Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2001-10-29
2003-08-12
Berhane, Adolf D. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
Reexamination Certificate
active
06606260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to switch mode power supplies and more particularly to small systems power supplies for entry control systems and the like.
2. Background Description
Apartment buildings, office buildings, condominium complexes, gated residential communities, industrial parks and other secured locations often include an entrance access control system. One type of access control system, known as a telephone entry system (TES), provides building security as well as tenant access control to a particular building, apartment complex, etc. The access control system controls entry at one or more other building entry points, e.g., doors, garage doors, etc. A typical access control system includes a main control unit located at a primary entrance and depending on the size of the structure or area being monitored additional remote units may be provided to control remotely located doors. The access control system may also monitor the connected entry points for unauthorized access. For a TES type access control system, visitors wishing to enter the building/complex contact tenants or other building personnel over the TES who are capable of admitting the visitor by remotely unlocking the entrance, e.g., from the tenant's apartment.
The main control unit controls the main entrance and may include a keypad and auto-dialer and be connected to a public telephone line. Remote units, typically communicate with the main unit to provide remote access to authorized personnel. The main unit can identify tenants seeking entry by personal access code, authorize entry, monitor for unauthorized entry at the remote doors, etc. A tenant directory may be displayed on the control unit itself or on an adjacent sign. The directory includes tenant codes which are corresponding directory numbers for each person, business or other parties in the building (tenants) that are capable of unlocking the entrance.
When a visitor enters a tenant code into the keypad, the main control unit automatically dials the corresponding tenant's telephone number. Then, the called tenant has an opportunity to establish the identity of the visitor. The tenant, using the same everyday telephone upon which the call was received, unlocks the entrance, e.g., by pressing a predetermined telephone number on the keypad. Currently, each main unit and connected remote units includes its own low voltage power supply.
FIG. 1A
is a schematic of a state of the art power supply
50
. Alternating Current (AC) is supplied through a typical, small wall transformer stepping voltage down from a 110 VAC to 9 VAC in this example. The 9 VAC is provided to a full wave rectifier
52
, a bridge rectifier in this example. The bridge rectifier
52
rectifies the 9 VAC to provide a 9V rectified DC, which is passed to a capacitor filter
54
. The capacitor
54
filters transients from the rectified voltage, providing an unregulated 9 volts DC that may include an acceptable ripple voltage. In this example, a voltage regulator powered by the unregulated 9V includes a zener diode
56
biasing a transistor
58
to provide 3V. The 3 volt supply regulator, converts the unregulated 9 volts to a clean 3 volt regulated output.
Once the capacitor
54
charges, essentially to the peak magnitude of the input AC, i.e., the upper magnitude of the rectified DC, the unregulated voltage across the capacitor
54
remains essentially constant. The unregulated voltage appears as a relatively clean DC (i.e., constant) voltage as long as the DC is unloaded. As long as the capacitor voltage remains constant, i.e., at no load, no current passes from the AC input through the rectifier to the unregulated voltage. However, the unregulated DC powers a voltage regulator which converts the unregulated DC to a supply voltage, e.g., 3 volts in this example. Typically, the regulator draws current for a load. Load current discharges the capacitor
54
slightly between AC peaks, causing the ripple voltage on the regulated DC. So, the ripple voltage is symptomatic of load current discharging the capacitor
54
between AC voltage peaks and, then, recharging the capacitor
54
during each peak.
The amount of ripple is set by design. The load current may be specified small enough that ripple voltage on the unregulated DC voltage is less than 5-10%. Output current flows constantly from the capacitor
54
; and, input current flows through the rectifier
52
only during a small portion of each AC cycle, i.e., at voltage peaks. Unfortunately, during these short periods when rectifier current does flow, very high input current flows.
FIG. 1B
is a comparison of the AC input voltage
60
, unfiltered DC
62
, the filtered unregulated supply voltage
64
and current
66
through the rectifier generating the unregulated voltage and regulated voltages. For example, for a 3V DC supply to provide 0.1 Amps (0.3W), regulator transistor
58
continuously draws 0.1 Amps from the 9V unregulated supply (0.9W). For a ripple voltage less than 10% (0.9V), the total charge removed by load current (between peaks) must be replaced, roughly during 13% of each half cycle at each peak. Therefore, remembering that I=Cdv/dt, the current necessary to recharge the capacitor
54
, averages about 0.8 Amps during that 13% recharge period of each cycle. So, much higher peak current flows through the rectifier
52
during the peak periods than the DC current being supplied. Further, since this peak current both starts (when the input voltage rises above the unregulated supply voltage) and terminates even more rapidly (when the input line voltage begins to reverse polarity) reactance from input path inductances can become significant.
Thus, to avoid component failure from high current or reduced supply voltages from inductance and resistive line losses (i.e., voltage drops across input line impedance), the bridge rectifier must be capable of handling brief but high peak currents and a higher gage wire must be used than the actual consumed power otherwise would merit. Also, if the AC input is a low voltage, e.g., 9 volts from a plug-in wall transformer, instead of typical house current of 110 volts, the input transformer must also be capable of handling this large peak current. Since input components such as the transformer must be heavier duty and the wire between the input transformer and the bridge rectifier must be a higher gage, they are more expensive than the average current (and correspondingly the power consumed) would otherwise necessitate.
Furthermore, power companies discourage high peak current requirements. The current from a single such small wall transformer to power a DC supply may account for an insignificant percentage of the total current required for a single house and so may not be a concern. However, aggregated over an entire neighborhood, where a large number of these small transformers are powering small DC power supplies, each adding higher peak currents, supplying the aggregate current can become a major problem. This is becoming the norm as small low voltage appliances are becoming popular. So, just as larger components are required for providing AC to these DC supplies, power companies must use larger generators, power lines, etc., to satisfy the aggregate peak currents for these neighborhoods.
The power consumption concern with these prior art supplies is quantified as power factor. Power factor (PF) reflects how efficiently electricity is being used. The power provided (apparent power) in kilovolt amperes (kVA) includes both the actual power used (consumed) in kilowatts (kW) as well as reactive power (also in kVA) and PF=consumed/apparent. Typically, power factor is lower in the presence of non-linear devices such as solid state or switch mode power supplies.
Power companies charge customers based on the apparent power supplied to a particular facility or home not on the actual power consumed. It is important to consumers to keep power costs low and so, to efficiently consume the power being provided. In other w
Berhane Adolf D.
Fitch Even Tabin & Flannery
The Chamberlain Group, Inc.
LandOfFree
Switch mode power supply for a telephone entry system or the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switch mode power supply for a telephone entry system or the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switch mode power supply for a telephone entry system or the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3081059