Zener vs Fast-Act Diodes
Maxwell, Wed Dec 12 2012, 09:25PMI would like to propose a new thread dedicated to the discussion of eddy-current quenching with the use of Zener Diodes as opposed to standard anti-parallel coil diodes.
As background, we all understand that eddy currents destroy CG efficiency. The faster the eddy currents within the coil are quenched, the lesser the 'suck-back' effect will be experienced.
Re: Zener vs Fast-Act Diodes
Yandersen, Wed Dec 12 2012, 09:43PM
Um, Maxwell is trying to say, that if you put a zener diode in series with dempher diode, than current will dissipate faster, resulting in a shorter pulse time making it able to shot without suckback.
Okay, if you drive your coilgun from battery switching it on and off with IGBT or MOSFET, it will work the best way possible. But if cap is discharged to the coil via thyristor, than current will start dissipating as soon as cap will finish flushing it's energy into coil.
Whatever, isn't it better to recuperate unused energy back instead of just warming the world around you? Battery-driven halfbrige can do that, non-polar cap discharged to the coil through the SCR will recuperate energy back in inverse polarity, so adding a second stage driven from the same cap will not just reuse energy, but will inverse it back for a second shot. Just think recuperation-wise instead of "bite a little and throw away". Even in ideal conditions, just a small part of magnetic field energy may possibly get converted into kinetic energy of projectile. So the major part of energy is either wasted or recuperated. I choose recuperation as I'm half-jewish. :)
Yandersen, Wed Dec 12 2012, 09:43PM
Um, Maxwell is trying to say, that if you put a zener diode in series with dempher diode, than current will dissipate faster, resulting in a shorter pulse time making it able to shot without suckback.
Okay, if you drive your coilgun from battery switching it on and off with IGBT or MOSFET, it will work the best way possible. But if cap is discharged to the coil via thyristor, than current will start dissipating as soon as cap will finish flushing it's energy into coil.
Whatever, isn't it better to recuperate unused energy back instead of just warming the world around you? Battery-driven halfbrige can do that, non-polar cap discharged to the coil through the SCR will recuperate energy back in inverse polarity, so adding a second stage driven from the same cap will not just reuse energy, but will inverse it back for a second shot. Just think recuperation-wise instead of "bite a little and throw away". Even in ideal conditions, just a small part of magnetic field energy may possibly get converted into kinetic energy of projectile. So the major part of energy is either wasted or recuperated. I choose recuperation as I'm half-jewish. :)
Re: Zener vs Fast-Act Diodes
Maxwell, Wed Dec 12 2012, 10:29PM
I've been reading about your exploration into non-polar caps - it's quite intriguing and a new development in the CG world, very nice job.
While I love the energy recuperation method of the non-polars, I would like to keep this thread dedicated to the traditional CG development.
(I'll likely start a new thread with facts known about the non-polar cap CG's).
We should also hard-define the term 'dempher diode'.
Maxwell, Wed Dec 12 2012, 10:29PM
I've been reading about your exploration into non-polar caps - it's quite intriguing and a new development in the CG world, very nice job.
While I love the energy recuperation method of the non-polars, I would like to keep this thread dedicated to the traditional CG development.
(I'll likely start a new thread with facts known about the non-polar cap CG's).
We should also hard-define the term 'dempher diode'.
Re: Zener vs Fast-Act Diodes
Yandersen, Thu Dec 13 2012, 01:15AM
Here is the schematic of the simpliest IGBT driven monkey-design coilgun:
D is a dempher diode,
DZ is a zener in series with dempher diode - once the IGBT is switched off, coil' current fastly depletes by heating up the zener.
Even it does not let energy to be recuperated back, at least it minimizes the suckback effect.
Yandersen, Thu Dec 13 2012, 01:15AM
Here is the schematic of the simpliest IGBT driven monkey-design coilgun:
D is a dempher diode,
DZ is a zener in series with dempher diode - once the IGBT is switched off, coil' current fastly depletes by heating up the zener.
Even it does not let energy to be recuperated back, at least it minimizes the suckback effect.
Re: Zener vs Fast-Act Diodes
Maxwell, Thu Dec 13 2012, 02:35AM
Right.
I wouldn't call it monkey-designed though, I would call it armature. I'm not going to discourage any new folk from building a simple CG. Play nice.
Has anyone taken measurements of the current/voltage inside the coil after the IGBT is shut down?
What sizing diodes, both regular (dempher) and zener should be considered?
Maxwell, Thu Dec 13 2012, 02:35AM
Right.
I wouldn't call it monkey-designed though, I would call it armature. I'm not going to discourage any new folk from building a simple CG. Play nice.
Has anyone taken measurements of the current/voltage inside the coil after the IGBT is shut down?
What sizing diodes, both regular (dempher) and zener should be considered?
Re: Zener vs Fast-Act Diodes
Yandersen, Thu Dec 13 2012, 04:32AM
So far I haven't seen zeners over 5W of power. Need to try this design to see how many of them should be paralleled in order not to fry from overrated surge current. Zener dissipates hundred times more enrgy than dempher diode (voltage drop over dempher is 0.8V, while zener may be up to 200V). I think, for single stage bazooka dozen of zeners will be fine. For hundred-amps multistage I would take 3 zeners in parallel.
Yandersen, Thu Dec 13 2012, 04:32AM
So far I haven't seen zeners over 5W of power. Need to try this design to see how many of them should be paralleled in order not to fry from overrated surge current. Zener dissipates hundred times more enrgy than dempher diode (voltage drop over dempher is 0.8V, while zener may be up to 200V). I think, for single stage bazooka dozen of zeners will be fine. For hundred-amps multistage I would take 3 zeners in parallel.
Re: Zener vs Fast-Act Diodes
Turkey9, Thu Dec 13 2012, 06:42AM
I don't think this circuit works the way you think it does. First off, what are you meaning when you say dempher diode? I've never heard of it and neither has google.
Why do you want to use a zener to dissipate the energy? It seems that the idea is that because the zener has a larger voltage across it when it is reverse biased, it will burn more energy as heat? This isn't true. The zener will simply clamp the reverse voltage to whatever its breakdown voltage is. A normal diode will do the same thing, but to 0.6V. The only thing different that your circuit does is change the point where the diode will stop dissipating energy. This isn't good as you don't want the diode to stop until all the current is gone.
Think of it this way; the fastest way to dissipate the energy stored in the magnetic field after the power has been cut off is to simply short the coil. A short has a voltage drop across it of zero.
I ran a couple LTspice sims to show my point. The zener combo doesn't dissipate enough energy to stop the coil current from oscillating. In real life, this reverse current will have no where to go and will build the voltage higher and higher until something breaks.
I'm not trying to be harsh and I'm sorry if it's come out like that.
If I'm wrong in my thinking, present evidence to the contrary and I'll happily admit I was wrong. The coilgun community definitely needs innovations as it's been pretty stagnant of late.
Something that might work well to dissipate the current as fast as possible is to use a MOSFET that turns on at the right time instead of a diode. The MOSFET has a very small voltage drop across it. This trick has been used for years in switching power supplies to reduce loss across the diode.
Turkey9, Thu Dec 13 2012, 06:42AM
I don't think this circuit works the way you think it does. First off, what are you meaning when you say dempher diode? I've never heard of it and neither has google.
Why do you want to use a zener to dissipate the energy? It seems that the idea is that because the zener has a larger voltage across it when it is reverse biased, it will burn more energy as heat? This isn't true. The zener will simply clamp the reverse voltage to whatever its breakdown voltage is. A normal diode will do the same thing, but to 0.6V. The only thing different that your circuit does is change the point where the diode will stop dissipating energy. This isn't good as you don't want the diode to stop until all the current is gone.
Think of it this way; the fastest way to dissipate the energy stored in the magnetic field after the power has been cut off is to simply short the coil. A short has a voltage drop across it of zero.
I ran a couple LTspice sims to show my point. The zener combo doesn't dissipate enough energy to stop the coil current from oscillating. In real life, this reverse current will have no where to go and will build the voltage higher and higher until something breaks.
I'm not trying to be harsh and I'm sorry if it's come out like that.
If I'm wrong in my thinking, present evidence to the contrary and I'll happily admit I was wrong. The coilgun community definitely needs innovations as it's been pretty stagnant of late.
Something that might work well to dissipate the current as fast as possible is to use a MOSFET that turns on at the right time instead of a diode. The MOSFET has a very small voltage drop across it. This trick has been used for years in switching power supplies to reduce loss across the diode.
Re: Zener vs Fast-Act Diodes
Ash Small, Thu Dec 13 2012, 11:45AM
You can get zeners in a 'stud package'. They are certainly a lot higher than 5W. I'll try to find some links, and add them to this post later.
(A lot of 'old' motorcycles used stud zeners mounted on heatsinks for voltage regulation, sometimes dissipating huge amounts of power. I have a few stud zeners lying around in my parts bin.)
EDIT: here is a link to lots of 50W zeners:
I'll try and find some links to even higher wattage ones later.
EDIT: And here is a link to some 100W, 27V zeners on Ebay:
I'm sure you could find the voltage ratings you require if you do a bit of 'googling'.
High power zeners DO exist!
Ash Small, Thu Dec 13 2012, 11:45AM
Yandersen wrote ...
So far I haven't seen zeners over 5W of power.
So far I haven't seen zeners over 5W of power.
You can get zeners in a 'stud package'. They are certainly a lot higher than 5W. I'll try to find some links, and add them to this post later.
(A lot of 'old' motorcycles used stud zeners mounted on heatsinks for voltage regulation, sometimes dissipating huge amounts of power. I have a few stud zeners lying around in my parts bin.)
EDIT: here is a link to lots of 50W zeners:
I'll try and find some links to even higher wattage ones later.
EDIT: And here is a link to some 100W, 27V zeners on Ebay:
I'm sure you could find the voltage ratings you require if you do a bit of 'googling'.
High power zeners DO exist!
Re: Zener vs Fast-Act Diodes
Yandersen, Thu Dec 13 2012, 11:51AM
Turkey, In school, at 6th grade, we learned a simple formula for power which is
P=U*I,
where U is a voltage drop and I is a current. That is for zener. As for the coil' current change rate, another one exists:
dI/dt=dU/L,
which means that the rate of current change is proportional to the voltage drop across the inductor. Zener increases that voltage drop so current dissipates faster. Let's say, coil has 0.5Ohm of resistance and current running through it is 100A. The voltage drop will be 50V. Some time after current will decrease to 10A. Voltage drop will be 5V resulting in 10 times slower current' drop rate. In result, current dissipates for infinite time. Dempher diode adds 1V resulting in 51V in total for 100A and 6V for 10A. With addition of one 200V zener voltage drop is 251V and 206V, respectively. In other words, current dissipates almost linearly and with much higher rate. The more zener voltage is, the faster current will deplete. Most of the energy will be dissipated on zeners, and just a little on the coil.
Yandersen, Thu Dec 13 2012, 11:51AM
Turkey, In school, at 6th grade, we learned a simple formula for power which is
P=U*I,
where U is a voltage drop and I is a current. That is for zener. As for the coil' current change rate, another one exists:
dI/dt=dU/L,
which means that the rate of current change is proportional to the voltage drop across the inductor. Zener increases that voltage drop so current dissipates faster. Let's say, coil has 0.5Ohm of resistance and current running through it is 100A. The voltage drop will be 50V. Some time after current will decrease to 10A. Voltage drop will be 5V resulting in 10 times slower current' drop rate. In result, current dissipates for infinite time. Dempher diode adds 1V resulting in 51V in total for 100A and 6V for 10A. With addition of one 200V zener voltage drop is 251V and 206V, respectively. In other words, current dissipates almost linearly and with much higher rate. The more zener voltage is, the faster current will deplete. Most of the energy will be dissipated on zeners, and just a little on the coil.
Re: Zener vs Fast-Act Diodes
Sulaiman, Thu Dec 13 2012, 01:49PM
Dempher = Damper
Sulaiman, Thu Dec 13 2012, 01:49PM
Dempher = Damper
Re: Zener vs Fast-Act Diodes
klugesmith, Thu Dec 13 2012, 04:38PM
Peace, guys. Let's put a damper on bad-mouthing other contributors.
@Turkey9: I applaud your use of initial conditions in simulation, instead of putting in a charging source and a switch. Great idea. Too bad your LTSpice inductor model's parasitic resistance value, important in this discussion, is not visible in the drawing.
Shorting the coil (e.g. with a MOSFET) is how you MAXIMIZE the current pulse duration. A practical and extreme example is superconducting coils with superconducting shorting switches.
Some of you might be interested in this old thread about energy recovery in a coil pulser, without switches that turn off while conducting.
Its last post (before now) has a LTSpice simulation by me.
klugesmith, Thu Dec 13 2012, 04:38PM
Peace, guys. Let's put a damper on bad-mouthing other contributors.
@Turkey9: I applaud your use of initial conditions in simulation, instead of putting in a charging source and a switch. Great idea. Too bad your LTSpice inductor model's parasitic resistance value, important in this discussion, is not visible in the drawing.
Turkey9 wrote ...
Think of it this way; the fastest way to dissipate the energy stored in the magnetic field after the power has been cut off is to simply short the coil. A short has a voltage drop across it of zero. ...
I think your simulations confirm that the current stops faster with zerner diode, because the "braking" EMF is substantially higher than just I_coil * R_coil.Think of it this way; the fastest way to dissipate the energy stored in the magnetic field after the power has been cut off is to simply short the coil. A short has a voltage drop across it of zero. ...
Shorting the coil (e.g. with a MOSFET) is how you MAXIMIZE the current pulse duration. A practical and extreme example is superconducting coils with superconducting shorting switches.
Some of you might be interested in this old thread about energy recovery in a coil pulser, without switches that turn off while conducting.
Its last post (before now) has a LTSpice simulation by me.
Re: Zener vs Fast-Act Diodes
Ash Small, Thu Dec 13 2012, 07:25PM
That's a pretty impressive use of LC circuits Rich.
Your simulation:
.
demonstrates it well.
It's interesting to see how they solve this problem at CERN.
I've been working on a circuit to pulse a magnetron based ion source using a valve (vacuum tube), to inject protons into an accelerator. This circuit 'may' be relevant to my project, I'll have to look into it some more.
Ash Small, Thu Dec 13 2012, 07:25PM
That's a pretty impressive use of LC circuits Rich.
Your simulation:
.
demonstrates it well.
It's interesting to see how they solve this problem at CERN.
I've been working on a circuit to pulse a magnetron based ion source using a valve (vacuum tube), to inject protons into an accelerator. This circuit 'may' be relevant to my project, I'll have to look into it some more.
Re: Zener vs Fast-Act Diodes
Pinky's Brain, Thu Dec 13 2012, 07:50PM
Pinky's Brain, Thu Dec 13 2012, 07:50PM
Yandersen wrote ...
So far I haven't seen zeners over 5W of power.
TVS diodes are basically zeners and are designed to handle a lot more power.So far I haven't seen zeners over 5W of power.
Re: Zener vs Fast-Act Diodes
Turkey9, Fri Dec 14 2012, 08:55AM
Wow, a couple errors in my sims through off all the results. Thank you very much for correcting me! Here is a shot of the sims fixed, showing as you explained that a simple diode creates an infinite current die off. The zener circuit does cut it off extremely fast. I also ran the sim with TVS diodes and they worked exactly like the zeners.
As an interesting note, this circuit seems to create an extreme amount of ringing after the current has fallen to zero. It never reaches the full amplitude of the capacitor initial charge but could still mess with any control electronics.
Also an observation from the sims showed that the larger the voltage drop across the zener, the faster the current died off but the less current actually flowed through the zener. This agrees with conservation of power but seemed a little surprising to me at first.
Here are the pics of the sims that I ran. Previously, I forgot that the capacitor would be disconnected from the circuit after a half period of the oscillations. That's why the first sims I ran showed that current was left in the system and the inductor continued to ring. This was the biggest problem I saw with the circuit. Good thing that that was an error!
I would also like to apologize for accusing you of an error when in fact it was my mistake.
Turkey9, Fri Dec 14 2012, 08:55AM
Wow, a couple errors in my sims through off all the results. Thank you very much for correcting me! Here is a shot of the sims fixed, showing as you explained that a simple diode creates an infinite current die off. The zener circuit does cut it off extremely fast. I also ran the sim with TVS diodes and they worked exactly like the zeners.
As an interesting note, this circuit seems to create an extreme amount of ringing after the current has fallen to zero. It never reaches the full amplitude of the capacitor initial charge but could still mess with any control electronics.
Also an observation from the sims showed that the larger the voltage drop across the zener, the faster the current died off but the less current actually flowed through the zener. This agrees with conservation of power but seemed a little surprising to me at first.
Here are the pics of the sims that I ran. Previously, I forgot that the capacitor would be disconnected from the circuit after a half period of the oscillations. That's why the first sims I ran showed that current was left in the system and the inductor continued to ring. This was the biggest problem I saw with the circuit. Good thing that that was an error!
I would also like to apologize for accusing you of an error when in fact it was my mistake.
Re: Zener vs Fast-Act Diodes
Adrenaline, Fri Dec 14 2012, 02:18PM
Adrenaline, Fri Dec 14 2012, 02:18PM
Turkey9 wrote ...
Here is a shot of the sims fixed, showing as you explained that a simple diode creates an infinite current die off.
You can get an even faster delay with a series resistor. I don't have a lot of confidence is SPICE solving freewheeling diode problems and ideal components. We know from experimentation the current does not asymptotically approach zero, it gets there quickly with just a freewheeling diode.Here is a shot of the sims fixed, showing as you explained that a simple diode creates an infinite current die off.
Re: Zener vs Fast-Act Diodes
Yandersen, Fri Dec 14 2012, 07:03PM
The only difference between putting zener instead of a rsistor is that with zener voltage spike' amplitude is controlled - it almost independable of the current.
P.S.: it is very sad, that you guys implement an LT spice to understand operation of a simple circuit with 3 components, even though doing it wrong sometimes. It is not surprising that american coilgunning sucks. Well, putting zener in series with diaper diode will do it a little better... :) Who is going to be the first to build a coilgun with zener? Maybe, in next century you will discover the better way to wind a coils? :)\
Yandersen, Fri Dec 14 2012, 07:03PM
The only difference between putting zener instead of a rsistor is that with zener voltage spike' amplitude is controlled - it almost independable of the current.
P.S.: it is very sad, that you guys implement an LT spice to understand operation of a simple circuit with 3 components, even though doing it wrong sometimes. It is not surprising that american coilgunning sucks. Well, putting zener in series with diaper diode will do it a little better... :) Who is going to be the first to build a coilgun with zener? Maybe, in next century you will discover the better way to wind a coils? :)\
Re: Zener vs Fast-Act Diodes
Turkey9, Fri Dec 14 2012, 09:32PM
No reason to sling insults. Being able to use tools to visualize circuits is MUCH better than guessing at what something will do. I don't know of anyone that enjoys being called stupid, so cut it out. Also, don't make this a nationality issue.
I think that TVS diodes will be the way to go. Here is a link to a 400W one with 200V standoff voltage that are only $0.40 a piece. I'm going to use some on my 18 stage coilgun I'm working on currently. I'll keep everyone updated with the results.
Turkey9, Fri Dec 14 2012, 09:32PM
No reason to sling insults. Being able to use tools to visualize circuits is MUCH better than guessing at what something will do. I don't know of anyone that enjoys being called stupid, so cut it out. Also, don't make this a nationality issue.
I think that TVS diodes will be the way to go. Here is a link to a 400W one with 200V standoff voltage that are only $0.40 a piece.
I'm going to use some on my 18 stage coilgun I'm working on currently. I'll keep everyone updated with the results.Re: Zener vs Fast-Act Diodes
Ash Small, Sat Dec 15 2012, 12:50AM
I second the 'insult' thing. It's starting to get a bit much.
Just prove your design is better...That's insult enough to those who can't build one as good.
You don't want the mod's getting involved here....neither do we....You have some good ideas, Yan, don't get youself banned from posting here.
Ash Small, Sat Dec 15 2012, 12:50AM
I second the 'insult' thing. It's starting to get a bit much.
Just prove your design is better...That's insult enough to those who can't build one as good.
You don't want the mod's getting involved here....neither do we....You have some good ideas, Yan, don't get youself banned from posting here.
Re: Zener vs Fast-Act Diodes
Yandersen, Sat Dec 15 2012, 09:13AM
I looked into a datasheet and it did not impressed me. What we need is something bigger in size - like in SCR's metal case if it exists. Just imagine like hundred Joules of heat will be dissipated during 100us pulse - the heat will not have a time to go around a semiconductor crystal and will warm it up. The temperature must not go over the critical limit (over few hundreds degC). Transient voltage suppressors are the good direction of looking, but power rating must be a few dozen times higher.
And here is the question comes about paralleling of zeners: if warming decreases zener voltage, than paralleling will not help. Does it?
Yandersen, Sat Dec 15 2012, 09:13AM
I looked into a datasheet and it did not impressed me. What we need is something bigger in size - like in SCR's metal case if it exists. Just imagine like hundred Joules of heat will be dissipated during 100us pulse - the heat will not have a time to go around a semiconductor crystal and will warm it up. The temperature must not go over the critical limit (over few hundreds degC). Transient voltage suppressors are the good direction of looking, but power rating must be a few dozen times higher.
And here is the question comes about paralleling of zeners: if warming decreases zener voltage, than paralleling will not help. Does it?
Re: Zener vs Fast-Act Diodes
Ash Small, Sat Dec 15 2012, 11:39AM
It looks like the max junction temperature for those is 150C. Cooling (heatinks, etc.) will be of no real use whatever the package for pulsed operation because, as Yan points out, the heat has no time to dissipate. I assume some of the stud zeners I linked to above have a larger 'die' (if that's the correct term), and should, therefore, not get as hot for the same power dissipation. The power has to be dissipated as heat, so I'd assume that a package with a larger die size would be preferable here.
Ash Small, Sat Dec 15 2012, 11:39AM
It looks like the max junction temperature for those is 150C. Cooling (heatinks, etc.) will be of no real use whatever the package for pulsed operation because, as Yan points out, the heat has no time to dissipate. I assume some of the stud zeners I linked to above have a larger 'die' (if that's the correct term), and should, therefore, not get as hot for the same power dissipation. The power has to be dissipated as heat, so I'd assume that a package with a larger die size would be preferable here.
Re: Zener vs Fast-Act Diodes
Turkey9, Sat Dec 15 2012, 06:06PM
Those would work for the design that I'm working on, but this one will probably be more along the lines of a normal amateur coilgun.
Data sheet says it can handle a current pulse of 300A. I assume, similar to SCRs, that it can handle a larger pulse if it has a shorter duration. Still not a stud package but the die may very well be much larger than the surface mount parts.
Turkey9, Sat Dec 15 2012, 06:06PM
Those would work for the design that I'm working on, but this one will probably be more along the lines of a normal amateur coilgun.
Data sheet says it can handle a current pulse of 300A. I assume, similar to SCRs, that it can handle a larger pulse if it has a shorter duration. Still not a stud package but the die may very well be much larger than the surface mount parts.
Re: Zener vs Fast-Act Diodes
Yandersen, Sat Dec 15 2012, 08:12PM
That is exactly what we need, good job, Turkey!
The size of the die can be rougly estimated by a "parasitic" capacitance of a junction - the bigger it is, the larger the crystal. In our case, that capacitance will not have any impact on performance, as well as a reverse leakage current; voltage stabilization precision does not need to be high also. Generally saying, all we need is just a cheapest zener with highest pulsed reverse current rate. The one above is suitable. Maybe, it doesn't even need to be paralleled.
Howether, looking deeper into a datasheet it is mentionable, that 300A is a rating not for 200V ones. Advertising even in an electronics, yeah... Well, taking into account much shorter pulse time, I would be dare to say it will not burn, but you can not be sure by 100%.
BTW, there are bidirectional zeners available - with those damper diode is not necessary - just bidirectional zener in parallel with the coil and that is it.
Yandersen, Sat Dec 15 2012, 08:12PM
That is exactly what we need, good job, Turkey!
The size of the die can be rougly estimated by a "parasitic" capacitance of a junction - the bigger it is, the larger the crystal. In our case, that capacitance will not have any impact on performance, as well as a reverse leakage current; voltage stabilization precision does not need to be high also. Generally saying, all we need is just a cheapest zener with highest pulsed reverse current rate. The one above is suitable. Maybe, it doesn't even need to be paralleled.
Howether, looking deeper into a datasheet it is mentionable, that 300A is a rating not for 200V ones. Advertising even in an electronics, yeah... Well, taking into account much shorter pulse time, I would be dare to say it will not burn, but you can not be sure by 100%.
BTW, there are bidirectional zeners available - with those damper diode is not necessary - just bidirectional zener in parallel with the coil and that is it.
Re: Zener vs Fast-Act Diodes
Maxwell, Sat Dec 15 2012, 11:36PM
How would something like this fare:
Maxwell, Sat Dec 15 2012, 11:36PM
How would something like this fare:
Re: Zener vs Fast-Act Diodes
Yandersen, Sun Dec 16 2012, 07:21AM
Depends on the voltage - see the table. The higher the voltage, the smaller the pulse current. So basicly, before buying those diodes one should find out the magnitude of the current when coil is shutting off. Say, it is 300A. Assume you decided to use those 1500W diodes. Than divide 1500W by 300A and get 5V - that is the zener's rating you looking for if you choosed this type of diodes. Pretty small, huh? Don't worry, for single pulse 50V rated will be suitable. So buy dozen of those to get 600V spike connecting them in series. Or the same number of 600V ones in parallel (I would recommend series connection). But it is better to search for bigger zeners (more W), so to use just one. But the best solution is to return energy back into cap instead of burn it on zener.
Check this one:
Even though it says 5kW, peak current rating is 219A for 274V clamped. And price is good.
Yandersen, Sun Dec 16 2012, 07:21AM
Depends on the voltage - see the table. The higher the voltage, the smaller the pulse current. So basicly, before buying those diodes one should find out the magnitude of the current when coil is shutting off. Say, it is 300A. Assume you decided to use those 1500W diodes. Than divide 1500W by 300A and get 5V - that is the zener's rating you looking for if you choosed this type of diodes. Pretty small, huh? Don't worry, for single pulse 50V rated will be suitable. So buy dozen of those to get 600V spike connecting them in series. Or the same number of 600V ones in parallel (I would recommend series connection). But it is better to search for bigger zeners (more W), so to use just one. But the best solution is to return energy back into cap instead of burn it on zener.
Check this one:
Even though it says 5kW, peak current rating is 219A for 274V clamped. And price is good.
Re: Zener vs Fast-Act Diodes
2Spoons, Sun Dec 16 2012, 09:48PM
Absolutely. Especially for multi-stage systems where you'd like to have that unused energy available for successive stages.
The drawback is complexity.
Zener clamping is a reasonably simple step along the road to perfection.
If obtaining monster zeners is problematic, why not shift some of the load to a nice big transistor?
2Spoons, Sun Dec 16 2012, 09:48PM
Yandersen wrote ...
But the best solution is to return energy back into cap instead of burn it on zener.
But the best solution is to return energy back into cap instead of burn it on zener.
Absolutely. Especially for multi-stage systems where you'd like to have that unused energy available for successive stages.
The drawback is complexity.
Zener clamping is a reasonably simple step along the road to perfection.
If obtaining monster zeners is problematic, why not shift some of the load to a nice big transistor?
Re: Zener vs Fast-Act Diodes
Yandersen, Mon Dec 17 2012, 06:13AM
LOL! Transistor can not handle as much as zener can. Well, if you have some to spare... Anyway, if you have transistor that can handle such a current, why not to build a halfbridge?
Yandersen, Mon Dec 17 2012, 06:13AM
LOL! Transistor can not handle as much as zener can. Well, if you have some to spare... Anyway, if you have transistor that can handle such a current, why not to build a halfbridge?
Re: Zener vs Fast-Act Diodes
2Spoons, Tue Dec 18 2012, 10:48PM
You can LOL all you like, but there is a much wider range of big transistors (FETs and IGBTs would also work) available. Impulse handling comes down to die size.
As for why not a halfbridge? I'll say it once again: simplicity.
2Spoons, Tue Dec 18 2012, 10:48PM
You can LOL all you like, but there is a much wider range of big transistors (FETs and IGBTs would also work) available. Impulse handling comes down to die size.
As for why not a halfbridge? I'll say it once again: simplicity.
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