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unijunction equivalent circuit?

Started by Joseph H Allen August 29, 2013
So is there any simple circuit using conventional NPN and PNP transistors?

I've seen this circuit
http://sub.allaboutcircuits.com/images/quiz/02139x02.png in _Sourcebook of
Electronic Circuits_, but it doesn't really work- it latches but does not
release when used in a relaxation oscillator.  Perhaps it did work with
lower gain transistors.

-- 
/*  jhallen@world.std.com AB1GO */                        /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0:p%79-77?1:0:p<1659?79:0:p>158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}
On Thu, 29 Aug 2013 22:34:19 +0000 (UTC), jhallen@TheWorld.com (Joseph
H Allen) wrote:

> >So is there any simple circuit using conventional NPN and PNP transistors? > >I've seen this circuit >http://sub.allaboutcircuits.com/images/quiz/02139x02.png in _Sourcebook of >Electronic Circuits_, but it doesn't really work- it latches but does not >release when used in a relaxation oscillator. Perhaps it did work with >lower gain transistors.
You need at least one Vbe resistor (on the NPN) to establish a holding current trip point. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 29 Aug 2013 15:49:18 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Thu, 29 Aug 2013 22:34:19 +0000 (UTC), jhallen@TheWorld.com (Joseph >H Allen) wrote: > >> >>So is there any simple circuit using conventional NPN and PNP transistors? >> >>I've seen this circuit >>http://sub.allaboutcircuits.com/images/quiz/02139x02.png in _Sourcebook of >>Electronic Circuits_, but it doesn't really work- it latches but does not >>release when used in a relaxation oscillator. Perhaps it did work with >>lower gain transistors. > >You need at least one Vbe resistor (on the NPN) to establish a holding >current trip point. > > ...Jim Thompson
A quick surf produces this.... * http://www.duncanamps.com/spice/miscsemi/2n2646.sub * *Default N-Channel Unijunction Transistor .SUBCKT XUJT 1 2 3 DE 1 4 EMITTER VE 4 5 DC 0 HVE 6 0 VE 1K RVE 0 6 1MEG BBB 5 7 I=0.00028*V(5,7)+0.00575*V(5,7)*V(6) CBB 5 7 35P ***RB1 7 2 38.15 RMOD ***RB2 3 5 2.518K RMOD RB1 7 2 RMOD 38.15 RB2 3 5 RMOD 2.518K .MODEL RMOD R TC1=.01 .MODEL EMITTER D (IS=21.3P N=1.8) .ENDS XUJT * Motorola IP=.5U IV=6M VB1(sat)=3 Rbb=6.1K Vob1=3.6: E, B1, B2 .SUBCKT X2N2646 1 2 3 DE 1 4 EMITTER VE 4 5 DC 0 HVE 6 0 VE 1K RVE 0 6 1MEG BBB 5 7 I=0.00028*V(5,7)+0.00575*V(5,7)*V(6) CBB 5 7 35P ***RB1 7 2 38.15 RMOD ***RB2 3 5 2.518K RMOD RB1 7 2 RMOD 38.15 RB2 3 5 RMOD 2.518K .MODEL RMOD R TC1=.01 .MODEL EMITTER D (IS=21.3P N=1.8) .ENDS X2N2646 This is in B-source notation. In your Spice variant you may need to replace BBB with GVALUE notation. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Can you use a pseudo PUT or do you need a UJT?

If a PUT works, try:   http://www.4qdtec.com/putpr.html

Steve 

On a sunny day (Thu, 29 Aug 2013 22:34:19 +0000 (UTC)) it happened
jhallen@TheWorld.com (Joseph H Allen) wrote in <kvoi9b$r1n$1@pcls7.std.com>:

> >So is there any simple circuit using conventional NPN and PNP transistors? >
I dunno but I have a bunch of 2N2646 UJTs from ebay for cheap. Those work OK.
On Thu, 29 Aug 2013 22:34:19 +0000 (UTC), the renowned
jhallen@TheWorld.com (Joseph H Allen) wrote:

> >So is there any simple circuit using conventional NPN and PNP transistors? > >I've seen this circuit >http://sub.allaboutcircuits.com/images/quiz/02139x02.png in _Sourcebook of >Electronic Circuits_, but it doesn't really work- it latches but does not >release when used in a relaxation oscillator. Perhaps it did work with >lower gain transistors.
You need to keep the value of (RB1 || RB2) << the timing resistor, and maybe a high-value B-E resistor on the NPN. A synthetic PUT made with discrete transistors won't have the "gate" to "anode" voltage capability of a real PUT (typically st like 40V) due to the B-E breakdown voltage. Flipping the PNP to get a PNP with high B-E breakdown and miserably low beta might work, but the peak current will be increased (reducing the maximum value of the timing resistor). Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com