Power supply circuit for direct voltage regulators with step-up configuration

Abstract: The circuit switches the power supply of the integrated circuit over to the input voltage of the switching regu­ lator during the initial starting phase, and over to the output of said regulator once the steady state has been reached.

Description: This invention refers to a supply circuit for direct voltage regulators with a step-up switching configuration. Power supply circuits for direct voltage regulators with a step-down switching configuration are known whose output voltage is obtained, during the starting phase, from the input voltage of the regulator through series arrangements, which ensure a considerable voltage drop, and whose output voltage is obtained, during the operating conditions, from the output voltage of the regulator. Examples of said circuits are described in US-A-4717867 and in EP-A-167194. Voltage regulators with a step-up switching configuration are generally realized with an integrated circuit whose direct supply voltage Vcc is usually taken from the output of the regulator itself. In fact, since this voltage at the steady state has a higher value than the input voltage Vin, it enables the circuit to operate more efficiently. This way of supplying the integrated circuit is satisfactory providing the output voltage remains higher, during each operating phase, than the minimum value Vccm (flashover threshold of the regulator) that the supply voltage of the integrated circuit must have in order to ensure its regular operation. At the moment of the switching on of the regulator and until the output voltage stabilizes at its steady state value Vout > Vin, the output voltage itself has an initial value Vouti lower than the input voltage Vin by a quantity equal to the voltage drop V FD that occurs at the terminals of a directly polarized diode (which for a silicon diode is equal to approximately 0.6 V); therefore it can be assumed that the aforesaid efficient operation is ensured also during the initial starting phase if the condition Vin - V FD = Vouti ≧ Vccm is fulfilled. Some integrated circuits however are made with technologies (such as for example the CMOS metal gate technology) which require flashover voltages Vccm which although being lower than Vin are higher than the Vin - V FD difference, and which therefore do not ensure efficient operation during the starting phase. The scope of present invention is to provide a regulator supply circuit which can be triggered even with a Vccm voltage higher than the Vin - V FD difference, provided it is Vccm ≦ Vin. The power supply circuit according to the invention applies to direct voltage regulator with a step-up switching configuration comprising an integrated switching circuit which, at the steady state, has its supply voltage taken from an output voltage of the regulator and supplies current pulses to an inductor, the voltage pulses originated at the terminals of the inductor being utilized to increase the charging voltage of a condenser, and is characterized by the presence in combination of: a first solid state switch and a second solid-state switch for respectively connecting a supply terminal of the aforesaid integrated circuit directly to the input terminal or to the output terminal of the regulator; a control unit connected by an input terminal to the output terminal of the regulator, for controlling said first and second switch respectively by a first and a second output terminal, which: actuates the closing of said first switch at the moment of the switching on of the regulator; actuates the opening of the first switch and the closing of the second switch when the output voltage at the output terminal of the regulator has reached a given threshold value (Vout) which ensures the efficient operation of the integrated circuit. Other preferred embodiments are indicated further on in the claims. The features of the invention will be more clearly evident from the following description of an exemplificative, non-restrictive embodiment, making reference to the accompanying drawings, in which: Fig.1 shows a block diagram of a voltage regulator of known type; Fig.2 shows a block diagram of a regulator according to the invention; Fig.3 shows a block diagram of an embodiment of the unit S of Fig. 2; Fig.4 shows a block diagram of an embodiment of the unit T of Fig. 3; Fig.5 shows an example of a circuit embodying the diagrams referred to in Figs. 2, 3 and 4. Fig.1 shows the block diagram of a known type of voltage regulator, in which Vin represents the input voltage, Vout represents the output voltage and CI represents an integrated circuit supplied, through the input 5, by the output voltage Vout. It comprises a solid-state switch I which, under controll of the driver circuit D, applies intermittent pulses of input voltage Vin to the terminals of the inductor L. The voltage pulses thus applied to the terminals of L are discharged, through the diode D, onto the condenser C so as to increase its charging voltage Vout. Fig .2 shows the block diagram of a power supply unit according to the invention, in which I1 represents a solid-state switch provided with a control electrode, I2 represents an electronic component consisting of a diode or of another solid-state switch provided with a control electrode, and S represents a control unit, supplied by the Vin voltage through the conductor 1, which controls the ouput voltage Vout through the conductor 6. When the regulator is turned on, S actuates the closing of the switch I1, keeping it closed until the Vout voltage reaches a given threshold value which ensures the efficient operation of CI. At this point, S actuates the opening of I1. S also actuates the simultaneous closing of I2, in the case the latter is a switch provided with a control electrode (whereas, in the case I2 is a diode, the latter automatically becomes conductive as soon as Vout > Vin occurs). Fig. 3 shows the block diagram of an embodiment of the unit S of Fig. 2. This diagram assumes that the switch I1 is made in such a way that it closes when the voltage on the control electrode is lower than Vin and opens when it is higher. When the regulator is switched on, the unit T maintains its output 9 at a voltage level smaller than or equal to Vin until the diode Q is cut off. As soon as Q becomes conductive, the output 9 increases to a voltage value equal to Vout; T senses the increase in voltage of the conductor 9 to the aforesaid value and closes I2, by the output 8, in the case I2 is not a diode. Fig. 4 shows the block diagram of an exemplificative embodiment of the unit T of Fig. 3. According to said diagram, at the moment of switching on the unit A supplies power to 8 through the conductor 2 and at the same time energizes the output 3 thereby closing I1. At the same time A, by means of the conductor 7, sends B a holding command. Upon receipt of said command, B sends a holding signal to the output 4, said signal keeping the switch I1 closed. After which, A de-energizes its output 3. When the switching regulator starts operating in the switching mode and the Vout increases to a value higher than Vin, the voltage of 9 is increased to the Vout value by means of the diode Q and I1 is consequently opened. As soon as A senses, by means of the conductor 3, that the voltage of 9 has increased to the Vout value, it de-energizes and at the same time removes the excitation from B, by means of 7. Should I2 not be a diode, B, as soon as it is de-energized, sends a closing signal to I2, by means of 8. At this point, the step-up regulator begins to operate normally at its steady state, the supply circuit S is de-energized, and does not therefore take part in any way whatsoever in the overall consumption of energy. Fig. 5 shows a circuit made according to the diagrams referred to in figures 2, 3 and 4, in which the various component parts are composed as follows: unit A: of the P-channel 10, 11, 16, 20 and 21 and of N-channel 15 and 19 MOS transistors; unit B: of the resistor R1, the dual-collector transistor 28, the (N-channel) MOS transistors 13, 14, 18, 22, 23 and the (P-channel) transistor 17; diode Q: of the dual-collector transistor 27; switch I: of the (N-channel) MOS transistor 24; I1 and I2: of the (P-channel) MOS transistors 12 and 26, respectively. At the moment the voltage Vin is applied, the condenser Cl is discharged and consequently all the Vin is applied, as Vgs, to the transistors 16 and 21, which begin to conduct. The transistor 16 activates 15, which in turn activates 12 and consequently brings the Vin to the input 5 of CI, less the small voltage drop Vds at the terminals of 12. By 15 becoming conductive, the transistors 10, 11 and 20 are triggered. The transistors 21 and 20 together contribute towards activating 18 which maintains the gate of 14 at a low level voltage; in this way 13 becomes conductive thanks to 11 and the entire circuit assumes a stable condition, and remains so even when the condenser C is charged and 16 and 21 (and consequently also the N-channel MOS transistor 15) are cut off. Under these conditions 26 is off, since its gate is connected to that of 18 which is at high voltage level. As a result, the Vcc is supplied to the integrated circuit by Vin through 12 in conduction, with 26 off. As soon as the regulator begins to operate normally (and Vout has consequently increased to a value higher than Vin), 12 switches off since its gate voltage is increased to a high value by 27 and its drain voltage is increased to a slightly higher value by 26 (Vgate and Vdrain voltages both higher than Vsource). Likewise, the mirror circuit composed of 10, 11 and 20 switches off; the gate of 18 discharges onto 28 and R1; the transistor 26 becomes conductive and the pair 14 and 19 is activated, cutting off the pair 13 and 15. From this moment on, the power to the entire circuitry is supplied by the Vout, deducted the small voltage drop V DS at the terminals 26. It should be noted that once the power of the CI is sup plied by the Vout through 26, the start circuit no longer absorbs any current. Numerous variations, additions or replacements of parts with others functionally equivalent may be made to the previously described embodiment without however deviating from the scope of the claims. One such variation consists of the possibility of replacing the transistor 26 with a diode, or a bipolar transistor or a MOS transistor, the latter two assuming a diode-connection. With this replacement the connecting conductor 8 is superfluous since the new component is forward biased as soon as the voltage Vout increases to a value higher than Vin + V FD of the component itself.

Claims: A power supply circuit for direct voltage regulator with a step-up switching configuration, said regulator comprising an integrated switching circuit (CI) which, at the steady state, has its supply voltage taken from an output voltage of the regulator and supplies current pulses to an inductor (L), the voltage pulses originated at the terminals of the inductor bei used to increase the charging voltage of a condenser (C), characterized by the presence in combination of: a first solid state switch (I1) and a second solid-state switch (I2) for respectively connecting a supply terminal (5) of the aforesaid integrated circuit (CI) directly to the input terminal or to the output terminal of the regulator; a control unit (S) connected by an input terminal (6) to the output terminal of the regulator, for controlling said first and second switch (I1 ,I2) respectively by a first (9) and a second (8) output terminal, which: actuates the closing of said first switch (I1) at the moment of the switching on of the regulator; actuates the opening of the first switch (I1) and the closing of the second switch (I2) when the output voltage at the output terminal of the regulator has reached a given threshold value (Vout) which ensures the efficient operation of the integrated circuit (CI). A power supply circuit for direct voltage regulator with a step-up switching configuration, said regulator comprising an integrated switching circuit (CI) which, at the steady state, has its supply voltage taken from an output voltage of the regulator and supplies current pulses to an inductor (L), the voltage pulses originated at the terminals of the inductor being used to increase the charging voltage of a condenser (C), characterized by the presence in combination of: a first solid state switch (I1) and a second solid-state switch (I2) respectively connecting the supply terminals of the aforesaid integrated circuit (CI) to the input and output terminals of the regulator, the second switch (I2) being a diode; a control unit (S) connected by an input terminal (6) to the output terminal of the regulator, for controlling said first switch (I1) by an output terminal (9), which: actuates the closing of the first solid state switch (I1) at the moment of the switching on of the regulator; actuates the opening of the first switch (I1) when the voltage at the output terminal of the regulator has reached a given threshold value (Vout) which ensures the efficient operation of the integrated circuit (CI). A circuit as claimed in Claim 1, characterized by the fact that the first switch (I1) is made in such a way that it closes when the voltage on its control electrode is lower than the input voltage (V IN ) of the circuit itself, and opens when the same voltage is higher than said input voltage (Vin), and by the fact that the control unit (S) comprises a diode (Q) connected between its input terminal (6) and its first output terminal (9), and a device (T) which, when the power supply circuit is switched on, maintains said first output terminal (9) at a voltage level lower than or equal to said input voltage (V IN ) until said diode (Q) becomes conductive, and which closes the second switch (I2) as soon as the same diode (Q) becomes conductive. A circuit as claimed in Claim 2, characterized by the fact that the first switch (I1) is made in such a way that it closes when the voltage on its control electrode is lower than the input voltage (V IN ) of the circuit itself, and opens when the same voltage is higher than said input voltage (Vin), and by the fact that the control unit (S) comprises a diode (Q) connected between its input terminal (6) and its first output terminal (9), and a device (T) which, when the power supply circuit is switched on, maintains said first output terminal (9) at a voltage level lower than or equal to said input voltage (V IN ) until said diode (Q) becomes conductive. A circuit as claimed in Claim 3, characterized by the fact that said device (T) comprises a first unit (A) and a second unit (B) connected to said first output terminal (9) of the control unit (S) by a first and a second respective output (3,4), and connected to each other by a first and a second conductor (2,7), in which: the first unit (A), when switched on,: powers the second unit (B) through said first conductor (2); energizes its output terminal (3) connected to said first output terminal (9) of the control unit (S) thus commanding the closing of the first switch (I1); sends a holding command to the second unit (B) by said second conductor (7); de-energizes its output terminal (3) connected to said first output terminal (9) of the control unit (S) after sending the second unit (B) said holding command; the second unit (B), on receipt of a holding command by said second conductor (7), sends a signal to its output (4) connected to said first output terminal (9) of the control unit (S) to keep the first switch (I1) closed; the first unit (A) de-energizes as soon as, through its output (3) connected to said first output terminal (9) of the control unit senses the increase of the voltage level of the same terminal to the (Vout) value supplied by the regulator at its steady state, and, at the same time, de-energizes the second unit (B) through said second conductor (7); the second unit (B), when de-energizing, sends to the second switch (I2) a closing signal. A circuit as claimed in Claim 4, characterized by the fact that said device (T) comprises a first unit (A) and a second unit (B) connected to said first output terminal (9) of the control unit (S) by a first and a second respective output (3,4), and connected to each other by a first and a second conductor (2,7), in which: the first unit (A), when switched on,: powers the second unit (B) through said first conductor (2); energizes its output terminal (3) connected to said first output terminal (9) of the control unit (S) thus commanding the closing of the first switch (I1); sends a holding command to the second unit (B) by said second conductor (7); de-energizes its output terminal (3) connected to said first output terminal (9) of the control unit (S) after sending the second unit (B) said holding command; the second unit (B), on receipt of a holding command by said second conductor (7), sends a signal to its output (4) connected to said first output terminal (9) of the control unit (S) to keep the first switch (I1) closed; the first unit (A) de-energizes as soon as, through its output (3) connected to said first output terminal (9) of the control unit senses the increase of the voltage level of the same terminal to the (Vout) value supplied by the regulator at its steady state, and, at the same time, de-energizes the second unit (B) through said second conductor (7). A circuit as claimed in any of the previous Claims, characterized by the fact that the first and second switches (I1,I2) are composed of P-channel MOS transistors. A circuit as claimed in Claim 4 or 6, characterized by the fact that the second switch (I2) consists of a MOS transistor with its drain connected to the gate.

Inventors: PALARA SERGIO, SUERI STEFANO, PALARA, SERGIO, SUERI, STEFANO
Applicants: SGS THOMSON MICROELECTRONICS, SGS-THOMSON MICROELECTRONICS S.R.L.
Application year: 1990
Main classification: H02M3
IPC codes: G05F1, H02M1