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Old 16th February 2014, 01:32 PM   #21
euro21 is online now euro21  Hungary
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This is my revised version.
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Old 16th February 2014, 02:26 PM   #22
euro21 is online now euro21  Hungary
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Sorry I forgot the picture.
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Old 16th February 2014, 02:48 PM   #23
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Circuit is looking good. As has been mentioned earlier, keep the gate stopper resistors close to the MOSFET as you have drawn the schematic.

My recommendation is to have the zener protection diodes connected directly between the source and gate terminals. Move the anode of the zener diode to the junction between the gate of the MOSFET and the gate stopper resistor.

Reason is if you are probing around in the circuit while energized and connect your meter lead to the gate of the MOSFET the lead capacitance is enough to create a voltage spike across the gate stopper resistor that can blow the gate of the MOSFET.

The reason I mention this is I've blown up a few CCS's before realizing this detail. The higher the operating voltage the better the chance of letting out some of the magic smoke in the MOSFET if the protection zener is configured as shown in your latest drawing.
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Old 16th February 2014, 03:33 PM   #24
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Originally Posted by Gary P View Post
My recommendation is to have the zener protection diodes connected directly between the source and gate terminals. Move the anode of the zener diode to the junction between the gate of the MOSFET and the gate stopper resistor.
Reverse leakage current for these Onsemi zenners seem to be too small to affect MOSFETs, so its OK.

For testing purpose I would recommend to build separate pads with hole D ~ 1 - 1.2 mm. It's much convenient then touching component's leads, and prevents probe slipping.
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Old 16th February 2014, 03:54 PM   #25
ctaudio is offline ctaudio  United States
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I'd suggest placing R5 at a location that is easy to probe. It makes setting and checking the current more convenient.
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Old 16th February 2014, 05:31 PM   #26
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Hi, sulcorebutia,

1) Do you plan to include multi-turn trim pot on the CSS add-on board?

2) What is approximate date of final product shipping?
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Old 16th February 2014, 06:01 PM   #27
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Originally Posted by LinuksGuru View Post
Hi, sulcorebutia,

1) Do you plan to include multi-turn trim pot on the CSS add-on board?

2) What is approximate date of final product shipping?
1) Yes
2) No nothing confirmed yet.


Do you happen to know any free software that make/draw PCB layout? If I don't provide the PCB layout, the producer will use his own way to make the PCB and possibly will also ignore our concern like, heat dissipation pad or shortest distance between stopping resistor and mosfet etc.
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Old 16th February 2014, 06:03 PM   #28
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Originally Posted by Gary P View Post
Circuit is looking good. As has been mentioned earlier, keep the gate stopper resistors close to the MOSFET as you have drawn the schematic.

My recommendation is to have the zener protection diodes connected directly between the source and gate terminals. Move the anode of the zener diode to the junction between the gate of the MOSFET and the gate stopper resistor.

Reason is if you are probing around in the circuit while energized and connect your meter lead to the gate of the MOSFET the lead capacitance is enough to create a voltage spike across the gate stopper resistor that can blow the gate of the MOSFET.

The reason I mention this is I've blown up a few CCS's before realizing this detail. The higher the operating voltage the better the chance of letting out some of the magic smoke in the MOSFET if the protection zener is configured as shown in your latest drawing.
Gary, thanks for your input. Your experience is extremely vital to this project!!
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Old 16th February 2014, 06:04 PM   #29
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Sorry I forgot the picture.
Thank you euro21!
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Old 16th February 2014, 06:38 PM   #30
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Originally Posted by sulcorebutia View Post
Do you happen to know any free software that make/draw PCB layout? If I don't provide the PCB layout, the producer will use his own way to make the PCB and possibly will also ignore our concern like, heat dissipation pad or shortest distance between stopping resistor and mosfet etc.
For the beginning, you can use Eagle Freeware Edition
https://www.cadsoftusa.com/download-eagle/freeware/

Board size will be limited to 100 x 80 mm (4 x 3.2 inches), and 2 layers, that's enough for this project.

You may also try freeware open source KiCAD which is much more powerful then free version of Eagle, but I don't know how mature it is.

KiCad EDA Software Suite - Kicad EDA - KiCad EDA
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