U.S. Philips Corporation

Antonius A Marinus

Guy L De Bondt

Patrick E Smeets

Henricus C Buthker

Hubertus Cornelis Miermans

Etienne N Eberson

A ballast for a compact fluorescent lamp includes a down-converter for operating the lamp with a DC current during stable operation and a charge pump for igniting the lamp. The converter includes an inductor and a first series circuit of a first diodie and a first switching element. An output capacitor shunts the lap terminals. The charge pump includes a second series circuit of second diodie and a second switching element coupled to the lamp terminals with the second diode polarized to prevent the discharge of the output capacitor when the second switching element is conductive. The inductor cooperates with the first and second diodes and the second switching element to build up the voltage across the outpout capacitor to the ignition voltage level of the lamp.

Discharge lamp ballast circuit with charge pump igniter

The power supply apparatus serves to convert an electric direct voltage, acting as an input voltage, into an output voltage and comprises positive and negative input terminals (1, 3) which are arranged to receive the input voltage. The power supply apparatus also comprises a first series connection (7) of, at least a first coil (9) and a controllable switching element (11), which series connection interconnects the input terminals (1, 3), and a limiter circuit (29) which comprises a first capacitor (31) and a second series connection (33) of at least a second coil (35), a first rectifier element (37) and a second rectifier element (39), said second series connection being connected parallel to the first series connection in such a manner that the cathodes of the first and second rectifier elements are oriented towards the positive input terminal (1), one electrode of the first capacitor being connected to the anode of the second rectifier element and its other electrode to the junction (43) of the first coil and the switching element. The second series connection (33) also comprises an auxiliary voltage source (55) which is arranged to supply a direct voltage amounting to approximately half the input voltage and whose positive pole is oriented towards the positive input terminal (1). The presence of the auxiliary voltage source (55) prevents that upon switching off of the switching element (11) a voltage jump occurs across the switching element, which jump could cause an undesirably high energy dissipation in the switching element and also a disturbance (EMI).

Power supply apparatus comprising an improved limiter circuit

In a standby mode, a switched-mode power supply circuit may be operated in a burst mode with reduced secondary voltages (Vo1, Vo2) for supplying a standby voltage (Vo1) at a very high efficiency. In a normal operating mode of the power supply, a control circuit (1) is maintained in its on-state by a power supply voltage (Vcc) generated by the power supply. The control circuit (1) supplies control pulses (Vd) for switching the power supply. The burst mode is obtained by decreasing the power supply voltage (Vcc) generated for the control circuit (1) to such an extent that, without any further provisions, the control circuit (1) reaches an off-state in which no control pulses (Vd) are generated. In the standby mode, the control circuit (1) is supplied with current by a power supply circuit (4). In the off-state, the control circuit (1) takes up a smaller power supply current (Icc) from the power supply circuit (4) than it is supplying and the power supply voltage (Vcc) increases until the control circuit (1) reaches the on-state and starts generating the control pulses (Vd). In the on-state, the control circuit (1) takes up a larger current from the power supply circuit (4) than it is supplying and the power supply voltage (Vcc) decreases until the control circuit (1) reaches the off-state again. In this way, the power supply, in the standby mode is each time active during first periods and inactive during second periods. To bring the power supply voltage to the standby mode, the power supply voltage (Vcc) generated for the control circuit (1) is decreased in such a way that also the secondary voltage (Vs1, Vs2) are decreased.

Switched-mode power supply

A power supply circuit for generating a stabilized power supply generally comprises a series arrangement of a primary winding of a transformer and a switch. The switch is controlled by a control circuit, an input of which receives a signal related to the output voltage of the power supply circuit. The control circuit determines the duty cycle of the switch. Dependent on the power consumption of the lead connected to the output of the power supply circuit, the duty cycle is either increased or decreased. The duty cycle has a given minimum value which is caused by the inertia of the switch upon switching on and switching off. The minimum duty cycle may be reached, inter alia, when the power supply circuit works in an apparatus using a standby mode. With reference to the power to be supplied to the lead and/or with reference to the duty cycle, the power supply circuit according to the invention determines the moment when the frequency of the control signal to be generated by the control circuit is switched to another fixed frequency.

Power supply circuit and control circuit for use in a power supply

Switched-mode power supplies in which a series arrangement of a bipolar transistor and a MOS field effect transistor is used are known and referred to as cascode circuits. In these circuits the bipolar transistor is switched (with the MOS field effect transistor) via the emitter instead of with the base. Since the collector current of the bipolar transistor may vary over a large range, the base should be proportionally driven to prevent the bipolar transistor from getting either above or below its normal operating range. By making use of an extra winding on a transformer arranged in series with the cascode circuit, a non-dissipative proportional drive of the base of the bipolar transistor is obtained. The extra winding is coupled to the base via an inductance.

Switch mode power supply with BJT/MOSFET cascode circuit

In switched-mode power supply circuits the switch is rendered conducting for a longer period (or more frequently), dependent on the load connected to the power supply circuit, so as to ensure that the transformer can transfer enough energy to the secondary side for charging the output capacitor to a sufficient extent. To ensure that the transformer can always supply all energy stored in the transformer to the secondary side, a demagnetizing detection circuit detects the demagnetization of the transformer. If the load decreases (for example, in standby operation) the on-time of the switch is reduced. However, this on-time may achieve a minimum value so that the power supply circuit no longer functions properly. To obtain an efficiently operating power supply circuit, both in normal operation and in a low-load state, the control circuit of the power supply circuit has at least two modes, i.e. a first mode (standby operation) in which the control pulses are applied to the switch at a fixed frequency and the demagnetizing signal has no influence, and a second mode (normal operation) at a variable frequency, in which second mode the frequency of the control pulses is variable and, if necessary, the demagnetizing signal can delay the control pulses applied to the switch when the transformer is not fully demagnetized.

Switched mode power supply circuit including a control circuit having

A switched mode power supply circuit includes a controllable switch for controlling the current in the supply transformer of the power supply circuit. During normal operation of the power supply, its DC output voltage is maintained at a substantially constant, first value in spite of variations of the DC input voltage and of the load on the output voltage by controlling the duration of the conductivity time of the switch. A function generator supplies a signal, which is a given function of the output voltage, to a control input of a pulse duration modulator for determining the duration of the conductivity time. At an output voltage which is considerably lower than the first value, the signal of a starting circuit is passed on by a selection circuit to the said control input in order to increase the conductivity time of the switch. This signal corresponds to a shorter switch conductivity time than does the signal of the function generator. At the instant when the output voltage reaches the first value, the selection circuit blocks the passage of the start signal and passes on the signal of the function generator. The power supply thus provides a soft start with limited energy dissipation.

Switched-mode power supply circuit including a starting circuit

A switched mode power supply circuit includes a controllable switch in series with an inductive element between the terminals of a DC input voltage. A control circuit renders the switch alternately conductive and non-conductive. A rectifier for deriving a DC output voltage is coupled to the inductive element. To prevent the inductive element from becoming saturated, a switching element is coupled to the control circuit for maintaining the controllable switch in its blocked state only during a time interval which immediately follows an interval of conductance of the controllable switch and during which the voltage across the inductive element has the same polarity as when the rectifier is conductive.

SMPS apparatus having a demagnetization circuit

A switched-mode power supply circuit having a transformer and a first controllable switch on the primary side of the transformer. A first section is in the form of a flyback d.c. converter including a first secondary winding of the transformer for generating a first d.c. output voltage which is stabilized, by a control, against d.c. input voltage variations of the circuit and of a first load. A second section including a second secondary winding of the transformer constitutes a forward d.c. converter having a second controllable switch for generating a second d.c. output voltage. The ratio between the period of conductance of the second switch and the period of the control signal of the first switch is independent of the frequency of this signal.

Switched-mode power supply circuit

A switched-mode power supply circuit for converting a DC input voltage into a DC output voltage comprises a series arrangement of a controllable power switch and an inductive element coupled between the input voltage terminals. Control means are provided for rendering the power switch alternately conducting and non-conducting and a rectifier is coupled to the inductive element for making the output voltage available. The inductive element and a capacitor coupled thereto form a part of a resonant circuit in which a voltage oscillation is present in the time periods when the switch and the rectifier are currentless. The circuit further comprises means for interrupting the oscillation present in the resonant circuit at an instant when the voltage across the inductive element or the current through the capacitor is substantially zero. In one embodiment, the dissipation in the circuit is reduced and the circuit is synchronized.

Switched-mode power supply with low loss interrupted oscillation

A switched-mode power supply circuit with having an operating state and a stand-by state in which the value of a first output voltage is considerably lower than in the operating state, whereas the value of a second output voltage is substantially the same. With the aid of a duration-determining circuit (Tr7, Tr8, R17, C12) which is controlled by a switch (Tr6) operative during the stand-by state, a low-frequency burst mode is maintained during this state in which the switch of the supply circuit conducts a number of consecutive times and subsequently becomes non-conductive during a given period. As a result the dissipation in the circuit is reduced.

Switched-mode power supply having a standby state

A switched-mode power supply circuit for converting a d.c. input voltage into a d.c. output voltage. The circuit includes a controllable power switch (Tr1) connected in series with the primary winding (L1) of a transformer (T). This winding forms part of a resonant circuit. To reduce the power losses caused by turning on the switch, the drive path of the switch incorporates a delay network (R11, C9) for each time delaying the turn-on until an instant which is substantially half a cycle of the resonance frequency later than the initial instant of the decrease of the voltage across the switch during its previous cut-off time.

Switched-mode power supply with delay network to reduce switching losses

A switched-mode power supply circuit having an operating state and a stand-by state in which the value of a first output voltage is considerably lower than in the operating state, whereas the value of a second output voltage is substantially the same. With the aid of a duration-determining circuit (Tr7, Tr8, R17, C12) which is controlled by a switch (Tr6) operative during the stand-by state, a low-frequency burst mode is maintained during this state in which the switch of the supply circuit conducts a number of consecutive times and subsequently becomes non-conductive during a given period. As a result the dissipation in the circuit is reduced.

A switched-mode self-oscillating supply voltage circuit for converting an input voltage into an output d.c. voltage which is substantially independent of variations of the input voltage and/or a load connected to the output voltage. The circuit comprises a first controllable switch connected in series with a transformer winding and a second controllable switch for turning-off the first switch. The conduction period of the first switch is controlled by means of a control voltage present on a control electrode of the second switch. The circuit can be switched-over to a stand-up state in which the energy supplied to the load is reduced to zero. A starting network is connected between the input voltage and the second switch so that the current therein flows through the second switch during the period of time this switch conducts and does not flow to the control electode of the first switch in the stand-by state.

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Eindhoven, Netherlands

Antonius A Marinus