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I need a power supply that would supply about 0.5W with solid efficiency and last for several decades.
I look at a non-isolation source with LinkSwitch-TNZ and I have a few questions.
1. Fusible resistor.
The constructor used a 8,2 Ohm 1W fusible resistor, it has two functions
- protects capacitor C6 and "circuit breaker" from high current when the power supply is switched on
- in the event of a failure, it should act as a fuse and burn out
What's wrong with me?
It seems too big for both dimensions and insurance current.
If you look at the datasheet, the resistor will burn only at a power dissipation at a 16W resistor and size is 100mm x 3,5mm.
Any other more suitable and smaller solutions?
a) use 8.2 ohm SMD 0603 resistor, burn at lower current, the flame that it would bother me
b) use 8.2 ohm SMD 0603 resistor and SMD fuse 70mA, I don't like it, it's two parts
c) anything else?
2. Zero cross detector
Z1 and Z2 pins are configured to provide a lossless (<5 mW) zero
crossing detection (ZCD) circuit
If I understand correctly, ZCD is a separate function block inside the LinkSwitch-TNZ IC and is not required for the IC function.
In other words, if I don't need a ZCD, can I omit the components crossed out in orange?
The FB description is somewhat ambiguous, plus in the DER-874 there are errors in the marking of the components (the figure and the description replace the resistors)
If I come up with the plug in the picture, the resistor divider R5 / R4 should keep the FB at 2V at the output voltage 6V. In DEE
This will only happen if the current to the FB is about 39uA , in DER874 is Resistors R3 (probably thinks R5) and R4 divides the voltage such that
the FB pin is set to 2 V. When the current delivered into this pin exceeds IFB (49 μA), a
low logic level (disable) is generated at the output of the feedback circuit.
If I want an output voltage such as 4V use R5 44.2k R4 320k ?