Battery charging apparatus

Abstract

The battery charging apparatus is made with small and low-cost components. It includes a first transistor (T 1 ) with a control input through which the charging current flows into a battery (B) and a current source (T 3, T 4, R 1, R 2 ) for a control current flowing to the control input of the first transistor. The current source sets or adjusts the control current so that the first transistor is non-conducting or blocked and the charging current flowing into the battery is shut off when a predetermined maximum charging voltage is reached at the battery.

1 - 5 . (canceled) 
     
     
         6 . An apparatus for charging a battery, comprising:
 a first transistor having a base and a collector, through which a charging current flows to a battery connected to the charging apparatus when the battery is being charged;   an adjusting arrangement having a current source and a Zener diode arrangement, wherein the current source is connected to the base of the first transistor to supply a control current for the first transistor, wherein the Zener diode arrangement is connected to the base of the first transistor, the Zener diode arrangement having a Zener voltage, and wherein the adjusting arrangement is configured to adjust or set the control current, such that the first transistor becomes non-conducting or blocked and the charging current flowing into the battery is interrupted when a predetermined maximum charging voltage at the battery is reached; and   a second transistor having a base, a collector and an emitter, wherein the emitter of the second transistor is connected to the base of the first transistor, wherein the base of the second transistor is connected to the collector of the first transistor, wherein the collector of the second transistor is connected to the current source, and wherein the second transistor is configured to keep the base of the first transistor at a potential that is less than the charging voltage of the battery connected to the charging apparatus after blocking the first transistor such that the base-emitter path of the first transistor is reliably blocked.   
     
     
         7 . The apparatus of  claim 6 , wherein the current source includes a third transistor, a fourth transistor, a first resistor and a second resistor. 
     
     
         8 . The apparatus of  claim 7 , wherein the base of the third transistor is connected to the collector of the fourth transistor and the base of the fourth transistor is connected to the emitter of the third transistor and the emitter of the third transistor and the base of the fourth transistor are connected via a second resistor to the base of the first transistor and the emitter of the fourth transistor is connected to the base of the first transistor. 
     
     
         9 . The apparatus of  claim 6 , wherein the base of the second transistor is connected to the collector of the first transistor via a resistor-capacitor circuit path, having a resistor and a capacitor. 
     
     
         10 . The apparatus of  claim 9 , wherein the resistor-capacitor circuit path is configured to delay a switching on of the second transistor. 
     
     
         11 . The apparatus of  claim 6 , wherein the Zener diode arrangement includes a plurality of Zener diodes being connected in series. 
     
     
         12 . The apparatus of  claim 6 , wherein the battery includes at least one lithium ion battery cell. 
     
     
         13 . The apparatus of  claim 6 , further comprising:
 a series circuit branch having a plurality of diodes and the first transistor connected in series with each other, wherein the current source is connected across the series circuit branch so that a voltage drop across the diodes drives the current source.   
     
     
         14 . The apparatus of  claim 6 , further comprising:
 an R/C circuit arrangement for delaying a switching on of the second transistor, wherein the R/C circuit arrangement is connected to a base of the second transistor; and   a series circuit branch having a plurality of diodes and the first transistor connected in series with each other, wherein the current source is connected across the series circuit branch so that a voltage drop across the diodes drives the current source.   
     
     
         15 . The apparatus of  claim 14 , wherein if the battery voltage at its output terminal is less than a base-emitter voltage of the first transistor, corresponding to the Zener voltage of the Zener diode arrangement, the control current supplied by the current source substantially flows into the base of the first transistor so that it is conducting, and wherein if the battery charging voltage at the output terminal has reached the base-emitter voltage of the first transistor, corresponding to the Zener voltage, the control current supplied by the current source by the Zener diode arrangement substantially flows to ground, so that the first transistor becomes non-conducting and interrupts the charging current to the battery. 
     
     
         16 . The apparatus of  claim 6 , wherein the adjusting arrangement includes a first adjusting transistor and a second adjusting transistor, a base of first adjusting transistor being connected with a collector of the second adjusting transistor, wherein a base of the second adjusting transistor is connected with an emitter of the first adjusting transistor, and wherein an emitter of the second adjusting transistor is connected with the base of the first transistor, wherein the base is the base of the first transistor. 
     
     
         17 . The apparatus of  claim 16 , further comprising:
 an input terminal;   wherein a collector of the first adjusting transistor is connected to the input terminal, wherein a base of the first adjusting transistor is connected by an electrical element to the input terminal, wherein an emitter of the second transistor and the base of the second adjusting transistor are connected via another electrical element to the base of the first transistor.   
     
     
         18 . The apparatus of  claim 16 , further comprising:
 an R/C circuit arrangement for delaying a switching on of the second transistor, wherein the R/C circuit arrangement is connected to a base of the second transistor; and   a series circuit branch having a plurality of diodes and the first transistor connected in series with each other, wherein the current source is connected across the series circuit branch so that a voltage drop across the diodes drives the current source.   
     
     
         19 . The apparatus of  claim 6 , further comprising:
 an R/C circuit arrangement for delaying a switching on of the second transistor, wherein the R/C circuit arrangement is connected to the base of the second transistor so to cause a delayed switching on of the second transistor, wherein the turn-on of the second transistor is delayed, so that the second transistor is blocked and the current source is prevented from being turned off, and so that a higher charging current flows when the charging apparatus is turned on.   
     
     
         20 . The apparatus of  claim 6 , wherein the Zener diode arrangement includes a plurality of Zener diodes connected in series, and wherein the plurality of Zener diodes have negative temperature coefficients so as to compensate for a temperature behavior of the base-emitter voltage of first transistor.