The only problem with this is that the thermal sensor controlling the fan speed must be transferred to the cooler as well. But this is certainly possible if the kind and parameters of the internal sensor are known.
The only problem with this is that the thermal sensor controlling the fan speed must be transferred to the cooler as well. But this is certainly possible if the kind and parameters of the internal sensor are known.
The external sensor is NTC is 10k Beta 3435,
the internal sensor is also 10k, don't know if the Beta is the same.
Hello,
Mine is mounted with 1 FDL100N50F (SOA DC60V40A-200V10A 2500W 150°C)
with 250W tdp 6 heat tube good CPU cooler i have 300W48V without trouble,
diode go very hot though !!!
it would go higher power by tripling diode number but ok as is for my usage.
2) The FET will promptly explode. The problem outlined by Syonyk (https://syonyk.blogspot.com/2018/06/the-atorch-purple-fan-mosfet-destroyer.html) still exists. I think the problem is an opamp stage driving the fet: it is bode unstable, and the oscillations exceed the ±20v Vgs spec. My fet failed short circuit - which will cause big problems if connected straight to a Lipo battery (it's funny that the brand name is "ATORCH" - this should be taken literally).
That's good to know. Do you also know, which are the temperatures the beta value is related to (e.g. 25°C/85°C) ?
2) The FET will promptly explode. The problem outlined by Syonyk (https://syonyk.blogspot.com/2018/06/the-atorch-purple-fan-mosfet-destroyer.html) still exists. I think the problem is an opamp stage driving the fet: it is bode unstable, and the oscillations exceed the ±20v Vgs spec. My fet failed short circuit - which will cause big problems if connected straight to a Lipo battery (it's funny that the brand name is "ATORCH" - this should be taken literally).I just ordered one of these (DL24 actually, not DL24P) but it won't arrive until mid July. Anyway, having a look at the schematic I think the problem is the low-pass filter to the integrator op-amp consisting of R6 and C5. I've built many constant current sources using op-amps. I never put a low-pass filter on the current feedback to the op-amp. That creates another pole, which likely is the cause of the instabilities mentioned. Quick fix is to simply remove C5. If anyone here who has a DL24P can try that, please let me know if it works.
In layman's terms we want any fluctuations in the current to feed back into the integrator op-amp right away, instead of being delayed by the low-pass filter. If they're delayed, the integrator response will lag, possibly leading to the harmful oscillations.
Back to back 10V to 15V zeners between the gate and source is a good failsafe regardless, even if removing C5 fixes the instability issue.
Another interesting observation from the DL24(P) circuit diagram: Why do they waive the pull down resistor at the mosfet gate ? As far as I remember with earlier models there have been some accidents with connecting the power supply / battery to the load before it was powered on. Perhaps a permanently open gate ?
Normally that wouldn't be an issue if the loop was stable. The MOSFET would be turned on in the absence of a battery but the opamp would respond fast enough once the battery was connected to bring it back to the linear region before any damage was done. Or at least that's my experience with the circuits I've made. I often set the current prior to connecting the battery. No issues with MOSFETs blowing once I connected the battery.
Side note: If anyone wants to try a power upgrade, I found a good candidate for a replacement MOSFET:
https://www.mouser.com/ProductDetail/747-IXFH94N30P3
300V drain-source breakdown voltage, 94 amps maximum current, 1.04 kW maximum power dissipation
And it's relatively inexpensive at only $12.99. I imagine with water cooling you might be able to reach 1 kW.
Ok, just to be sure that I got you correctly. Say without a battery, the Mosfet gate can be in some undefined state, i.e. perhaps it is somewhat opened up. Then, when connectiing the battery, the regulator would close the gate since there is no positive set-voltage at the op amp. In this way a strong current through the Mosfet would be avoided, if this 'coming to life moment' of the op amp is fast enough, right ? On the other hand, I think that adding a pull down resistor to the gate (~ 100kOhm) would improve the safety anyway. Btw it's pretty similar to the grid resistance in the case of tube valves. Here the extra resistance is important to avoid some static charge of the grid. Furhermore it helps preventing oscillations of the tube.
I just had a look to the data sheet. Firstly I'm really surprised about the package size, it's only a TO-247, just like the original one. This is a strong hint that the actual (long term) heat dissipation ability is strongly limited. Secondly it is not meant for linear applications. And lastly, if you look at the SOA diagram, then you find the last limiting line is the one for 1msec pulse duration. Since there is even no 10msec line (not to mention DC), from my limited experience, I'm pretty sure, that DC operation wouldn't work.
I'm just testing the linear IXTK60N50L2 and it seems to be good for about 400W in DC (up to 400V). But this won't be the power I'll go up to, because the cooling power of my CPU cooler seems to be limited to about 150W. Neverthelesss, that's fine for my application. What I want is a stable device, which max power is given ONLY by the coolers maximum heat dissipation ability.
Thinking about this some more, another way to accomplish the same thing is to simply clamp the maximum g-s voltage via a zener diode. If you look at MOSFET data sheets, generally low g-s voltages result in current limiting. For example, since this is a 20 amp tester, you could clamp the g-s voltage at a value that limits the drain current to ~30 amps. Even if a battery is connected, no more than 30 amps would flow, but the driving op-amp would quickly bring that down to the set current. With the stock MOSFET, limiting Vgs to about 5.5V would keep the maximum drain current in the 30 to 40 amp area.
It's possible DC might not work but the IXTK60N50L2 sounds like a good candidate. I personally have no need to go above even 150 watts as I would be mostly testing single cells.
It seems to be that you and me we are unrevaling a dialog here. It has been said almost everything about these loads in the last years. But only almost ;-) I have the feeling that your application is rather low voltage but high current, right ? I think for that it is absolutely necessary to strengthen both the 'polarity diode' and the current guiding tracks on the PCB. From my guessing, I would say the original state is ok for currents up to 5 amps, but not much more. For me it's fine to stay below 150W either, but also my current needs are rather low.
As written several times, I want to have a reliable device but without any magic smoke. I think the idea to limit the gate voltage with a suitable Zener is a really good one. Actually I'm using two 15V Zeners back to back to save the Mosfet from any instabilities. As soon as I have the time, I will connect a scope to the gate and look for the regulation behaviour. I'm not sure for the moment, did you made the comment about the extra cap in the feedback channel ? Anyway, this is indeed something, which should be clarified. Perhaps the instabilities can be cured in this way. The operation voltages of the regulator is in the range of 3.5 to roughly 5 Volt with the above Mosfet for the currents and voltages I used so far. So instead of the 15V one can probably switch to a much lower Zener voltage and thus solving the overcurrent issue at the same time.
Actually I make a whole series of temperature measurements under various heat loads. So far I tested the IXTK60N50L2 up to 160W at 80V. For the low voltage / high current regime, I need a more powerful supply (currentwise) which I do not have at home. I hope I can do these measurements in our physics lab tomorrow. As soon as the measurements are completed I will post the results here.
1) Probably a good idea to keep both polarities of Zener diodes. It can't hurt, but it will clamp any negative oscillations.
2) Good idea connecting the reverse polarity diode to the heat sink.
3) Thermal compound is very important here given the small surface area of the MOSFET-heat sink interface. From my experience working with Peltiers, a poor thermal interface can result in a 5°C or more temperature differential between the device attached to the heat sink and the heat sink.
4) For greater reliability I agree about replacing the stock MOSFET.
5) If I need to go much over 150 watts I would consider mounting the MOSFET on a heat sink remotely. I have some heat sinks I've used for Peltier projects which have a thermal cofficient of around 0.05°C/W when used with a 160mm fan. Even for 1000 watts load, that's only a temperature rise of about 50°C above ambient.
6) 70°C is well below the absolute maximum operating temperature of the MOSFET and reverse polarity diode. That implies reliable operation.
7) The instability at low currents may be caused by C5, or perhaps by the integrator having too low a time constant. I'll examine this part of the circuit when my device comes.
Like you, for now I'm more interested in a reliable, stable, accurate load than I am about increasing TDP.
Thanks to everyone who has posted their findings. I've ordered a DL24 armed with knowledge about it's limitations, and what needs to be done.
I ordered the version with no cooler, and will be installing an old corsair water cooler I've got on standby (just topped it up with a few extra ml of distilled water so it should last a few years). I'm planning on putting a ~12V TVS diode on the gate unless I decide to add a zener to limit gate voltage to like 7V or so, and a 15A fuse on the input so that I don't blow up anything when the stock mosfet inevitably shorts.
If the stock crappy mosfet dies, I'll probably get an IXTH64N10L2. The 60N20L2 would be a perfect fit, but it costs twice as much, I don't really need more than like 60V ever, and I'm water cooling it and don't plan to push more than 150W, so I don't know if the lower thermal impedance is really worth double the cost.