Hi,
Isn't this exactly what you want?
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You say 4..5A but you use 100nF / 22uF capacitors only.
You know it just takes 22us to charge/discharge the 22uF capacitor with 5A by 5V.
I'd expect about 1000uF capacitors in parallel to fast ceramics capacitors.
* Add a freewheeling circuitry to bypass surges to your zener and Mosfet
I doubt that the zener becomes conductive at high printer current. This makes no sense.The load is a thermal printer and it draws high current only when the complete line is black. This is where the zener breaks down.
Exactly. I would recommend 1K and 330nF. It allows fast spikes to go through the supply to the load, but will prevent long-term overvoltages (for example, using a wrong transformer/supply). What's the MOS ON resistance? Maybe with its value and a capacitor, you can calculate a filter these dangerous spikes I mentioned before, with 1K and 330nF it will take about 1,5ms to react, say 2ms. With a 20milli ohms RDSon and a 47uF capacitor (C69) the overvoltage shouldn't be longer than 1ms. A higher RDS will filter the spikes better.
´I was trying different RC combinations. It did finally work for 1K and 2.2uF.
Also tried 1K and 4.7uF and it worked well with that too
Capacitor value any less than 1uF was a issue.
The TVS diode data sheet gives you all necessary information to calculate a continuous input voltage rating of your circuit. 18V is surely beyond the limit.
The bad thing is that it's difficult to protect the diode against this kind of overload, even with a fuse. There's a good chance to damage the diode, resulting either in a complete short, or high leakage currents below the standoff voltage.
TVS diodes must never be used with enduring input above the standoff voltage.
My recommendation:We sure will give the voltage information on manual but the DC Jack used will be standard size and there are good changes that users can plug any random adaptors.
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