Low frequency switching voltage pre-regulator

[0002] This invention generally relates to voltage regulation. More particularly, this invention relates to a low-frequency, low-power switching voltage pre-regulator having automatic sleep-mode switchover.

[0003] Linear voltage regulators generate a substantially constant output voltage V_OUTfrom a relatively variable input voltage. Linear voltage regulators also provide low quiescent sleep current. Linear voltage regulators are operative to provide the regulated output voltage V_OUTover a range of input voltages. Such linear regulators are used to provide dc voltage signals for circuits designed to receive substantially constant voltage levels with low voltage ripple. Linear voltage regulators may also be designed to provide the constant output voltage V_OUTindependent of a relatively large input voltage V_IN. Accordingly, linear voltage regulators that are designed to operate with higher V_OUT/V_INratios are desirable. For example, linear regulators may provide a substantially constant 7.6 Volts output voltage independent of input voltages for input voltage up to a maximum of 42 Volts. Such linear regulators are desirable in devices or electronic circuits having a Voltage source with a variable output that may be configured to provide Voltage signals to other circuitry requiring stable Voltage signals. By way of example, such linear voltage regulators having substantially constant output voltage V_OUTand having a large V_OUT/V_INration are desirable in hybrid analog and digital electronic circuits. Such prior art linear regulators, however, typically generate a relatively large amount of heat that is dissipated, for example, through a relatively large metal heat sink mechanically coupled with the linear regulator.

[0004] FIG. 1 is a diagram showing a prior art a cascade design voltage regulator 100 having a switching pre-regulator circuit 102 and a linear regulator circuit 104. The switching pre-regulator circuit 102 receives the input voltage V_INat an input terminal 108 and produces a chopped voltage V_CHat a junction terminal 110. The chopped voltage V_CHis generated by the switching pre-regulator circuit 102 typically through electrical elements such as chokes, and diodes. The magnitude of the chopped voltage V_CHis less than the input voltage V_INand substantially within a desired input voltage range for the linear regulator circuit 104. The magnitude of chopped voltage V_CHwill generally cycle up and down between an upper limit and a lower limit for the switching pre-regulator circuit 102. The cycle is commonly referred to as a limit cycle.

[0005] The linear regulator circuit 104 receives the chopped voltage V_CHat the junction terminal 110 and generates a smooth, regulated output voltage V_OUTof a substantially constant level at its output terminal 112. Because the chopped voltage V_CHreceived by the linear regulator circuit 104 is substantially lower than the input voltage V_IN, the linear regulator circuit 104 operates more efficiently dissipating less power and thereby the cascade design voltage regulator 100, has improved voltage conversion efficiency. A cascade design voltage regulator 100 may include a feedback voltage V_FB, which is derived from the output voltage V_OUTof the linear regulator circuit 104 and received by the switching pre-regulator circuit 102. The switching pre-regulator circuit 102 thereby generates the chopped voltage V_CHin response to the feedback voltage V_FB.

[0006] It is desirable to conserve the amount of power consumed while controlling the operation of the linear voltage regulator circuit 104. Prior art voltage regulators do not provide for control to switch the pre-regulator circuit 102 to a sleep mode when the output voltage V_OUTis not needed, or power from the voltage regulator is not needed. For example, the voltage regulator can be placed in a standby condition when a circuit to which the voltage regulator 100 provides the output Voltage V_OUTneeds minimal power, and thereby minimize the power dissipated by the regulator. It is further desirable that such regulators would be controlled by signals commonly generated by microprocessors. Accordingly, there is a need in the art voltage regulators having a low frequency, low-power switching voltage pre-regulator circuit.

[0007] Embodiments of this invention provide low-frequency, low power switching voltage pre-regulator circuit for providing a chopped voltage to a linear voltage regulator circuit.

[0008] In view of the above noted limitations of the prior art, an object of the present invention is to provide an improved voltage regulator that minimizes the amount of power dissipated by the voltage regulator circuit and is capable of being controlled with a pulse width modulated (“PWM”) signal of the type generally provided by a microprocessors in order to obtain. More particularly, an input is provided to control a voltage pre-regulator circuit to provide a sleep mode for the voltage regulator when a circuit with which the voltage regulator may be coupled does requires minimal power.

[0009] In one aspect, a low-frequency switching voltage pre-regulator circuit, includes an input node, a pulse width modulated (“PWM”) signal input node; and a chopped voltage node. The input node may be configured to receive an input voltage signal V_INhaving a magnitude in the range from and including about 20 Volts to and including about 58 Volts. The PWM input node may be configured to receive a PWM signal having a frequency substantially in the range from about 5 kiloHertz to and about 15 kiloHertz and a duty cycle in the range from about 25% to 50%. The pre-regulator circuit may be configured to generate a chopped voltage V_CHat the chopped voltage node in response to the PWM signal and the input voltage V_INand independent of the magnitude of the input voltage V_IN. The chopped voltage V_CHmay have a magnitude in the range from about 6 Volts to about 10 Volts.

[0010] The low-frequency switching voltage pre-regulator may further include a chopping circuit coupled with the input node, a bucking circuit, a feedback and sense circuit, and a pre-driver switching circuit. The chopping circuit may be configured to receive the input voltage V_INand generates a bucking signal in response to a switching signal. The bucking circuit is coupled with the chopping circuit generates the chopped voltage V_CHat a chopped voltage node in response to the bucking signal. The feedback and sense circuit is coupled with the chopped voltage node and provides a feedback signal in response to the magnitude of the chopped voltage V_CH. The pre-driver switching circuit is coupled with the PWM input node and with the feedback and sense circuit selectively generates the switching signal in response to the feedback signal and PWM signal.

[0011] In a method for controlling a voltage output in response to a input voltage includes selectively generating a chopped voltage signal in response to a pulse width modulated (“PWM”) signal received from microprocessor and an input voltage having a magnitude substantially within a range from and including about 20 Volts to and including about 58 Volts, the chopped voltage having a magnitude independent of the input voltage and being substantially within the range from and including about 6 Volts to and including about 10 Volts, the magnitude of the chopped voltage being independent of the magnitude of the input voltage.

[0012] The method may further include generating the PWM signal from a microprocessor circuit, wherein the PWM signal has a frequency between about 5 kiloHertz and 15 kiloHertz and about a 33 percent duty cycle.

[0013] Other systems, methods, features, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.

[0014] The invention may be better understood with reference to the following figures and detailed description. The components in the figures are not necessarily to scale, emphasis being placed upon illustrating the principles of the invention. Moreover, like reference numerals in the figures designate corresponding parts throughout the different views.

[0015] FIG. 1 represents a block diagram for a prior art cascade design voltage regulator;

[0016] FIG. 2 represents a schematic diagram for an embodiment for a voltage pre-regulator; and

[0017] FIG. 3 represents a schematic diagram for an alternate embodiment for a voltage pre-regulator.

[0018] Herein, the phrase “coupled with” is defined to mean directly connected to or indirectly connected with through one or more intermediate components.

[0019] FIG. 1 is a block diagram for a prior art a cascade design voltage regulator 100 having a switching pre-regulator circuit 102 and a linear regulator circuit 104. The cascade design voltage regulator 100 generates a substantially constant output voltage V_OUTfrom a relatively large range of input voltage V_IN. The switching pre-regulator circuit 102 receives an input voltage V_INat an input voltage node 108 and produces a chopped voltage V_CHat a junction terminal 110. The chopped voltage V_CHhas a Voltage magnitude that is generally less than the input voltage V_INand substantially on the order of the desired voltage input range for the linear regulator circuit 104. The linear regulator circuit receives the chopped voltage V_CHand generates the substantially constant output voltage V_OUT.

[0020] Referring now to FIG. 2 there is schematically shown an embodiment of a low-frequency, low-power switching voltage pre-regulator circuit 104 having automatic sleep-mode switchover. The pre-regulator circuit includes the input voltage node 108, the chopped voltage node 110, and a pulse width modulated (“PWM”) signal input node 202. The pre-regulator circuit is configured to generate the chopped voltage V_CHindependent of the magnitude of the input voltage V_INand in response to a PWM signal received at the PWM signal input node 202. The pre-regulator circuit 104 generates the chopped voltage V_CHat the chopped voltage node 110 when a PWM signal is received at the PWM input node 202 and switches to a sleep mode when the PWM signal is not received at the PWM input node 202. In the sleep mode, the magnitude of the voltage at the chopped voltage node 110 is substantially equal to V_IN, and current flow through the pre-regulator circuit 104 is minimal. Therefore, the voltage pre-regulator circuit 104 may be controlled by the PWM signal received at the PWM input node 202.

[0021] In one aspect, the input voltage V_INmay have a magnitude of between 20 Volts and 58 Volts and the PWM signal is a control signal of the type generated by a microprocessor circuit and having frequency between 5 kiloHertz and 15 kiloHertz and a duty cycle between 25% and 50%, and preferably about 33%. It is desirable for the pre-regulator to generate a substantially constant chopped voltage V_CHhaving a magnitude in the range from 6 Volts to 10 Volts, and preferably about 7.6 Volts. The voltage pre-regulator 104 is configured to generate a substantially constant dc chopped voltage V_CH, although those skilled in the art will recognize that the dc chopped voltage V_CHmay have an insubstantial amount of limit cycle ripple.

[0022] The pre-regulator circuit 104 further includes a chopping circuit 204, a feedback and sense circuit 206, and a pre-driver switching circuit 208. The chopping circuit 204 is coupled with the input voltage node 108 and has an output node 210 that defines the chopped voltage output node 110. The feedback and sense circuit 206 has an input coupled with the chopping circuit output node 210. The pre-driver circuit 208 is coupled with the PWM input node 202 at a PWM interface node 212 and a feedback node 214 coupled with the feedback and sense circuit 206. The pre-driver circuit 208 is configured to propagate the PWM signal to the chopping circuit 204 in response to a feedback signal received from the feedback and sense circuit at the feedback node 214. In one embodiment, the PWM signal is propagated to the chopping circuit 204 via a current limiting resistor 216 having a resistance of 100 kiloOhms.

[0023] The chopping circuit 204 is configured to generate the chopped voltage V_CHat the output 210 in response to a switching signal received from the pre-driver circuit 208 via a current limiting resistor. The chopping circuit 204 includes a three-terminal power-switching semiconductor transistor 218 and a bucking circuit 222. The switching transistor 218 includes a source, a drain, and a gate. In an embodiment, the switching transistor is a P-channel enhancement type MTP5P06V MOSFET transistor having a drain-to-source withstand voltage of at least 60 Volts. The source of the switching transistor 218 is coupled with the voltage input node 108 and the gate of the switching transistor 218 is coupled with the pre-driver circuit 208. In an embodiment, the gate of the switching transistor 218 is coupled with the pre-driver circuit 208 via the current limiting resistor 216. The drain of the switching transistor 218 is coupled with the bucking circuit 222. The switching transistor 218 is configured to propagate the input voltage V_INto the bucking circuit in response to a switching signal received from the pre-driver circuit 208.

[0024] The chopping circuit 204 may additionally include an input bias network 220. The input bias network 220 includes an input diode 224 and an input resistor 226 both coupled between the gate and the source of the switching transistor 218. The input diode 224 regulates the voltage between the source and the gate of the switching transistor 218 when the switching transistor is switched on and the input resistor balances the voltage between the source and the gate of the switching transistor 218 when the switching transistor is switched off. In an embodiment, the input resistor has a resistance of 100 kiloOhms and the input diode 224 has a breakdown voltage of approximately 10 Volts assuring that the voltage between the source and the gate does not exceed 10 Volts.

[0025] The bucking circuit 222 includes bucking coil 248, a charge well 230, and a return diode 228. The bucking coil 248 has a first terminal coupled with the drain of the switching transistor 218 at a bucking node 250 and a second terminal defining the chopping circuit output 210. The charge well 230 is coupled between the second terminal of the bucking coil 248 at chopping circuit output 210 and a ground reference (0 Volts). The return diode 228 is coupled between the bucking node 250 and the ground reference.

[0026] When the input voltage V_INis propagated to the bucking circuit 222 by the switching transistor 218, a magnetic field is created in the bucking coil 248 to charge. When the input voltage V_INis removed by the switching transistor 218, the field in the bucking coil collapses and causes electric current to conduct to the chopping circuit output node 210. The current at the chopping circuit output node 210 flows to the charge well 230 and to the output 210. Electric charge accumulates in the charge well 230 in response to the current therein and a voltage is generated at chopping circuit output node 210. In the absence of the input voltage V_IN, the charge on the charge well 230 causes a current that can flow to the output node 210. The return diode 228 provides a return path from the ground reference to the bucking coil 248 in the absence of the input voltage V_INat the bucking node 250. In an embodiment, the charge well 230 is a capacitor having a capacitance of 300 microFarads.

[0027] The feedback and sense circuit 206 includes a feedback transistor 232, a bias network 234, and a sense diode 252. The feedback and sense circuit 206 detects the voltage at the chopping circuit output node 210 and generates a feedback signal in response thereto. The feedback transistor 232 includes a source, a gate and a drain. In an embodiment, the feedback transistor is an N-channel enhancement type 2N7000 MOSFET or similar transistor. The drain of the feedback transistor 232 defines the output of the feedback and sense circuit 206 and is coupled with the feedback node 214 and the drain of the feedback transistor 232 is coupled with the ground reference.

[0028] The sense diode 252 is coupled between the chopping circuit output node 210 and the bias network 234. The bias network 234 is coupled between the sense diode 252 and a ground reference and has an output coupled with the gate of the feedback transistor 232. The sense diode 252 is configured to conduct electric current when the magnitude of the voltage at the chopping circuit output node 210 equals or exceeds a pre-selected value. The bias network 234 is configured to switch the feedback transistor 232 in response to current through the sense diode 252 and the feedback transistor 232 thereby generates a feedback signal at the feedback node 214. In an embodiment, the sense diode 252 has a breakdown voltage of 4.7 Volts and bias network includes a first bias resistor 236 and second a second bias resistor 238 each having a resistance value of 30 kiloOhms.

[0029] The pre-driver circuit 208 includes a pre-driver transistor 240 and a PWM interface network 242. The pre-driver transistor 240 includes a source, a drain, and a gate. In an embodiment, the feedback transistor is an N-channel enhancement type 2N7000 MOSFET or similar transistor. The gate of the pre-driver transistor 240 is coupled with the feedback node 214, the source of the pre-driver transistor 240 is coupled with the ground reference and the drain of the pre-driver transistor 240 is coupled with the gate of the switching transistor 218. The pre-driver circuit 208 is configured to propagate the PWM signal to the switching transistor 218 in response to the feedback signal at the feedback node 214. The PWM interface circuit 242 receives the PWM signal at the PWM interface node 212. When the PWM signal is propagated by the pre-driver circuit 208 to the switching transistor 218, the switching transistor 218 propagates the input voltage V_INto the bucking coil 248 and allows electric current to flow from the input voltage node 108 to charge the charge well 230 and to the chopped voltage output node 210. In the absence of the PWM signal, the pre-regulator circuit 104 will switch to a sleep mode, whereby the input voltage V_INis propagated to the chopping circuit output node 210 and the switching transistor 218 will conduct minimal current. Because the current through the switching transistor 218 is minimal, power dissipated by the pre-regulator circuit 104 is reduced. In an embodiment, the pre-regulator circuit 104 may cycle between sleep mode and an on mode.

[0030] The PWM interface circuit 242 includes a first bias resistor 244 and a second bias resistor 246. The first bias resistor 244 is coupled between the PWM interface node 212 and the ground reference. The second bias resistor 246 is coupled between the PWM interface node and the feedback node 214. In an embodiment, the first bias resistor 244 has a resistance of 200 kiloOhms and the second bias resistor 246 has a resistance of 20 kiloOhms.

[0031] Referring now to FIG. 3, an alternate embodiment of a low-frequency, low-power switching voltage pre-regulator circuit 104 having automatic sleep-mode switchover and realized with bipolar active transistors is shown. The pre-regulator circuit includes the input voltage node 108, the chopped voltage node 110, and a pulse width modulated (“PWM”) signal input node 202. The pre-regulator circuit 104 is configured to generate the chopped voltage V_CHindependent of the magnitude of the input voltage V_INand in response to a PWM signal received at the PWM signal input node 202. The pre-regulator circuit 104 further includes the chopping circuit 204, the feedback and sense circuit 206, and the pre-driver switching circuit 208.

[0032] The chopping circuit 204 includes a three-terminal bi-polar semiconductor switching transistor 318, a switchover resistor 302, a bypass resistor 304, and the bucking circuit 222. The bi-polar switching transistor 318 includes a collector, an emitter, and a base. In an embodiment, the bi-polar switching transistor 318 is a PNP type MPSA56 Amplifier transistor having a collector-to-emitter withstand voltage of at least 60 Volts. The emitter of the bi-polar switching transistor 318 is coupled with the voltage input node 108 and the base of the bi-polar switching transistor 318 is coupled with the pre-driver circuit 208. In an embodiment, the base of the bi-polar switching transistor 318 is coupled with the pre-driver circuit 208 via the current limiting resistor 216. The collector of the bi-polar switching transistor 318 is coupled with the bucking circuit 222. The bypass resistor 304 is coupled between the emitter of the bi-polar switching transistor 318 and the bucking circuit 222. The bypass resistor 304 is configured to provide for a sleep mode when the bi-polar switching transistor 318 is turned off. In an embodiment, the bypass resistor 304 has a high impedance. It is preferred that the bypass resistor has an impedance of substantially 33 kOhms. When the bi-polar switching transistor 318 is turned off, the bypass resistor 304 propagates the input voltage V_INto the bucking circuit 222 and thereby to the chopped voltage node 110, and minimizes current flow from the input voltage node 108 to the chopped voltage node 110. The bi-polar switching transistor 318 is configured to propagate the input voltage V_INto the bucking circuit in response to a switching signal received from the pre-driver circuit 208.

[0033] The feedback and sense circuit 206 includes a bi-polar feedback transistor 332, the bias network 234, and the sense diode 252. The bi-polar feedback transistor 332 includes a collector, an emitter, and a base. In an embodiment, the bi-polar feedback transistor 332 is an NPN type MPSA06 or similar transistor. The collector of the bi-polar feedback transistor 332 defines the output of the feedback and sense circuit 206 and is coupled with the feedback node 214 and the emitter of the bi-polar feedback transistor 332 is coupled with the ground reference. In an embodiment, the sense diode 252 has a breakdown voltage of 6.0 Volts and bias network includes a first bias resistor and second a second bias resistor each having a resistance value of 30 kiloOhms.

[0034] The pre-driver circuit includes a bi-polar pre-driver transistor 340 and the PWM.interface network 242. The pre-driver transistor 340 includes a emitter, a collector, and a base. In an embodiment, the bi-polar pre-driver transistor 340 is an NPN type MPSA06 or similar transistor. The base of the pre-driver transistor 240 is coupled with the feedback node 214, the emitter of the pre-driver transistor 240 is coupled with the ground reference and the collector of the pre-driver transistor 240 is coupled with the base of the switching transistor 218. The pre-driver circuit is configured to propagate the PWM signal to the switching transistor 218 in response to the feedback signal at the feedback node 214. The PWM interface circuit 242 receives the PWM signal at the PWM interface node 212. When the PWM signal is propagated by the pre-driver circuit 208 to the switching transistor 218, the switching transistor propagates the input voltage V_INand current flow to the bucking coil 248 to charge the charge well 230 and to the chopped voltage node 110.

[0035] The voltage embodiments described herein provide a low-frequency, low-power voltage pre-regulator circuit operable to provide a chopped voltage to a linear regulator circuit. The pre-regulator circuit may be controlled to switch to a sleep mode, whereby the input voltage may be propagated to the output of the pre-regulator circuit, while minimizing current flow through the pre-regulator circuit. By way of example, it may be desirable to switch the voltage pre-regulator to the sleep mode when current requirements at the output of the pre-regulator are minimal. Because the current flow through the pre-regulator circuit can be reduced, the power dissipated by the pre-regulator circuit can also be reduced.

[0036] Various embodiments of a low-frequency, low-power voltage pre-regulator have been described and illustrated. However, the description and illustrations are by way of example only. Many more embodiments and implementations are possible within the scope of this invention and will be apparent to those of ordinary skill in the art. For example, characteristics for the electrical and electronic elements described herein may be varied to implement a voltage regulator within the scope of this invention. In addition, various electrical and electronic components may be combined to implement a voltage pre-regulator within the scope of this invention. The voltage regulator may be used with any other device that requires low-power voltage regulation. Therefore, the invention is not limited to the specific details, representative embodiments, and illustrated examples in this description. Accordingly, the invention is not to be restricted except in light as necessitated by the accompanying claims and their equivalents.