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I am trying to help my daughter with a circuit design for a solar panel battery charger. We need to have a signal that the battery is undercharged. It appears to me that your MC34164 will do this. I am using datasheet MC34164/D November 2001 - Rev. 3 to review the product. I am an engineer but not an electronic engineer, so I have several ;stupid; questions. 1) It appears that if pin 2 of an MC34164-5 is connected to the positive terminal of the battery, and pin 3 is connected to common ground, pin 1 will go to ground when the battery voltage drops to about 4.25V, and it will sink up to about 6mA. Is that correct? I hope so, because that would be great! 2) Figure 15 of the data shows a Voltage Monitor. Does the LED light when the battery is low, or when the battery is high? I think low, but please advise. 3) Please explain how the Solar Powered Battery Charger of Fig. 16 operates. When the battery is low, I presume it turns off the transistor so the current from the solar panel goes to the battery. Is that correct? Also, it appears that the MC34164 prevents overcharging the battery. Is that correct? Do you adjust the overcharge value by changing the external resistor value? If so, approximately what value resistor should be used?

You are correct on items 1 and 2. We will need to review 3 more to be sure. 1A) Pin 1 is pulled to ground when Pin 2 at the battery falls below around 4.25 V, typical. The Sink rating is noted to be around 6.0 mA on Page 1 of the spec. 2A) When the Battery goes low, then the Pin 1 will be pulled low, allowing a completed circuit for the LED to conduct current and turn on. When the battery is high, the LED circuit is open and the LED will not conduct current, therefore it is off. Answered by:
ON Semiconductor
2011-06-15 17:51:48.0