Schottky Diode Placement Question
03-26-2002, 01:46 PM
#16
Tech Adept
I have a whole paper typed up on Schottkey diodes, problem is its on my work computer, Ill get it tomorrow and put it up.
The correct diode to use is part SD830 which is available at www.diodes.com
One of the over looked parameters, and most important, is the low forward voltage drop of about 0.35V. Tomorrow you will get the more detailed explination.
The correct diode to use is part SD830 which is available at www.diodes.com
One of the over looked parameters, and most important, is the low forward voltage drop of about 0.35V. Tomorrow you will get the more detailed explination.
03-27-2002, 11:47 AM
#17
Tech Elite
Thread Starter
Pat-
Are you sure that it is not the SB530? I have seen these types on a lot of Sponsered Drives Cars. Also the 530 has this improvement over the 830:
For use in Low Voltage, High Frequency Inverters, Free Wheeling, adn Polarity Protection Applications
Thanks
Mike Webb
Are you sure that it is not the SB530? I have seen these types on a lot of Sponsered Drives Cars. Also the 530 has this improvement over the 830:
For use in Low Voltage, High Frequency Inverters, Free Wheeling, adn Polarity Protection Applications
Thanks
Mike Webb
03-27-2002, 01:20 PM
#18
Tech Adept
Mike- I havent got to check that diode out yet, so it may be better, but I do know the SD830 is a good diode and is supplied with many ESC's.
Here is my explination of the Schottkey Diode.
When electricity is flowing to any magnetic device and is cut there is a lag in the circuit because of inductance current will still want to flow. What a diode does is gives the back current a path to dissipate by shorting out the device. A Schottky diode is used because of its low forward voltage drop of arround 0.35V. This low forward voltage drop is important because if the forward voltage drop of the diode is higher than that of the FETs and electricity travels in the path of least resistance the diode will be bypassed and the FETs in the ESC will absorb this back current. Since electric motors act as generators when they are moving but no current is applied the situation is even worse than in a relay. The reason for the external diode is since the current comes from the motor backwards there will be voltage drop along the wires of the ESC, this effectively raises the forward voltage drop of the diode, rendering it less effective. For anyone that cares you can buy the diodes at about $1 a piece the part number is SD830 from www.diodes.inc you have to buy a bunch though. ESC’s generally have this diode built in, but due to size constraints they use a smaller diode (now usually surface mount diodes, usually) and naturally a smaller diode can not handle as much current so is less effective or easier to burn up. Adding a schottky diode to a motor that is connected up to any forward only ESC (including ones that don’t require it) will protect the ESC better. So a schottkey diode isn’t just to improve braking like many people think, that is just a useful side effect of using one.
Here is my explination of the Schottkey Diode.
When electricity is flowing to any magnetic device and is cut there is a lag in the circuit because of inductance current will still want to flow. What a diode does is gives the back current a path to dissipate by shorting out the device. A Schottky diode is used because of its low forward voltage drop of arround 0.35V. This low forward voltage drop is important because if the forward voltage drop of the diode is higher than that of the FETs and electricity travels in the path of least resistance the diode will be bypassed and the FETs in the ESC will absorb this back current. Since electric motors act as generators when they are moving but no current is applied the situation is even worse than in a relay. The reason for the external diode is since the current comes from the motor backwards there will be voltage drop along the wires of the ESC, this effectively raises the forward voltage drop of the diode, rendering it less effective. For anyone that cares you can buy the diodes at about $1 a piece the part number is SD830 from www.diodes.inc you have to buy a bunch though. ESC’s generally have this diode built in, but due to size constraints they use a smaller diode (now usually surface mount diodes, usually) and naturally a smaller diode can not handle as much current so is less effective or easier to burn up. Adding a schottky diode to a motor that is connected up to any forward only ESC (including ones that don’t require it) will protect the ESC better. So a schottkey diode isn’t just to improve braking like many people think, that is just a useful side effect of using one.
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