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I'm guessing that his transducer needs to be driven at ≈40kHz. The amplifier's response as drawn is about 1.3dB down at 40kHz. It also slews at about 12V/usec, meaning you can only get about 100V p-p at 40kHz out of it, even with no load. Sinewave simulation shows lots of distortion at 40kHz with 80V p-p output. The output of the LT1001 is a triangle wave under these conditions.You're right and Q5 is the constant current load for it.
I've just simulated it in LTSpice and it works perfectly.
Q3 is upside down.You're right and Q5 is the constant current load for it.
I've just simulated it in LTSpice and it works perfectly.
It turns into a low-beta transistor when you swap emitter and collector.Maybe it's a symmetrical transistor ?
on1aag.
The simulation oscillates when you place the transistor correctly..model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=100 Bf=132.1 Ne=1.375 Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 Nc=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p Mjc=.5312 Vjc=.75 Fc=.5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p Itf=0 Vtf=0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild)
It can be fixed by doing the following:
- Use a faster op-amp.
- Reduce R12 to increase the voltage gain of the buffer and put less strain on the op-amp, be careful too higher gain will cause oscillation.
- Reduce the compensation cacitor values, again watch out for oscillation.
My (poor) excuse is that it's the default orintation for PNP transistors with LTSpice and all other simulators I've used have the emitter pointing upward as the default for PNP transistors.Q3 is upside down.![]()
Yes, as it now has more gain, it ocillates around 500mV at about 1MHz.Hi Ron,
I noticed that too, at 1 MHz and above it looks a bit "playfull".
on1aag.
It looks like you're building an inverter.Sounds good. I will do that along with a minor change to the emitter - follower circuit. I would like to use Darlington pair. Doing so I need to add 2 more diodes. The signal frequency will be varied from 6Hz - 60Hz so I probably won't have any issues with gain roll-off. I never dealt with switching amplifiers or components before so I doubt I can design a Class D amplifier at this point. So I will just stick to linear for now.
Thank you for your help.![]()
Another thing is that at low speeds the voltage must be reduced to avoid core saturation. With a PWM or modified sinewave inverter this is easy, the duty cycle is just reduced.
So the voltage has to be reduced If I were to reduce the speed of AC motor by lowering the frequency? But that would reduce the torque. Thanks once again.
A PWM inverter uses class D amplification of a sinewave (the motor does the filtering itself), as the frequency is reduced the ampltude of the sinewave is also reduced.
PWM is probably your safest option, for 60Hz the frequency doesn't need to be too high 1kHz would do but it would whine so you're better off keeping it to >20KHz.
It's linear, for example for to run a 120VAC motor at 6Hz the voltage needs to be reduced to 12VAC.Anyways thank you for educatting me on this matter. Is there a way to calculate V/Hz ratio?
That would do it.And will LM25037 be a suitable choice for this application ?
It's linear, for example for to run a 120VAC motor at 6Hz the voltage needs to be reduced to 12VAC.
That would do it.
Oh and if anyone is getting tired of my old picture, I have a new one I can upload. But before I do that, I would like some comments on it...