Hsu, are you referring to use of an opto-coupler, such as 4N25? Use of
these devices will allow the regulator bridge and FET to be connected to the
transformer primary which will reduce current requirements a large amount.
The frequency response of the couplers appears to be limited by the RC time
constant of the photo transistor base capacitance and external current
limiting resistor. It would be interesting to compare the effects of the
resistor value with RMS drive voltage to the device.
A failure of the FET in the bridge circuit will cause an over voltage to
the tube filament/heater. Some means to prevent that needs to be added.
73,
Gerald K5GW
In a message dated 7/10/2011 5:37:54 A.M. Central Daylight Time,
hsu4qro@gmail.com writes:
Hi John,
You are correct. But a problem ,AD's true RMS chip is not a inexpensive
device.
I have an idea, using a inexpensive CdS photoresistor-LED or micro-bulb
photocoupler( like N110 in ICOM PS-35 power supply) because bulb and
CdS
photoresistor with very bad frequency response
so the sampling voltage will associate with true RMS volt (I guesss)
...
If the noise is not a problem and the tube's cathode is oxide-coated ,
the switching regulator is the best. but monolithic IC maximal out put
current
only 10A (ST's L4970) others need external power MOS FET.
73!Hsu
----- Original Message -----
From: "John G3UUT" <amps@grebe.plus.com>
To: <amps@contesting.com>
Sent: Sunday, July 10, 2011 5:12 PM
Subject: Re: [Amps] AC filament voltage regulator
> I've also been thinking about this problem and the reason I'm not keen
> on a DC regulator is that the distortion and peak current of the mains
> current waveform is already pretty bad with a capacitor input B+ supply
> and making it worse by adding the heater as well will undoubtedly make
> the regulation of the B+ worse. This is particularly a problem when
> using portable generators.
>
> I've not taken this down to circuit level yet but my idea was to use one
> of the Analog Devices RMS to DC convertors as its important to maintain
> the RMS of the AC constant - especially when using poor quality mains
> from a generator. Hsu - this is the problem with your circuit. My
> other idea was to use a biphase rectifier with a centre taped
> transformer and schottky rectifiers to reduce the diode losses - which
> are quite significant with a 5 V heater.
>
> 73 John G3UUT
>
> On 10/07/2011 03:03, Dr. David Kirkby wrote:
>> On 07/10/11 01:12 AM, Hsu wrote:
>>> I do not think a DC regulator for direct heater tube is a good idea,I
draw a block diagram for AC filament regulator
here:http://www.zmdz.com/bbs/incomefiles/20117/1089098780.JPG, just a block
diagram.any advice? I
know we have another selection,CVT. a special transformet.
>>> 73!Hsu
>> What's wrong with a DC regulator?
>>
>
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