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 . An apparatus for charging a battery, said apparatus comprising 
 a first transistor (T 1 ) with a control input, through which a charging current flows to a battery (B) connected to the first transistor when said battery (B) is being charged; and    a current source (T 3 , T 4 , R 1 , R 2 ) for a control current for said first transistor, said current source being connected to the control input of the first transistor (T 1 ) to supply said control current;    wherein said current source comprises means for adjusting or setting said control current, so that the first transistor is non-conducting or blocked and said charging current flowing into said battery is shut off when a predetermined maximum charging voltage at said battery is reached.    
     
     
         2 . The apparatus as defined in  claim 1 , further comprising a Zener diode (ZD) connected to the control input of the first transistor (T 1 ), said Zener diode having a Zener voltage that is exceeded so that the control current no longer flows from said current source (T 3 , T 4 , R 1 , R 2 ) to the control input of the first transistor (T 1 ) but flows away through the Zener diode (ZD), as soon as said predetermined maximum charging voltage at said battery is reached.  
     
     
         3 . The apparatus as defined in  claim 1 , further comprising a second transistor (T 2 ) connected to said first transistor (T 1 ), and wherein said second transistor keeps said control input of the first transistor (T 1 ) at a potential that is less than the charging voltage of said battery (B) connected to the first transistor (T 1 ) after blocking the first transistor (T 1 ).  
     
     
         4 . The apparatus as defined in  claim 3 , further comprising R/C circuit means (R 4 ,C) for delaying a switching on of the second transistor (T 2 ) and wherein said R/C circuit means is connected to a control input of the second transistor (T 2 ).  
     
     
         5 . The apparatus according to  claim 1 , further comprising a series circuit branch comprising a plurality of diodes (D 1 , D 2 , D 3 ) and said first transistor (T 1 ) connected in series with each other, and wherein said current source (T 3 , T 4 , R 1 , R 2 ) is connected across said series circuit branch so that a voltage drop across said diodes drives said current source (T 3 , T 4 , R 1 , R 2 ).