DER-9

Generic PCB for DVD Player using TinySwitch-II

February 4, 2004

Page 7 of 26

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4

Circuit Description

4.1

Input EMI Filtering

C1 and C2 are the bulk capacitors. Together with L1 and L2, they form the EMI filter.

TinySwitch-II’s built-in frequency jitter helps achieve low EMI in spite of this very simple

EMI filter.

C18 is an option for a high voltage ceramic capacitor in case a single electrolytic

capacitor is required for the bulk capacitor.

4.2

Primary Clamp Snubber

D5, R1, R2, and C3 form the primary clamp snubber to clamp the voltage spike at the

Drain pin after TinySwitch-II turn-off. D5 is a 1N4007G, a glass-passivated version of the

standard 1N4007, with controlled reverse recovery. Its use, along with R2, improves EMI

and efficiency.

4.3

Output filtering

C6, C8, C10, C12 and C14 are the main output capacitors. C7, C9, C11 and C13, along

with L3, L4, L5 and R8, form second-stage output filters.

4.4

Output Feedback

U2, VR1, and R15 form the voltage feedback network. The 5V output voltage setpoint is

set by the voltage drops of U2, VR1, and R15. The TinySwitch-II unique feedback

scheme, with constant feedback current over line and load changes, means that the

current in the zener does not change, thus the voltage drops in U2, VR1, and R15 do not

change. This yields tight regulation in spite of the circuit’s simplicity and low cost.

4.5

“DC Switch”

J4 is connected to a switch, wherein if it is closed, the 5V output drops to about 1.2V,

because the zener ZR1 is essentially shorted out. All the outputs drop to about 1/5

their normal voltages. During this condition, the load draws very little current. Because

of TinySwitch-II’s EcoSmart operation, it draws very little input power - <200 mW. This

“DC Swtich” can be used in place of a normal “AC Switch” that’s used to disconnect the

AC power. The DC Switch is lower cost because it does not have to be Safety–rated,

and is lower voltage.

4.6

+8V Option

Q1, R4, R5 and R6 form a linear regulator to generate +8V in case of +8V is required.

VR3 is another solution of generating +8V. Yet another option is to use a zener as a

series pass element.

4.7

–22V option

R8 and C13 form a post-stage filter for –22V.