[SOLVED] help needed to cut-off Battery Power Supply to device while battery is charging

Dear All,

I have used the following circuit to charge my 3.6v, 1500mAh NiMH (3 AA cells in series) battery. I have to cut-off battery power supply to the device while the battery is charging. Because, I have to give power supply around 7 volts to charge the battery (3 cells x 1.5v + 3v). If I connect the AC/DC power supply to the battery, this power also goes to the device and the device could have fried. So, I need to cut-off power supply to the device from Battery while the battery is being charged. Also, I cannot use any charger IC bcoz of budget. Can anyone help me solve the issue pl?

thanks
pmk

What resources do you have it terms of components? If you haven't, then it's all a budget question.

hahaha! Not a budget question. I don't like to use ICs not only for cash budget but also current budget. If we use ICs it consumes unnecessary quotient current. Thats why I hesitate to use ICs. I have to run PIC MCU, Wireless Receiver and Wireless Transmitter in my device and entire unit is run by 3.6v, 1500mAh NiMH battery. If I don't charge the battery there will not be a problem to run the device from battery. If I am charging the battery I have to use 9v AC/DC adopter and that voltage also directly goes into device and the device will be fried. Thats why I need to cut-off the power from battery while charging. Can I do that without ICs?

thanks
pmk

Will the battery always be connected as in your drawing or is the battery moved around between charger and to whatever device it's supposed to run?

Yes. Battery always connected to the device and if battery low we can charge the battery using battery charger. Battery cannot be moved.

thanks
pmk

I wonder about the three terminal plug. When you connect the adapter into it, is the third terminal connected or not. It's just a mechanical switch and would be great if possible to use.

why can't you used regulator after the battery?

If we use ICs it consumes unnecessary quotient current in idle conditions. Thats why, I hesitate to use regulators/ICs in my circuit. Anyway, I found that we can connect the device directly to the battery even if battery is being charged. Because, even the 9v AC/DC supply connected to Battery for charging, there is no 9v arrived at battery and only current flows into battery and also found that only small amount of voltage increase at Battery terminal. For example, If I connect 9v AC/DC adopter to 3.6v, 1500mAh battery for charging, I found the voltage at battery is around only 4.3v. So, no need to worry about connecting 5v device to Battery directly. For your information, I used constant current charging to charge my battery. Thanks to you all for your help provided.

thanks
pmk