U.S. Philips Corporation

Joseph A Plagge

Johannes E Algra

Jouw Van Der Akker

A self-oscillating power supply circuit comprises a series arrangement of the primary winding (N.sub.1) of a transformer (TR), the main current path of a first semiconductor switch (T.sub.1) and a current measuring resistor (R.sub.1). The first semiconductor switch is driven by a second semiconductor switch (T.sub.2) which in turn is controlled by a comparator (CP). The voltage across the current measuring resistor is applied to the non-inverting input (6) of the comparator and, a reference voltage obtained from a reference voltage source (RS) is applied to the comparator inverting input (5). By arranging a capacitor (C.sub.2) between the output of the second semiconductor switch and the inverting input (5) of the comparator, the first semiconductor switch rapidly turns-off at the end of the forward phase at an accurately determined current through the primary winding. By applying a lower reference voltage to the comparator at a higher mains voltage, an output current is obtained from the transformer secondary winding (N.sub.2) for the load L, which is substantially independent of the mains voltage.

High speed power supply circuit with circuit with positive feedback

A power supply circuit composed of a series arrangement of the primary winding of a transformer (TR), a first transistor (T.sub.1) and a current measuring resistor (R.sub.2). The first transistor (T.sub.1) is switched by means of a second transistor (T.sub.2). The second transistor is controlled by the combination of a first signal which is proportional to the intensity of the current through the current measuring resistor (R.sub.2) and a second signal which is the voltage, filtered by a low-pass filter, across the secondary winding (n.sub.2) of the transformer.

Power supply circuit

A self-oscillating power supply circuit comprises a series arrangement of the primary winding (N.sub.1) of a transformer (TR), the main current path of a first semiconductor switch (T.sub.1) and a current measuring resistor (R.sub.1). The first semiconductor switch is driven by a second semiconductor switch (T.sub.2) which in turn is controlled by a comparator (CP). The voltage across the current measuring resistor is applied to the non-inverting input (6) of the comparator and, a reference voltage obtained from a reference voltage source (RS) is applied to the comparator inverting input (5). By arranging a capacitor (C.sub.2) between the output of the second semiconductor switch and the inverting input (5) of the comparator, the first semiconductor switch rapidly turns-off at the end of the forward phase at an accurately determined current through the primary winding. By applying a lower reference voltage to the comparator at a higher mains voltage, an output current is obtained from the transformer secondary winding (N.sub.2) for the load (L) which is substantially independent of the mains voltage.

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 (R.sub.3, R.sub.4) connected across the battery by means of a switch (S.sub.1) 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 (D.sub.1, D.sub.2) during the flyback intervals.

A circuit for energizing a load (10) with different input voltages comprises a transformer (6), having a primary winding (n.sub.1) in series with a switching transistor (T.sub.1) the load (10), and a current sensing resistor (R.sub.2) between the input terminals. The secondary winding (n.sub.2), in series with a diode (D.sub.1) connected is in parallel with the load. A starting resistor (R.sub.1) starts the circuit oscillating via a positive-feedback loop comprising, in series, a first resistor (R.sub.4), a capacitor (C.sub.1) and a second resistor (R.sub.5). This feedback loop is coupled between one end of the secondary winding and the base of the switching transistor. A control transistor (T.sub.2), whose base is connected to the current-sensing resistor (R.sub.2), turns off the switching transistor as a function of the primary current. The energy stored in the transformer is then delivered to the load by an output current in the secondary winding. This output current increases as the input voltage increases as a result of an increasing saturation of the switching transistor via the positive feedback. A zener diode (Z.sub.1) is coupled to the switching transistor so that, above a specific input voltage, the zener diode turns on and drains away the base current of the switching transistor so as to limit the output current.

Growing community of inventors

Nijmegen, Netherlands

Joseph A Plagge