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Relaxation oscillators and SPICE

Started by Piotr Wyderski January 1, 2015
I am unable to simulate the followingg PUT-based relaxation oscillator 
in the most recent LTspice (with BC547B and BC557B):

https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png

Nothing wants to oscillate.

Looking for a bug I have also tried the simplest possible neon lamp
oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are 
no scillations either: the voltage on the capacitor saturates at 50.25V.

What magic should I apply to make such circuits work as expected?

	Best regards, Piotr
On 1/1/2015 6:36 AM, Piotr Wyderski wrote:
> I am unable to simulate the followingg PUT-based relaxation oscillator > in the most recent LTspice (with BC547B and BC557B): > > https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > > Nothing wants to oscillate. > > Looking for a bug I have also tried the simplest possible neon lamp > oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are > no scillations either: the voltage on the capacitor saturates at 50.25V. > > What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
Works fine for me. Frequency of 62Hz.
On Thu, 01 Jan 2015 13:36:40 +0100, Piotr Wyderski wrote:

> I am unable to simulate the followingg PUT-based relaxation oscillator > in the most recent LTspice (with BC547B and BC557B): > > https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > > Nothing wants to oscillate. > > Looking for a bug I have also tried the simplest possible neon lamp > oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are > no scillations either: the voltage on the capacitor saturates at 50.25V. > > What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
It is probably having a "hard start" issue where the oscillation will not begin.
On Thu, 01 Jan 2015 13:36:40 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>I am unable to simulate the followingg PUT-based relaxation oscillator >in the most recent LTspice (with BC547B and BC557B): > >https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > >Nothing wants to oscillate. > >Looking for a bug I have also tried the simplest possible neon lamp >oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are >no scillations either: the voltage on the capacitor saturates at 50.25V. > >What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
Two possible issues... (1) Model parameter BF of transistors may be so high that current thru 220K exceeds holding current. Try increasing 220K OR add a resistor, NPN base to ground, to raise holding current above what 220K can support. (2) Oscillators, in any form of Spice, _often_ will not start on their own. Try .IC of capacitor as zero volts. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.
In article <m83f0n$cvj$1@node2.news.atman.pl>, peter.pan@neverland.mil 
says...
> > I am unable to simulate the followingg PUT-based relaxation oscillator > in the most recent LTspice (with BC547B and BC557B): > > https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > > Nothing wants to oscillate. > > Looking for a bug I have also tried the simplest possible neon lamp > oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are > no scillations either: the voltage on the capacitor saturates at 50.25V. > > What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
You need to start the SIM at 0 volts. Jamie
On 1.1.15 14:36, Piotr Wyderski wrote:
> I am unable to simulate the followingg PUT-based relaxation oscillator > in the most recent LTspice (with BC547B and BC557B): > > https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > > Nothing wants to oscillate. > > Looking for a bug I have also tried the simplest possible neon lamp > oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are > no scillations either: the voltage on the capacitor saturates at 50.25V. > > What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
The 220k timing resistor is too small, keeping the PUT continuosly on. The following thing oscillates. --- clip clip --- Version 4 SHEET 1 908 704 WIRE 576 80 48 80 WIRE 848 80 576 80 WIRE 48 144 48 80 WIRE 576 144 576 80 WIRE 48 272 48 224 WIRE 240 272 48 272 WIRE 384 320 304 320 WIRE 576 320 576 224 WIRE 576 320 384 320 WIRE 48 384 48 272 WIRE 848 384 848 80 WIRE 384 416 384 320 WIRE 576 416 576 320 WIRE 240 464 240 368 WIRE 320 464 240 464 WIRE 384 576 384 512 WIRE 48 688 48 448 WIRE 384 688 384 640 WIRE 576 688 576 496 WIRE 848 688 848 464 FLAG 384 688 0 FLAG 576 688 0 FLAG 48 688 0 FLAG 848 688 0 SYMBOL pnp 304 368 R180 SYMATTR InstName Q1 SYMATTR Value BC557B SYMBOL npn 320 416 R0 SYMATTR InstName Q2 SYMATTR Value BC547B SYMBOL res 560 128 R0 SYMATTR InstName R1 SYMATTR Value 3.9k SYMBOL res 560 400 R0 SYMATTR InstName R2 SYMATTR Value 3.9k SYMBOL res 32 128 R0 SYMATTR InstName R3 SYMATTR Value 1Meg SYMBOL cap 32 384 R0 SYMATTR InstName C1 SYMATTR Value 33n SYMBOL voltage 848 368 R0 SYMATTR InstName V1 SYMATTR Value 9V SYMBOL LED 368 576 R0 SYMATTR InstName D1 TEXT -80 640 Left 2 !.tran 0 1 0 --- clip clip --- -- -TV
On Thu, 01 Jan 2015 13:36:40 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>I am unable to simulate the followingg PUT-based relaxation oscillator >in the most recent LTspice (with BC547B and BC557B): > >https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > >Nothing wants to oscillate. > >Looking for a bug I have also tried the simplest possible neon lamp >oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are >no scillations either: the voltage on the capacitor saturates at 50.25V. > >What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
This neon thing oscillates. The current has to be kept low. Version 4 SHEET 1 880 680 WIRE 32 48 -32 48 WIRE 144 48 112 48 WIRE 256 48 144 48 WIRE 144 112 144 48 WIRE -32 128 -32 48 WIRE 256 128 256 48 WIRE -32 240 -32 208 WIRE 144 240 144 208 WIRE 256 240 256 192 FLAG -32 240 0 FLAG 144 240 0 FLAG 256 240 0 SYMBOL Misc\\neonbulb 144 160 R0 SYMATTR InstName U1 SYMATTR SpiceLine Zon=500 Ihold=200u SYMBOL cap 240 128 R0 WINDOW 0 73 12 Left 2 WINDOW 3 74 47 Left 2 SYMATTR InstName C1 SYMATTR Value 1&#2013266101; SYMBOL res 128 32 R90 WINDOW 0 -7 54 VBottom 2 WINDOW 3 41 58 VTop 2 SYMATTR InstName R1 SYMATTR Value 1E6 SYMBOL voltage -32 112 R0 WINDOW 0 -87 31 Left 2 WINDOW 3 -94 68 Left 2 SYMATTR InstName V1 SYMATTR Value 200 TEXT 312 64 Left 2 !.tran 4 uic -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thu, 01 Jan 2015 13:36:40 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>I am unable to simulate the followingg PUT-based relaxation oscillator >in the most recent LTspice (with BC547B and BC557B): > >https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > >Nothing wants to oscillate. > >Looking for a bug I have also tried the simplest possible neon lamp >oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are >no scillations either: the voltage on the capacitor saturates at 50.25V. > >What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
Try checking "skip initial operating point" in the sim/edit/trans menu. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
In article <m83f0n$cvj$1@node2.news.atman.pl>, peter.pan@neverland.mil 
says...
> > I am unable to simulate the followingg PUT-based relaxation oscillator > in the most recent LTspice (with BC547B and BC557B): > > https://upload.wikimedia.org/wikipedia/commons/9/9f/PUT_LED_blinker.png > > Nothing wants to oscillate. > > Looking for a bug I have also tried the simplest possible neon lamp > oscillator (with Vstrike=100V, Vhold=50V, R=220k, C=1u), but there are > no scillations either: the voltage on the capacitor saturates at 50.25V. > > What magic should I apply to make such circuits work as expected? > > Best regards, Piotr
To add to that... You need to put real part numbers on the transistors and the NPN needs to have a pull down R at the base to common/grd so that it'll discharged the cap in the base of the NPN etc.. A 220K should work or something in that ball park. Only going by your schematic, using an LED. I suppose a Neon maybe behave differently. Jamie
Tauno Voipio wrote:

> The 220k timing resistor is too small, keeping the PUT continuosly on. > The following thing oscillates.
Thank you all very much, in both cases the non-oscillation seems to be caused by too low resistor value. In the case of the PUT-based circuit I have not enough experience to judge whether Spice is right or wrong, but I remember well my experiments performed over a decade ago with a *real* neon oscillator. It used to work with pretty any reasonable resistor. The simulation provided by John does not oscillate with 470k and with 560k it oscillates *exactly twice*. With 680k it works well. I must confess that my excitement about Spice has just entered a colder period... :-/ Once again, thank you for your help! Best regards, Piotr