help regarding the revering the polarity of load using mosfet

[shabeerahmed]

dear friends
kindly help me out to solve the problem which i am facing in my ckt i was using two p channel mosfet to reverse the polarity of load.there was a problem in the ckt which i will go to explain we have design the ckt to used for reverse load polarity but our ckt is using upto 30v hence we are facing the problem in the mosfet because the vgs(th) is between the 2-5v due which its was firing the mosfet can any one sugget the alternative ckt to due the same for any input voltage and appling pwm across the gate terminal thanking you
when we apply the 30v across the source terminal of the mosfet then they mosfet are switching on with any controlling signal across the gate kindly sugget the alternative circuit

 

[crutschow]

We could perhaps suggest an alternate circuit if you would first post the circuit you have.

 

[audioguru]

You need N-channel Mosfets on the lower side. You need P-channel Mosfets on the upper side that are driven with NPN transistors.
Then the N-channel Mosfets turn on and off normally and the NPN transistors turn on the P-channel Mosfets then their gate-source resistors turn them off.

 

[shabeerahmed]

i have attached the circuit so please check this and help me out

 

[shabeerahmed]

kindly look into the schematics and give your idea so i can implement this

 

[shabeerahmed]

i have attached the schematics file so please give your valuable suggetion thanking you

 

[audioguru]

The gate of the P-channel DMP3160 Mosfet must be close to +30V to turn it off and must be from +20V to +25.5V to turn it on.
The gate of the N-channel FDN5630 Mosfet must be close to 0V to turn it off and must be from +6.0V to +10V to turn it on.

I said before to use NPN transistors to drive the gates of the P-channel Mosfets. Use resistors to limit the gate voltage so it is never less than +20V.

 

[shabeerahmed]

can you please give me model ckt or else is there any p channel mosfet part so i can achieve the 30v condition

 

[shabeerahmed]

hi
i have modified the schematics and just have look if there is correction please advice
me

 

[audioguru]

I cannot find the maximum gate-source voltage rating of your newly selected P-channel Mosfet.
Your transistors will cause their gate-source voltage to be 30V which will probably destroy the Mosfets. There must be a resistor in series with the collector and gate to form a voltage divider with R1 and R2 to limit the Vgs voltage to 10V.

The value of R1 and R2 is very low so the current and heating in the BC547 transistors will be very high.

The transistors do not have a series base resistor to limit the current so the signal source or the base might blow up.
I hope you know that the transistors are inverters.

You do not show and do not say what voltage is your signal source so it might not have enough voltage (+6V to +10V) to properly turn on your N-channel Mosfets.

 

[shabeerahmed]

i am using a battery which have voltage 5v to 30v and constant 1A so in need to reverse the polarity of my load by using mosfet as switching device but when my voltage is exceeding the 7.9 voltage at the source terminal the two p channel mosfet are firing on due which my mosfet are buring down so please suggeted me amy best alternate circuit so i can solve this problem because i am new in this field thanking you

 

[shabeerahmed]

my n channel mosfet are ground always so this may act as h-bridge

 

[audioguru]

when my voltage is exceeding the 7.9 voltage at the source terminal the two p channel mosfet are firing on

When an NPN transistor is turned off then the Mosfet connected to it should also turn off.
Since the Mosfet turns on when the supply voltage exceeds 7.9V then the emitter and collector of the NPN transistor is probably connected backwards.

my n channel mosfet are ground always

Is the gate or is the drain pin of the Mosfet at ground? Why?

You never answered my question about the input signal voltages that control the circuit.

Please post the very simple corrected schematic with the Mosfets, NPN transistors and resistors. Show the input signal voltages when the load polarity is one way and show the input signal voltages when the load polarity is the other way.

 

[shabeerahmed]

the detail of circuits
first of all i need to reversed they polarity of load which can be achieve by using h-bridge configuration, in may case this circuit is work till 7v at source terminal and i get 7volts at the drain terminal by applying controlling signal voltage 5
for example
if we apply the pwm to the gate of 5v then i can achived the desired output for any voltage level at source terminal

 

[audioguru]

The Vgs threshold rating of a Mosfet is when it is barely turned on, it is almost turned off.

Since your controlling voltage is 5V then you must use Mosfets that turn on properly with a 5V gate voltage. They are called "logic-level" Mosfets.
Since your supply goes as high as 30V then you must use a circuit that limits the Vgs of the P-channel Mosfets to 10V like a 10V zener diode.

The NPN transistors with a resistor in series with the collector are absolutely needed to prevent the P-channel Mosfets from an over-voltage on their gate. The NPN transistors need a resistor in series with the base to limit the base current. The 1k value of the gate-source resistors on the P-channel Mosfets is much too low.

 

[shabeerahmed]

The Vgs threshold rating of a Mosfet is when it is barely turned on, it is almost turned off.

Since your controlling voltage is 5V then you must use Mosfets that turn on properly with a 5V gate voltage. They are called "logic-level" Mosfets.
Since your supply goes as high as 30V then you must use a circuit that limits the Vgs of the P-channel Mosfets to 10V like a 10V zener diode.

The NPN transistors with a resistor in series with the collector are absolutely needed to prevent the P-channel Mosfets from an over-voltage on their gate. The NPN transistors need a resistor in series with the base to limit the base current. The 1k value of the gate-source resistors on the P-channel Mosfets is much too low.

sir kindly give the image of the module circuit because i am new to this field
thanking you

 

[audioguru]

sir kindly give the image of the module circuit because i am new to this field
thanking you

I don't know what is a "module circuit".

 

[ronv]

H Bridge

They make IC's that are perfect for your application. Google L298 or 754410.
If you want to spend more money on a discrete design something like below might work.
The N Channel Mosfets need to be logic level or they won't turn on so don't use the numbers on the diagram. I just picked some numbers for the simulation.

 

[audioguru]

They make IC's that are perfect for your application.

Sure. But they are not available in his 3rd world country. Him and his teacher are in a different world or different planet from us and do not know about and cannot get modern Western parts. I don't know why they come here.[/quote]