Forums

Class C Power Oscillator

Started by bitrex September 24, 2015
I'm trying to design an ultrasonic class C power oscillator to use with 
a project I'm working on.  I'm vaguely basing it off a circuit I recall 
seeing in an early 1960s-era book called "Industrial Transistor 
Circuits".  It seems I'm not remembering it correctly, and I don't 
really know much about the design of this type of oscillator as it's 
having some problems oscillating in simulation, even doing the "start 
supply voltages at 0 V" thing.

I'd like to use a small air core, maybe 1.5 inches in diameter by 5 
inches in length, something like that.

Here's the .asc:

Version 4
SHEET 1 880 680
WIRE 64 32 -80 32
WIRE 208 32 208 -16
WIRE 208 32 64 32
WIRE 608 64 304 64
WIRE 208 112 208 32
WIRE 304 112 304 64
WIRE 608 112 608 64
WIRE -272 128 -272 96
WIRE -80 128 -80 32
WIRE 64 128 64 32
WIRE 64 144 64 128
WIRE -272 240 -272 208
WIRE 304 240 304 192
WIRE 608 240 608 192
WIRE 608 240 304 240
WIRE 64 256 64 192
WIRE 208 256 208 192
WIRE 208 256 64 256
WIRE 464 288 320 288
WIRE -80 320 -80 208
WIRE -16 320 -80 320
WIRE 96 320 48 320
WIRE 464 336 464 288
WIRE 608 336 608 240
WIRE 208 368 208 256
WIRE 400 368 320 368
WIRE -80 416 -80 320
WIRE -80 416 -160 416
WIRE -32 416 -80 416
WIRE 96 416 96 320
WIRE 96 416 48 416
WIRE 144 416 96 416
WIRE 208 560 208 464
WIRE -160 640 -160 416
WIRE 400 640 400 368
WIRE 400 640 -160 640
FLAG 208 -16 Vcc
FLAG 208 560 0
FLAG 464 336 0
FLAG 608 336 0
FLAG -272 240 0
FLAG -272 96 Vcc
SYMBOL ind2 192 96 R0
WINDOW 3 34 74 Left 2
SYMATTR InstName L1
SYMATTR Value 47µH
SYMBOL ind2 288 96 R0
SYMATTR InstName L2
SYMATTR Value 100µH
SYMBOL npn 144 368 R0
SYMATTR InstName Q1
SYMATTR Value 2SCR533P
SYMBOL ind2 336 384 R180
WINDOW 0 36 80 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName L3
SYMATTR Value 4.7µH
SYMBOL cap 48 128 R0
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL res 592 96 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -96 112 R0
SYMATTR InstName R2
SYMATTR Value 47k
SYMBOL res 64 400 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 470
SYMBOL cap 48 304 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 100n
SYMBOL voltage -272 112 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 12
TEXT 296 8 Left 2 !K1 L1 L2 L3 1
TEXT -392 296 Left 2 !.tran 0.1 startup uic
On Thursday, September 24, 2015 at 8:31:14 AM UTC-4, bitrex wrote:
> I'm trying to design an ultrasonic class C power oscillator to use with > a project I'm working on. I'm vaguely basing it off a circuit I recall > seeing in an early 1960s-era book called "Industrial Transistor > Circuits". It seems I'm not remembering it correctly, and I don't > really know much about the design of this type of oscillator as it's > having some problems oscillating in simulation, even doing the "start > supply voltages at 0 V" thing. > > I'd like to use a small air core, maybe 1.5 inches in diameter by 5 > inches in length, something like that. > > Here's the .asc: > > Version 4 > SHEET 1 880 680 > WIRE 64 32 -80 32 > WIRE 208 32 208 -16 > WIRE 208 32 64 32 > WIRE 608 64 304 64 > WIRE 208 112 208 32 > WIRE 304 112 304 64 > WIRE 608 112 608 64 > WIRE -272 128 -272 96 > WIRE -80 128 -80 32 > WIRE 64 128 64 32 > WIRE 64 144 64 128 > WIRE -272 240 -272 208 > WIRE 304 240 304 192 > WIRE 608 240 608 192 > WIRE 608 240 304 240 > WIRE 64 256 64 192 > WIRE 208 256 208 192 > WIRE 208 256 64 256 > WIRE 464 288 320 288 > WIRE -80 320 -80 208 > WIRE -16 320 -80 320 > WIRE 96 320 48 320 > WIRE 464 336 464 288 > WIRE 608 336 608 240 > WIRE 208 368 208 256 > WIRE 400 368 320 368 > WIRE -80 416 -80 320 > WIRE -80 416 -160 416 > WIRE -32 416 -80 416 > WIRE 96 416 96 320 > WIRE 96 416 48 416 > WIRE 144 416 96 416 > WIRE 208 560 208 464 > WIRE -160 640 -160 416 > WIRE 400 640 400 368 > WIRE 400 640 -160 640 > FLAG 208 -16 Vcc > FLAG 208 560 0 > FLAG 464 336 0 > FLAG 608 336 0 > FLAG -272 240 0 > FLAG -272 96 Vcc > SYMBOL ind2 192 96 R0 > WINDOW 3 34 74 Left 2 > SYMATTR InstName L1 > SYMATTR Value 47�H > SYMBOL ind2 288 96 R0 > SYMATTR InstName L2 > SYMATTR Value 100�H > SYMBOL npn 144 368 R0 > SYMATTR InstName Q1 > SYMATTR Value 2SCR533P > SYMBOL ind2 336 384 R180 > WINDOW 0 36 80 Left 2 > WINDOW 3 36 40 Left 2 > SYMATTR InstName L3 > SYMATTR Value 4.7�H > SYMBOL cap 48 128 R0 > SYMATTR InstName C1 > SYMATTR Value 10n > SYMBOL res 592 96 R0 > SYMATTR InstName R1 > SYMATTR Value 10k > SYMBOL res -96 112 R0 > SYMATTR InstName R2 > SYMATTR Value 47k > SYMBOL res 64 400 R90 > WINDOW 0 0 56 VBottom 2 > WINDOW 3 32 56 VTop 2 > SYMATTR InstName R3 > SYMATTR Value 470 > SYMBOL cap 48 304 R90 > WINDOW 0 0 32 VBottom 2 > WINDOW 3 32 32 VTop 2 > SYMATTR InstName C2 > SYMATTR Value 100n > SYMBOL voltage -272 112 R0 > WINDOW 123 0 0 Left 2 > WINDOW 39 0 0 Left 2 > SYMATTR InstName V1 > SYMATTR Value 12 > TEXT 296 8 Left 2 !K1 L1 L2 L3 1 > TEXT -392 296 Left 2 !.tran 0.1 startup uic
Hi bitrex, (I didn't download your spice file.) I've tried to simulate oscillators a few times in LTspice with various degrees of success. One trick is to kick start them... a big voltage or current pulse to get things going. What's the power, freq, and load impdeance of your oscillator? George H.
I'm not at my computer ATM, but in order to start reliably, the oscillator needs to be in Class A at zero signal, and have enough gain to be unstable. Otherwise a slow turn-on or brief brownout can stop it from oscillating. 

Cheers

Phil Hobbs 
>One trick is to kick start them... a big voltage or >current pulse to get things going. �
Better to use a _small_ kickstart--just enough to get past roundoff and the various SPICE voltage and current tolerances. That leaves the active device in the small-signal regime, so you can verify that it starts reliably. Cheers Phil Hobbs
On Thursday, September 24, 2015 at 9:09:07 AM UTC-4, Phil Hobbs wrote:
> >One trick is to kick start them... a big voltage or > >current pulse to get things going. � > > Better to use a _small_ kickstart--just enough to get past roundoff and the various SPICE voltage and current tolerances. That leaves the active device in the small-signal regime, so you can verify that it starts reliably. > > Cheers > > Phil Hobbs
right... forget about the simulation.. how does a pure class C osc get started in real life even? Mark
On 09/24/2015 10:36 AM, makolber@yahoo.com wrote:
> On Thursday, September 24, 2015 at 9:09:07 AM UTC-4, Phil Hobbs wrote: >>> One trick is to kick start them... a big voltage or >>> current pulse to get things going. >> >> Better to use a _small_ kickstart--just enough to get past roundoff and the various SPICE voltage and current tolerances. That leaves the active device in the small-signal regime, so you can verify that it starts reliably. >> >> Cheers >> >> Phil Hobbs > > right... forget about the simulation.. > > how does a pure class C osc get started in real life even? > > Mark >
Two ways. Bad ones, i.e. those whose quiescent bias is Class C, require a kick at turn-on. Good ones, which have unstable Class A quiescent bias, start up from noise. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Thu, 24 Sep 2015 07:36:59 -0700, makolber wrote:

> On Thursday, September 24, 2015 at 9:09:07 AM UTC-4, Phil Hobbs wrote: >> >One trick is to kick start them... a big voltage or current pulse to >> >get things going. >> >> Better to use a _small_ kickstart--just enough to get past roundoff and >> the various SPICE voltage and current tolerances. That leaves the >> active device in the small-signal regime, so you can verify that it >> starts reliably. >> >> Cheers >> >> Phil Hobbs > > right... forget about the simulation.. > > how does a pure class C osc get started in real life even? > > Mark
This is a rewording of what Phil said: Kickstart (eeww), or arrange the thing so that it's biased to be a class- A oscillator on startup, and therefor starts oscillating on its own. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On 9/24/2015 7:31 AM, bitrex wrote:
> I'm trying to design an ultrasonic class C power oscillator to use with > a project I'm working on. I'm vaguely basing it off a circuit I recall > seeing in an early 1960s-era book called "Industrial Transistor > Circuits". It seems I'm not remembering it correctly, and I don't > really know much about the design of this type of oscillator as it's > having some problems oscillating in simulation, even doing the "start > supply voltages at 0 V" thing. > > I'd like to use a small air core, maybe 1.5 inches in diameter by 5 > inches in length, something like that. > > Here's the .asc:
(snip) I can rearrange the parts and get it to oscillate easily as a non-linear (class ?)arrangement. Here ya go... Version 4 SHEET 1 880 680 WIRE -80 32 -144 32 WIRE 64 32 -80 32 WIRE 208 32 208 -16 WIRE 208 32 64 32 WIRE 608 64 304 64 WIRE -144 112 -144 32 WIRE 208 112 208 32 WIRE 304 112 304 64 WIRE 608 112 608 64 WIRE -272 128 -272 96 WIRE -80 128 -80 32 WIRE 64 128 64 32 WIRE 64 144 64 128 WIRE -272 240 -272 208 WIRE 304 240 304 192 WIRE 608 240 608 192 WIRE 608 240 304 240 WIRE 64 256 64 192 WIRE 208 256 208 192 WIRE 208 256 64 256 WIRE -144 272 -144 176 WIRE -80 272 -80 208 WIRE -80 272 -144 272 WIRE 464 272 -80 272 WIRE 464 288 464 272 WIRE 464 288 320 288 WIRE 608 336 608 240 WIRE 208 368 208 256 WIRE 400 368 320 368 WIRE 144 416 -160 416 WIRE 208 560 208 464 WIRE -160 640 -160 416 WIRE 400 640 400 368 WIRE 400 640 -160 640 FLAG 208 -16 Vcc FLAG 208 560 0 FLAG 608 336 0 FLAG -272 240 0 FLAG -272 96 Vcc SYMBOL ind2 192 96 R0 WINDOW 3 34 74 Left 2 SYMATTR Value 47uH SYMATTR InstName L1 SYMBOL ind2 288 96 R0 SYMATTR InstName L2 SYMATTR Value 100uH SYMBOL npn 144 368 R0 SYMATTR InstName Q1 SYMATTR Value 2SCR533P SYMBOL ind2 336 384 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L3 SYMATTR Value 4.7uH SYMBOL cap 48 128 R0 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL res 592 96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res -96 112 R0 SYMATTR InstName R2 SYMATTR Value 47k SYMBOL voltage -272 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL cap -160 112 R0 SYMATTR InstName C2 SYMATTR Value 1n TEXT 296 8 Left 2 !K1 L1 L2 L3 1 TEXT -392 296 Left 2 !.tran 0 2m 1m startup uic
On Thu, 24 Sep 2015 08:31:08 -0400, bitrex wrote:

> I'm trying to design an ultrasonic class C power oscillator to use with > a project I'm working on. I'm vaguely basing it off a circuit I recall > seeing in an early 1960s-era book called "Industrial Transistor > Circuits". It seems I'm not remembering it correctly, and I don't > really know much about the design of this type of oscillator as it's > having some problems oscillating in simulation, even doing the "start > supply voltages at 0 V" thing. > > I'd like to use a small air core, maybe 1.5 inches in diameter by 5 > inches in length, something like that. >
Turn it into an amplifier and jigger it around until you have lots of gain at 0 degrees phase shift. Here's a start. It's for your non-working amplifier and it shows gain, which puzzles the heck out of me -- but figuring it out is your job. Version 4 SHEET 1 880 680 WIRE 64 32 -80 32 WIRE 208 32 208 -16 WIRE 208 32 64 32 WIRE 608 64 304 64 WIRE 208 112 208 32 WIRE 304 112 304 64 WIRE 608 112 608 64 WIRE -272 128 -272 96 WIRE -80 128 -80 32 WIRE 64 128 64 32 WIRE 64 144 64 128 WIRE -272 240 -272 208 WIRE 304 240 304 192 WIRE 608 240 608 192 WIRE 608 240 304 240 WIRE 64 256 64 192 WIRE 208 256 208 192 WIRE 208 256 64 256 WIRE 464 288 320 288 WIRE -80 320 -80 208 WIRE -16 320 -80 320 WIRE 96 320 48 320 WIRE 464 336 464 288 WIRE 608 336 608 240 WIRE 208 368 208 256 WIRE 400 368 320 368 WIRE 400 400 400 368 WIRE -288 416 -352 416 WIRE -192 416 -224 416 WIRE -80 416 -80 320 WIRE -80 416 -112 416 WIRE -32 416 -80 416 WIRE 96 416 96 320 WIRE 96 416 48 416 WIRE 144 416 96 416 WIRE -352 448 -352 416 WIRE 400 496 400 480 WIRE -352 560 -352 528 WIRE 208 560 208 464 FLAG 208 -16 Vcc FLAG 208 560 0 FLAG 464 336 0 FLAG 608 336 0 FLAG -272 240 0 FLAG -272 96 Vcc FLAG 400 496 0 FLAG -352 560 0 SYMBOL ind2 192 96 R0 WINDOW 3 34 74 Left 2 SYMATTR Value 47µH SYMATTR InstName L1 SYMBOL ind2 288 96 R0 SYMATTR InstName L2 SYMATTR Value 100µH SYMBOL npn 144 368 R0 SYMATTR InstName Q1 SYMATTR Value 2SCR533P SYMBOL ind2 336 384 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L3 SYMATTR Value 4.7µH SYMBOL cap 48 128 R0 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL res 592 96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res -96 112 R0 SYMATTR InstName R2 SYMATTR Value 47k SYMBOL res 64 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 470 SYMBOL cap 48 304 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100n SYMBOL voltage -272 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 384 384 R0 SYMATTR InstName R4 SYMATTR Value 50 SYMBOL res -96 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 50 SYMBOL voltage -352 432 R0 WINDOW 123 24 124 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value2 AC 1 SYMATTR InstName V2 SYMATTR Value 0 SYMBOL cap -224 400 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 100n TEXT 296 8 Left 2 !K1 L1 L2 L3 1 TEXT -392 296 Left 2 !.tran 0.1 startup uic TEXT -392 328 Left 2 !;ac dec 40 10k 10meg -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Thu, 24 Sep 2015 08:31:08 -0400, bitrex wrote:

> I'm trying to design an ultrasonic class C power oscillator to use with > a project I'm working on. I'm vaguely basing it off a circuit I recall > seeing in an early 1960s-era book called "Industrial Transistor > Circuits". It seems I'm not remembering it correctly, and I don't > really know much about the design of this type of oscillator as it's > having some problems oscillating in simulation, even doing the "start > supply voltages at 0 V" thing. > > I'd like to use a small air core, maybe 1.5 inches in diameter by 5 > inches in length, something like that.
L3 shorts out the base bias. Put in a blocking cap and it sings. The "treat it as an amplifier" analysis says that it should work with R1 at 100 ohms, but in reality if you put R1 much less than 10k then Bad Things happen -- I don't know why, chasing that down can be an exercise for you, the reader, to figure out. You may want to try a plain ol' Colpitts topology and see if you can find a combination that works. Version 4 SHEET 1 880 680 WIRE 64 32 -80 32 WIRE 208 32 208 -16 WIRE 208 32 64 32 WIRE 608 64 304 64 WIRE 656 64 608 64 WIRE 208 112 208 32 WIRE 304 112 304 64 WIRE 608 112 608 64 WIRE -272 128 -272 96 WIRE -80 128 -80 32 WIRE 64 128 64 32 WIRE -272 240 -272 208 WIRE 304 240 304 192 WIRE 608 240 608 192 WIRE 608 240 304 240 WIRE 64 256 64 192 WIRE 208 256 208 192 WIRE 208 256 64 256 WIRE 464 288 320 288 WIRE -80 320 -80 208 WIRE -16 320 -80 320 WIRE 96 320 48 320 WIRE 464 336 464 288 WIRE 608 336 608 240 WIRE 208 368 208 256 WIRE 400 368 320 368 WIRE -80 416 -80 320 WIRE -32 416 -80 416 WIRE 96 416 96 320 WIRE 96 416 48 416 WIRE 144 416 96 416 WIRE -80 480 -80 416 WIRE 208 560 208 464 WIRE -80 640 -80 544 WIRE 400 640 400 368 WIRE 400 640 -80 640 FLAG 208 -16 Vcc FLAG 208 560 0 FLAG 464 336 0 FLAG 608 336 0 FLAG -272 240 0 FLAG -272 96 Vcc FLAG 656 64 Vout SYMBOL ind2 192 96 R0 WINDOW 3 34 74 Left 2 SYMATTR Value 47�H SYMATTR InstName L1 SYMBOL ind2 288 96 R0 SYMATTR InstName L2 SYMATTR Value 100�H SYMBOL npn 144 368 R0 SYMATTR InstName Q1 SYMATTR Value 2SCR533P SYMBOL ind2 336 384 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L3 SYMATTR Value 4.7�H SYMBOL cap 48 128 R0 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL res 592 96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res -96 112 R0 SYMATTR InstName R2 SYMATTR Value 47k SYMBOL res 64 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 470 SYMBOL cap 48 304 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100n SYMBOL voltage -272 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PWL(0 0 5m 12) SYMBOL cap -96 480 R0 SYMATTR InstName C3 SYMATTR Value 100n TEXT 296 8 Left 2 !K1 L1 L2 L3 1 TEXT -392 296 Left 2 !.tran 10m startup uic -- Tim Wescott Wescott Design Services http://www.wescottdesign.com