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**EnvellFen** · 09-09-2012, 08:03 AM

Most serious overvoltage consideration probably assume the neutral mains is grounded via some building grounding system, so the front-end mains input then DC high voltage would have any components like in the example C1, C2A, C2B exceeding their maximum voltage and dialectric puncturing. It has no dedicated protection components at this point in the example, but the rectifier filter/low pass filter capacitors will have dielectric breakdown and punch through at some voltage above their ratings.

After this point in the schematic T1 [transformer] and U2 [optocoupler] are the real protection. They separate/isolate the mains and higher voltage DC on the left from the low voltage on the right for charging the battery. T1 steps the voltage down and provides isolation. U2 sends some sample of what's happening on the low voltage on the right side back to the left higher voltage side - feedback for regulating voltage, maybe current sensing, limiting, possibly no-load standby.

Chip U1 on the bottom left is the power switcher, which uses the feedback mentioned above to probably control duty cycle or pulse width. If you look at the arrows in the optocoupler U2 you can see the direction of the feedback from output back to the high voltage side. Optocouplers are an encapsulated LED emmiter and receiver in which case the spacing/barrier between the two provides isolation. You can build them for greater separations of course. Like when you operate your TV remote control you could say you are opto-isolated ;-).

http://en.wikipedia.org/wiki/Opto-isolator

Not sure all common plug-pack mobile phone chargers have optocouplers. Given its such low power there are probably alternatives.

The danger is somewhat dependent on what other loads are connected into the same circuit and same switchboard [assuming single phase supply]. All the other things connected offer possible diversion points for any spike.

Generally the closer any lightning hit is to the building you're plugged into the greater the possible danger. For some humour will throw in that if you unplugged everything else in your house but kept your mobile phone connected this'd be likely worse than having other stuff plugged in ;-).

09-09-2012, 08:03 AM	#17
EnvellFen Join Date Nov 2005 Posts 507 Senior Member	Most serious overvoltage consideration probably assume the neutral mains is grounded via some building grounding system, so the front-end mains input then DC high voltage would have any components like in the example C1, C2A, C2B exceeding their maximum voltage and dialectric puncturing. It has no dedicated protection components at this point in the example, but the rectifier filter/low pass filter capacitors will have dielectric breakdown and punch through at some voltage above their ratings. After this point in the schematic T1 [transformer] and U2 [optocoupler] are the real protection. They separate/isolate the mains and higher voltage DC on the left from the low voltage on the right for charging the battery. T1 steps the voltage down and provides isolation. U2 sends some sample of what's happening on the low voltage on the right side back to the left higher voltage side - feedback for regulating voltage, maybe current sensing, limiting, possibly no-load standby. Chip U1 on the bottom left is the power switcher, which uses the feedback mentioned above to probably control duty cycle or pulse width. If you look at the arrows in the optocoupler U2 you can see the direction of the feedback from output back to the high voltage side. Optocouplers are an encapsulated LED emmiter and receiver in which case the spacing/barrier between the two provides isolation. You can build them for greater separations of course. Like when you operate your TV remote control you could say you are opto-isolated ;-). http://en.wikipedia.org/wiki/Opto-isolator Not sure all common plug-pack mobile phone chargers have optocouplers. Given its such low power there are probably alternatives. The danger is somewhat dependent on what other loads are connected into the same circuit and same switchboard [assuming single phase supply]. All the other things connected offer possible diversion points for any spike. Generally the closer any lightning hit is to the building you're plugged into the greater the possible danger. For some humour will throw in that if you unplugged everything else in your house but kept your mobile phone connected this'd be likely worse than having other stuff plugged in ;-).
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