Re: M3 blocks changing PoKeys PWM
Posted: Sat May 28, 2016 1:24 am
J:
The frequencies they talk about are thr firing frequency. Its about two different laser setups..
My laser for example, has one input, TTL, it has no pot or power setting. When it shoots, it shots at full
power, but at 5khz. The PWM is a 5Khz signal, so each time it fires, it fires 100% current, but for a variable
time from 0 - 200us per shot. The net effect of this is "average" power. if you shoot 100% but only 10% of the
time, you get an effective 10% power. the faster you do this, the smoother the average. Some makers
then allowed the operation to vary in frequency. I could set my 5khz to 2khz for example.
Much of this is because of the responce of various lasers. Mione has a rise time of about 100uS, so if pulsed
at 5khz, there is just enough time for its power to hit 100% before the pulse is turned off. This allows the
gas to recover some and the next pulse can then achieve the same power. If I were to pulse at 2Khz, Id get
actually higher power as the recovery time is longer and the amplitude would get higher, faster.
The timing of the shots has a lot to do with instantaneous power vs average power.
As to frequency of 20Khz, there really is no such limit. It depends on what input your feeding the PWM.
If you feed PWM into the analogue pot input, any frequency is good, the higher the better. (The pot
after all can be considered to have a frequency of infinity..). The PWM here is not really used for anything
other than generating an "average" voltage. Rather then a pot feeding 2.5Volts from 5volts,
the PWM feeds 5volts at 20 khz at 1/2 duty cycle, the result being an average of 2.5volts. No difference.
In the TTL input, its similar but not the same. Here we trigger the power supply to feed, and to feed at a maximum
ma as set by the analogue pot. There is little information on how it works, and Ive never seen a schematic
of the high voltage supplies. BUT, there arent too many ways of controlling MA in a plasma circuit. That I do
have some experience in. In fact one of only ways I can think of, if one cannot control the electron count with a
filament, is to control the HV at a frequency. To pulse it on and off at a frequency where the average current is
15ma or whatever you have set with the pot.
Heres what my conclusion is as to how it works inside a chinese laser hv supply, I could be wrong, but
all the evidence Ive seen points to this conclusion..
You have a pot input with an analogue value on it. This is fed internally to a voltage to frequency
chip that shoots the HV transformer at a frequency that is proportional to the desired average MA.
This frequency is generated all the time when a voltage is applied to the pot pin, but controlled
by a gate.
You also have a TTL input, which is a simple switch , it turns on that gate that allows the
above frequency to feed the HV transformer. If its on, and a voltage is causing the
volt-freq circuit to run, you get laser proportional to the pot voltage.
The TTL therefore controls the length of any shot. It will have an inherent min on
time and shutoff time based on its own electronics and the ability of the tube to dissipate
its stored HV.
If one ties the TTL to ground, thus turning on the switch, and simply pulses PWM
to the analogue pin, the same effect is seen, but now the electronics of the PWM input
, its volt->freq convertor and such will control the minimum on/off times of the laser.
In essence then, there is no real difference in how one does it, other than the
on/off time variance one may see using one method over the other. BUT, you never really
need both, so one PWM is enough. If using the POT on the board, all will work the same,
just a different form of smoothing. We fool ourselves when we use the concept of
"power level" in this regard I think, what we're really controlling is on-time, and the effect
of a gas recovery rate, which is important only in that it affects any linearity of
power responce. (Typically a nonlinear power curve );
If you dont allow the gas in the tube to recover, it will eventually get depleted. There are chemical
interactions in the gas which must have time to occur, so the 18ma or 22ma limit is basically that,
a timing that allows recovery.
So whether you use the TTL input or the PWM input to control the supply its basically the same.
I could be all wet on this, I have no detailed schematic, but observing my 3 lasers and what
happens with the K40 as they get hooked up has led me to the above mental model of how
it all works. Seems to work for me so far. :)
Art
The frequencies they talk about are thr firing frequency. Its about two different laser setups..
My laser for example, has one input, TTL, it has no pot or power setting. When it shoots, it shots at full
power, but at 5khz. The PWM is a 5Khz signal, so each time it fires, it fires 100% current, but for a variable
time from 0 - 200us per shot. The net effect of this is "average" power. if you shoot 100% but only 10% of the
time, you get an effective 10% power. the faster you do this, the smoother the average. Some makers
then allowed the operation to vary in frequency. I could set my 5khz to 2khz for example.
Much of this is because of the responce of various lasers. Mione has a rise time of about 100uS, so if pulsed
at 5khz, there is just enough time for its power to hit 100% before the pulse is turned off. This allows the
gas to recover some and the next pulse can then achieve the same power. If I were to pulse at 2Khz, Id get
actually higher power as the recovery time is longer and the amplitude would get higher, faster.
The timing of the shots has a lot to do with instantaneous power vs average power.
As to frequency of 20Khz, there really is no such limit. It depends on what input your feeding the PWM.
If you feed PWM into the analogue pot input, any frequency is good, the higher the better. (The pot
after all can be considered to have a frequency of infinity..). The PWM here is not really used for anything
other than generating an "average" voltage. Rather then a pot feeding 2.5Volts from 5volts,
the PWM feeds 5volts at 20 khz at 1/2 duty cycle, the result being an average of 2.5volts. No difference.
In the TTL input, its similar but not the same. Here we trigger the power supply to feed, and to feed at a maximum
ma as set by the analogue pot. There is little information on how it works, and Ive never seen a schematic
of the high voltage supplies. BUT, there arent too many ways of controlling MA in a plasma circuit. That I do
have some experience in. In fact one of only ways I can think of, if one cannot control the electron count with a
filament, is to control the HV at a frequency. To pulse it on and off at a frequency where the average current is
15ma or whatever you have set with the pot.
Heres what my conclusion is as to how it works inside a chinese laser hv supply, I could be wrong, but
all the evidence Ive seen points to this conclusion..
You have a pot input with an analogue value on it. This is fed internally to a voltage to frequency
chip that shoots the HV transformer at a frequency that is proportional to the desired average MA.
This frequency is generated all the time when a voltage is applied to the pot pin, but controlled
by a gate.
You also have a TTL input, which is a simple switch , it turns on that gate that allows the
above frequency to feed the HV transformer. If its on, and a voltage is causing the
volt-freq circuit to run, you get laser proportional to the pot voltage.
The TTL therefore controls the length of any shot. It will have an inherent min on
time and shutoff time based on its own electronics and the ability of the tube to dissipate
its stored HV.
If one ties the TTL to ground, thus turning on the switch, and simply pulses PWM
to the analogue pin, the same effect is seen, but now the electronics of the PWM input
, its volt->freq convertor and such will control the minimum on/off times of the laser.
In essence then, there is no real difference in how one does it, other than the
on/off time variance one may see using one method over the other. BUT, you never really
need both, so one PWM is enough. If using the POT on the board, all will work the same,
just a different form of smoothing. We fool ourselves when we use the concept of
"power level" in this regard I think, what we're really controlling is on-time, and the effect
of a gas recovery rate, which is important only in that it affects any linearity of
power responce. (Typically a nonlinear power curve );
If you dont allow the gas in the tube to recover, it will eventually get depleted. There are chemical
interactions in the gas which must have time to occur, so the 18ma or 22ma limit is basically that,
a timing that allows recovery.
So whether you use the TTL input or the PWM input to control the supply its basically the same.
I could be all wet on this, I have no detailed schematic, but observing my 3 lasers and what
happens with the K40 as they get hooked up has led me to the above mental model of how
it all works. Seems to work for me so far. :)
Art