If you want more control you can use a LM317 as a current source.Note: The USB port available on some power supply units is only for charging other devices while your Surface is charging and can’t be used to transfer data.įor info on how to properly care for the power cord and power supply, see Clean and care for your Surface. You can also use a 12V car headlight in seruies with the battery. In practice this will be not exact what happens because the battery will start around 7V so at the start more current will flow. 3V x 0.1A = 0.3W so take a 0.5 or 1W resistor. Your battery is 9V so you have 12-9=3V over. If your adapter is 12V and capable to deliver 100 mA then you need to select a current limitting resistor. You can charge it witth 1000 mA but then it will be charged in one houre and if you do not stop on time it can explode or get very very hot. So if it is a 1000 mAh battery, you can charge it save with 100 mA. If it is a nimh or nicd you need to look the capacity of the battery and limmit the charge current to 1/10th of that capacitie. What type of rechargable 9V battery you try to charge ? Here is the Fairchild datasheet for the MC34063A:Īnd here is the Texas Instruments datasheet for the MC34063A: Using a higher frequency would allow using a smaller-value (and probably smaller size and cheaper) inductor. You can play with the values above and see how they affect the component values that result. Here is a web-based tool that will give you the schematic and will calculate the component values, automatically:Ĥ) Vripple = the peak-to-peak output voltage ripple that you can tolerateĥ) Fmin = the desired switching frequency (up to 100 kHz). It is usually done with a "switch-mode power supply" (smps) circuit.Įdit: OK, you can raise 5 Volts to 9 Volts very, very easily, using the MC34063A chip, if you don't need more than about 300 mA of current. (You will probably also need to have a resistor in between the charger and the battery, to limit the current to a level that is safe for the battery.)įor methods and circuits to raise the supply voltage, from 5 Volts to about 9 Volts, do a search for "boost converter" or "boost mode" smps. To be able to do that, you would need a circuit to raise the supply voltage to at least as high as the desired battery voltage. In this case, you are wanting to charge a higher-voltage battery from a lower-voltage supply. There are also dedicated battery-charging circuits, with features such as automatically stopping charging when the battery is fully charged, and contouring the voltage and current levels during charging. You will need to know what voltage the battery should be charged from (it is always a little higher than the desired final battery voltage), and what the ideal charging current might be. Usually, you would also need to limit the current flowing into the battery, during charging, so the battery wouldn't get too hot, so it wouldn't be damaged or explode. In order to charge a battery, the charging voltage must be at least as high as the desired battery voltage, and not too much higher. Re: How to charge a 9 volt from a 5 volt supply
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