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Old 29th September 2012, 03:48 PM   #551
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Anyone expert on the AD637 rms-DC converter? Input in above sim is 1V p-p, output from the chip is 699uV DC. I thought it should be 707mV DC?

I'm just going to have to hook it up in real life. I don't have the necessary patience for these stupid simulators!
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Last edited by dirkwright; 29th September 2012 at 04:09 PM.
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Old 29th September 2012, 04:43 PM   #552
davada is offline davada  Canada
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Originally Posted by dirkwright View Post
The opamps will run just fine on +/-5V, so I guess the rest of it will be OK also. Since a 9V rechargable battery is anything but 9volts, I guess 5V is a good value to shoot for in the oscillator.
Back in Jan this year Dick shipped me his Twin T to use while he was away.
I wanted a bit more headroom form it so I wired two 9V battery clips in series for the pos rail and the same for the neg rail. Not only did I get the headroom I didn't have to change batteries as often.
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Old 29th September 2012, 10:22 PM   #553
vicnic is offline vicnic  Latvia
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Originally Posted by dirkwright View Post
The opamps will run just fine on +/-5V, so I guess the rest of it will be OK also. Since a 9V rechargable battery is anything but 9volts, I guess 5V is a good value to shoot for in the oscillator.
It is one serious problem for to run my oscillators from low voltage: AGC integrator must has at least -7V...-10V on it's output, for to drive Jfet properly. It is possible to reduce this voltage app. two times, but you need make some little changes in schematic. Seems, that simplest way is to connect resistor R15 to the negative supply wire instead of GND.
Victor
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Old 29th September 2012, 11:59 PM   #554
EssB is offline EssB  United Kingdom
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Originally Posted by jackinnj View Post
Here's an equation which describes the VTL LDR behavior --r2 is very high as the errors of a few percent are offsetting. I plugged the datasheet from the VTL5C9 into Eureqa and went to the deli for a sandwich:

Click the image to open in full size.

The lines are quite compressed at the low R end, so the errors exceed 10% as the current approaches 40mA.

Edit == Yes, there are too many parens!
Jackinnj,
I feel like I may have wasted your time a bit. When I got into the original Vactrol spice model I found it was table driven anyway. However spice only does linear interpolation between the data points which can be seen on the test plots, so I converted the model to use your equation.
To borrow your expression, that turned out to be a little above my pay grade, but I learned a few things about spice and now it works fine. It might run a bit slowly but so what. Checking the test plot (now smooth) It looks like you took the points from plot line no.2 on the spec sheet graph.

I've yet to sort out the time constants, they don't look quite right.
Simon.
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Last edited by EssB; 30th September 2012 at 12:02 AM. Reason: crop image
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Old 30th September 2012, 12:55 AM   #555
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Quote:
Originally Posted by vicnic View Post
It is one serious problem for to run my oscillators from low voltage: AGC integrator must has at least -7V...-10V on it's output, for to drive Jfet properly. It is possible to reduce this voltage app. two times, but you need make some little changes in schematic. Seems, that simplest way is to connect resistor R15 to the negative supply wire instead of GND.
Victor
OK, thanks. I'll just leave it alone for now.
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Old 30th September 2012, 11:59 AM   #556
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Quote:
Originally Posted by dirkwright View Post
Anyone expert on the AD637 rms-DC converter? Input in above sim is 1V p-p, output from the chip is 699uV DC. I thought it should be 707mV DC?

I'm just going to have to hook it up in real life. I don't have the necessary patience for these stupid simulators!
It's not instantaneous -- and your averaging capacitor may too large. Try running the sim with an o'scope and watch the buf output increase to the RMS value.
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Old 30th September 2012, 09:32 PM   #557
davada is offline davada  Canada
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Originally Posted by EssB View Post
Jackinnj,
I feel like I may have wasted your time a bit. When I got into the original Vactrol spice model I found it was table driven anyway. However spice only does linear interpolation between the data points which can be seen on the test plots, so I converted the model to use your equation.
To borrow your expression, that turned out to be a little above my pay grade, but I learned a few things about spice and now it works fine. It might run a bit slowly but so what. Checking the test plot (now smooth) It looks like you took the points from plot line no.2 on the spec sheet graph.

I've yet to sort out the time constants, they don't look quite right.
Simon.

Hi Simon,

I haven't looked at these models.
What are they using for an element? Is it R or something else?
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Last edited by davada; 30th September 2012 at 09:33 PM. Reason: Redundant signature
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Old 30th September 2012, 10:19 PM   #558
EssB is offline EssB  United Kingdom
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Hi David,
It's a bunch of behavioural current sources but the core is a simple lookup table with entries for LDR resistance against LED current. If you have LTSpice you can have a look inside Tom Gootee's VTL5C2 model here http://www.fullnet.com/~tomg/VTL5C2.ZIP.
The models do model the response time, not sure if it's accurate.
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Old 30th September 2012, 11:05 PM   #559
davada is offline davada  Canada
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Originally Posted by EssB View Post
Hi David,
It's a bunch of behavioural current sources but the core is a simple lookup table with entries for LDR resistance against LED current. If you have LTSpice you can have a look inside Tom Gootee's VTL5C2 model here http://www.fullnet.com/~tomg/VTL5C2.ZIP.
The models do model the response time, not sure if it's accurate.

Hi Simon,

I don't know if you are aware of this but in LTspice you can use an ordinary resister as a behavioral resistor. I used a resistor to do a lamp model last year and it worked quite well. A resistor might be better suited for an LDR. You can plug jackinnj's formula straight in. That would just leave you with figuring out how to do the time constants.

Cheers,
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Last edited by davada; 30th September 2012 at 11:09 PM.
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Old 1st October 2012, 03:15 PM   #560
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