Power supply circuit
First Claim
1. A power supply circuit for charging a battery comprising:
- a first series circuit comprising a primary winding of a transformer, a first transistor, a first resistor and a second series circuit comprising a secondary winding of the transformer and a first rectifier diode, said second series circuit having connection terminals for connection to the battery, a positive feedback network including a first capacitor connected between a junction of the secondary winding and the first rectifier diode and a base of the first transistor, a second transistor coupled to the first resistor and the first transistor for turning off the first transistor, a switching amplifier coupled between the connection terminals for the battery for turning on the second transistor above a first value of the battery voltage and for turning off the second transistor below a second value of the battery voltage, the second battery voltage value being less than the first value, said switching amplifier having a first input, a second input and an output, means coupling said first input to a tap on a voltage divider, a switch coupling the voltage divider between the connection terminals for the battery during periods when the first transistor is turned off, means coupling said second input to the connection terminal of the battery facing the first rectifier diode, means coupling said switching amplifier output to a base of the second transistor, and means coupling the first input of the switching amplifier by means of a second rectifier diode to the junction of the secondary winding and the first rectifier diode with the forward direction of the second rectifier diode, as seen from said junction, being the same as that of the first rectifier diode.
1 Assignment
0 Petitions
Accused Products
Abstract
A self-oscillating power supply circuit for charging a battery in which energy is stored in a transformer (Tr) during the so-called forward intervals. This energy is applied as a charge current to the battery (6) during the flyback intervals. To prevent overcharge of the battery, the circuit includes a battery voltage protection circuit (10) receiving its power supply from the battery. A fraction of the battery voltage is applied to this circuit by means of a voltage divider (R3, R4) connected across the battery by means of a switch (S1) during the flyback intervals. To prevent the voltage drop across the internal resistance of the battery from influencing the measurement of the battery voltage, the battery voltage is measured after the end of a flyback interval and before the commencment of the next forward interval. This is achieved by short-circuiting the inputs (11, 12) of the protection circuit (10) by means of two diodes (D1, D2) during the flyback intervals.
19 Citations
16 Claims
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1. A power supply circuit for charging a battery comprising:
- a first series circuit comprising a primary winding of a transformer, a first transistor, a first resistor and a second series circuit comprising a secondary winding of the transformer and a first rectifier diode, said second series circuit having connection terminals for connection to the battery, a positive feedback network including a first capacitor connected between a junction of the secondary winding and the first rectifier diode and a base of the first transistor, a second transistor coupled to the first resistor and the first transistor for turning off the first transistor, a switching amplifier coupled between the connection terminals for the battery for turning on the second transistor above a first value of the battery voltage and for turning off the second transistor below a second value of the battery voltage, the second battery voltage value being less than the first value, said switching amplifier having a first input, a second input and an output, means coupling said first input to a tap on a voltage divider, a switch coupling the voltage divider between the connection terminals for the battery during periods when the first transistor is turned off, means coupling said second input to the connection terminal of the battery facing the first rectifier diode, means coupling said switching amplifier output to a base of the second transistor, and means coupling the first input of the switching amplifier by means of a second rectifier diode to the junction of the secondary winding and the first rectifier diode with the forward direction of the second rectifier diode, as seen from said junction, being the same as that of the first rectifier diode.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A shaver comprising:
- a motor connected via a switching device to a pair of connection terminals for a battery, and a power supply circuit coupled to the connection terminals for charging a battery when connected to the connection terminals, said power supply circuit comprising, a first series circuit including a primary winding of a transformer, a first transistor, said pair of connection terminals and a first resistor, a second series circuit including a secondary winding of the transformer and a first diode coupled to the connection terminals, a positive feedback network including a first capacitor connected between a junction of the secondary winding and the first diode and a base of the first transistor, a second transistor coupled to the first resistor and to the first transistor for turning off the first transistor, a switching amplifier coupled to the connection terminals for turning on the second transistor above a first value of the battery voltage and for turning off the second transistor below a second lower value of the battery voltage, a switch coupling a first input of the switching amplifier to a first of said connection terminals during periods when the first transistor is turned off, means coupling an output of the switching amplifier to a base of the second transistor to turn the second transistor on and off at the first and second values, respectively, of the battery voltage, and a second diode coupling said first input of the switching amplifier to the junction of the secondary winding and the first diode with the first and second diodes polarized in the same direction relative to said junction.
Specification