Multiple Output DC-DC Converter With Different Ranges of Output Assurance and Capable of Tolerating Load Transients

1. Field of the Invention

The present invention relates to the fields of electronics and computer systems. More specifically, the present invention relates to DC-DC converters having specific applications in computer systems.

2. Background Information

The power supplies in a computer system are designed to meet the specific power requirements of the integrated circuit chips (ICs) that are the components of the system. The nominal operating voltages for the ICs are typically known because most ICs are manufactured to meet industry standards for device operation. For example, the nominal supply voltage for transistor-transistor logic (TTL) devices is 5.0 volts while the nominal supply voltage for complementary metal oxide semiconductor (CMOS) devices is 3.3 volts. Ideally, a power supply will deliver the nominal voltage levels with perfect assurance and precision, but power supplies are typically inaccurate due to a number of factors. A typical range of assurance for a power supply is plus or minus five percent. Thus, most ICs are further designed to operate within a range of plus or minus five percent of the nominal voltage.

However, some ICs are less tolerant of power supply inaccuracies, requiring ranges of assurance that are a lot more precise than what are offered by typical off the shelf power supplies, whereas, other ICs may require nominal operating voltages other than the standard TTL and CMOS voltages supported by the off the shelf power supplies. The operating voltage of an IC having either one or both of these characteristics can be supplied by a DC-DC converter that converts a DC output of the power supply into the desired DC operating voltage and/or the desired range of assurance, such as the DC-DC converter disclosed in copending U.S. patent application Ser. No. 08/184,387, filed Jan. 24, 1994, entitled A High Performance DC-DC Converter.

As discussed in the copending application, three critical considerations in designing DC-DC converters for computer systems are efficiency, load transients, and cost. It is inefficient and costly to provide a DC-DC converter to meet each of the different range accuracy and/or nominal operating voltage requirements of the various IC components of a computer system.

Thus, it is desirable to provide a DC-DC converter that can output multiple nominal operating voltages with different ranges of assurance. It is further desirable that the DC-DC converter can accommodate load transients in one or more of its outputs. As will be disclosed in more detail below, the multiple output DC-DC converter of the present invention advantageously achieves these and other desirable results.

The desired results are advantageously achieved by providing a primary voltage generation circuitry and an auxiliary voltage generation circuitry to a DC-DC converter. The primary voltage generation circuitry generates a primary voltage output, and the auxiliary voltage generation circuitry, in cooperation with the primary voltage generation circuitry, generates an auxiliary voltage output. The primary voltage generation circuitry includes a switching circuit element and an inductor element, whereas the auxiliary voltage generation circuitry includes an inductor element complementary to the inductor element of the primary voltage generation circuitry. The inductor element of the auxiliary voltage generation circuitry references the primary voltage output, and relies on a minimum load at the primary voltage output. Preferably, the auxiliary voltage generation circuitry further includes reference circuitry elements for regulating the auxiliary voltage output to a precise assurance range.

In an alternate embodiment, the inductor element of the auxiliary voltage generation circuitry references an independent reference voltage instead of the primary voltage output. Furthermore, the primary voltage generation circuitry is provided with a loading circuitry for removing the minimum load requirement at the primary voltage output. The loading circuitry includes another switching element complementary to the above mentioned switching element of the primary voltage generation circuitry.

FIG. 1 illustrates the relevant portions of one embodiment of the multiple output DC-DC converter of the present invention.

FIG. 2 illustrates the relevant portions of an alternate embodiment of the multiple output DC-DC converter of the present invention.

FIG. 3 illustrates one exemplary application of the multiple output DC-DC converter of the present invention.

In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well known systems are shown in diagrammatic or block diagram form in order not to obscure the present invention unnecessarily.

Referring now to FIG. 1, a diagram illustrating the relevant portions of the first embodiment of the multiple output DC-DC converter of the present invention is shown. As illustrated, the multiple output DC-DC converter 10 comprises primary voltage generation circuitry 12 for generating a primary voltage output Vcc.sub.1, and auxiliary voltage generation circuitry 14 for generating an auxiliary voltage output Vcc.sub.2. The two voltage generation circuitry 12 and 14 are coupled to each other at node 16, and cooperate with each other through their inductor windings L1 and L2, which will be described in more detail below.

The primary voltage generation circuitry 12 receives a primary voltage Vdd.sub.1 as input, and uses Vdd.sub.1 to generate the primary voltage output Vcc.sub.1. The auxiliary voltage generation circuitry 14 receives a first input voltage at node 16, and uses the first input voltage to generate the auxiliary voltage output Vcc.sub.2. The auxiliary voltage generation circuitry 14 also receives a second voltage Vdd.sub.2 as input, and uses Vdd.sub.2 to regulate Vcc.sub.2.

In one embodiment, Vdd.sub.1 is 5.0 volts; and Vcc.sub.1 and Vcc.sub.2 are 3.3 volts and 5.1 volts respectively. The voltage at node 16 and Vdd.sub.2 are 3.3 volts and 12 volts respectively. Vcc.sub.2 is regulated to a precision of plus or minus 2%.

The key elements of the primary voltage generation circuitry 12 include a switching field effect transistor (FET) Q1, an inductor winding L1, a capacitor C1, and a diode D1, coupled to each other as shown. The inductor winding L1 in cooperation with capacitor C1 together filter the digital pulses at the source of Q1 to generate Vcc.sub.1. D1 is used to clamp the voltage at the source of Q1, when Q1 is in a low state. The primary voltage generation circuitry 12 is intended to represent a broad category of circuitry found in traditional single output DC-DC converters, including but not limited to the DC-DC converter disclosed in the above identified copending U.S. Patent Application, which is hereby fully incorporated by reference.

The auxiliary voltage generation circuitry 14 comprises an inductor winding L2, a series pass FET Q2, and a precision reference U1. Additionally, the auxiliary voltage generation circuitry 14 comprises a diode D2, capacitors C2-C4, and resistors R1-R5. The circuit elements are coupled to each other as shown. The digital pulses from Q1 are coupled from L1 to L2 during the low state of Q1, which occurs when Q1 is off. In other words, the voltage at node 16 is provided to the anode of D2 when Q1 is off. As illustrated, L2 references Vcc.sub.1. As a result, the pulses to D2 are offset by Vcc.sub.1. Additionally, the winding ratio of L2 and L1 is set in a manner such that adequate rectified and filtered DC voltage input is provided to Q2, which is a small differential greater than the desired auxiliary voltage output Vcc.sub.2, thereby minimizing power loss in Q2. Q2 in turn, in cooperation with C3, generates and outputs Vcc.sub.2. U1 in cooperation with the resistors R1-R5 and capacitor C4 receives Vdd.sub.2 as input, and uses Vdd.sub.2 to provide gate voltage to Q2. U1 controls this gate voltage by comparing an internal reference to the voltage at the junction of R4 and R5 to regulate Vcc.sub.2. To achieve the desired high precision for Vcc.sub.2, it will be appreciated that high precision circuit elements have to be used for U1 and the resistors, in particular R4 and R5.

As will be appreciated, for this embodiment, since L2 references Vcc.sub.1 through direct coupling to the primary voltage generation circuitry 12, L2 also relies on a minimum load being maintained on Vcc.sub.1.

In the above described 3.3 v and 5 v embodiment, the low state of Q1 is at -0.4 v. The pulses to D2 are offset by +3.3 v. The input voltage to Q2 is set to 0.5 v-2.0 v greater than the 5.1 v. Lastly, Vdd.sub.2 is set to 12 v, and the minimum load on Vcc.sub.1 is about 0.1 amp.

Referring now to FIG. 2, a block diagram illustrating the relevant portions of an alternate embodiment of the multiple output DC-DC converter of the present invention is shown. Similar to the above described embodiment, the multiple output DC-DC converter 10' comprises primary voltage generation circuitry 12' for generating Vcc.sub.1 and auxiliary voltage generation circuitry 14' for generating Vcc.sub.2. The two voltage generation circuitry 12' and 14' are not coupled to each other, except they still cooperate with each other through their complementary inductor windings L1 and L2.

Also similar to the above described embodiment, the primary voltage generation circuitry 12' receives a primary voltage Vdd.sub.1 as input, and uses Vdd.sub.1 to generate the primary voltage output Vcc.sub.1. However, while the auxiliary voltage generation circuitry 14' still receives the second voltage Vdd.sub.2 as input, and uses Vdd.sub.2 to regulate Vcc.sub.2, L2 of the auxiliary voltage generation circuitry 14' references an independent reference voltage Vdd.sub.3 instead.

In one embodiment, Vdd.sub.1 and Vdd.sub.3 are both 5.0 volts. Vcc.sub.1 and Vcc.sub.2 are 3.3 volts and 5.1 volts respectively. Vdd.sub.2 is 12 volts and Vcc.sub.2 is regulated to a precision of plus or minus 2%.

Similar to the above described embodiment, the key elements of the primary voltage generation circuitry 12' still include a switching field effect transistor (FET) Q1, an inductor winding L1, a capacitor C1, and a diode D1, coupled to each other as shown. These key circuit elements cooperate with each in the same manner as described earlier. The primary voltage generation circuitry 12' is also intended to represent a broad category of circuitry found in traditional single output DC-DC converters, including but not limited to the DC-DC converter disclosed in the above identified copending US Patent Application.

However, the primary voltage generation circuitry 12' further comprises loading circuitry 20 for removing the requirement of having a minimum load at Vcc.sub.1. In other words, the load at Vcc.sub.1 can go to zero. The key elements of the loading circuitry 20 comprise a FET Q3, a capacitor C5, resistors R6 and R7, a diode D3, and preferably a ferrite bead FB1, coupled to each other as shown. The loading circuitry 20 is coupled to the rest of the primary voltage generation circuitry 12' at node 18.

When Q1 turns off, Q3 will turn on, thereby clamping the source of Q1 to ground. The output pulses on L2 are maintained, as well as sufficient voltage at the drain of Q2 of the auxiliary voltage generation circuitry is maintained. R6 and C5 cooperate to delay the turning on of Q3 until Q1 is fully turned off. D3 is used to turn off Q3 fast, so that it is off before Q1 turns on. R7 limits the current through Q3 to simulate the minimum load. FB1 is preferably provided to choke out RF.

Similar to the above described embodiment, the auxiliary voltage generation circuitry 14' comprises an inductor winding L2, a series pass FET Q2, and a precision reference U1. Additionally, the auxiliary voltage generation circuitry 14' comprises a diode D2, capacitors C2-C4, and resistors R1-R5. The circuit elements are coupled to each other as shown, and cooperate with each other in similar manner as described above, except for the fact that L2 is referenced to the independent input voltage Vdd.sub.3, and the current at L2 is decoupled from L1.

Now, without Q3, when Q2 turns off at low current on L1, the current in L1 would become discontinuous (i.e. go to zero), and the voltage at the source of Q2 will go to Vcc.sub.1, rather than the clamped voltage of D1. When this happens, the output voltage of L2 will drop to a low value and Q2 will lose regulation. In other words, Vcc.sub.2 will not be in the required regulated band, and an IC component coupled to Vcc.sub.2 will become inoperative. However, with Q3, Q2 will not lose regulation, thereby ensuring that Vcc.sub.2 will be in the required regulated band, and the receiving IC component will be operative.

As a result of the decoupling, output ripple of Vcc.sub.1 is reduced as compared to the above described embodiment, where L2 is referened to Vcc.sub.1. Furthermore, under this embodiment, the phases of L1 and L2 may be either in-phase or out-of-phase.

Referring now to FIG. 3, a block diagram illustrating an exemplary application of the multiple output DC-DC converter of the present invention is shown. As illustrated, the multiple output DC-DC converter 10 is coupled to provide its primary voltage output to a processor 26 and standard CMOS devices 28 of a computer system 24. Additionally, the multiple output DC-DC converter 10 is coupled to provide its auxiliary voltage output to IC components 30 with special voltage requirements. In the illustrated embodiment, the multiple DC-DC converter 10, the processor 26, the CMOS devices 28, and the ICs 30 are disposed on a circuit board 32, known as a mother board in the art. The circuit board 32 includes a socket (hidden by the processor 26) for receiving the processor 26. The CMOS devices 28 and the ICs 30 may be surface mounted to the circuit board 32 in a variety of well known surface mount techniques.

While the present invention has been described in terms of the illustrated embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described. The method and apparatus of the present invention can be practiced with modification and alteration within the spirit and scope of the following claims. The description is thus to be regarded as illustrative instead of restrictive on the present invention.