5V USB portabe source with 4x AA batteries

[Yossef Gofer]

Dear friends,
I am interested in building a portable USB source (or charger) for gadgets like smartphones, using as input 4 AA alkaline batteries. I looked through many posts in the web, and came up with the following requirements:
1. Since it is not for apple’s iphone there is no need to care for data lines potentials.
2. 4 x AA alkaline cells give approximately 1.56x4 V, and it goes lower. Trying to assemble such a device with 7805 +5V regulator did not do well. The output voltage I got was 4.85V, and charging currents did not exceed 50 mA. I guess the input voltage is not sufficient. However, if possible I’d use different approach sine the efficiency of this kind of device is poor.
3. I disassembled a car charger, a DC-DC down converter rated at 5V 2A, designed around 34063 switching regulator. This did not work well with the ~6.24V. It could not deliver the 200-400 mA, although the indicator led did lit (even with shorted data lines). I have no drawing, nor components values, but it looks very similar to many circuits of the kind. Is it possible to modify the circuit, at least theoretically, to work with ca. 6V input? If so, what is the modification needed?
I guess that serious answers necessitate data, like components values. As I am a very low-level electronics hobbyist, general conceptual answers will not be much of help (sorry!). Thus, I propose to ask for specific components values or so, those that are crucial for the modification, and I’ll de my best to answer.
If anyone has any other nice idea as to how to DIY such a gadget, I will be more than happy to hear,
Thank you all,
Yossef Gofer

 

[kam1787]

You can use a regulator that has a low voltage differential requirement {7805 needs > 2V5 or so, hence Vin needs to be > 7V5}

or just use an IN4001 or higher current rated diode; 6V - V7 = 5V3 which is fine. You do not need exactly 5V. Of course the voltage will drop as the battery voltage drops [as they discharge].

You might look on Instructables, or Google.

 

[tpetar]

Dear friends,
I am interested in building a portable USB source (or charger) for gadgets like smartphones, using as input 4 AA alkaline batteries. I looked through many posts in the web, and came up with the following requirements:
1. Since it is not for apple’s iphone there is no need to care for data lines potentials.
2. 4 x AA alkaline cells give approximately 1.56x4 V, and it goes lower. Trying to assemble such a device with 7805 +5V regulator did not do well. The output voltage I got was 4.85V, and charging currents did not exceed 50 mA. I guess the input voltage is not sufficient. However, if possible I’d use different approach sine the efficiency of this kind of device is poor.
3. I disassembled a car charger, a DC-DC down converter rated at 5V 2A, designed around 34063 switching regulator. This did not work well with the ~6.24V. It could not deliver the 200-400 mA, although the indicator led did lit (even with shorted data lines). I have no drawing, nor components values, but it looks very similar to many circuits of the kind. Is it possible to modify the circuit, at least theoretically, to work with ca. 6V input? If so, what is the modification needed?
I guess that serious answers necessitate data, like components values. As I am a very low-level electronics hobbyist, general conceptual answers will not be much of help (sorry!). Thus, I propose to ask for specific components values or so, those that are crucial for the modification, and I’ll de my best to answer.
If anyone has any other nice idea as to how to DIY such a gadget, I will be more than happy to hear,
Thank you all,
Yossef Gofer

First dont try to charge Li-Po/Li-Ion with high voltage, even 5-6V is to much and dangerous without special controller.

7805 need at least 2,5-3V difference between input and output voltage to operate with 5V on output, plus 7805 is linear regulator which will waste some amount of battery power. This design is very bad.

Use dedicated battery charging IC. Check Microchip, they are very small and cheap. Designs require very few additional parts, usually two caps and one resistor, or something similar, and required PCB area is very small.


Best regards,
Peter

:wink: