Author Topic: Opto - Transistor Pulsing Circuit  (Read 14553 times)

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Opto - Transistor Pulsing Circuit
« 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 :)

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Re: Opto - Transistor Pulsing Circuit
« Reply #1 on: August 22, 2010, 10:13:04 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 :)

Do you have the technical specs of that optocoupler?
 
 
 
 

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Re: Opto - Transistor Pulsing Circuit
« Reply #2 on: August 22, 2010, 11:25:07 am »

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.








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.

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.

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Re: Opto - Transistor Pulsing Circuit
« Reply #3 on: August 22, 2010, 14:07:32 pm »
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...
« Last Edit: August 22, 2010, 14:58:24 pm by Donaldwfc »

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Re: Opto - Transistor Pulsing Circuit
« Reply #4 on: August 22, 2010, 14:31:37 pm »
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
« Last Edit: August 22, 2010, 14:54:35 pm by Donaldwfc »

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Re: Opto - Transistor Pulsing Circuit
« Reply #5 on: August 22, 2010, 16:11:23 pm »
In which range is the frequency?
Also how do you measure the voltage?
Note that my circuit is inverting if used in that way.
I'd prefer the 12A mosfet, as the Uds is not as high (6V is enough).

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Re: Opto - Transistor Pulsing Circuit
« Reply #6 on: August 22, 2010, 19:16:58 pm »
I'd like to be able to use it in the range of a few hundred hz to 20 khz
i have 12 volts from the power supply
2.4 - 2.8 volts going into the primary
5-6 volts at the cell
also measured at the output of the power supply it was drawing between 2 and 3 amps
the heat sink and transformer started getting hot

also i should mention, i have a diode before the primary and a diode after the primary, so this should take up 2 volts, but i am thinking of removing these (i still have another diode backwards across the primary as required)

This is the step up I am currently using, but i will be making another one sooner or later

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Re: Opto - Transistor Pulsing Circuit
« Reply #7 on: August 22, 2010, 19:38:58 pm »
What do you think of this? ... With the 12 amp MOSFET
Do I need the capacitor in there?