H Bridge

[Jonathan Leppert]

I'm designing a high current H-bridge to provide power to a thermoelectric
cooler/heater. I have selected the International Rectifier IR3221 high side
switch along with the suggested MOSFETs to form a low footprint H-bridge.
However, it has some type of provision to start DC motors (its intended
application) in a kind of soft-start mode, variable by some type of PWM. I
really don't need this feature and in fact I'm confused by the explanations
for it in the datasheet. Is there any way to bypass this -- in the example
application circuit and demoboard they have all kinds of extra components
for this feature. If anyone could give me an idea on what exactly this is,
and what I can do with that pin (ss) as far as what it needs for the device
to work properly. All I need is to be able to switch a current source on and
off and to change the polarity with this H-bridge, what would be the
simplest circuit using this device to do that? Is this even the best way to
go about all this?

The data sheet for the IR3221 can be viewed below:

http://www.irf.com/product-info/datasheets/data/ir3221.pdf

Thanks,

Jonathan

 

[Tim Dicus]

I'm designing a high current H-bridge to provide power to a thermoelectric
cooler/heater. I have selected the International Rectifier IR3221 high side
switch along with the suggested MOSFETs to form a low footprint H-bridge.
However, it has some type of provision to start DC motors (its intended
application) in a kind of soft-start mode, variable by some type of PWM. I
really don't need this feature and in fact I'm confused by the explanations
for it in the datasheet. Is there any way to bypass this -- in the example
application circuit and demoboard they have all kinds of extra components
for this feature. If anyone could give me an idea on what exactly this is,
and what I can do with that pin (ss) as far as what it needs for the device
to work properly. All I need is to be able to switch a current source on and
off and to change the polarity with this H-bridge, what would be the
simplest circuit using this device to do that? Is this even the best way to
go about all this?

The data sheet for the IR3221 can be viewed below:

http://www.irf.com/product-info/datasheets/data/ir3221.pdf

Thanks,

Jonathan

Hi Jonathan,

This refers to the schematic of the IRL3221 20A H-Bridge Demoboard on page
10 of the datasheet:

You can delete CP1 (2.2uf cap). It controls the soft start feature. It
really does not need to be removed to disable the soft start, just leave the
"Duty Cycle" line disconnected at the connector.

Hope that helps,

Tim

 

[John Popelish]

I'm designing a high current H-bridge to provide power to a thermoelectric
cooler/heater. I have selected the International Rectifier IR3221 high side
switch along with the suggested MOSFETs to form a low footprint H-bridge.
However, it has some type of provision to start DC motors (its intended
application) in a kind of soft-start mode, variable by some type of PWM. I
really don't need this feature and in fact I'm confused by the explanations
for it in the datasheet. Is there any way to bypass this -- in the example
application circuit and demoboard they have all kinds of extra components
for this feature. If anyone could give me an idea on what exactly this is,
and what I can do with that pin (ss) as far as what it needs for the device
to work properly. All I need is to be able to switch a current source on and
off and to change the polarity with this H-bridge, what would be the
simplest circuit using this device to do that? Is this even the best way to
go about all this?

The data sheet for the IR3221 can be viewed below:

http://www.irf.com/product-info/datasheets/data/ir3221.pdf

Thanks,

Jonathan

The soft start function is programmed by the RC network applied to the
ss pin. You can make it as fast or as slow as you want, including
eliminating that function. If all you need is full heat, full cool
and off, this chip should do it. If you want to PWM regulate the
current, you will need some additional components.

 

[Tim Dicus]

I'm designing a high current H-bridge to provide power to a thermoelectric
cooler/heater. I have selected the International Rectifier IR3221 high side
switch along with the suggested MOSFETs to form a low footprint H-bridge.
However, it has some type of provision to start DC motors (its intended
application) in a kind of soft-start mode, variable by some type of PWM. I
really don't need this feature and in fact I'm confused by the explanations
for it in the datasheet. Is there any way to bypass this -- in the example
application circuit and demoboard they have all kinds of extra components
for this feature. If anyone could give me an idea on what exactly this is,
and what I can do with that pin (ss) as far as what it needs for the device
to work properly. All I need is to be able to switch a current source on and
off and to change the polarity with this H-bridge, what would be the
simplest circuit using this device to do that? Is this even the best way to
go about all this?

The data sheet for the IR3221 can be viewed below:

http://www.irf.com/product-info/datasheets/data/ir3221.pdf

Thanks,

Jonathan

Hi Jonathan,

My first post was a little lacking in information about the soft start
feature. I was called away by business, so I sent what I had already
written. So to continue...

The block diagram on page 1 shows a resistor (R) and a capacitor (C). These
components determine the time constant for the RC circuit and control the
voltage rise time at the SS pin.

The resistor from +Bat to R, and the diode (looks like it should be a 5v
zener in your case), must remain. These limit the SS pin to 5 volts (5.5v
max here!).

The other capacitor(s) from +Bat to 0v is(are) for surge/sag/spike
protection. The diagram on page 10 shows a couple of 2000uf caps and a 100nf
cap in parallel. Inductive devices like motors are really noisy
electrically.

The "Duty Cycle" input on the connector (page 10 again) is is designed to be
controlled by an open-collector device, like a 2N3904 or 2N2222. Otherwise
the soft start won't work. It should pull the line low momentarily only,
then release. The rise time on the RC circuit will control the soft start
sequence from there.

Hope that is more complete.

Tim

 

[Jonathan Leppert]

The resistor from +Bat to R, and the diode (looks like it should be a 5v

zener in your case), must remain. These limit the SS pin to 5 volts (5.5v
max here!).

So to completely bypass the soft start function I just leave these
components connected? No need for the caps/RC network since there will be no
input on the pin to begin with right? Physical space is at a premium so I'm
trying to eliminate as many components and complexity as possible, not to
mention I have to control four separate TE devices.

Sorry, bear with me, software person (trying) to do some hardware, your help
is greatly appreciated.

jon

 

[Tim Dicus]

So to completely bypass the soft start function I just leave these
components connected? No need for the caps/RC network since there will be no
input on the pin to begin with right? Physical space is at a premium so I'm
trying to eliminate as many components and complexity as possible, not to
mention I have to control four separate TE devices.

Sorry, bear with me, software person (trying) to do some hardware, your help
is greatly appreciated.

jon

Hi Jon,

Leave the resistor from +Bat and the 5.1v zener diode connected as it is.
That will produce 5.1 volts at the junction of the two. Connect SS pin to
the junction of the two. In other words, replace R with a wire or trace and
remove capacitor C.

The two large caps may not be needed if your load is resistive rather than
inductive. Leave the 100nf cap and maybe a single 1000uf surge/sag cap.

Tim