DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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Nick
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Nick » Tue Jul 09, 2019 6:32 pm

The other thing you could try is stacking 4 or 5 of these

https://uk.rs-online.com/web/p/mlccs-mu ... s/1795969/
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by IslandPink » Tue Jul 09, 2019 6:42 pm

I couldn't hear any difference myself between 330n and 470n , if it's any help.
I should order some of the ones that are supposed to come 3/2020, at least I have enough to use for current projects.
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Nick » Tue Jul 09, 2019 6:53 pm

Resistance isn't futile it's V / I.

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by IslandPink » Tue Jul 09, 2019 7:45 pm

480 milligrams of loveliness !
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by izzy wizzy » Tue Jul 09, 2019 10:15 pm

Thanks Nick and Mark. Ordered from Mouser. I've gone for the 0.33u. I did a quick sim and the difference is so tiny. If there is something that I've missed, I would think the time constant could be restored by upping the 470k reistors to 680k. It seems only to alter the performance below 10Hz. Well that's my crude understanding of the situation and in the end, I probably won't know the difference .... I hope.

Cheers,
Stephen

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by IslandPink » Tue Jul 09, 2019 10:40 pm

I ordered 10 from Mouser.
It's mad that such a small thing is so important, but honestly, getting the right caps there is the difference between 'very good' and 'magic' . I keep thinking back to what Jono Noble said years ago, which I tried to argue against : .. "everything matters, enormously". He was so right.
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick » Tue Jul 09, 2019 10:46 pm

Quite a big discount for over 50. Im getting 16 boards, so 32 for me.

Andrew you're sorting mine right?

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Andrew » Wed Jul 10, 2019 7:55 am

Hopefully, but I am not immune from parts shortages either.
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick » Wed Jul 10, 2019 8:28 am

Andrew wrote:
Wed Jul 10, 2019 7:55 am
Hopefully, but I am not immune from parts shortages either.
No of course, just saying that Mouser component has quite a big discount for >50.

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by izzy wizzy » Sat Aug 10, 2019 9:06 am

Any news on the higher current versions? If those PCBs aren't available for a 3A application and I was to use an SMPS before the reg and off board the reg and pass transistor, could the small board be used? Or alter the heatsink connection to enable a bigger sink to be used?

Cheers,
Stephen

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Andrew » Mon Aug 12, 2019 9:40 am

I can get some boards done. I was hoping there might be a few takers to help cover costs, you need to order a decent amount to make it worthwhile.

SMPS would work fine on the smaller PCB, but you might get HF artifacts breaking thru. Nevertheless, as long as the heatsink can cope, which it should do, you'll be fine. I'll need to check on the voltage drop across the pass transistor, I think its in the region of 1.7v.
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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Ray P » Mon Aug 12, 2019 9:59 am

Andrew wrote:
Mon Aug 12, 2019 9:40 am
I can get some boards done. I was hoping there might be a few takers to help cover costs, you need to order a decent amount to make it worthwhile.
5 US dollars for ten boards (as long as you don't want anything special like 2oz copper but even that isn't that much more) plus shipping. Probably about 20$ all in but about 3weeks for delivery.

https://jlcpcb.com/

They're good quality professional boards. I've used them several times and never been disappointed.

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by izzy wizzy » Mon Aug 12, 2019 11:10 am

Andrew wrote:
Mon Aug 12, 2019 9:40 am
I can get some boards done. I was hoping there might be a few takers to help cover costs, you need to order a decent amount to make it worthwhile.

SMPS would work fine on the smaller PCB, but you might get HF artifacts breaking thru. Nevertheless, as long as the heatsink can cope, which it should do, you'll be fine. I'll need to check on the voltage drop across the pass transistor, I think its in the region of 1.7v.
Thanks Andrew. If the small boards will do with some heatsinking modifications, then I can cope with that. I'm after 4 please.

The SMPS ripple will have some HF artifacts no doubt. I have the SMPS powering the GM70 direct at present and inserted some CM chokes between to great effect last night so some treatment like that will happen before the VCCS.

Cheers,
Stephen

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick » Sat Aug 24, 2019 4:07 pm

I just finished 6 of the boards. All test well except 1, which produces the right voltages but behaves differently.

By which I mean it goes directly to the set voltage without the slow start, and adjusting the trimmer pot gives an immediate reaction where the others move more slowly.

I can check solder joints but can't see anything obvious. I don't know the circuit, but I'm wondering if there's a hysteresis resistor somewhere? Just a guess, probably wrong.

Any pointers where to look? If not I'll work through.

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Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by izzy wizzy » Sat Aug 24, 2019 5:15 pm

Check the value of the 47k resistor feeding the 100u capacitor. If it was low or has been shorted via a solder blob, the cap will charge up stright away rather than following slowly.

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