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Old 4th March 2012, 12:23 PM   #111
FdW is offline FdW  Netherlands
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Lazybutt,

It has arrived in good nick, Thanks . It looks great, but sadly I am not able to use it until next weekend, there really is no time available

Regards,
Frans.
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Old 10th March 2012, 03:10 AM   #112
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For those who purchased this fantastic device, here are a few useful info from Locky_z:

1- Power voltage:
The specification from Locky_z is 32-40V DC @ 2.5A
There was some concerns raised by one of the GB subscriber that one of the OpAmp : the LM358 is spec'ed at 32V max. The unit has been tested up to more than 40V, without any problem whatsoever, and the OpAmp probably has some safety margin.
=> For those who are concerned, it is preferrable to power the unit @ 32V maximum, or to change the OpAmp for a higher voltage OpAMp such as the LT1013.
This OpAmp only controls the relays and can be changed without any effect on the calibration

2- Leaky capacitors
This week, Locky_Z discovered that a few of his capacitors stock were leaky. The capacitors concerned are the ones in the 100uF@25V position as in the picture below. Faulty ones are blue colored 330uF/25V branded YEELEE. (if yours are from a different model or brand, then you should be fine)
Although all units shipped were tested by Locky_z, and checked by myself prior to shipment, it is still recommended to change these caps as a precautionary measure. Any good quality caps will do, but it is recommended to change to 35V rated ones

All units shipped from now on will be exempt of the issue.

Click the image to open in full size.

Don't hesitate to post here if you have any question or comments. I know Locky_z is reading the thread regularly, and I can also transfer to him in case there are language issues. Surely there are also knowledgeable members here who will be able to help!

Cheers
Fred
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Old 10th March 2012, 08:30 AM   #113
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If the required current for the PSU is 2500mA (Locky_Z indicated earlier 3Amp), then it's easy to buy a power supply: search for 'HP 32V 2500' at ebay and find many new and second hand power supplies for HP Officejets.
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Old 10th March 2012, 09:04 AM   #114
locky_z is offline locky_z  China
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Quote:
Originally Posted by Lazybutt View Post
For those who purchased this fantastic device, here are a few useful info from Locky_z:

1- Power voltage:
The specification from Locky_z is 32-40V DC @ 2.5A
There was some concerns raised by one of the GB subscriber that one of the OpAmp : the LM358 is spec'ed at 32V max. The unit has been tested up to more than 40V, without any problem whatsoever, and the OpAmp probably has some safety margin.
=> For those who are concerned, it is preferrable to power the unit @ 32V maximum, or to change the OpAmp for a higher voltage OpAMp such as the LT1013.
This OpAmp only controls the relays and can be changed without any effect on the calibration


Fred
If you want to replace LM358, you must need single supply OPAMP,such LT1013,
replace LM358 no need re-calibration.


The parameter of OP07 substitute is:
Small input offset voltage
Vicomm between Vee+2 to Vcc-2
Small input bias current.
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Old 10th March 2012, 12:06 PM   #115
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Quote:
Originally Posted by AmpliFire View Post
If the required current for the PSU is 2500mA (Locky_Z indicated earlier 3Amp), then it's easy to buy a power supply: search for 'HP 32V 2500' at ebay and find many new and second hand power supplies for HP Officejets.
Good news for GB subscribers!
Actually the voltage and max current of the PSU is more a function of how far you want to test your devices.... I suppose 3A as originally stated is a kind of maximum the power transistors will take, but 2.5A or even less is perfectly acceptable if you're not going to push the curves very far
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Old 10th March 2012, 01:30 PM   #116
locky_z is offline locky_z  China
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If you have more powerful supply, The CT3 can measure to 5A or more,


Near the Over-CurrentLED, there is a switch position, you can add a button on it.
When you want to test more current curve,you can press the button ,then the protect circuit will disable, As long as the supply current is large enough, it will measure burn until.


The modified HP psu is able to output current of 2.6A~4.5A usually. when the HP psu protect,It will shutdown,you need to re-power it.
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Old 10th March 2012, 02:02 PM   #117
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What is the heatsink size if you use higher current? Also what is the current protectlimit when it starts shutting down?
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Old 11th March 2012, 12:43 AM   #118
locky_z is offline locky_z  China
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I don't know the HP psu current protect limit, I test some that had modified to 38~41V output,The shutdown current from 2.3 to 4.6A.


The CT3 protect circuit is below
Click the image to open in full size.
The current protect limit determined by Rds of PMOS / 2SA970 / 18K / R*
I also adjust R* and make current protect limit >=2.5A, but when temperature increase, The Rds increase,so the current protect limit reduce.


When CT3 not being measuring, only LM317 heat, Q1~Q4 not heat.
You only need a thickness is 4mm, the side length of 40mmx40mm, the length is 12cm of angle aluminum as a heat sink is enough.

Because measure process is fast, If a curve have 100 point, It only need less 3 second then OK, and the current is from low to high,Q1~Q4 work in high-power is less 1 second. So Q1~Q4 is a little warm.
But if you set AD sample to more than 18 times, and set voltage step amplitude is too small, The measure process will long time,Q1~Q4 heat will increase.
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Old 12th March 2012, 05:35 PM   #119
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Hi locky
Tanks for your explanation about current limit
I have one tought about this
Why would one want to test at such hi currents if then when in use the devices are limited by the amount of heath they dissipate

For example (on my F5 TO247) will never be biased so to dissipate more than 50W.
with 25 V rails that would be 2 A.

Can I ask you If you could explain how to set up the formulas for testing VGS of P channels Mosfets
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Old 13th March 2012, 12:25 AM   #120
locky_z is offline locky_z  China
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You can press 'Load condition' and choice 'PMOS Vgs-Id(Fix Vce)' when you want to test PMOS.
Click the image to open in full size.

Combined with the following schematic
Click the image to open in full size.

Because PMOS need negative Vgs,so set Vb is from 0 to -6V,step 0.1V
Constant Vce is -10V mean Vds is -10V.
Because PMOS gate current is tiny,so RB you can choice 6K or 500ohm or 91K
If you select RC=75ohm, The max current is about 400mA
If you select RC=4.5ohm, the max current more 2.5A

The Curve type Define window:
X-Axis define is Vgs=abs(Vbe) ,Y-Axis define is Id=abs(Ic)
Function abs() mean absolute value,
Becasue PMOS Vgs and Id is negative,so their Vgs-Id curve will be in the third quadrant, Use abs() function to change them to first quadrant.
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