Help regarding H bridges.....

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
Hello everyone,


I have IRF 540 and IRF 9540 MOSFET and i want to drive motors of 24V and 10-12amps, so it require a H-Briges.....
something like this.....so please give your view will this MOSFET il fine...??
 

praondevou

Joined Jul 9, 2011
2,942
Yes they should be ok for that current/voltage. Not more (continuous)

How do you want to drive the p-channel FETs?

I assume you know ho to connect them, right? The two 9540 are the upper MOSFETs, the 540 the lower MOSFETs. At 24V bus voltage you can then not drive the 9540 directly pulling it's gate to ground, maximum Vgs is 20V.

The capacitors you indicated need to be as close as possible to the bridge.
At this current you will also need a good heatsink.
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
Hi again,

I assume you know ho to connect them, right? The two 9540 are the upper MOSFETs, the 540 the lower MOSFETs. At 24V bus voltage you can then not drive the 9540 directly pulling it's gate to ground, maximum Vgs is 20V.
Please about the min gate voltage when Vcc is 12V and 24V respectively for both MOSFET is there any need of pull ups resistance and how much max. current can i draw?..!!
 

Audioguru

Joined Dec 20, 2007
11,249
The gate on the IRF540 needs to be 0V to turn it off and be +10V to +12V to turn it on. A PIC output voltage is too low.

The gate on the IRF9540 needs to be +24V to turn it off and be +12V to +14V to turn it on. A PIC cannot do this.

You need a transistor voltage amplifier for the IRF540 and you need a level converter for the IRF9540.
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
The gate on the IRF9540 needs to be +24V to turn it off and be +12V to +14V to turn it on. A PIC cannot do this.
But if Gate voltage increase from 15V it will burn out( i think)....
and i don't want to add Transistor i am thinking to add 7406/7
 

Audioguru

Joined Dec 20, 2007
11,249
I can't remember if a modern PIC has enough output current to drive extremely old TTL logic.
The 7406 inverts so the PIC logic will need to be changed.

The 7406 and 7407 have open collector outputs so they need output resistors that make voltage dividers (the max allowed gate-source voltage for the Mosfets is 20V).
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
When i was testing single MOSFET ( 9540/540) they were working fine....
But when I completed this above schematic on PCB ...
1. The all gate were connected with 4.7K resistance in series
2. Then the Gate ( with resistance 4.7K) were shorted with cross connection
as shown i fig...

The multimeter was connected in place of motors it was not exceeding than 2-2.1V ...
the MOSFET was also heated upp I am using 12 vcc
 

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Audioguru

Joined Dec 20, 2007
11,249
Why can't you understand that the P-channel Mosfets need to have their gate voltages near the +24V supply voltage?
Why can't you understand that a voltage divider must feed the gates?

In your sketch, the gate of the P-channel Mosfet was 0V when signal B from the PIC went low and was +5V when signal B from the PIC went high.
Your sketch does not show where the source pins of the P-channel Mosfets are so you should draw them connected to the +24V supply.

Then the gate-source voltage is 24V or 19V so the gate-source might be destroyed (the max allowed voltage is 20V) and both P-channel Mosfets were always turned on and were never turned off.
Then when the N-channel Mosfets were turned on there was a dead short of the power supply through the Mosfets which creates a lot of heat.

The N-channel Mosfets should be drawn with their source pins connected to 0V. Then when signal A from the PIC went high the gate-source voltage was only 5V so some Mosfets might turn on a little and other Mosfets will not turn on because they need 10V.

These old Mosfets are guaranteed to turn on very well when their gate-source voltage is 10V. Maybe you should replace the ordinary old IRF540 Mosfet with a more modern logic-level mosfet like an IRL540 that is guaranteed to turn on very well when its gate-source voltage is 4V.
 
I am working on a mosfet H bridge project for a battery powered cart. I am working on the regen part to control charging the batteries. But being forward and reverse and trying to get the polarity correct for the regen no matter the direction is kind of fun. Thanks for your input for the other poster as it helps me also
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
Hi again,

Why can't you understand that the P-channel Mosfets need to have their gate voltages near the +24V supply voltage?
Why can't you understand that a voltage divider must feed the gates?
OK, you are correct the P MOS need supply voltage to turn off...
Please post a schematic for that....
Very strange I thought I had this posted... ? Disappeared.
I will add that snuber circuit also but after complete of H briges...!!
 

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praondevou

Joined Jul 9, 2011
2,942
The 7406 and 7407 have open collector outputs so they need output resistors that make voltage dividers (the max allowed gate-source voltage for the Mosfets is 20V).
Is that what you had in mind?


I will add that snuber circuit also but after complete of H briges...!!
What snubber circuit??

Also, can you please answer the question if you are planning to use high speed PWM? In that case the level shifter from the app note I posted is better suited.
The deadtime shouldn't be a problem in this circuit here but you may consider create an additional one inside the PIC (then you need 4 outputs) or before the 7407 gates.
 

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Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
Hi,
Also, can you please answer the question if you are planning to use high speed PWM? In that case the level shifter from the app note I posted is better suited.
The deadtime shouldn't be a problem in this circuit here but you may consider create an additional one inside the PIC (then you need 4 outputs) or before the 7407 gates.
I want to know according to this circuit i need 4 output from uC.....
can't we work only with two??

if you are planning to use high speed PWM? In that case the level shifter from the app note I posted is better suited.
Yes i think it will be on max speed
 

Audioguru

Joined Dec 20, 2007
11,249
Now you show a schematic with a 12V supply to the Mosfets and two 12V "switches".
What will you use as 12V switches that can be driven from the PIC?

The Mosfets have a high gate-source capacitance and the high value of the 10k resistors will charge and discharge them too slowly for high speed PWM.
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
What will you use as 12V switches that can be driven from the PIC?
It was for testing purpose..

The Mosfets have a high gate-source capacitance and the high value of the 10k resistors will charge and discharge them too slowly for high speed PWM.
You are right and now i am testing H-BRIDGES with this schematic....

What will you use as 12V switches that can be driven from the PIC?
I am thinking to use any voltage amplifiers your opinion will be nice, now i want to use it for 24V supply ...
 

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