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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 11th Nov 2017, 6:23 am   #1
Diabolical Artificer
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Default BRY39 - Solid state switches.

Found a small bag of these the other day whilst trying to sort and list my tranny stash. They're described as a "programable unijunction transistor" or "silicon controlled switch", but unlike a bog standard SCR have four legs with a anode and cathode gate.

Surprisingly they were made up to 97 according to the Philips datasheet I found but mine are a lot older. Firstly how are they programmable or is that just spiel?

Second what were they traditionally used for? it says motor control ont said datasheet, but at a power diss of 275mW they wouldn't switch anything big, maybe not even a relay. I have visions of them in a pre IC adding machine or somesuch. I guess they're obsolete now but have yet to have a play with them.

Thirdly are they basically a SCR apart from having an anode gate that is.?

Andy.
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Old 11th Nov 2017, 8:12 am   #2
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Default Re: BRY39 - Solid state switch's.

Sometimes used as a trigger device in a phase-shift thyristor motor controller. Programmable as in you can program the break-over voltage by choosing resistor values.

David
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Old 11th Nov 2017, 8:17 am   #3
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Default Re: BRY39 - Solid state switch's.

I'm sure I remember them being used in TV's...Philips...RBM..?

Lawrence.
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Old 11th Nov 2017, 9:47 am   #4
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Default Re: BRY39 - Solid state switch's.

I like to think of a relaxation oscillator built using one sitting there just going quietly "PUT PUT PUT PUT PUT......"

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Old 11th Nov 2017, 9:48 am   #5
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Default Re: BRY39 - Solid state switch's.

Frame oscillator in the RBM A823 chassis?
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Old 11th Nov 2017, 10:05 am   #6
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Default Re: BRY39 - Solid state switch's.

With a capacitor and a charging resistor, UJTs and PUTs make basic ramp generators and can save a few components over doing it with bipolars, and when every penny counts....

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Old 11th Nov 2017, 10:11 am   #7
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Default Re: BRY39 - Solid state switch's.

Quote:
Originally Posted by Nuvistor View Post
Frame oscillator in the RBM A823 chassis?
Spot on Frank:

http://www.americanradiohistory.com/...ch=%22bry39%22

Lawrence.
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Old 11th Nov 2017, 6:34 pm   #8
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Default Re: BRY39 - Solid state switch's.

Used on DC motor control circuits in fork lift trucks etc, they can provide both frequency and PWM signals to control the main and commutating SCR's.
They had some horrible habits with regard to temperature and aging.

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Old 11th Nov 2017, 7:05 pm   #9
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Default Re: BRY39 - Solid state switch's.

They are good devices, easy to use as timers. Better than UJT's in my opinion, as the intrinsic stand-off ratio (fixed by manufacture for a UJT, and not particularly consistent from sample to sample) is programmable by a couple of resistors.

However, I reckon that they were obsoleted by the 555 timer, which is the natural go-to component for most people. More 'legs' but more versatile, negligible temperature drift, and totem-pole output!
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Old 11th Nov 2017, 8:12 pm   #10
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Default Re: BRY39 - Solid state switch's.

To Ed's list of horrible behaviours I'd add thoroughly reprehensible behaviour in the presence of high dV/dt. And it's this which gets dramatically worse with temperature (So also do SCRs)

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Old 11th Nov 2017, 8:44 pm   #11
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Default Re: BRY39 - Solid state switch's.

I remember them.... they were one of the 'odd' semiconductor devices [along with Unijunctions, and a strange combination of a heating-element and a semiconductor impregnated with a Platinum catalyst that served to detect combustible gases] that emerged in the 1960s but never really found a place for themselves and faded into obscurity.

Same could be said for the 1950s "symmetrical" junction-transistor [whose emitter and collector could be interchanged].
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Old 12th Nov 2017, 7:28 am   #12
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Default Re: BRY39 - Solid state switch's.

Thanks chaps. I've found the basic relaxation osc circuit and a few other bits online for PUT's, but nothing specific for the BRY39. The 2N6027 comes up in searches for PUT's but this has no cathode gate. In the example for the 2N6027 here - http://www.circuitstoday.com/programmable-ujt there is an unused P region, does this mean the 39 has an extra N region which is the cathode gate?

They're programmable as mentioned by a couple of resistors a bit like setting variable zener's.

A few term's come up in relation to the operation of the 39 which I'm struggling with. I presume negative resistance isn't the same as current gain in that it's linear or almost linear. Still reading up and searching for info so hopefully things will become clearer.

Andy.
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Old 12th Nov 2017, 7:35 am   #13
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Default Re: BRY39 - Solid state switch's.

Ah, the 'Figaro' sensor.

I think we're currently on the threshold of a number of types of discrete semiconductors going extinct.

I've noticed that low voltage dual gate mosfets have gone. A few 12v ones are lingering. The range of varactor diodes is shrinking rapidly. Avago (now Broadcom) have axed a lot of their MMIC parts saying turnover was too low.

Companies guard commercially-sensitive data such as sales figures like the crown jewels. But if they are ditching everything below some magic (and also secret) figure, how do I as a designer know if anything is safe to put in my next design?

David
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Old 12th Nov 2017, 1:20 pm   #14
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Default Re: BRY39 - Solid state switches.

Rather than using a UJT or a PUT, I think its better to wire a PNP and NPN transistor together to make a PUT. This was done to create the vertical oscillator on one of my vintage computer monitors. Also I have a Conrac video monitor that uses a UJT as the vertical scan oscillator.

At least if the PUT is made from two common garden transistors, its easy to repair/replace it.

Becoming even more obsolete and oddball than the UJT is the CUJT, or complimentary UJT, I have yet to lay my hands on one, a type number is the D5K1.
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Old 12th Nov 2017, 2:13 pm   #15
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Default Re: BRY39 - Solid state switches.

The BRY39 may have not worked well in some applications but in the frame osc in the RBM A823 CTV they did not give me a lot of problems. I may have replaced the odd one but for me it was not a common occurance, others may have had different experiences.

That chassis gave lots of other problems though.
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Old 12th Nov 2017, 2:56 pm   #16
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Default Re: BRY39 - Solid state switches.

Quote:
Originally Posted by Diabolical Artificer View Post
Thanks chaps. I've found the basic relaxation osc circuit and a few other bits online for PUT's, but nothing specific for the BRY39. The 2N6027 comes up in searches for PUT's but this has no cathode gate. In the example for the 2N6027 here - http://www.circuitstoday.com/programmable-ujt there is an unused P region, does this mean the 39 has an extra N region which is the cathode gate?
The BRY39 is PNPN with a connection to every region. The 2N6027 just omits a connection to the inner P region.

I've used the cathode gate for connecting a resistor between here and cathode, to speed-up stored charge dissipation after it's been conducting. Otherwise you have to wait several microseconds before normal operation resumes. It's also useful for triggering the device 'on'.

Quote:
Originally Posted by Argus25 View Post
Rather than using a UJT or a PUT, I think its better to wire a PNP and NPN transistor together to make a PUT. This was done to create the vertical oscillator on one of my vintage computer monitors. Also I have a Conrac video monitor that uses a UJT as the vertical scan oscillator.

At least if the PUT is made from two common garden transistors, its easy to repair/replace it.
The trouble is, it is hard to find PNP transistors with a reverse Vbe of more than 5V, whereas the BRY39 does 60V (from memory). The internal PNP transistor is, as a result, low current gain, but that does not matter as thyristor action only requires the sum of the NPN and PNP alpha gains be greater than 1, and the internal NPN transistor has plenty of gain.

I've used the BRY39 twice in the 'day job,' once was as a start-up component in an off-line switch-mode power supply. A large resistor charged up a 470μF capacitor to about 20V (as determined by a Zener diode on the anode gate. The PUT then fired, dumping the charge into another capacitor on its cathode, connected to the SMPS control circuitry. The energy available powered the control circuitry long enough to start up, at which point an auxiliary secondary winding on the power transformer took over providing power.

The other application was a protection crowbar across a low-power 8V supply rail which powered a pressure transducer in a liquid oxygen tank. To stop self-heating, there was a requirement that the transducer be powered for 4 seconds maximum. This was defined by software, but in case the software crashed leaving power 'on,' I used a BRY39 and a few components to generate a 5second delay. If the supply rail hadn't been killed by then, the PUT fired and crowbarred it. I needed only the BRY39, a timing capacitor and resistor, the two programming resistors, and a small blocking diode. The whole thing was powered by the rail it was protecting (250μA current drain till it 'fires').

I'm also using it as the 'on' period timer in a small battery-to-HT&LT power supply for battery valve radios, one of which happens to be playing right now! This is where I needed the cathode-gate resistor. Varying the voltage on the anode-gate controls the period, allowing output voltage regulation. It works well, though I agree dedicated control IC's exist!

Last edited by kalee20; 12th Nov 2017 at 3:01 pm. Reason: Grammar
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Old 12th Nov 2017, 3:49 pm   #17
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Default Re: BRY39 - Solid state switches.

Hi Gents, Kalee's note about the PNP transistors with high Vbe is valid, the only ones I know are the BCY30 family where it is about 30V.
These were used with ZTX61 (NPN) devices in timers for professional gear pre BRY39's being available.
This combination went through a lot of testing and proved reliable.

Ed
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Old 12th Nov 2017, 9:26 pm   #18
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Default Re: BRY39 - Solid state switches.

Quote:
Originally Posted by kalee20 View Post
The trouble is, it is hard to find PNP transistors with a reverse Vbe of more than 5V, whereas the BRY39 does 60V (from memory).
The transistor BC640 (pnp) has a reverse Vbe of 11V, which is better than most silicon transistors which are usually around 6 or 7V, which makes the 639/640 pair handy for some applications, plus they are robust for their size. I found this out when testing a few in a specific application that zenered the B-E junction, which is never a good idea, each time its done the hfe degrades a little.
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Old 13th Nov 2017, 8:55 am   #19
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Default Re: BRY39 - Solid state switches.

BRY39 also in some early G8 TV's.
https://www.vintage-radio.net/forum/...ad.php?t=18596
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Old 13th Nov 2017, 11:07 am   #20
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Default Re: BRY39 - Solid state switches.

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The transistor BC640 (pnp) has a reverse Vbe of 11V, which is better than most silicon transistors...
Not according to ON Semiconductors data (attached)! They say 5V.

The only silicon transistor that I know with any half-decent reverse Vbe capability is the OC200 (20V), and possibly others in that series.

It might pair-up with an NPN to create a BRY39 replacement, at least to this voltage.
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