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Where, N is the secondary or primary turns ratio and D is the switch duty cycle. The nominal turns ratio for both

secondaries of T2 is 0.13. As the input voltage varies over the course of an AC line cycle, the power controller varies

D to maintain a constant voltage on the secondary supplies. Because the voltages of the secondary outputs are

related by the turns ratios, it is possible to regulate multiple, isolated outputs by monitoring just one of the

secondaries. In this case, the controller regulates the main output by monitoring its own supply winding. The voltage

produced at C32 is approximately 10 V. This voltage is filtered via L4/C33 to further reduce switching noise and

produce the VPWR supply, which drives the transmitter circuitry. The 10 V supply is also applied to the input of linear

regulator U5, which produces a 5 V V

controlling device.

2.5

Power Path Component Requirements

The power converter is designed for worldwide operation and is expected to operate from line voltages ranging from

90-240 V AC. This results in peak voltages approaching 350 V DC, and hence, filter capacitors C30 and C31 must be

rated to accommodate these peak voltages.

In the flyback (Q4 OFF) state, the peak voltage generated on the primary winding of T2 (the collector of Q4), strictly

as a result of the circuit operation, is higher than Vin. This voltage is given as follows:

Vin



Vpk



1 ( D

)

In addition, transformer leakage inductance results in an additional increase, above Vpk, at Q4 turn off. This results in

peak voltages approaching 500 V being possible at the collector of Q4.

Resistor R41 should be a high power rated (≥ 3 W), wire wound resistor that can support the surge requirements of

the system.

Capacitor C29 must be X1 or X2 rated to accommodate the turn on surge, which occurs when power is applied to the

device, as well as surge immunity according to EN 61000-4-5 and EN 50065-2-1. The capacitor used in the high

voltage board design is a 300 V AC Panasonic ECQUG series metalized polyethylene film device, which is rated for

direct across-line application. It accommodates the surge requirements of the specifications mentioned earlier.

L3 should be rated for ≥ 0.2 A of current.

Capacitor C28 must be a Y1-rated safety capacitor. The capacitor used in the high voltage board design is a 4000 V

AC TDK CD series mid-high voltage ceramic device. This device is rated for direct line-ground applications and

accommodates the surge requirements of the previously mentioned specifications.

It is important to note that a bleeder resistor may need to be used, depending on the discharge path for the PLC

coupling capacitor C9. When power is disconnected, this capacitor will still be charged unless it can discharge

through the power supply. In the Cypress high voltage boards, it was tested that the voltage discharges quickly

enough to meet the safety requirements of CENELEC EN60950. However, other power supplies may not discharge

the voltage quickly enough and in that case, a bleeder resistor (> 1 M 0.25 W, working voltage >360 V DC) should

be used.

2 . 5 . 1

P r o t e c t i o n C i r c u i t

Basic protection against line transients is provided by transient suppressor D1. The high voltage boards employ a

Panasonic ZNR type device with a peak surge current capability in excess of 1000 A and a voltage rating of 275 V

AC. This type of device has the advantage of low shunt capacitance, 120 pF in this case, which ensures that it does

not degrade the PLC signal. Protection against catastrophic circuit failure is provided by fuse F1, which is a 2 A, 250

V AC Slow-Blow device. This protection circuit is shown in

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Cypress Powerline Communication Board Design Analysis

power supply for the Cypress PLC device and optionally, an external

Figure 6

Document No. 001-55427 Rev. *E

and the BOM is listed in

Table

Equation 2