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I have the following charging circuit based on the BQ2002 which will charge a NiMH battery using a 5V micro USB cable. I built the circuit already and noticed that the TIP32C is not getting hot and the circuit is not drawing any current, but its able to charge the battery just fine.

The circuit is supposed to turn off when the thermistor gets too hot.

Are there any major connection issues or are my resistor values wrong?

I would like to draw around 550 mA of current.

Thanks in advance

[![enter image description here][1]][1]

Below is the schematic which I updated The circuit is working now but not drawing enough current. How do I deliver more current?

[1]: https://i.stack.imgur.com/i5gRU.pngenter image description here

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  • \$\begingroup\$ Where does your 'VCC' supply come from? Why is your 'USB 5V Input' only connected to the circuit thru a 200k resistor? \$\endgroup\$ – brhans May 17 at 15:52
  • \$\begingroup\$ @brhans the VCC supply comes from the 5V input, am I doing anything wrong? \$\endgroup\$ – AdlietMeyer May 17 at 15:56
  • \$\begingroup\$ You don't show any design specs and tolerances \$\endgroup\$ – Sunnyskyguy EE75 May 17 at 16:19
  • \$\begingroup\$ How does VCC come from the 5V Input when you haven't connected them together? \$\endgroup\$ – brhans May 17 at 16:24
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    \$\begingroup\$ "the circuit is not drawing any current, but its able to charge the battery just fine" - Free energy!!! \$\endgroup\$ – Bruce Abbott May 18 at 7:37
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BQ2002 NiMH Charging Circuit not working

Thank goodness your circuit does not work. Did you read the datasheet for the BQ2002?

The datasheet clearly shows how to connect the controller:

enter image description here

  1. You have no connection from Bat to the NiMH you are charging ....so no voltage sensing.
  2. You have no current limiting or detection in the charge path, so no way to control the charging current.
  3. You give no idea of the cell/pack voltage, but the circuit you show would only work for 1 or 2 cells since the diode drop would be close to 1V and the TIP32C saturation voltage is over 1V.
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  • \$\begingroup\$ Yes, I am only charging 2 Cells. So do I just need to connect all the 'VCC' to the 5V input? to answer '2' do I just add a resistor on the charging path? \$\endgroup\$ – AdlietMeyer May 18 at 3:50
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    \$\begingroup\$ You need a solution for both 1. and 2. Look for applicable schematic on the Internet, there are many. This is barely going to work for two cells. \$\endgroup\$ – Jack Creasey May 18 at 3:57

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