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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 13th Nov 2017, 12:19 pm   #21
Argus25
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Default Re: BRY39 - Solid state switches.

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Originally Posted by kalee20 View Post
Not according to ON Semiconductors data (attached)! They say 5V.
Yes, that what the sheet says, but all the specimens I have zener at very close to 11V. If you have one give it a try and you will see what I mean...

I just grabbed a BC640 from my stock, connected the B-E with a 1k5 series resistor across a 13V supply, it zeners at exactly 10.95V

Hugo.

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Old 13th Nov 2017, 12:56 pm   #22
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Default Re: BRY39 - Solid state switches.

I have also attached a circuit where a PUT equivalent is configured as a vertical oscillator, for the amber video monitor inside the famous IBM5155 portable computer, although the monitor was designed by Zenith.

Doing a PUT with transistors means there is access to the junction of the PNP's collector and the NPN's base which can be handy for setting up the DC conditions and also making sure the NPN part turns off properly. I put a red ring around it and labels. The sawtooth voltage is produced across C303. I have attached this because you don't see this very often. So I'm not the only person that thinks a PUT should be made from transistors
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Old 13th Nov 2017, 1:48 pm   #23
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Default Re: BRY39 - Solid state switches.

Interesting circuit, Argus, and actually uses the configuration in the complementary manner than the BRY39 is aimed at!

I guess the voltage on C303 ramps down, until the emitter voltage on Q301 goes below the voltage on Q301 base (which is set by R307, R308, the programming resistors). Then Q301 starts to conduct, avalanche latching action occurs, C303 gets a snatch recharge jerking its voltage up, till the configuration unlatches and allows a repeat.

This one means it's the NPN transistor which has to withstand a degree of reverse Vbe, not the PNP!
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Old 13th Nov 2017, 2:10 pm   #24
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Default Re: BRY39 - Solid state switches.

Kalee20,

On that zener voltage thing, you will notice a lot of data sheets for small signal transistor specify 5V. This is really a value that equal to this or below, the b-e junction is guaranteed not to zener.

Most small silicon signal transistors zener the b-e at between 7 and 8V, even though the sheets say 5V. Of course they are seldom used in this mode, though Bosch made some dynamo voltage regulators where they used the b-e zener voltage of a 2N3906 transistor (attached), and didn't connect the collector, so hfe degradation was never a problem. It acts as about a 7.8V zener that has a positive temperature coefficient. However, if you look at ON Semiconductors data sheet it will list the B-E voltage at 5V!

For any transistor type, if you want to know what the actual b-e zener voltage is you have to test it. This is how I found out that the BC640 has a substantially higher zener voltage than most.
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Old 13th Nov 2017, 2:22 pm   #25
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Default Re: BRY39 - Solid state switches.

Zener/avalanche breakdown of a diode is often used to generate noise for testing purposes. The HP346A family used for noise figure measurement for example.

Zener diodes intended as such can have quite a lot of junction capacitance, and are limited to low freq use because of the roll-off caused.

Some homebrewers use noise from avalanching B-E junctions of microwave transistors as a wider-band alternative.

The HP noise diodes had special extra densely doped rings around the actual diode area to control dopant migration.

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Old 13th Nov 2017, 2:30 pm   #26
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Default Re: BRY39 - Solid state switches.

Yes, I agree, and most transistors will not break down at their data sheet absolute maximum ratings. LED's also, are usually specified at 3V max reverse voltage, but withstand several times more than this before breakdown occurs.

When it does occur, reverse current flows which may or may not cause damage, depending on how much current flows and what the associated power is. But, whether the device shows breakdown or not, operating outside Absolute Maximum ratings on a commercial design is a no-no unless you get the manufacturer's blessing!
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Old 13th Nov 2017, 3:07 pm   #27
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Default Re: BRY39 - Solid state switches.

Very few circuits zener the B-E's but the classic is the two transistor multivibrator (unless diodes are used to protect the B-E's). So you see the mistake sometimes of these running off a 9V or 12V supply, when it should be 5V or no more. The relentless zenering slowly degrades the transistor's hfe (Motorola did some interesting research papers on this) Then one day, the multivibrator won't start. The mechanism of hfe degradation is ill understood.
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Old 13th Nov 2017, 3:16 pm   #28
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Default Re: BRY39 - Solid state switches.

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Originally Posted by Mike Phelan View Post
They were used in the 1972 continental K9 chassis as well, in the control module for the SMPS. From around 1975 or 1976, they used an IC instead.

Also the BRY39 has a slightly different cousin, the BR101.
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Old 13th Nov 2017, 3:40 pm   #29
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Default Re: BRY39 - Solid state switches.

That's marketed more as a thyristor with both gates accessible.

There's also the BRY61, with just 3 terminals: cathode, anode, anode-gate. Which is characterised as a PUT.

Comparing a PUT against a conventional UJT, the emitter corresponds with the anode, base 2 corresponds with the cathode (and lower programming resistor) and base 1 with the upper programming resistor.
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Old 13th Nov 2017, 10:25 pm   #30
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Default Re: BRY39 - Solid state switches.

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Interesting circuit, Argus, and actually uses the configuration in the complementary manner than the BRY39 is aimed at!
The thing I always like about discrete transistor designs is that you can easily convert the design say from neg ground to positive by flipping the polarity of each transistor npn to pnp, pnp to npn, reversing any diodes and electrolytic caps, then presto you have the same circuit with reverse polarity grounds and reversed signal polarities.

The transistor version of the PUT is the only circuit I know of, that when you flip the transistor polarities, you have exactly the same circuit or part and nothing changes.

So for a "complimentary" transistorized PUT in a positive ground circuit, simply it would appear that the emitter arrows are reversed, the "gate" stays the same. In other words it is a "dual polarity part" when seen as one entity.

In the case of the UJT there is the complimentary UJT or CUJT, but there is no CPUT (as its one and the same if its made from transistors at least) so the idea of a CPUT is Kaput !
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Old 13th Nov 2017, 10:41 pm   #31
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Default Re: BRY39 - Solid state switches.

Good point! In fact, making the thing from discretes, you can make it TRUE dual polarity! Whereas with the BRY39 device, you can't quite get there as the internal NPN and PNP structures are optimised for different characteristics, gain at the expense of Vbe for the NPN, and speed plus Vbe at the expense of gain for the PNP.

I did try discrete NPN and PNP for the SMPS impulse start circuit referred to earlier. I found that the thing would fire once, but fail to unlatch (too much gain) if a recycle and restart attempt was required... Plus I'd have needed base voltage protection diodes. I didn't pursue this at the time, as the single component BRY39 was available, so why would I not use it.
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