Powering an IR2155

[Figbash]

Hello,

I'm having a little trouble understanding how to power an
International Rectifier IR2155 half-bridge self-oscillating MOSFET
driver. The datasheet shows a basic usage model where the device is
powered by the high-voltage to be switched:

http://www.irf.com/product-info/datasheets/data/ir2155.pdf

However, the supply pin has a 15.6V Zener across it, which causes the
supply voltage to drop to 15.6V. So my Vhi clamps to 15.6V, instead
of 80~100V. Obviously defeating the point.

The footnotes on the device max table mentions that it must be powered
by a current source, and I've only seen one example of that using an
LM334Z, which I don't understand.

Any ideas how to supply this thing? FYI: the input voltage I'm trying
to switch is 80~100V DC from a boost converter. I thought about just
using a 555 with a simple mosfet driver, but would like to understand
this odd device's power requirements, just for the sake of curiosity.

Thanks,

Peter

 

[Pimpom]

Figbash wrote:

Hello,

I'm having a little trouble understanding how to power an
International Rectifier IR2155 half-bridge self-oscillating
MOSFET
driver. The datasheet shows a basic usage model where the
device is
powered by the high-voltage to be switched:

http://www.irf.com/product-info/datasheets/data/ir2155.pdf

However, the supply pin has a 15.6V Zener across it, which
causes the
supply voltage to drop to 15.6V. So my Vhi clamps to 15.6V,
instead
of 80~100V. Obviously defeating the point.

It doesn't. Only Vcc, not VB is clamped to 15.6V. VB is
bootstrapped by the diode and the cap between VB and VS and
therefore can rise sufficiently above the output voltage to drive
the high-side MOSFET's gate.

The footnotes on the device max table mentions that it must be
powered
by a current source, and I've only seen one example of that
using an
LM334Z, which I don't understand.

The footnote explains that clearly. The LM334 is a CONSTANT
current device. The IR2155 needs a supply that is essentially
current, not voltage. The combination of high voltage and high
resistance provides that.

Any ideas how to supply this thing? FYI: the input voltage I'm
trying
to switch is 80~100V DC from a boost converter. I thought
about just
using a 555 with a simple mosfet driver, but would like to
understand
this odd device's power requirements, just for the sake of
curiosity.

The basic application circuit "Typical Connection" already shows
how to supply it. (They should really give serial numbers to the
components). The resistor from the high voltage supply to VSS
provides the current supply path. You just have to calculate the
resistance.
The IR2155 consumes up to 5mA. This amount of current should be
available when the supply voltage is at its lowest - 80V in your
case. So the maximum resistance is (80-15.6)V/5mA = 12.88k. A 10k
resistor should be OK. It should be of sufficient wattage to keep
from burning up at the highest exopected supply voltage. I'll
leave it to you to work that out.

 

[Grant]

On Mon, 14 Mar 2011 10:29:39 -0700 (PDT), Figbash <peter.j.torelli@gmail.com> wrote:

Hello,

I'm having a little trouble understanding how to power an
International Rectifier IR2155 half-bridge self-oscillating MOSFET
driver. The datasheet shows a basic usage model where the device is
powered by the high-voltage to be switched:

http://www.irf.com/product-info/datasheets/data/ir2155.pdf

However, the supply pin has a 15.6V Zener across it, which causes the
supply voltage to drop to 15.6V. So my Vhi clamps to 15.6V, instead
of 80~100V. Obviously defeating the point.

Obviously you didn't notice the dropping resistor in the top left corner
of the schematic

Grant.

The footnotes on the device max table mentions that it must be powered
by a current source, and I've only seen one example of that using an
LM334Z, which I don't understand.

Any ideas how to supply this thing? FYI: the input voltage I'm trying
to switch is 80~100V DC from a boost converter. I thought about just
using a 555 with a simple mosfet driver, but would like to understand
this odd device's power requirements, just for the sake of curiosity.

Thanks,

Peter

 

[Jamie]

Figbash wrote:

Hello,

I'm having a little trouble understanding how to power an
International Rectifier IR2155 half-bridge self-oscillating MOSFET
driver. The datasheet shows a basic usage model where the device is
powered by the high-voltage to be switched:

http://www.irf.com/product-info/datasheets/data/ir2155.pdf

However, the supply pin has a 15.6V Zener across it, which causes the
supply voltage to drop to 15.6V. So my Vhi clamps to 15.6V, instead
of 80~100V. Obviously defeating the point.

The footnotes on the device max table mentions that it must be powered
by a current source, and I've only seen one example of that using an
LM334Z, which I don't understand.

Any ideas how to supply this thing? FYI: the input voltage I'm trying
to switch is 80~100V DC from a boost converter. I thought about just
using a 555 with a simple mosfet driver, but would like to understand
this odd device's power requirements, just for the sake of curiosity.

Thanks,

Peter
Yup. The Clamp is for the pump chip itself how ever, it does look like

via the simple schematic there, if you need more than 15 volts between
the source and gate to turn it on fully, putting in a voltage divider
before the clamp that drives the diode needs to be installed, so that
you can get more in the charge pump output might work.


Jamie