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I think that's what I drew up first. But I ended up with a lot of power dissipated in the resistor, when the output was dialed down to zero. ... maybe you've got some idea more involved than R + pass element??

George H.

Keeping the detector from melting when (not if) some student turns on the room lights is generally considered goodness. ;)

Cheers

Phil Hobbs

(who also tries to design idiot-resistant stuff)

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

A class-B totem pole is pretty easy to do. I like BJTs for that e.g. ZXTP01500/FCX458, both with beta > 100 and 50 MHz f_T. BJTs minimize the flat spot in the transfer curve.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Right, Sorta randomly I picked the VP2450 (well it comes in a to-92)

and it has only ~3V of turn on.... I did muck around with the power rails (bench supply, up to 24V.)

Huh, OK I didn't think of trying a cap there.

I got this common emitter design working yesterday. It's something I've done more often.. .this is the first time I tried a common base. (I'm likely not thinking about it correctly, but in my mind I just figured it transferred whatever current I pulled out of the emitter to the collector... and it would 'work out' whatever Vbe, Vbc it needed to make that happen.)

I did try some lower values for the G-S resistor, that should let the fet turn off faster.

George H.

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Goggling Class B totem pole, it looks like it will take me a long time to carve one. :^)

But I think I know what you mean. I think I'll need three transistors (one to buffer the HV.... I'm not really allowed to use more transistors than opamps... gets out of my comfort zone. :^)

George h.

Use a CE amplifier stage to get the full voltage swing, as you're already doing, then just hang NPN and PNP emitter followers on its collector. Connect the NPN collector to +HV, the PNP collector to ground, and both the emitters to the output. The feedback network will provide bias to the NPN, and the PNP only comes on when you're reducing the output voltage rapidly.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Oh, and an LND150 in series with the output for current limiting. That protects the transistors and provides first-line protection for the detector as well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

The shunt regulator has a lot of advantages as compared to series regulation if you're willing to sacrifice efficiency to trade off to get it, but it seems a mostly discarded topology "nowadays"

Just in case anyone gives a tinker's dam, google's signal-to-noise ratio has become so low that it's hard for me to get enthused about using it anymore. That's why my first impulse these days is to reach for a trusted book. This followup comes from my office, which contains a comprehensive library. Unfortunately, most of my books likely to address "totem poles," the Peases, the Williams, et al, are out in the lab. Most, but certainly not all. _AoE III_ happens to be in the office today (next to _AoE II_). Its index says totem poles are found in Chapter 9 on page 695. (Note Win, the phrase "totem pole" actually appears on page 696.) Win kindly allows the public free access to _AoE III_ Chapter 9 [1] in the very unlikely event that anybody here lacks their own copy. Allow me to ask a couple of questions about Figures 9.110 and 9.111. What's a good source for the +800V (DC?) in Figure 9.110? Is that a totem pole shown in Figure 9.111? Thank you in advance.

Note.

1. formatting link

73,

--
Don Kuenz, KB7RPU

I'm not that big a fan, mostly on account of the horribly asymmetric slew and attendant poor load regulation. Good HV transistors are available cheap (see above).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Depletion fets are fun:

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

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Covers eyes... I'll read that in a bit. I started my own totem pole, but then figured I'd first look at my common emitter design that worked.

Well turns out it mostly worked because I had reduced the G-S resistor (R1 is my schem.) to 1 k ohm. That lets the gate charge faster... It seemed to wig out (with HV) at around 4 kohm, so I could probably live with ~1.5k ohm. Vgs max is 3V, so I'm pulling 2 mA worst case... and my poor npn is dissipating ~600mW... I guess I might be able to add a collector resistor. It seems a little close to the edge, and maybe an active chargin g thingie (as per Phil H.) is worth looking at.

As a final question for Phil (well last one for an hour.) Your comment about building a -250 V supply made me think I should check out how my diode was constructed. page 7 here,

ap-series.pdf

Anode and cathode both float, but the cathode is tied to the pillar, Do you think this means I really want a negative voltage? I'd guess that has to help for capacitive reasons if nothing else.

George H.

Don, I couldn't find a pic of a totem pole anywhere in AoE (2 or 3) But I'm starting from this from wiki.

which seems to be copied at lots of other sites.

George H.

You can cascode a low-voltage optoisolator under a depletion fet, or a tube. There is some old color TV tube (tetrode?) that's good to 30 KV or something.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Yeah, you mentioned depletion fets before. Thanks for the pic! One issue (that could certainly be dealt with.) is that they are on. (and you have to turn them off.) which means that I have to make sure the low voltage is on before the HV and (LV) off last.

I guess that might make 'em somewhat easier... slow turn on rather than slow turn off.

George H.

Negative bias lets you wire it up to a normal TIA with positive output. OTOH if your customers are used to PMTs, then positive bias and negative output might be what you want.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

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Right, I'm not planning on a TIA. Either a fast opamp/follower. or maybe right into a comparator. (Comparator, because I might want to try some active quenching.. but that's three steps away from now.)

Typ. circuit looks like

HV | R(quench ~100k) | _ (diode) ^ | +--->out | R(sense ?100- 1k ohm) | GND

For a lower voltage spad I did it with one resistor doing both jobs, sense and quench.

George H.

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OK I read it. (Mine didn't work) So this looks like a push-pull, but with the CE amp as a HV buffer/ level shift.

Thanks George H.