new oscillator circuit shared By Nelson Rocha

evostars

50% duty cycle astable oscillator
« Reply #175,  »
copied from this webpage

50% duty cycle astable oscillator

The 555 oscillator now produces a 50% duty cycle as the timing capacitor, C1 is now charging and discharging through the same resistor, R2 rather than discharging through the timers discharge pin 7 as before. When the output from the 555 oscillator is HIGH, the capacitor charges up through R2 and when the output is LOW, it discharges through R2. Resistor R1 is used to ensure that the capacitor charges up fully to the same value as the supply voltage.

However, as the capacitor charges and discharges through the same resistor, the above equation for the output frequency of oscillations has to be modified a little to reflect this circuit change. Then the new equation for the 50% Astable 555 Oscillator is given as:
(see picture)

Note that resistor R1 needs to be sufficiently high enough to ensure it does not interfere with the charging of the capacitor to produce the required 50% duty cycle. Also changing the value of the timing capacitor, C1 changes the oscillation frequency of the astable circuit.

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 555osc50.gif - 9.49 kB, 427x306, viewed 5 times.

Re: new oscillator circuit shared By Nelson Rocha
« Reply #176,  »
made a new equal mass L3 with 2.5mm2 wire

 IMG_20181025_004323.jpg - 189.87 kB, 1280x720, viewed 5 times.

Re: new oscillator circuit shared By Nelson Rocha
« Reply #177,  »

https://youtu.be/zo0UR5BgK1M

found what I was looking for jk flip flop CD4027BE with a 555 gives 50% duty cycle

Matt Watts

Re: new oscillator circuit shared By Nelson Rocha
« Reply #178,  »
Or just a D-FF.   :-)


evostars

Re: new oscillator circuit shared By Nelson Rocha
« Reply #179,  »
Quote from Matt Watts on October 25th, 09:59 AM
Or just a D-FF.   :-)

a what?
digital friends forever? dff?
can you explain more. I'm not familiar with IC's

Matt Watts

Re: new oscillator circuit shared By Nelson Rocha
« Reply #180,  »
A D Type Flip-Flop, also known as a latch.  It can be configured as a simple divide-by-two logic device that ensures the output is always 50% duty cycle.

http://www.learnabout-electronics.org/Digital/dig53.php

The only unfortunate thing is almost all of these simple logic parts are now surface mount.  Here's one that would do the job if you can find a way to solder it down:
http://www.ti.com/lit/ds/symlink/sn74lvc1g80-q1.pdf


Re: new oscillator circuit shared By Nelson Rocha
« Reply #181,  »Last edited
I see there are still some of these around:
http://www.ti.com/lit/ds/symlink/cd40175b.pdf

A bit overkill (four in a package), but it will work for a single stage (since the clock line is tied together).

evostars

Re: new oscillator circuit shared By Nelson Rocha
« Reply #182,  »
i got a cd4027  that will work the same

 CD4027BE.jpg - 409.52 kB, 1920x1080, viewed 4 times.


Matt Watts

Re: new oscillator circuit shared By Nelson Rocha
« Reply #183,  »
Yeap.  It sure will.

I have dozens of 7474 chips around here, but it appears you can't buy them anymore.

evostars

50% Duty Cycle Ocillator Circuit
« Reply #184,  »Last edited
It works :D
got pulses from 30 to 130 kHz all 50% duty cycle.
made the schematic for backup

that 1k us actually 1k8
and I replaced the 10K pot
with two precision trimpots 4k6 in series with 680 ohm.

I noticed a slight decline in frequency, that gradually stabelised. Just recharged the 12V 7Ah battery, maybe need a voltage stabeliser for the 555

I also used 10nF frim pin 5 to ground as is usual with 555.
added a 330uF and 0.1 uF to stabelise power even more.

 CD4027BE.jpg - 184.84 kB, 1867x765, viewed 7 times.

Re: new oscillator circuit shared By Nelson Rocha
« Reply #185,  »
added a nice led, and hooked it up to the new 12V battery. very happy with the results.
only need to add a precision tripod to fine tune

 IMG_20181025_231900.jpg - 212.22 kB, 1280x720, viewed once.

Re: new oscillator circuit shared By Nelson Rocha
« Reply #186,  »
Added the circuit to the mosfet. signal looks good. battery voltage pulsing at gate, slight ringing, not to bad.
Mosfet is still connected to the old board, so I first should disconnect some old parts of the gate drive transformer circuit.
Then, power the coils.
Re: new oscillator circuit shared By Nelson Rocha
« Reply #187,  »Last edited
4 Vdc on Drain. looking good. yellow is the gate, blue the source of the mosfet. they overlap perfect, so the inductive spike isnt seen by the osc circuit, as it rides on the wave.
probes are 1:1 so the inductive spike is already -17V this is with C4 88nF  at 4Vdc
Its all looking good so far. lets turn up the voltages

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Re: new oscillator circuit shared By Nelson Rocha
« Reply #188,  »
All looks good and works.
back to playing with C4 and C5 and tuning.
Will need to get used to tuning like this...
Re: new oscillator circuit shared By Nelson Rocha
« Reply #189,  »
maybe c4 AND c5 are series resonant.
I'll make them equal size
C2
« Reply #190,  »
The C2 capacitor seems to be parallel over L1 and it looks like a greeny like C3, probably around 0,22uF
without load on L3 the current is 0.62A at 12V
with resistive load (burning lamp from car) the current drops to 0.23A

I have seen that adding C2 increases the current. I have worked without it, so I will put it back in. 0.22uF
C2 hot
« Reply #191,  »
I used 12V but current rose very high.
C2 0.22uF became very hot. Need smaller value. maybe its a fake greenie with another value

Re: new oscillator circuit shared By Nelson Rocha
« Reply #192,  »
I now have 1nF for both C2 and C3 as they seem to be equal with nelsons circuit.

Now the current is indeed higher without load, than with load. but only small.
I will increase to 10nF on C2 and C3

The disruptive discharg is also visible again, but not properly tunable. probably due to C4 and C5 being equal size and resonant (80nF)
Re: new oscillator circuit shared By Nelson Rocha
« Reply #193,  »
now using 10nF for C2 and C3.  made C4 big again 2.3uF C5 needs to be tuned.
This is starting to look like it. already can see a discharge like i want it.
frequency is a bit high 125kHz but if it works it works. I guess making C4 a bit smaller would charge it faster, so I could lower the frequency of the discharge
Larger C4 for lower freq discharge
« Reply #194,  »
made C4 bigger
17x 0.22uf makes 3.6 uF

now tune it down for perfect discharge

then tune c5 to resonate at that frequency

 IMG_20181026_171238.jpg - 191.83 kB, 720x1280, viewed 3 times.

Re: new oscillator circuit shared By Nelson Rocha
« Reply #195,  »
strange frequency didnt go down... maybe depended on C3 as well. make it larger.. 22nF

C5L2 are now resonant around 63kHz with c5 being around 80nF

Matt Watts

Re: new oscillator circuit shared By Nelson Rocha
« Reply #196,  »
Quote from evostars on October 26th, 01:41 AM
4 Vdc on Drain. looking good. yellow is the gate, blue the source of the mosfet. they overlap perfect, so the inductive spike isnt seen by the osc circuit, as it rides on the wave.
probes are 1:1 so the inductive spike is already -17V this is with C4 88nF  at 4Vdc
Its all looking good so far. lets turn up the voltages
Does the MOSFET run hot?

If it does, you will need a strong gate driver to push enough current for hard switching.

The rise and fall of switching is termed "slew rate", or how much voltage change there is per time interval.  On your scope shot, the yellow trace looks good.  I'm hoping the low slew rate on the blue trace is because of what your MOSFET is connected to (highly inductive).  A quick temperature test will confirm.

evostars

more info from nelson
« Reply #197,  »Last edited
Quote from Matt Watts on October 26th, 03:34 PM
Does the MOSFET run hot?

If it does, you will need a strong gate driver to push enough current for hard switching.

The rise and fall of switching is termed "slew rate", or how much voltage change there is per time interval.  On your scope shot, the yellow trace looks good.  I'm hoping the low slew rate on the blue trace is because of what your MOSFET is connected to (highly inductive).  A quick temperature test will confirm.
yes test with L1
I cool the mosfet with fan/cool block
doesnt get hot from touch

nelson shared c4 is 2.2uf
i wasn't far aeat with 2.6uf :)

L2/c5 resonance has a positive spike discharge of 350V on the maximum voltage.

l1 and l2 need distance 15mm

l3 is in the middle

Matt Watts

Re: new oscillator circuit shared By Nelson Rocha
« Reply #198,  »
Quote from evostars on October 26th, 03:40 PM
yes test with L1
I cool the mosfet with fan/cool block
doesnt get hot from touch
Okay.  At 122kHz a 460 should be ice cold with no heatsink unless you are pushing nearly maximum amps through it.  When the switching is done right, you won't notice any heat until about 1.5 MHz.  MOSFETs get hot when they spend too much time sitting between on and off.

evostars

Re: new oscillator circuit shared By Nelson Rocha
« Reply #199,  »
Quote from Matt Watts on October 26th, 03:45 PM
Okay.  At 122kHz a 460 should be ice cold with no heatsink unless you are pushing nearly maximum amps through it.  When the switching is done right, you won't notice any heat until about 1.5 MHz.  MOSFETs get hot when they spend too much time sitting between on and off.
thanks Matt.
I'll turn the fan off and check again.
I kniwba mosfet in non linear mode has  high Rds and gets hot. So it should be cold. that 460 can handle 20A!