Nice transistor for capacitor multipliers

That is a very cool part with a very strange data sheet.

Phil, What does your capacitor multiplier configuration look like? ...Jim Thompson

It's usually a 2-pole RC lowpass with an emitter follower hung on it, plus another (much lower Z) RC decoupling the collector, to help get rid of the V_A and C_CB contributions.

The huge V_EBO saves me a protection diode too.

Cheers

Phil Hobbs

Presumably we can expect it to have reasonable reverse beta.

--sp

It looks like it's not far off symmetric, but it must have a super-thin base to get betas like that, so you're probably right. The forward and reverse on-resistance plots are pretty similat too.

Pity the f_T vs I_c plot is screwed up.

Cheers

Phil Hobbs

Yup. There are some interesting plots there, but no I_C vs I_B or V_CE characteristics, and the f_T plot is a mess.

I don't like having to back out things like V_A from the SPICE model, but there it is.

Cheers

Phil Hobbs

It's not even a transistor. It's a For Muting.

The transfer curve is "Propagation Characteristics."

"This product might cause chip aging and breakdown under the large electrified environment. Please consider to design ESD protection circuit."

Well, I guess my data sheets would look bad if I typed them in Japanese.

Beat degradation at low currents is due to crud ('ISE' in the Spice model) in the silicon... given the high normal current beta, I'd expect fairly decent performance at low currents. ...Jim Thompson

The 2sd2704k is an "ordinary" transistor, with very low saturation voltage, which goes with high reverse beta, and nearly symmetrical characteristics (swap E and C). Very good for the inverted-mode switching that we used to use in the old days (late 60s), before low Ron CMOS. Instead of 20 to 50mV of low-current switch saturation, we get to enjoy mV or even sub-mV levels of saturation.

On Wed, 05 Aug 2015 16:16:58 -0400, Phil Hobbs Gave us:

Check out these guys' characteristics, Phil....

Hmm, interesting. Haven't seen a ~symmetrical transistor for quite some time.

I once picked up a baggie of 2SD1273, quite some years ago (from Mouser). Unavailable now I think, old stock aside. They have the unusual property of being a superbeta type with several amperes capacity, in a TO-220F.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

The 2SD2704K: 870 < beta < 2700, V_CEO = 20, V_EBO = 25 (!), pretty low V_CEsat, ~20 cents. It's slow (35 MHz) but looks great for cleaning up power supplies. The high beta lets you use bigger resistors, IOW longer RCs for the same caps.

Cheers

Phil Hobbs

-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics

hobbs at electrooptical dot net

Pretty much like a bog-standard smallish MOSFET, except for the very low capacitances, especially the magical low drain-gate capacitance, and the fancy price. Plus it only comes in die form. Nice part, but not suitable for cap multipliers.

Cheers

Phil Hobbs

On Thu, 06 Aug 2015 08:04:22 -0400, Phil Hobbs Gave us:

I was not trying to give you an example of something for your needs or even the subject of this current thread. I was trying to show you a damn nice device family, i.e. eGAN. Please try not to be so thick.

And they have more than that one, and yes a very nice feature is the extremely small packaging.

I looked at using a powermos source follower as a low noise voltage regulat or. The idea was to bias the gate permanently with an electrochemical batte ry. It didn't regulate well enough for the circuit I wanted for but I presu me the noise level was actually lower than with a shunt regulator.

But not in a to-92 pac. :^)

I've got a low noise power supply with cap mult's on the output.

Is it a higher beta that makes them better?

George H.

That and a low V_CEsat, so that the beta holds up at low V_CE.

I like to put an RC in the collector as well, because it improves the high frequency performance (which is limited by Early voltage and C_CB) and helps get rid of spikes. That eats into V_CE, so low sat helps there too.

Cheers

Phil Hobbs

OK thanks, I don't think it's the high frequency that is the problem. I'm feeding the cap mult. from a voltage regulator. (which was a mistake.. darn thing is the major noise source.) The last time I looked it had a broad noise peak in the 10 kHz range. And it's only at high currents (~ 50-100 mA) that I notice "issues".

George H.

You've got an LC resonance with the output inductance. See Errol Dietz's classic article at

A cap multiplier should be knocking 10kHz stuff down by a good 80 dB.

Cheers

Phil Hobbs

The PNP chopper is more common (perhaps because history started with germanium devices). A modern replacement for the old 2N404 is CMPT404A

and the data sheet is likewise a bit sparse/odd (a chopper with no reverse saturation specified ?!?)