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  • RudranandS commented on vIRCking's instructable USB Car Charger3 days ago
    USB Car Charger

    For those who are asking about high heat dissipation or unable to charge device. LM7805 does not magically converts 12v to 5v. It will dissipate the 7v as heat. It rapidly changes it's resistance in while maintaining a fixed ratio of res(7805) : res(load) to Volt(IN)-5v : 5v. For example if input is 12v and load resistance is 5ohm (i.e. 1A load current @ 5v), the ratio of resistance will be (12-5) : 5 -> 7 : 5, thus 7805 will have a resistance of 7ohm when input is 12v and load current is 1A. At 41.6% efficiency a 5W load will appear 12W load to the battery. However it is more preferred than efficient SMPS when the output voltage has to be extremely stable or when energy consumption is low or when energy is cheaper than the IC itself. For those who wish to make a very simple, cheap ...

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    For those who are asking about high heat dissipation or unable to charge device. LM7805 does not magically converts 12v to 5v. It will dissipate the 7v as heat. It rapidly changes it's resistance in while maintaining a fixed ratio of res(7805) : res(load) to Volt(IN)-5v : 5v. For example if input is 12v and load resistance is 5ohm (i.e. 1A load current @ 5v), the ratio of resistance will be (12-5) : 5 -> 7 : 5, thus 7805 will have a resistance of 7ohm when input is 12v and load current is 1A. At 41.6% efficiency a 5W load will appear 12W load to the battery. However it is more preferred than efficient SMPS when the output voltage has to be extremely stable or when energy consumption is low or when energy is cheaper than the IC itself. For those who wish to make a very simple, cheap & efficient SMPS i would suggest them AD84064 ic or more common 34063 ic (w/ 2 more resistors to add than AD84064).https://www.aliexpress.com/item/20PCS-AD84064Q-AD8...https://www.aliexpress.com/w/wholesale-mc34063.htm...

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