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Old 11th January 2012, 02:02 PM   #2541
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...There are times were I wish I knew how to use LTSpice..
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Old 12th January 2012, 09:48 PM   #2542
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whats input impedance of sshv2
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Old 12th January 2012, 09:53 PM   #2543
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Should be in the Megs because it uses cascode Mosfets with near zero gate currents.
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Old 14th January 2012, 05:52 PM   #2544
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Default SSHV1 Calculator

Hi all,

After several loops of small corrections, back and forth advises and recommendations from Salas (himself!), I am happy to present the latest version of the calculator for Salas SSHV1.

Most explanations needed are inside the spreadsheet. Ask if you need help.

https://docs.google.com/open?id=0B4R...NkMjExMzY3NTE5

Salas: you may post the link in the first page of the thread...

Fred

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Old 14th January 2012, 05:55 PM   #2545
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Nice. I will upload it in the original SSHV1 post as linked from page#1
You forgot to put your name on the calc by the way.
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Old 14th January 2012, 06:00 PM   #2546
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Default SSHV2 Calculator

...and there's more !

Here is the calculator for SSHV2. I call this "Beta", until the circuit and more specifically calculator have both been extensively tested and gathered feedback.

The SSHV2 circuit is convenient enough that no complicated calculations are required to make a build... but the objective of this spreadsheet was to provide approximate values of resistors for those (like me) that wish to replace trimmers with fixed value resistors. For extreme accuracy, a bit of fine tuning should be necessary anyway....

https://docs.google.com/open?id=0B4R...k1YmYyODI3NDYx

Cheers!

Fred
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Old 14th January 2012, 06:05 PM   #2547
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Quote:
Originally Posted by Salas View Post
You forgot to put your name on the calc by the way.
Ho yes...! I guess I'm too modest
This is a modest contribution anyway, and anyone is free to use and modify

Will include in next update....
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Old 14th January 2012, 06:11 PM   #2548
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I mentioned it, its linked up already. Check it out: Simplistic Mosfet HV Shunt Regs
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Old 14th January 2012, 06:16 PM   #2549
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Quote:
Originally Posted by Lazybutt View Post
...and there's more !

Here is the calculator for SSHV2. I call this "Beta", until the circuit and more specifically calculator have both been extensively tested and gathered feedback.

Cheers!

Fred
Although that one has trimmers for both ICCS and Vout its good to know the dissipation for choosing sinks in each application. A welcome addition. Thanks.
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Old 14th January 2012, 07:05 PM   #2550
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Quote:
Originally Posted by Salas View Post
Although that one has trimmers for both ICCS and Vout
There's one more thing I use it for: trimmers dissipation calculation!

If you're going to use SSHV2 at higher currents (say 60mA or more), you will set the trimmer at a fairly low value (around 15 Ohm for VR4 to get a Vgs of -1.4V and 60mA CCS if my calculation is correct.. * ).

That is "only" 0.05W (or 10% of the trimmer rating), but with a 500R trimmer you're only using 3% of the trimmer resistive element, so theoretically exceeding the trimmer's "practical" rating.

I'm sure most trimmers will survive this treatment, but I've had a bad surprise in the past with a trimmer becoming hot (that was another shunt reg), and worst of all it had a negative tempco (meaning heat => lower resistance => more current => more heat => lower resistance, etc..)

In that case it would be preferable to use a 100R or 200R trimmer depending on the adjustement range desired, and/or to change R3 to a smaller value.

In the end I would suggest changing R3 for a 220 Ohm, and VR4 for a 100 Ohm in the schematic.
That way, the adjustment range would be 25mA to 100mA, and the dissipation would remain within acceptable levels

Fred



* Note: my calculations accuracy is still to be proven, I haven't built SSHV2 yet to verify my formulas work in real life..
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