can i replace SCR with mosfet (IRF840) ?
How do protect mosfet for back emf ?

 

This is very much on topic for All About Circuits, so I moved it to an appropriate forum.

 

You can replace an SCR with a MOSFET only if you have rectangular triggering--unfortunately, rectangular triggering is not common--it is generally single pulse or pulse train.

On the schematic provided, it appears that the gate pulse will be too short--to use the MOSFET, you must first determine the ring frequency of the resonant circuit and make sure that the 555 outputs a long enough pulse to run for >½cycle--it also appears that the 555 is wired wrong for astable operation--top of lower 270Ω resistor should connect to pin 7, rather than +12V.

A series rectifier protects against reverse voltage--this is a common arrangement--for best performance, use fast recovery rectifiers

My suggestion: Use the SCR--they will work well for the application and do not have the complications introduced with the MOSFET..

 

You can replace an SCR with a MOSFET only if you have rectangular triggering--unfortunately, rectangular triggering is not common--it is generally single pulse or pulse train.

On the schematic provided, it appears that the gate pulse will be too short--to use the MOSFET, you must first determine the ring frequency of the resonant circuit and make sure that the 555 outputs a long enough pulse to run for >½cycle--it also appears that the 555 is wired wrong for astable operation--top of lower 270Ω resistor should connect to pin 7, rather than +12V.

A series rectifier protects against reverse voltage--this is a common arrangement--for best performance, use fast recovery rectifiers

My suggestion: Use the SCR--they will work well for the application and do not have the complications introduced with the MOSFET..

hi . firstly, sorry for poor english .
my bridge diode is blow up(perhaps high current flowing in diode) and scr is latch up and do not turn off .
circuit need resistor ?whats resistor is helpful ? whats location of resistor?
replace switching section of circuit is need?
totem-poll ? or push-pull?

 

Ignition coil?

What is this circuit, as in what does it do?

Have you read our Terms of Service?

 

Ignition coil?

What is this circuit, as in what does it do?

Have you read our Terms of Service?

yes! but this circuit for other use(study HV)