Patent Application
20140265594
The invention relates to power supplies and more particularly the supplying of power from one printed circuit board (or backplane) to another printed circuit board, such as from a motherboard (MB) to a daughterboard (DB).
Often a circuit board receives power from a backplane or another circuit board. Common among these arrangements is the mounting of a daughterboard (DB) to a motherboard (MB) where power from the DB is supplied from the MB.
Operating a power supply at its maximum efficiency has become more important in recent years to conserve battery power, among other reasons. Generally a DC power supply has a maximum efficiency, inherent in its design, at a predetermined percentage of its maximum power output. For instance, a switched DC power supply may have a maximum efficiency at 70% when operating at 80% of its maximum output. When operating at other than 80% of its maximum power output the supply's efficiency may be less than 70%.
Several techniques are known to keep a power supply at its maximum efficiency even under changing operating conditions (e.g. where a computer goes from active to standby state). Clock frequencies, fan speeds, processor core shedding or the adding of cores, may occur to maintain maximum efficiency. See, U.S. Pat. No. 7,904,740 and U.S. Pat. No. 8,041,963.
In one embodiment, a switched mode power supply having a primary side circuit and a secondary side circuit interconnected by a transformer is disclosed. A capacitor is used to store power and at least one diode couples a primary winding of the transformer to the capacitor such that when a first switch of the switched power supply opens, the capacitor receives the back emf from the primary winding. A second switch turns on and off the pumping of the capacitor with the back emf. A third switch connects the capacitor to the primary side circuit when a detector detects the loss of AC power.
Several circuits are disclosed that provide improved DC power from a backplane as on a motherboard (MB) to a circuit board engaging the backplane such as a daughterboard (DB). In the following description, numerous specific details are set forth such as specific circuit components and associated potentials, in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known electrical circuit designs and implementations are not described in detail to avoid unnecessarily obscuring the disclosed matter.
The improvements described below are used on a MB with its compatible DBs where the MB collects or concentrates data relating to power, such as meter readings, and provides other control, for example for street lighting. The DBs provide communication links such as RF links, power line communication links, links to other networks, etc. This particular application is not critical to the present invention.
A MB 10 which includes a backplane 14 is illustrated in
In the prior art, the female connector 16 on the DB includes spring contacts, one for receiving each of the male prongs on the DB connector. In this way objects touching or dropped onto the MB will not short pins of a male connector. The problem with this arrangement, however, is that if one of the springs in one of the female connectors fails, it is a much larger job to change the connector on the MB or backplane as opposed to reworking a single DB because the spring is more likely to break or is more fragile than the connector pin.
The prior art arrangement is reversed in
In the embodiment described below, some of the DBs require different voltages for operation than others. The male and female connector used on MB/DB requiring different voltages is the same thus there must be some mechanism to alert the MB as to what voltage is required by the DB. As will be seen, as a DB is inserted into the MB, a signal representing the voltage required by that particular DB is sensed in a feedback path by the MB so that the proper potential is applied for operation of the DB. Additionally, since all the power for the DBs originates at the MB, a power failure at the MB may in some circumstances cause problems with the equipment or signal gathering facilities associated with DBs. As will be seen, if power fails on the MB the MB has sufficient power storage to allow the DB to send a message indicating that power has been lost. This “last gasp” of power is stored on the MB in a more efficient manner when compared to prior art arrangements, which provide for last gasp power.
On the secondary side of the power supply circuit of
The circuits of
Ordinarily, energy is stored on the capacitor 40 and it will supply sufficient power for a last gasp transmission. However, often the capacitance required of the capacitor 40 is relatively high since the secondary side of the power supply operates at a low voltage. It is well known that the energy stored on a capacitor is equal to:
where “c” is the capacitance and “v” is the voltage on the capacitor. It is apparent from this equation that increasing the voltage at which the energy is stored is a more effective way of providing additional energy as opposed to increasing the capacitance of the capacitor.
The circuits of
During normal operation the switch 53 is open, the switch 55 is closed, and the switch 33 continually opens and closes. When the switch 33 opens a back electromotive force (emf) (sometimes also referred to a counter emf) occurs on line 39 which is coupled to the capacitor 50. The potential on line 39 is equal to the inductance associated with the winding 36, times the rate of decay of the current, once switch 33 opens. In a typical application where the AC potential 30 is for instance 220 volts (rms), the potential on line 39 can exceed 220 volts×√{square root over (2)}. The capacitor 46 and diode 47 act as a charge pumping circuit (in
When the AC power fails and switch 53 closes, the potential from the capacitor 50 is fed into the primary side of the switched power supply. The energy from the capacitor 50 provides the last gasp power, permitting a transmission or other activity such as non-volatile storage or the shutting down of a critical function. While there is a penalty associated with increasing the voltage of a capacitor, it typically is less onerous than increasing the capacitance of the capacitor.
As discussed above, ideally a power supply such as the power supply of
Referring to
For operating a power supply at its maximum efficiency at all times no matter what the load as taught by the present application, the minimum voltage needed for operating the circuit is determined. This is shown in
In a typical application the cycling of the on and off states of the power supply, as shown in
A circuit for providing the on/off operation is shown in
As mentioned earlier, the MB of
In
The feedback on line 84 is determined by the ratio of the resistances of resistors 87 and 88. These values are selected as a function of the power supply potential needed by a DB. When the feedback on line 84 matches the reference potential coupled to the operational amplifier 82, the regulator receives a zero signal to indicate that the proper DB supply potential has been reached. When this occurs, the regulator 80 can continue to provide that potential without increasing the potential.
In operation, once the MB determines that a DB has been plugged in, the regulator 80 begins to provide a potential which starts, for example, at zero volts and increases until the feedback on line 84 indicates that the proper potential has been reached. When this occurs the regulator 80 then maintains that potential on line 90, this being the proper potential for the DB.
Thus, power supply circuitry has been described which enables efficient supply of power from an MB to a DB even where different potentials are required by different DBs.
