Preferred component values for the 4N25 Opto Isolator
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The zip file download date is - 22 / 06 / 2012
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http://www.mediafire.com/?itj2dll96tzy2 -
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To achieve a maximum switching speed of 2857 Hz, the opto isolator has to be driven harder to make sure that the gate turn off voltage falls below + 2 volts.
To test the 4N25 opto isolator performance, you need the following setup.
A power supply voltage fixed at 12 volts for both the diode & the photo transistor.
The diode requires a 270 ohm series resistor & the transistor collector requires a 1K6 Ohm series resistor 1/4 watt.
The diode is driven directly from the output of the 555 timer, similar to an LED.
With the resistor values selected, the maximum photo diode current will be 40mA & the maximum transistor collector current is 7.5mA.
The absolute maximum continuous forward diode current is 60mA with a forward drop of 1.13 volts, taken from the data sheet.
The photo diodes are on for 50% of the time, with a current of 40mA, which means an average current of 20 mA flows continuously.
The diodes are not driven at their maximum ratings.
There are a total of 12 opto isolator circuits used to construct the 6 battery tesla switch.
Only 6 of the opto isolator transistors are turned on at any one time, each one draws 7.5mA.
The 555 timer astable draws a maximum of 40mA with one LED.
The power consumption for the isolated power supply is (7.5mA * 6) + 40 mA = 85mA
The diagram shows 6 photo diodes in series & one series resistor
To calculate the series resistor :
12 volts - ( 6 * 1.13 volts ) = 5.22 Volts
5.22 Volts / 40mA = 130.5 Ohm 1/4 watt
Two series resistors 100R & 33R is sufficient, both are 1/4 watt 1% metal film.
There is a 470K variable resistor in the 555 astable circuit which can be used to adjust the frequency to some extent but its main purpose is to maintain a 50 % duty cycle.
Adjusting this resistor seems to affect the pulse width more than the frequency, so select the right capacitor to set the switching frequency instead.
The smallest capacitor that should be used for the astable circuit is 10nF & this gives a stable switching frequency of 2857 Hz.
The square wave cycle time is 350 micro seconds, the mosfet on time will be ( 175 micro seconds - a dead time of 40 micro seconds ) = 135 micro seconds of on time.
The dead time results in the mosfet not turning on instantly.
At a switching frequency of 2857 Hz, 1/4375 of the mosfet on time has been lost.
There is nothing you can do about the dead time.
If you want to eliminate the reduced power output issue, you have to increase the load current to take into consideration 1/4375 of the mosfet on time has been lost.
Reducing the load resistor by 1/4375 will fix the issue.
You can reduce the switching frequency if required, but a dead time of 40 micro seconds will still exist.
The output voltage from the tesla switch cannot be guaranteed due to the need to reduce the switching frequency considerably when the batteries become charged, thus the dead time will be removed periodically.
You will have to use some kind of switch mode power supply to regulate the output voltage.
Output capacitors & voltage regulators should be used to power sensitive loads.
The mosfets should ideally only be used to drive resistive loads to eliminate any heating effects caused by back EMF.
The 4N25 can be used within a switching frequency range of between, 2857 Hz or less.
Lowering the power consumption of the drive circuits means that smaller batteries can used to build portable free energy devices & there is less instability & stress on the toroid which is used to create the isolated 12 volt supplies. Thats the switching part of the circuit designed & tested, now the construction begins.
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If anyone wants the pcb design or requires a pcb to be made, you can contact me via facebook,
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https://www.facebook.com/media/set/?set=a.234713343271460.55413.100001983889140&type=1 -
- All of the electonic parts are available via
http://www.rapidonline.com/. or
http://www.ebay.co.uk/sch/i.html?_nkw=electronic+componentsThis is a big project & has turned out to be quite expensive as there are quite a large number of parts to buy & make, partly so that the pcbs can be produced properly.
The expensive parts are the high current switches, thick copper braid, lots of mosfets, heatsinks, transistors & batteries.
I am still short of a few items, so I won't have a working circuit until August 2012.
If anyone can donate that would help me build quicker.
Prebuilt PCBs can be purchased in August 2012 for UK customers, so if you are interested, let me know.
Smaller, more compact PCBs will be possible as soon as the practical tests have been completed, to see how much heat the voltage regulators make.
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