36-1500 V: transistor driven step-up transformer

[Dominic-Luc Webb]

No, I am not engineer. I just experiment with photomultiplier
tubes for amateur astronomy. I am looking at using a pair of BDX33C
transistors in a symetrical oscillator circuit, like the
basic electronics examples with 2 resistors and caps setting
the frequency used to make LEDs blink. I think same is also seen
for morse code practice rigs. Applications is same, but need
higher frequency and drive a transformer.

I once tried using a 555 timer (20-70 kHz)to drive a high
frequency transformer and this was a dismal failure, never
getting high voltage and the voltage sagged with even the
slightest load. I have what is good transformer, and now
want to replace the other weak link, the 555.

Hunting around, I do not see examples on the net of anyone
having powered a PMT from a couple of discrete transistors like
this, but it seems like the BDX33C (real common, so those
who know transistors surely know this one) should be able to
drive a larger load than a 555. Does this sound sane?


Dominic

 

[John Fields]

On Sat, 27 Mar 2004 23:13:05 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:

No, I am not engineer. I just experiment with photomultiplier
tubes for amateur astronomy. I am looking at using a pair of BDX33C
transistors in a symetrical oscillator circuit, like the
basic electronics examples with 2 resistors and caps setting
the frequency used to make LEDs blink. I think same is also seen
for morse code practice rigs. Applications is same, but need
higher frequency and drive a transformer.

I once tried using a 555 timer (20-70 kHz)to drive a high
frequency transformer and this was a dismal failure, never
getting high voltage and the voltage sagged with even the
slightest load. I have what is good transformer, and now
want to replace the other weak link, the 555.

---
You'll need to post what your transformer looks like electrically and
what current your PM tube needs to operate before you can get any real
answers, I think.
---

Hunting around, I do not see examples on the net of anyone
having powered a PMT from a couple of discrete transistors like
this, but it seems like the BDX33C (real common, so those
who know transistors surely know this one) should be able to
drive a larger load than a 555. Does this sound sane?

---
Yes, it can, but the sanity of it may lie in whether or not it's
necessary to use a Howitzer to kill a mosquito.

--
John Fields

 

[Dominic-Luc Webb]

---
You'll need to post what your transformer looks like electrically and
what current your PM tube needs to operate before you can get any real
answers, I think.

Transformer is homewound around steel core, roughly 6 mm diameter.
Copper is would 53 turns on primary side and 2500 turns on secondary.
Wire is well in excess of carrying capacity on both sides. PMTs used
for astrophotometry typically draw 1 mA or less, I would say.

The BDX33C seems like overkill, but is cheap. The previous circuit
using a 555 to drive a N3055 was too weak. The transformer used
had fewer windings, but progressively better transformers did not
improve the circuit much. For the present citcuit using the BDX33C
symmetrical design, I am thinking to use a potentiometer to adjust
the frequency, since high frequency transformers are very fussy
about this. The homewound one, BTW, desite being steel works
better than commercial ferrite-ceramic core types I have compared
to.

Dominic