with mark space ratio. I also had to make the total power remain about constant too for this and provide envelope modulation (piano or guitar backwards is particularly fun).

It depends a bit on the range of frequencies it has to cover whether or not this would be an acceptable solution for the OP.

--
Regards, 
Martin Brown
Reply to
Martin Brown

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the

555 is in the microseconds. Unless I am mistaken... which happened before :()
100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

What is the definition of "fast rise and fall time"? How fast? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

dently control the frequency and duty cycle(1% to 99%).

i needed but when completing the circuit, I found that when varying the fr equency.. the duty cycle was also changing !! or vice versa.

t is not fast enough. I can see on the scope that the 555 pulse starts to d eteriorates 2.5us while the lm393 starts about at 100us

er rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosec ond, But the 555 is in the microseconds. Unless I am mistaken... which happ ened before :()

to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in pic oseconds ! I will look into that.

How fast rise time ?? .. Fast , I am experimenting now, the fastest as poss ible !. I have been working on a circuit with a PIc chip like I said earlier works good, well kinda. OH. before I forget I did install some 5 and 10 turn POT, some old shop nea r my house had a drawer full, I took 6 for 20$ . The circuit seems to work at 12v input through the coil, But if I put 24v ( I have not tried 36v yet as seen on the schematic) the coil get pulsed on a nd off in a random fashion !! I'LL hook up the scope on the PIC see what happens And yes all the grounds are connected together and then connected to a meta l rod in a proper grounding fashion. K

Reply to
captoro

endently control the frequency and duty cycle(1% to 99%).

ht i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

ster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanos econd, But the 555 is in the microseconds. Unless I am mistaken... which ha ppened before :()

1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I s aw someone posted the mc10eo195 chip, very fast rise and fall time.... in p icoseconds ! I will look into that.

ssible !.

s good, well kinda.

ear my house had a drawer full, I took 6 for 20$ .

(I have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

tal rod in a proper grounding fashion.

here is the link:

formatting link

Reply to
captoro

independently control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

good, well kinda.

my house had a drawer full, I took 6 for 20$ .

have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

rod in a proper grounding fashion.

Make sure you hold onto that green wire while touching the other wires

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

good, well kinda.

my house had a drawer full, I took 6 for 20$ .

have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

rod in a proper grounding fashion.

Trying to figure out what you're attempting to make has become challenging. In the above link it states you have 6 MFETS in series? I can only imagine you mean they are in series on a heat sink but electrically together in parallel?

Next, you don't state if the 10uh coil is a high Q type and maybe a rather large one?

You do realize that with fast edges you'll end up with lots of voltage at the drain? Of course you could load the DRAIN down with caps and make an induction heater coil using the ringing to generate the 50khz average that is generally used.

Just a thought.

Jamie

Reply to
Jamie

ndently control the frequency and duty cycle(1% to 99%).

t i needed but when completing the circuit, I found that when varying the f requency.. the duty cycle was also changing !! or vice versa.

it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

ster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanos econd, But the 555 is in the microseconds. Unless I am mistaken... which ha ppened before :()

1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

rks good, well kinda.

near my house had a drawer full, I took 6 for 20$ .

4v (I have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

metal rod in a proper grounding fashion.

Hi, there are 8 Mosfet in parallel in tow rows. they are rated 400v . the problem I am getting is when I supply current to the coil, (which is pr obably not 10uH because I used the default one in Orcad, I'll need to calcu late if you want. It has 300 feet wire wrapped on a 2 inch diameter PVC and 3 inch long) . the problem is when I put on the 36v actually 24 v, the out put pin from the picchip stops randomly for oscillating .... I mean 1 second on 0.5 second off etc...

K
Reply to
captoro

independently control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

good, well kinda.

near my house had a drawer full, I took 6 for 20$ .

(I have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

metal rod in a proper grounding fashion.

probably not 10uH because I used the default one in Orcad, I'll need to calculate if you want. It has 300 feet wire wrapped on a 2 inch diameter PVC and

3 inch long) . the problem is when I put on the 36v actually 24 v, the output pin from the picchip stops randomly for oscillating ....

What is it you're making, a MOSFET killer ?>:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

independently control the frequency and duty cycle(1% to 99%).

needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

good, well kinda.

near my house had a drawer full, I took 6 for 20$ .

(I have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

metal rod in a proper grounding fashion.

probably not 10uH because I used the default one in Orcad, I'll need to calculate if you want. It has 300 feet wire wrapped on a 2 inch diameter PVC and

3 inch long) . the problem is when I put on the 36v actually 24 v, the output pin from the picchip stops randomly for oscillating ....

A quick sanity check registers in the insane region.

If you put 36V into 10uH, the back of my envelope says the current ramp is 3.6 MILLION AMPS/SECOND. Round numbers...1 kHz. 99% on time is still 3.6 thousand amps. And that's only the first pulse. I think you're gonna need bigger wire.

Unless you're located at the power substation, it's not surprising that something is shutting down.

The thing seems fraught with issues.

What are you trying to accomplish?

Reply to
mike

ependently control the frequency and duty cycle(1% to 99%).

ught i needed but when completing the circuit, I found that when varying th e frequency.. the duty cycle was also changing !! or vice versa.

ut it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the na nosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

rom 1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

as possible !.

works good, well kinda.

hop near my house had a drawer full, I took 6 for 20$ .

t 24v (I have not tried 36v yet as seen on the schematic) the coil get puls ed on and off in a random fashion !!

a metal rod in a proper grounding fashion.

age

s probably not 10uH because I used the default one in Orcad, I'll need to c alculate if you want. It has 300 feet wire wrapped on a 2 inch diameter PVC and 3 inch long) . the problem is when I put on the 36v actually 24 v, the output pin from the picchip stops randomly for oscillating ....

I modified the circuit value, because i said earlier that the coil value w as not good, Now after measuring it I posted up the corrected circuit. what I am trying to accomplish?? I am trying to replicate a motor winding But pulsed instead of using steady DC. But my pic randomly stops working, I would understand if the fuse blows, he ating wire ... but why would it stop, I am thinking it comes from the gro und, sharing the same ground as the coil. ?!?

K K

Reply to
captoro

independently control the frequency and duty cycle(1% to 99%).

i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

possible !.

works good, well kinda.

near my house had a drawer full, I took 6 for 20$ .

(I have not tried 36v yet as seen on the schematic) the coil get pulsed on and off in a random fashion !!

metal rod in a proper grounding fashion.

probably not 10uH because I used the default one in Orcad, I'll need to calculate if you want. It has 300 feet wire wrapped on a 2 inch diameter PVC and

3 inch long) . the problem is when I put on the 36v actually 24 v, the output pin from the picchip stops randomly for oscillating ....

not good, Now after measuring it I posted up the corrected circuit.

heating wire ... but why would it stop, I am thinking it comes from the ground, sharing the same ground as the coil. ?!?

might be resetting the pic. Put a led+resistor on one of the outputs and flash it during initialization of the pic. That will tell you if it's resetting.

I just looked at the pictures. I don't think you have a prayer of making that work. You've got wires running all over the place and huge magnetic fields being generated. Get the PIC and the pots and display in a shielded box away from the FETs with lots of power supply decoupling.

The shielding may not help much with magnetic coupling, but making the wiring shorter will help. You may be able to get the FET ground currents contained by careful management of what is wired to what and parallel conductors for + and - to minimize the magnetic field. If not, you can try transformer or IR coupling from the pic to the driver.

You can't just turn off the FETs with current in the inductor. The energy has to go somewhere. It's best to control where it goes. Google "Miller Capacitance" and see if you have enough drive to charge the EFFECTIVE input capacitance. That also explains why the FETS are so slow turn off...and will get hot.

Are we having fun yet?

Reply to
mike

ndependently control the frequency and duty cycle(1% to 99%).

hought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

but it is not fast enough. I can see on the scope that the 555 pulse start s to deteriorates 2.5us while the lm393 starts about at 100us

ch faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... whi ch happened before :()

from 1% to 100% and frequency from 200 to 2khz with fast rise and fall tim e. I saw someone posted the mc10eo195 chip, very fast rise and fall time... . in picoseconds ! I will look into that.

|
|
|
|
|
|
.

t as possible !.

er works good, well kinda.

shop near my house had a drawer full, I took 6 for 20$ .

put 24v (I have not tried 36v yet as seen on the schematic) the coil get pu lsed on and off in a random fashion !!

to a metal rod in a proper grounding fashion.

t

be

oltage

z

is probably not 10uH because I used the default one in Orcad, I'll need to calculate if you want. It has 300 feet wire wrapped on a 2 inch diameter P VC and 3 inch long) . the problem is when I put on the 36v actually 24 v, t he output pin from the picchip stops randomly for oscillating ....

p
t

ue was not good, Now after measuring it I posted up the corrected circuit.

, heating wire ... but why would it stop, I am thinking it comes from the ground, sharing the same ground as the coil. ?!?

I thought of using optos too, i just didnt have here that are fast enough. I think that might be the problem, The wires are the shortest I can put th em , Except for a load parallel to the coil with two diodes. k

Reply to
captoro

Except for a load parallel to the coil with two diodes.

Captoro, Why don't you back up and describe exactly what it is you're trying to accomplish.

Right now you seem hell-bent on letting out the magic smoke... driving a coil with no apparent way to absorb the resultant energy is guaranteed to kill your FET's. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

, Except for a load parallel to the coil with two diodes.

That's nonsense. Get the PIC out of the middle of all that high-current high-voltage stuff. You've got pot wires curling around the fets. No sight of any power supply bypassing. OR decoupling. You can't just "wish" that it works. You gotta design it so it works and rearrange the wiring so it can work. There's some art to this kind of circuit. The reason your pic might be resetting is not on the schematic you posted. Redraw the schematic with the grounds connected exactly the way they are in the wiring. Insert inductance and resistance in every ground lead. Then add some mutual coupling between those inductors. It's not magic, but it is tedious.

Get rational about the voltages/currents/risetimes you need. Fast as possible, is not a spec. Any mention of 10ps risetime for this circuit is ludicrous. Put numbers on what you need and design for that.

Reply to
mike

them ,

Should I make a board for the PIc & mosfet driver and a separate board the mosfet and coil??

k
Reply to
captoro

enough.

them ,

mosfet and coil??

Why don't you back up and describe exactly what it is you're trying to accomplish. You're making no sense. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

enough.

them ,

mosfet and coil??

You could make an argument for either. The idea is to get the PIC out of the middle of all that high current stuff and limit the "antennas" for all the interconnect rat's nest. The PIC/knobs/display is a useful piece of test equipment. In that respect, it makes some sense to package that together.

There's still too much undisclosed to be able to offer much help. On the path you're on, you're gonna learn how inductors behave. And you already know that. And when you finally get it working, you're likely to learn how to blow up fets 8 at a time...and magnetize everything within reach.

You still seem to be working on the "best as possible" theory. Figger out what you need before you build it. Numbers are your friend.

If you're gonna drive a motor, hook up the motor and deal with all the parasitic effects.

Reply to
mike

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