"John S"  wrote in message news:j94dt8$omf$2@dont-email.me...

On 11/5/2011 4:42 PM, DonMack wrote:
>
>
> "John S" wrote in message news:j946kc$a6t$3@dont-email.me...
>
> On 11/5/2011 3:29 PM, DonMack wrote:
>>
>>
>> "Jessica Shaw" wrote in message
>> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>>
>> Hi,
>>
>> I am using HIP4081A to drive an inductive load. I am controlling the
>> HIP chip with a microprocessor using PWM. The power supply of the chip
>> is +12 Volts. The HIP Chip is driving the H bridge made with four
>> NMOSFETS (IRF540N)
>
>> you have a rather large supply. Since you didn't give us the load(motor,
>> inductor, or what?)
>
> Her first sentence is "I am using HIP4081A to drive an inductive load."
>
> Yes but there are generally two types of inductive loads that have
> distinct types of troubleshooting. SMPS and motors both used a similar
> topology but have different purposes. I've never heard of a true
> h-bridge used for SMPS but I suppose it could be used... but then why
> wouldn't she simply say "I'm driving a motor"?

Ah! You mean driving the inductor of a buck converter?

Maybe, but I don't see that as relevant as regards an inductive load.
How are they different?

----------------

http://www.brannonelectronics.com/images/Cross%20Conduction%20Inhibit.pdf
http://www.fairchildsemi.com/an/AN/AN-6003.pdf
http://www.fairchildsemi.com/an/AN/AN-7019.pdf


For a SMPS such as a buck rconverter that uses an active diode(e.g., mosfet) 
you will end up with cross conduction.

http://en.wikipedia.org/wiki/Buck_converter

In the circuit it should be clear that if the diode is replaced with a 
switch and both switches are on then you get a short. With mosfets you'll 
get "shoot-through" or "cross-conduction".

In the SMPS design(or possibly other things) the "switches" are being 
toggled together and so every time they toggle there is a chance of shoot 
through.

In the case of a motor this should never happen since the purpose of the the 
3 extra mosfets is to provide a polarity exchange and not to act as an 
active diode. i.e., only one mosfet will be toggling per pulse instead of 
two. It's not the number of mosfets toggling per se but the configuration 
that allows shoot through.

For a motor the h-bridge is really acting as a single mosfet that limits the 
average current to the motor except when polarity is being reversed(which 
generally doesn't happen very often).  SMPS has a distinctly different 
behavior and generally require two mosfets.

Maybe a better way to put it, which I've already mentioned, is that an 
h-bridge for a motor should have shoot-through only during the change of 
polarity of the motor(again, which doesn&rsquo;t occur very often << 1hz) while 
for many SMPS circuits the shoot-through can occur every pulse of a 
mosfet(which generally run 50khz).

On 11/6/2011 12:20 AM, Jamie wrote:
> Jessica Shaw wrote:
>> Hi,
>>
>> I am using HIP4081A to drive an inductive load. I am controlling the
>> HIP chip with a microprocessor using PWM. The power supply of the chip
>> is +12 Volts. The HIP Chip is driving the H bridge made with four
>> NMOSFETS (IRF540N)
>>
>> HIP chip is driving the NMOSFETS which in turn injecting the current
>> into the load and the voltage is appearing across the load as a
>> sinusodial waveform of frequency 100KHz. The frequency of the PWM
>> signal is 100KHz.
>> The thing is that for example at 10% duty cycle, about 300 volts
>> appeared across the inductor load. I suspect that the 300 volts
>> appears at the source of the M1 transisotr as shown in the attached
>> diagram. This source point is connected to the pin 19 of the HIP chip
>> "BHS". According to the data sheet voltage on BHS should be 80 volts
>> maximum. But in my case it is 300 volts peak to peak. Can this voltage
>> make the HIP chip burnt and the transistors timing goes off?
>>
>> Problems:
>>
>> 1. The transistors get hot after 10 to 20 minutes ( M1 and M4 ).
>> 2. HIP chip also does not work right but it works more than 10 to 20
>> minutes sometimes more than that.
>>
>>
>> Questions:
>> Is the high voltage on the BHS reason of getting the transistors hot?
>> Because the Drain voltage is 12 volts and the source voltage is 300
>> volts when the inductor just started charging up?
>>
>> HIP chip circuit link
>> http://imageshack.us/photo/my-images/705/hip4081acircuitdiagram.png/
>>
>> any suggestions?
>> Note: BH_HIP and BL_HIP are shorted together and AH_HIP and AL_HIP are
>> shorted together.
>>
>>
>>
>> Thanks
>> Jess
> I am having problems reading that schematic, it's too small.
>
> But, I think I have enough of it in my head. It looks like you need to
> use some back EMF diodes on the inductive load to suppress the fly back
> energy that is released when you remove the current.
>
> On the high side this is going to cause you problems due to the fact
> that it places the Mos fets into the linear region and maybe even in the
> off state. You must remember that that the difference between the source
> and gate voltage must exceed the threshold voltage of the Fet Vgs(th).
> If the voltage appearing at the source is higher than your driving
> signal can over come to exceed this threshold, you'll either place the
> mosfet in linear mode, which will make it operate hot if you are pushing
> them. Also, you can damage the Fets.


It has a charge pump to supply the gates of the upper FETs. The diode 
and capacitor in the upper left corner of the schematic serves that 
purpose. A high speed diode should be used there as well.


> P.S.
>
> Use High speed diodes when doing so and place them across the poles of
> the coils, polarized to only conduct on the reverse path.
>
> Jamie

Jessica Shaw wrote:
> Hi,
> 
> I am using  HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)
> 
> HIP chip is driving the NMOSFETS which in turn injecting the current
> into the load and the voltage is appearing across the load as a
> sinusodial waveform of frequency 100KHz. The frequency of the PWM
> signal is 100KHz.
> The thing is that for example at 10% duty cycle, about 300 volts
> appeared across the inductor load. I suspect that the 300 volts
> appears at the source of the M1 transisotr as shown in the attached
> diagram. This source point is connected to the pin 19 of the HIP  chip
> "BHS". According to the data sheet voltage on BHS should be 80 volts
> maximum. But in my case it is 300 volts peak to peak. Can this voltage
> make the HIP chip burnt and the transistors timing goes off?
> 
> Problems:
> 
> 1. The transistors get hot after 10 to 20 minutes ( M1 and M4 ).
> 2. HIP chip also does not work right but it works more than 10 to 20
> minutes sometimes more than that.
> 
> 
> Questions:
> Is the high voltage on the BHS reason of getting the transistors hot?
> Because the Drain voltage is 12 volts and the source voltage is 300
> volts when the inductor just started charging up?
> 
> HIP chip circuit link
> http://imageshack.us/photo/my-images/705/hip4081acircuitdiagram.png/
> 
> any suggestions?
> Note: BH_HIP and BL_HIP are shorted together and AH_HIP and AL_HIP are
> shorted together.
> 
> 
> 
> Thanks
> Jess
I am having problems reading that schematic, it's too small.

  But, I think I have enough of it in my head. It looks like you need to
use some back EMF diodes on the inductive load to suppress the fly back 
energy that is released when you remove the current.

   On the high side this is going to cause you problems due to the fact 
that it places the Mos fets into the linear region and maybe even in the
off state. You must remember that that the difference between the source
and gate voltage must exceed the threshold voltage of the Fet Vgs(th).
   If the voltage appearing at the source is higher than your driving 
signal can over come to exceed this threshold, you'll either place the
mosfet in linear mode, which will make it operate hot if you are pushing
them. Also, you can damage the Fets.


  P.S.

   Use High speed diodes when doing so and place them across the poles of
the coils, polarized to only conduct on the reverse path.

Jamie

On 11/5/2011 4:42 PM, DonMack wrote:
>
>
> "John S" wrote in message news:j946kc$a6t$3@dont-email.me...
>
> On 11/5/2011 3:29 PM, DonMack wrote:
>>
>>
>> "Jessica Shaw" wrote in message
>> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>>
>> Hi,
>>
>> I am using HIP4081A to drive an inductive load. I am controlling the
>> HIP chip with a microprocessor using PWM. The power supply of the chip
>> is +12 Volts. The HIP Chip is driving the H bridge made with four
>> NMOSFETS (IRF540N)
>
>> you have a rather large supply. Since you didn't give us the load(motor,
>> inductor, or what?)
>
> Her first sentence is "I am using HIP4081A to drive an inductive load."
>
> Yes but there are generally two types of inductive loads that have
> distinct types of troubleshooting. SMPS and motors both used a similar
> topology but have different purposes. I've never heard of a true
> h-bridge used for SMPS but I suppose it could be used... but then why
> wouldn't she simply say "I'm driving a motor"?

Ah! You mean driving the inductor of a buck converter?

Maybe, but I don't see that as relevant as regards an inductive load. 
How are they different?

On 11/5/2011 4:45 PM, DonMack wrote:
>
>
> "John S" wrote in message news:j9472t$a6t$4@dont-email.me...
>
> On 11/5/2011 3:29 PM, DonMack wrote:
>>
>>
>> "Jessica Shaw" wrote in message
>> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>>
>> Hi,
>>
>> I am using HIP4081A to drive an inductive load. I am controlling the
>> HIP chip with a microprocessor using PWM. The power supply of the chip
>> is +12 Volts. The HIP Chip is driving the H bridge made with four
>> NMOSFETS (IRF540N)
>>
>> HIP chip is driving the NMOSFETS which in turn injecting the current
>> into the load and the voltage is appearing across the load as a
>> sinusodial waveform of frequency 100KHz. The frequency of the PWM
>> signal is 100KHz.
>> The thing is that for example at 10% duty cycle, about 300 volts
>> appeared across the inductor load. I suspect that the 300 volts
>> appears at the source of the M1 transisotr as shown in the attached
>> diagram. This source point is connected to the pin 19 of the HIP chip
>> "BHS". According to the data sheet voltage on BHS should be 80 volts
>> maximum. But in my case it is 300 volts peak to peak. Can this voltage
>> make the HIP chip burnt and the transistors timing goes off?
>>
>> Problems:
>>
>> 1. The transistors get hot after 10 to 20 minutes ( M1 and M4 ).
>> 2. HIP chip also does not work right but it works more than 10 to 20
>> minutes sometimes more than that.
>>
>>
>> Questions:
>> Is the high voltage on the BHS reason of getting the transistors hot?
>> Because the Drain voltage is 12 volts and the source voltage is 300
>> volts when the inductor just started charging up?
>>
>> HIP chip circuit link
>> http://imageshack.us/photo/my-images/705/hip4081acircuitdiagram.png/
>>
>> any suggestions?
>> Note: BH_HIP and BL_HIP are shorted together and AH_HIP and AL_HIP are
>> shorted together.
>>
>> ----
>>
>> I'm not hip to the hip...
>>
>> Troubleshooting tips:
>>
>> 1. The reason why mosfets get hot is too much current flowing through
>> them. This is either due to cross conduction or to large of a load. Use
>> a low resistive low(e.g., 1M ohm resistor) and see what gets hot.
>
> This is an excellent suggestion as it allows monitoring of the current
> as well as some protection against high current if there is cross
> conduction.
>
> ------------------
>
> There should be no cross conduction if this is for a motor, which is why
> I made the distinction, unless she is used some advanced energy recovery
> methods or active breaking. If there is cross conduction, which is easy
> to measure, then there is definitely some big issue going on.

Maybe I didn't mean cross conduction. What I was thinking was 
shoot-through when I said cross conduction.

"John S"  wrote in message news:j9472t$a6t$4@dont-email.me...

On 11/5/2011 3:29 PM, DonMack wrote:
>
>
> "Jessica Shaw" wrote in message
> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>
> Hi,
>
> I am using HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)
>
> HIP chip is driving the NMOSFETS which in turn injecting the current
> into the load and the voltage is appearing across the load as a
> sinusodial waveform of frequency 100KHz. The frequency of the PWM
> signal is 100KHz.
> The thing is that for example at 10% duty cycle, about 300 volts
> appeared across the inductor load. I suspect that the 300 volts
> appears at the source of the M1 transisotr as shown in the attached
> diagram. This source point is connected to the pin 19 of the HIP chip
> "BHS". According to the data sheet voltage on BHS should be 80 volts
> maximum. But in my case it is 300 volts peak to peak. Can this voltage
> make the HIP chip burnt and the transistors timing goes off?
>
> Problems:
>
> 1. The transistors get hot after 10 to 20 minutes ( M1 and M4 ).
> 2. HIP chip also does not work right but it works more than 10 to 20
> minutes sometimes more than that.
>
>
> Questions:
> Is the high voltage on the BHS reason of getting the transistors hot?
> Because the Drain voltage is 12 volts and the source voltage is 300
> volts when the inductor just started charging up?
>
> HIP chip circuit link
> http://imageshack.us/photo/my-images/705/hip4081acircuitdiagram.png/
>
> any suggestions?
> Note: BH_HIP and BL_HIP are shorted together and AH_HIP and AL_HIP are
> shorted together.
>
> ----
>
> I'm not hip to the hip...
>
> Troubleshooting tips:
>
> 1. The reason why mosfets get hot is too much current flowing through
> them. This is either due to cross conduction or to large of a load. Use
> a low resistive low(e.g., 1M ohm resistor) and see what gets hot.

This is an excellent suggestion as it allows monitoring of the current
as well as some protection against high current if there is cross
conduction.

------------------

There should be no cross conduction if this is for a motor, which is why I 
made the distinction, unless she is used some advanced energy recovery 
methods or active breaking. If there is cross conduction, which is easy to 
measure, then there is definitely some big issue going on. 

"John S"  wrote in message news:j946kc$a6t$3@dont-email.me...

On 11/5/2011 3:29 PM, DonMack wrote:
>
>
> "Jessica Shaw" wrote in message
> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>
> Hi,
>
> I am using HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)

> you have a rather large supply. Since you didn't give us the load(motor,
> inductor, or what?)

Her first sentence is "I am using HIP4081A to drive an inductive load."

Yes but there are generally two types of inductive loads that have distinct 
types of troubleshooting. SMPS and motors both used a similar topology but 
have different purposes. I've never heard of a true h-bridge used for SMPS 
but I suppose it could be used... but then why wouldn't she simply say "I'm 
driving a motor"?

On 11/5/2011 3:29 PM, DonMack wrote:
>
>
> "Jessica Shaw" wrote in message
> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>
> Hi,
>
> I am using HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)
>
> HIP chip is driving the NMOSFETS which in turn injecting the current
> into the load and the voltage is appearing across the load as a
> sinusodial waveform of frequency 100KHz. The frequency of the PWM
> signal is 100KHz.
> The thing is that for example at 10% duty cycle, about 300 volts
> appeared across the inductor load. I suspect that the 300 volts
> appears at the source of the M1 transisotr as shown in the attached
> diagram. This source point is connected to the pin 19 of the HIP chip
> "BHS". According to the data sheet voltage on BHS should be 80 volts
> maximum. But in my case it is 300 volts peak to peak. Can this voltage
> make the HIP chip burnt and the transistors timing goes off?
>
> Problems:
>
> 1. The transistors get hot after 10 to 20 minutes ( M1 and M4 ).
> 2. HIP chip also does not work right but it works more than 10 to 20
> minutes sometimes more than that.
>
>
> Questions:
> Is the high voltage on the BHS reason of getting the transistors hot?
> Because the Drain voltage is 12 volts and the source voltage is 300
> volts when the inductor just started charging up?
>
> HIP chip circuit link
> http://imageshack.us/photo/my-images/705/hip4081acircuitdiagram.png/
>
> any suggestions?
> Note: BH_HIP and BL_HIP are shorted together and AH_HIP and AL_HIP are
> shorted together.
>
> ----
>
> I'm not hip to the hip...
>
> Troubleshooting tips:
>
> 1. The reason why mosfets get hot is too much current flowing through
> them. This is either due to cross conduction or to large of a load. Use
> a low resistive low(e.g., 1M ohm resistor) and see what gets hot.

This is an excellent suggestion as it allows monitoring of the current 
as well as some protection against high current if there is cross 
conduction.

On 11/5/2011 3:29 PM, DonMack wrote:
>
>
> "Jessica Shaw" wrote in message
> news:22d12113-2587-468f-884d-770f00709408@bq8g2000vbb.googlegroups.com...
>
> Hi,
>
> I am using HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)

> you have a rather large supply. Since you didn't give us the load(motor,
> inductor, or what?)

Her first sentence is "I am using HIP4081A to drive an inductive load."

On 11/4/2011 7:14 PM, Jessica Shaw wrote:
> Hi,
>
> I am using  HIP4081A to drive an inductive load. I am controlling the
> HIP chip with a microprocessor using PWM. The power supply of the chip
> is +12 Volts. The HIP Chip is driving the H bridge made with four
> NMOSFETS (IRF540N)
>
> HIP chip is driving the NMOSFETS which in turn injecting the current
> into the load and the voltage is appearing across the load as a
> sinusodial waveform of frequency 100KHz. The frequency of the PWM
> signal is 100KHz.

Are those diodes 1N4002? If so, replace with high speed diodes. And also 
put high speed diodes to the +supply to bypass the FET substrate diodes.