The LT3080 is floating at high voltage, so pulling anything to ground is likely to result in fireworks. You may be able to short across C3 in the new regulator with an optocoupler, but you still have a leakage path through D2 and I'm not convinced the regulator will survive on start-up if you do that. That's something I'd simulate rather thoroughly (and then prototype).
If you want that long of a delay, I suggest using a time delay tube before the regulator.
Tom
If you want that long of a delay, I suggest using a time delay tube before the regulator.
Tom
It depends on what kind of soft start you want. If you want a voltage that slowly rises from 0 V to the final voltage, a cap multiplier will work well. However, if you want a long delay where the voltage remains 0 V for tens of seconds, a cap multiplier won't be useful.
Also note that cap multipliers don't always handle brownouts very well. I have an old tube amp where I used a cap multiplier in the power supply to provide some filtering. It works great, except when a heavy load on the power grid turns on. During that brief brownout, the filter cap in the multiplier discharges. When the mains voltage recovers, the mains hum just passes through the cap multiplier. So basically a few times an hour, the amp will go "hummmm...", which is annoying. Now, had I used the Maida Regulator after the cap multiplier, I would not have had that issue, but I didn't have that circuit available then.
Tom
Also note that cap multipliers don't always handle brownouts very well. I have an old tube amp where I used a cap multiplier in the power supply to provide some filtering. It works great, except when a heavy load on the power grid turns on. During that brief brownout, the filter cap in the multiplier discharges. When the mains voltage recovers, the mains hum just passes through the cap multiplier. So basically a few times an hour, the amp will go "hummmm...", which is annoying. Now, had I used the Maida Regulator after the cap multiplier, I would not have had that issue, but I didn't have that circuit available then.
Tom
lift ac heater with Maida B+?
Hi,
I am using one of your regulators for 300b Little Ceasar Amp. The D3A drivers for the 300b are using AC heaters. Would it be wise to raise the AC ground with a voltage divider that uses the B+, or would the AC of the heaters pollute the Maida output? See attached schematic.
Thanks!
Hi,
I am using one of your regulators for 300b Little Ceasar Amp. The D3A drivers for the 300b are using AC heaters. Would it be wise to raise the AC ground with a voltage divider that uses the B+, or would the AC of the heaters pollute the Maida output? See attached schematic.
Thanks!
Hi, the regulator seems to be working fine on my new 300b amp. The input is 433 smoothed with one 220uf cap. The output is 400 with no hum at all. I don't have much space so I am trying it without a heatsink but after a five minutes the STW11NK90Z creeps up over 100C. My question is: can I move the STW11 off the board about 5-6 cm away to bolt it onto the enclosure? Thanks!
Sure. Just keep the wires as short as possible. Also, you *MUST* use an insulating thermal pad between the STW11 and the chassis or you will connect the incoming DC to the chassis. Any TO-247 thermal pad will do.
You may find that the chassis will get rather hot, so you may need a heat sink after all.
Tom
Hi Tom, I bolted the SWT11 onto the enclosure with a heatsink on the outside. It worked very well for a few days, but then there was a puff of magic blue smoke. It turns out the mica pad that I put under the SWT11 had shifted enough to allow a short to the enclosure. It is in a cramped position and it must have moved while I was tightening it down. I have tried replacing the SWT11 but the initiation test doesn't show any regulation: when I short R9, 20v input comes out as 20v output. It looks like some of the smd components are fried. I have attached a couple of pictures. Do you have any advice for a fix? Thanks.
Just an update: I will order replacement diodes and reg. I just wasn't sure about D2. Is this a suitable replacement: PTVS9V0P1UTP,115 | Nexperia PTVS9V0P1UTP,115, Uni-Directional TVS Diode, 600W, 2-Pin SOD-128 | RS Components
Thanks!
Thanks!
Do you mean the TVS at D3? That should be a SMA6J18A or close equivalent. Anything between 12-18V reverse standoff should be okay.
The low current zener at D2 should be a MMSZ4697T1GOSCT. Should also have one at D4 unless using a MOSFET with built in source to gate protection.
Yes, replace the LT3080 as well.
The low current zener at D2 should be a MMSZ4697T1GOSCT. Should also have one at D4 unless using a MOSFET with built in source to gate protection.
Yes, replace the LT3080 as well.
In my design, the output voltage is limited by a compensation cap on the output. It's a 630 V cap and with ±10 % adjustment range on the trimpot and adding a bit of margin, I settled on 525 V max.
The other limit is the SOA limit of the cascode MOSFET on startup. Recall that the output of the regulator is effectively shorted to ground during startup, so the MOSFET will briefly see the full input voltage until the output cap has charged. The MOSFET needs to be selected such that it can survive this.
Tom
The other limit is the SOA limit of the cascode MOSFET on startup. Recall that the output of the regulator is effectively shorted to ground during startup, so the MOSFET will briefly see the full input voltage until the output cap has charged. The MOSFET needs to be selected such that it can survive this.
Tom
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Someone else mentioned before.
The idea of placing rectifier in front of Maida comes to my mind.
Has anyone ever tried that way?
I want to do that because of 2 reasons:
1. The Beauty of rectifier tube and its charming glow.
2. Although Maida has soft-start design on its own, rectifier tube provides another soft-start function, and it can act as a buffer between high volt AC and the Maida/load. And this makes the regulating system more safe, as the rising time of DC gets longer even.
Using regulator tube like 0D3 is another issue, I am worry about the noise it contribute to the system. But these regulator tubes also have special and fancy glow by nature, like violet or blue.
The idea of placing rectifier in front of Maida comes to my mind.
Has anyone ever tried that way?
I want to do that because of 2 reasons:
1. The Beauty of rectifier tube and its charming glow.
2. Although Maida has soft-start design on its own, rectifier tube provides another soft-start function, and it can act as a buffer between high volt AC and the Maida/load. And this makes the regulating system more safe, as the rising time of DC gets longer even.
Using regulator tube like 0D3 is another issue, I am worry about the noise it contribute to the system. But these regulator tubes also have special and fancy glow by nature, like violet or blue.