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Opto - Transistor Pulsing Circuit

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Donaldwfc:
I need help with a pulsing circuit, that takes pulses from an Opto-coupler, and pulses a Power Transistor or MOSFET.

I want to switch on/off the 12 volt power supply, up to 5 amps.

I don't have much experience with this stuff, and I can't quite figure it out, I graciously ask for help from anyone who has more experience!

I have tried 6 circuits already, and the one I am using now is my latest, but it still isn't working properly, it only puts about 2.5 volts across my primary, and the mosfet/heatsink gets hot while running around 1 amp.

I have lots of scavenged components from computer power supplies and stuff like that to work with.

Please help :)

Steve:

--- Quote from: Donaldwfc on August 22, 2010, 03:12:35 am ---I need help with a pulsing circuit, that takes pulses from an Opto-coupler, and pulses a Power Transistor or MOSFET.

I want to switch on/off the 12 volt power supply, up to 5 amps.

I don't have much experience with this stuff, and I can't quite figure it out, I graciously ask for help from anyone who has more experience!

I have tried 6 circuits already, and the one I am using now is my latest, but it still isn't working properly, it only puts about 2.5 volts across my primary, and the mosfet/heatsink gets hot while running around 1 amp.

I have lots of scavenged components from computer power supplies and stuff like that to work with.

Please help :)

--- End quote ---

Do you have the technical specs of that optocoupler?
 
 
 
 

haithar:
(http://jnaudin.free.fr/steorn/images/orbodrivers41.gif)
This circuit has worked fine for me. I don't know what you want to pulse (inductive loads ? resistive .. ?) but you can replace the 4 inductors with your load and use another mosfet if the current you need is higher than rated.
The optocoupler i use i the CNY 70, the resistor values were changed i think, depending on the opto coupler of course.









--- Quote from: Donaldwfc on August 22, 2010, 03:12:35 am ---I have tried 6 circuits already, and the one I am using now is my latest, but it still isn't working properly, it only puts about 2.5 volts across my primary, and the mosfet/heatsink gets hot while running around 1 amp.


--- End quote ---
What's the pulsing frequency? If you have a transformer and the frequency is too low most of the voltage will be at the mosfet (depending on how high the RDSon of the mosfet is), therefore heating up. Can you give more data on mosfet and transformer?
If there is current going through the transformer the switching part seems to work just fine.

Donaldwfc:
I have a PC817 Opto, and about 6 others like it that came from similar places, but I cant read the number or find data sheets for them. Data Sheet is attached.

The Mosfet I am currently using is a 2SK1400A.

And MUR460 Super Fast Diodes.

It's to pulse a VIC, so inductive load. Pulsing Frequency 1 Hz to 20,000 Hz

I am going to take a look for some other transistors to use, I tried using Power Transistors but I couldn't get them to work properly... figuring out the proper resistors and current to them to get enough current through the load...

Donaldwfc:
I just pulled a 40 amp MOSFET off of an old computer power supply, I think this would be good to use since it is over-rated, here is the Data Sheet, comments?

I also found a 12 Amp MOSFET

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