Diode Network - is that a Darlington Transistor

theHOFIT

Joined Dec 16, 2009
9
Slightly off-topic (so apologies for that):- I've always been impressed by the DCA-55, and have often wondered about not only how it works, but also the design philosophies (and of course, compromises) behind it.

To my mind, it's a brilliant (and cost-effective) little piece of kit. As are the others in the stable, by the way (the ESR-60, LCR-40 and SCR-100 ... to name but three). I might add that I've also had an old DCA-50e for some years, and it's never let me down!

So ... welcome to the forum, Jez. And keep your posts coming! :)
 

Thread Starter

onpiopah

Joined Jan 27, 2012
9
Hi Jez: I'll spend a bit more time trying to undestand the physiscs behind it first - I would like to figure it out for future reference, if i don't come up with a solution though I will greatly take up your offer to test the transistors for me.
Thanks.
 

Jez Siddons

Joined Oct 23, 2012
9
Slightly off-topic (so apologies for that):- I've always been impressed by the DCA-55, and have often wondered about not only how it works, but also the design philosophies (and of course, compromises) behind it.

To my mind, it's a brilliant (and cost-effective) little piece of kit. As are the others in the stable, by the way (the ESR-60, LCR-40 and SCR-100 ... to name but three). I might add that I've also had an old DCA-50e for some years, and it's never let me down!

So ... welcome to the forum, Jez. And keep your posts coming! :)
Thanks for your comments, much appreciated. A DCA50e, wow that takes me back to my early Peak days. Glad it's still working for you, it's done well. Circa 1997 I think.

Happy to answer pretty much any questions about our stuff, and about electronics in general of course.

Cheers for now,
Jez
 

Jez Siddons

Joined Oct 23, 2012
9
Hi Jez: I'll spend a bit more time trying to undestand the physiscs behind it first - I would like to figure it out for future reference, if i don't come up with a solution though I will greatly take up your offer to test the transistors for me.
Thanks.
Sounds good. It's well worth persisting with as it'll open up a window on all sorts of things that you'll come across in electronics. Keep me updated.
Cheers,

Jez
 

Jez Siddons

Joined Oct 23, 2012
9
I would test for transistor action with a power supply, a couple of resistors, and a multimeter.
I agree, you can't beat actually using a transistor to get a good feel for how it works and behaves.

The DCA55 is not aimed at replacing the need for good old fashioned experimentation and understanding. It's aim right from it's inception was to allow you to instantly identify parts, instantly identify leads and to measure some parameters. That then gives you the info you need to use the transistor in your experiments and projects. Also, the DCA55 is not just for transistors but also for instant identification of MOSFETs (enhancement mode and depletion mode), LEDs (including bicolour 2-lead and 3-lead types), diodes and diode networks (series, common cathode and common anode), JFETs and more. Great for when you just want an instant pinout, just connect any way round and press test.

Before the DCA55, I used transistor databooks/datasheets to get pinout information and basic parameter data. Of course that's not always handy and not always possible especially for poorly marked parts.

As a slight aside, the best understanding I ever made of transistors was when I studied the simple 1 transistor class-A amplifier (1 tranny, 4 resistors). It's a great circuit to appreciate the key transistor parameters of Vbe and HFE. It's also a great circuit that demonstrates how to make something that isn't "too" dependent on absolute value of HFE.

You can't beat playing with the actual components though as Ron said, even if you blow some up, it's all good! Choose cheap ones though (I have a shed full of BC183s).
 
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Thread Starter

onpiopah

Joined Jan 27, 2012
9
I decided to purchase 2 brand new transisitors B1647 and they tested exactly the same. So I suppose as an epilogue the resistor does cause a problem with the DCA55 and my trnasistors are working fine.
Jez, could you provide me with a link so I can build a (1 transistor class-A amplifier ) you cited above for my future testing of transistors.

Thanks for everyones help, much appreciated.
 

Jez Siddons

Joined Oct 23, 2012
9
I decided to purchase 2 brand new transisitors B1647 and they tested exactly the same. So I suppose as an epilogue the resistor does cause a problem with the DCA55 and my trnasistors are working fine.
Jez, could you provide me with a link so I can build a (1 transistor class-A amplifier ) you cited above for my future testing of transistors.

Thanks for everyones help, much appreciated.
For testing your 2SB1647 then an amplifier circuit isn't really necessary, I'd make up a simple light bulb circuit with the transistor. See attached picture that I've drawn for you. Switching on the switch will provide about 22mA of base current (most of the 12V across the 470R resistor). That base current will be enough to turn on the darlington and power the light bulb. This will prove that the transistor has current gain (as 22mA wouldn't normally be enough to light the bulb anyway).



If you're interested in a class-a amplifier circuit then the following circuit may be of interest to you. It's a simple class-a amplifier that will amplify by about 4.5 times (small AC signals). You can test it with a signal generator and an oscilloscope to see it in action. Let me (or anyone on here) know if you'd like more info on how it works. The circuit is aimed at low currents so not suitable for your big darlington as it stands.



I've drawn these quite quickly, so apologies if I've made any errors! I think they're ok!

Cheers,

Jez
 
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