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REPLACEMENT of BJT by MOSFET

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bmodi700

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Hello all,
I have 2 transistor in my circuit (dc to ac converter)

1)TIP41A(npn)
2)TIP42A(pnp)

i want to replace this by N-mos and P-mos
which MOSFET i can use??
waiting reply
 

peeyushsigma said:
can you post the schematic of the circuit..
Click to expand...
here is the schematic ..i want to use mosfet instead of transistor Q1 and Q2..
555dcac.gif
 

It is a horrible square-wave inverter with many voltage losses and very low output power.

With a 6V supply, the output of the 555 swings from about 0.2V to 4.6V when it has low output current.
The TIP41 and TIP42 each need a base-emitter voltage that is 0.7V.
Then the output voltage swing is from about 0.9V to 3.9V which is 3.0V peak to peak.

When the load power is 0.4W then the output swing of the 555 is from 1.5V to 4.4V and the base-emitter voltage for each transistor is 0.9V then the output swing is from 2.8V to 3.5V which is only 0.7V.
The voltage regulation is awful since it changes from 3V p-p to 0.7V p-p with a weak little load connected.

Ordinary Mosfets need up to 10V gate-source voltage EACH then the 555 cannot drive them.
 
Audioguru said:
It is a horrible square-wave inverter with many voltage losses and very low output power.

With a 6V supply, the output of the 555 swings from about 0.2V to 4.6V when it has low output current.
The TIP41 and TIP42 each need a base-emitter voltage that is 0.7V.
Then the output voltage swing is from about 0.9V to 3.9V which is 3.0V peak to peak.

When the load power is 0.4W then the output swing of the 555 is from 1.5V to 4.4V and the base-emitter voltage for each transistor is 0.9V then the output swing is from 2.8V to 3.5V which is only 0.7V.
The voltage regulation is awful since it changes from 3V p-p to 0.7V p-p with a weak little load connected.

Ordinary Mosfets need up to 10V gate-source voltage EACH then the 555 cannot drive them.
Click to expand...


SO can you suggest me any other circuit ?
 

here is the schematic ..i want to use mosfet instead of transistor Q1 and Q2..
Click to expand...
Hi
If you use mosfet , you have to use totem pole to drive it in a right condition so using BJT is unavoidable .
It is a horrible square-wave inverter with many voltage losses and very low output power.
Click to expand...
Hit to the point !
SO can you suggest me any other circuit ?
Click to expand...
Yes there are many other ways for this purpose . perhaps using a push pull converter based on SG3526 ( if you are looking for square wave of course )

Best Wishes
Goldsmith
 

simple-100W-inverter-circuit.png555dcac.gif

guys which one is better...555 one or CD4047???
my ultimate aim is to to glow 20w CFL bulb...
i also don't want to glow it by full intensity
so which one i can use of better result???

-waiting for reply
 

4047 definitively. It gives exact 50% duty cycle while 555 is not.
 
The Mickey Mouse square-wave inverter circuit with the CD4047 has "shoot-through" where both Mosfets are turned on for a moment each time they switch and short-circuit the 12V with a very high current spike.
 
Audioguru said:
The Mickey Mouse square-wave inverter circuit with the CD4047 has "shoot-through" where both Mosfets are turned on for a moment each time they switch and short-circuit the 12V with a very high current spike.
Click to expand...

Actually though a 'shoot-thru' situation might exist, i don't think it'll be catastrophic in this circuit since the transformer T1 is in the path and the MOSFETs aren't actually connected in series across the supply but rather in parallel.

The critical factors in this circuit is the design/ specs of the transformer ... i.e. the primary inductance & saturation currents , and the frequency of operation. Nothing has been said about these, yet they are the most critical for proper operation.

And of course - there is NO mention of regulation/ feedback/ control etc etc.
 
Last edited:
use this ckt sg3525 based pwm inverter. o/p diodes can be omitted
 

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