InnoSwitch-CH
The spark gap is best placed between output positive rail and one
of the AC inputs directly. In this configuration a 5 mm spark gap is
often sufficient to meet the creepage and clearance requirements of
many applicable safety standards. This is less than the primary to
secondary spacing because the voltage across spark gap does not
exceed the peak of the AC input.
Shield windings can also be used in conjunction with common
mode filter inductors at input to achieve improved conducted and
radiated EMI margins.
5. Values of components of the RC snubber connected across the
output SR MOSFET can help reduce high frequency radiated and
conducted EMI.
6. A π filter comprising of differential inductors and capacitors can
be used in the input rectifier circuit to reduce low frequency
differential EMI.
7. A 1 mF ceramic capacitor when connected at the output of the
power supply helps to reduce radiated EMI.
Drain Node
The drain switching node is the dominant noise generator. As such
the components connected the drain node should be placed close to
the IC and away from sensitive feedback circuits. The clamp circuit
components should be located physically away from the PRIMARY
BYPASS pin and associated circuit and trace lengths in this circuit
should be minimized.
Recommendations for Audible Noise Suppression
The state machine used in the InnoSwitch-CH IC automatically
adjusts the current limit so as to adjust the operating frequency at
light load. This helps to eliminate audible noise that typically results
from intermittent switching of the power supply at very light loads.
The loop area of the loop comprising of the input rectifier filter
capacitor, the primary winding and the InnoSwitch-CH IC primary-side
MOSFET should be kept as small as possible.
Figure 14 shows a design example for an InnoSwitch-CH IC based
charger design. Considerations provided in this design are marked in
the figure and are listed below:
In case of audible noise from a power supply, following should be
considered as guidelines for audible noise reduction:
1. Ensure that the flyback transformers are dip varnished.
2. Often the source of audible noise are ceramic capacitors. Check
both the bias winding and primary-side clamp capacitors. To find
the source substitute the clamp capacitor with a metalized film
type and the bias with an electrolytic type. By far the most
common source is the bias capacitor.
3. If the noise is generated by the bias winding filter capacitor,
generally, use of a capacitor of higher voltage rating will typically
resolve the issue. If the circuit board layout and any physical
enclosure size constraints, allow, an electrolytic capacitor should
be used instead.
Recommendations for EMI Reduction
1. Appropriate component placement and small loop areas of the
primary and secondary power circuits help minimize radiated and
conducted EMI. Care should be taken to achieve a compact loop
area for these loops.
2. A small capacitor in parallel to the clamp diode on the primary
side can help reduced radiated EMI.
3. A resistor in series with the bias winding helps reduce radiated EMI.
4. Common mode chokes are typically required at the input of the
charger to sufficiently attenuate common mode noise. The same
can be achieved by using shield windings on the transformer.
ꢀꢁꢂꢃꢄꢃꢅe ꢆꢇꢈꢉꢊe ꢁꢉeꢁ
ꢛꢓꢇꢏ ꢈꢐꢍeꢉ ꢙꢐꢐꢇꢛꢘꢃꢏꢊꢎꢢꢚꢪ
ꢏꢇ ꢄꢁꢃꢐꢏꢁꢃꢐ ꢎꢃꢢꢒꢇꢏ
ꢋꢇꢉ ꢌꢇꢇꢍ ꢎeꢁꢏ ꢆꢃꢐꢑꢃꢐꢌ
vꢃꢁ ꢏꢇ ꢒꢁꢆꢆ ꢎeꢁꢏ ꢏꢇ
ꢊꢇꢒꢒeꢉ ꢓꢁꢔꢇꢈꢏ ꢇꢐ
ꢒꢁꢆꢆ ꢃꢋ ꢒꢁꢉꢏ ꢋꢁꢃꢓꢆ
ꢗꢓꢁꢊe ꢋꢇꢉꢘꢁꢉꢍ
ꢫꢕꢇꢁꢉꢍ ꢊꢇꢐꢏꢁꢄꢃꢐꢁꢏꢃꢇꢐꢬ
ꢇꢏꢎeꢉ ꢆꢃꢍe ꢇꢋ ꢕꢇꢁꢉꢍ
ꢗꢓꢁꢊe ꢡꢗꢗ ꢁꢐꢍ ꢡꢗꢛ
ꢖeeꢒ ꢍꢉꢁꢃꢐ ꢁꢐꢍ
ꢊꢓꢁꢄꢒ ꢓꢇꢇꢒ ꢆꢎꢇꢉꢏ
ꢀꢁꢂꢃꢄꢃꢅe ꢍꢉꢁꢃꢐ
ꢁꢉeꢁ ꢇꢋ ꢛR ꢜꢝꢞ ꢋꢇꢉ
ꢌꢇꢇꢍ ꢎeꢁꢏ ꢆꢃꢐꢑꢃꢐꢌ
ꢁꢐꢍ ꢋeeꢍꢕꢁꢊꢑ
ꢆeꢐꢆe ꢉeꢆꢃꢆꢏꢇꢉꢆ
ꢐeꢁꢉ ꢏꢎe ꢙꢚ
ꢊꢁꢒꢁꢊꢃꢏꢇꢉꢆ ꢐeꢁꢉ ꢏꢎe ꢙꢚ
ꢭ ꢄꢄ
ꢖeeꢒ ꢛR ꢜꢝꢞ
ꢁꢐꢍ ꢇꢈꢏꢒꢈꢏ ꢊꢁꢒꢁꢊꢃꢏꢇꢉ
ꢏꢉꢁꢊeꢆ ꢆꢎꢇꢉꢏ
ꢣ.ꢣ ꢄꢄ ꢆꢒꢁꢉꢑ ꢌꢁꢒ ꢤꢥ.ꢦ ꢄꢄ ꢋꢇꢉ
ꢣ000 ꢄ ꢁꢓꢏꢃꢏꢈꢍe ꢊꢇꢄꢒꢓꢃꢁꢐꢏ ꢍeꢆꢃꢌꢐꢧ
ꢗꢓꢁꢊe ꢆꢓꢇꢏꢆ ꢕeꢏꢘeeꢐ ꢒꢉꢃꢄꢁꢉꢔ ꢁꢐꢍ
ꢆeꢊꢇꢐꢍꢁꢉꢔ ꢊꢇꢄꢒꢇꢐeꢐꢏꢆ ꢋꢇꢉ ꢝꢛꢨ
ꢃꢄꢄꢈꢐꢃꢅꢁꢏꢃꢇꢐ ꢩ ꢐꢇ ꢁꢉꢊꢃꢐꢌ ꢏꢇ
ꢙꢐꢐꢇꢛꢘꢃꢏꢊꢎꢢꢚꢪ ꢒꢃꢐꢆ
ꢟꢒꢏꢃꢇꢐꢁꢓ ꢠ ꢊꢁꢒꢁꢊꢃꢏꢇꢉ ꢊꢇꢐꢐeꢊꢏꢃꢇꢐ ꢏꢇ ꢏꢎe ꢒꢓꢈꢆ
ꢡꢈꢓꢑ ꢉꢁꢃꢓ ꢇꢐ ꢏꢎe ꢒꢉꢃꢄꢁꢉꢔꢢꢆꢃꢍe ꢋꢇꢉ ꢆꢈꢉꢌe ꢒꢉꢇꢏeꢊꢏꢃꢇꢐ
ꢗꢙꢢ7ꢦꢮꢭꢢ10ꢮꢥ1ꢣ
Figure 20. PCB Layout Guidelines. Bottom (Left Side), Top (Right Side).
13
Rev. J 10/17
www.power.com
POWERINT [ Power Integrations ]
