Re: Some Notes on Heater Surge Current [Long - really HIGH power tubes]

[mike s]

On Thursday, April 14, 2011 11:13:26 PM UTC+1, mick wrote:

>
>
> I just grabbed that book. Good isn't it?
>
> Let's see...
> opto-isolator fed from bias supply: input into PIC
> No further action without bias
> PIC ramps up heater(s)
> Allow some warm-up time
> Close a relay to allow B+ via a resistor
> Another delay
> Close second relay to short out B+ resistor & allow full supply
>
> owzat?
>

Nice, a "finite state machine". So now all that's needed is something similar for safe power down, oh and the nasty cases for when the person switching it on, or off, changes their mind part way through a sequence and throws the switch the other way.

My PSU is very simple, but as it has a fairly hefty directly heated rectifier I added a thermistor to protect against power switch jitter - which would tend to blow the mains fuse. Almost certainly because the rectifier was warm, but the smoothing cap discharged, so the rectifier behaved more like silicon than vacuum on these occasions.

Michael

[Big Bad Bob]

On 04/15/11 03:34, mike s so wittily quipped:
> On Thursday, April 14, 2011 11:13:26 PM UTC+1, mick wrote:
>
>>
>>
>> I just grabbed that book. Good isn't it?
>>
>> Let's see...
>> opto-isolator fed from bias supply: input into PIC
>> No further action without bias
>> PIC ramps up heater(s)
>> Allow some warm-up time
>> Close a relay to allow B+ via a resistor
>> Another delay
>> Close second relay to short out B+ resistor& allow full supply
>>
>> owzat?
>>
>
> Nice, a "finite state machine". So now all that's needed is something similar for safe power down, oh and the nasty cases for when the person switching it on, or off, changes their mind part way through a sequence and throws the switch the other way.

properly handling rapid on/off sequences would be a 'nice touch'. I'd
start the sequence from the beginning again each time. Probably the
safest way. As for power off, easiest method, just "power off".

> My PSU is very simple, but as it has a fairly hefty directly heated rectifier I added a thermistor to protect against power switch jitter - which would tend to blow the mains fuse. Almost certainly because the rectifier was warm, but the smoothing cap discharged, so the rectifier behaved more like silicon than vacuum on these occasions.

thermistors and similar components seem to be the most common way of
handling this 'old school' style.

[mick]

On Sat, 16 Apr 2011 23:55:20 -0500, flipper wrote:

> On Sat, 16 Apr 2011 20:19:12 -0700, Big Bad Bob
> > wrote:
>
>>On 04/15/11 03:34, mike s so wittily quipped:
>>> On Thursday, April 14, 2011 11:13:26 PM UTC+1, mick wrote:
>>>
>>>
>>>>
>>>> I just grabbed that book. Good isn't it?
>>>>
>>>> Let's see...
>>>> opto-isolator fed from bias supply: input into PIC No further action
>>>> without bias
>>>> PIC ramps up heater(s)
>>>> Allow some warm-up time
>>>> Close a relay to allow B+ via a resistor Another delay
>>>> Close second relay to short out B+ resistor& allow full supply
>>>>
>>>> owzat?
>>>>
>>>>
>>> Nice, a "finite state machine". So now all that's needed is
>>> something similar for safe power down, oh and the nasty cases for
>>> when the person switching it on, or off, changes their mind part way
>>> through a sequence and throws the switch the other way.
>>
>>properly handling rapid on/off sequences would be a 'nice touch'. I'd
>>start the sequence from the beginning again each time. Probably the
>>safest way. As for power off, easiest method, just "power off".
>>
>>> My PSU is very simple, but as it has a fairly hefty directly heated
>>> rectifier I added a thermistor to protect against power switch jitter
>>> - which would tend to blow the mains fuse. Almost certainly because
>>> the rectifier was warm, but the smoothing cap discharged, so the
>>> rectifier behaved more like silicon than vacuum on these occasions.
>>
>>thermistors and similar components seem to be the most common way of
>>handling this 'old school' style.
>
> Using a PIC strikes me as 'overkill' style.


Me too - but I just happen to like 'em! :-)
I've always liked nice simple RC timers, but a PIC is so cheap and easy
to use that they can easily work out cheaper. Also, you can change your
mind as to exactly how you want them to work without major rebuilding. As
for reliability, I suspect that they are pretty good. The PSU components
are more stressed.

I definitely like thermistors in transformer primaries. So simple, but so
effective.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

[Big Bad Bob]

On 04/16/11 21:55, flipper so wittily quipped:
> On Sat, 16 Apr 2011 20:19:12 -0700, Big Bad Bob
> > wrote:
>
>> On 04/15/11 03:34, mike s so wittily quipped:
>>> On Thursday, April 14, 2011 11:13:26 PM UTC+1, mick wrote:
>>>
>>>>
>>>>
>>>> I just grabbed that book. Good isn't it?
>>>>
>>>> Let's see...
>>>> opto-isolator fed from bias supply: input into PIC
>>>> No further action without bias
>>>> PIC ramps up heater(s)
>>>> Allow some warm-up time
>>>> Close a relay to allow B+ via a resistor
>>>> Another delay
>>>> Close second relay to short out B+ resistor& allow full supply
>>>>
>>>> owzat?
>>>>
>>>
>>> Nice, a "finite state machine". So now all that's needed is something similar for safe power down, oh and the nasty cases for when the person switching it on, or off, changes their mind part way through a sequence and throws the switch the other way.
>>
>> properly handling rapid on/off sequences would be a 'nice touch'. I'd
>> start the sequence from the beginning again each time. Probably the
>> safest way. As for power off, easiest method, just "power off".
>>
>>> My PSU is very simple, but as it has a fairly hefty directly heated rectifier I added a thermistor to protect against power switch jitter - which would tend to blow the mains fuse. Almost certainly because the rectifier was warm, but the smoothing cap discharged, so the rectifier behaved more like silicon than vacuum on these occasions.
>>
>> thermistors and similar components seem to be the most common way of
>> handling this 'old school' style.
>
> Using a PIC strikes me as 'overkill' style.

true, but fun to imagine. Still if you use the PIC to generate the HF
pulses, you won't need pulse logic. And if you use the PIC to measure
the voltages, you may not need any comparitors. And if you use the PIC
to make the decision of whether or not to send a pulse through the HF
toroid transformer, you could program it to behave in interesting ways,
like mimicing a 5xx rectifier (as an example). But yeah, for a
straightforward implementation of the above, not really needed. An
astable timer, comparitors, CMOS logic, and drivers would probably do it
(plus RC timing, state latches, and a couple of other things).

[Big Bad Bob]

On 04/17/11 08:33, flipper so wittily quipped:
> PICs are wonderful things as long as there's 'enough stuff' to justify
> the parts and effort, including firmware, but, in this case, it looks
> an awful lot like a 'kewl' solution in search of a problem

the cost of a microcontroller (and size reduction) might easily justify
it, IF you can reduce the total part count to a minimum, or gain some
kind of functionality or performance advantage. But to make it work
properly you'd need "yet another" regulated voltage for it, which might
be available ANYWAY since you need appropriate power to drive the
regulator logic.