GB2175463A - Ballasts and transformerless power supplies - Google Patents

Abstract

A load 2 is connected to an A.C. source via a capacitor 1 which acts as a voltage dropping device. The load current may be varied by switching in different capacitance values (Fig. 1c). A clock-operated switch (14) may be used to bypass the capacitor 1 at certain periods of the day (Fig. 2). The load may be an a.c. load, or a d.c. load may be supplied via a half-wave or full-wave rectifier (Fig. 4). A series resistor 3 may be provided for current limiting, and the output voltage may be limited by means of a zener diode 5, an auxiliary load resistor 7, or a capacitor 9 connected across the input of bridge rectifier 4 and in series with capacitor 1 across the supply. A switched jack socket (10), (Fig. 1d), may be used to prevent a rise in voltage at the output terminals when the load is removed. The load may be an incandescent lamp, a heating element, a vacuum- tube filament string, an electroplating device, a radio, or a refrigerator open-door alarm (Fig. 6). <IMAGE>

Description

SPECIFICATION Ballasts and transformerless power supplies The present invention relates to the use of capacitors as ballasts to limit the current and voltage of loads connected in series with them and the source of higher voltage, e.g., the mains voltage.

BACKGROUND OF THE INVENTION Before the use of phase controlled triacs rheostats were used to control the power to various loads, such as lamps. These had two drawbacks, namely the cost and heating effect caused by the wasted power dissipated in the rheostat resistance. The use of the solid-state triac, of course, reduces these, but creates a problem of RFI, necessitating the use of a filter. Also, the triac and associated circuitry raise the price of the control.

A power resistor is still used to drop voltage in the heater string of vacuum tubes, e.g., for a television, and the same objections mentioned above hold for such an application.

The only apparent use of a capacitor as a ballast to provide limited and correct current was for a fluorescent tube, but, this was unacceptable as current pulses at the commencement of each half cycle cause blinking and harm to the tube because of their high amplitude.

Patent AN 8,114,861 revealed the use of leading (capacitive) gate feed for a semiconductor thyristor, such as a triac or SCR. However, there was no hint that a capacitor could be used to supply useful primary power (as opposed to firing a switching device) for a load, and, in those cases where the said gate firing power was available for only the few microseconds after zero crossing of mains voltage, of course no load could be usefully powered thus.

SUMMARY OF THE INVENTION This invention proposes to feed the load to be powered with the current from the voltage source, e.g., the mains voltage, after it has been limited by a non-polar capacitor. The said load is mostly, in the context of this invention, a purely resistive load, such as an incandescent lamp, a (small) heating element, the said filament string, or another relatively-low-power a.c. load; or, a relatively-low-power d.c. load, using a rectifying means, as will be shown below, such as a radio, a refrigerator alarm device, an electroplating device, etc.

The load may have a small inductive component, but then allowence for the increase in circuit current through the load due to cancellation of part of the capacitive reactance by the inductive reactance of the load must be made.

Obviously, a limiting factor as regards the current capable of being supplied by this proposed power supply/ballast is the physical size of the capacitor(s), which must of course be capable of withstanding the full mains voltage (as least where the load voltage is low).

It should be realized that, while any ratio of load voltage to capacitor voltage (cot 0) is possible, by properly choosing the capacitor value, a useful range of capacitive reactance values is sometimes that for which the load voltage is approximately equal to or less than 20% of the total (load) voltage, for then, due to the 90" phase difference of the currents in load and capacitor, the latter acts as a constant current source (with a deviation of no more than-40%), which may be useful per se, and/or if the load resistance changes or the loads are changed (as when an independent power supply unit based on this invention is made). With the current constant, the voltage will be determined entirely by the load resistance. Of course, however, any suitable voltage determining device, e.g., a zener diode (or back-to-back pair of same), etc.may be used where needed.

On the other hand, capacitors of various values may be switched in and out of the circuit to change the power delivered to the load. If, for example, the load is an incandescent lamp, the power delivered with capacitive feed will be smaller, the greater the rated power, since greater rated power means lesser resistance, and, for lesser resistance, the voltage drop, and hence power, will be less. When the voltage across the said lamp is relatively low, the filament does not glow white, but some color between yellow and red, which gives a pleasant effect. This will be expanded upon below. (To obtain such an effect until now, a bulky step-down transformer would be needed.) Also, a switching means may choose between normal mains current and capacitive feed. An example employing a 24-hour electric switch is shown below.

The a.c., or, after rectification, d.c. current obtained using capacitive feed may be switched using a semiconductor thyristor.

While many of the embodiments of this invention are closed units, it would be possible to handle the voltage outputs, e.g., of the low-voltage power supplies, if the live mains contact is connected to the capacitor, so that the neutral is at, or near the power supply voltage. In that case, a safety indicating device is described below.

Also described are various means for ensuring that the voltage output does not rise above a certain limit when the load is absent.

As is evident from the above description, the proposed power supplies differ in quite a few aspects from the known ones: quadrature current which can lead to a constant-current source, being the cause. Other notable differences are the fact that a direct short circuit of the load may be incurred without damage, as no real power is wasted-on the contrary, the higher the load resistance (up to the maximum when the load resistance equals the capacitive reactance), the higher the real power dissipated; and, the existence of a short high-current pulse upon initial power-up; this latter may necessitate use of a protective resistance, of small value, in series with the circuit. Obviously, any load which is usually connected directly to the mains voltage, e.g., a lamp, does not need such protection.

Thus, a fuse would only be used if it is thought that the capacitor itself might fail, and then, only for a load which could not stand the mains voltage.

As has been seen, no real power is wasted using this invention in the ballast element, the capacitor. However, it should be noted that a small amount of power is dissipated in the protective resistance, when used. Also, reactive power flows, and, when the capacitor acts as a constant-current source, i.e., when the load voltage is much less than the supply (e.g., mains) voltage, the reactive power is actually much greater than the real power dissipated.However, there are two reasons why these proposed power supplies and methods are still preferred over those of the art: (1) the great economy in size and expense would allow in many cases the waste of a relatively small amount of power; (2) the existence of leading reactive power is actually beneficial when, as is very often the case, other devices are used simultaneously, at least part of the time, which said devices have a lagging, inductive component (in the same way that a corrective capacitor is used with a fluorescent light). E.g., if such a device is used in conjunction with a refrigerator (the open-door alarm described below), it will neutralize part of the motor's inductance when the motor is running.

The following Examples will illustrate the invention principle, but should not be taken as limiting.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 General invention principles.

Figure 2 Diurnal timer controlling power.

Figure 3 Capacitive feed controller by triac.

Figure 4 Basic d.c. power supply circuits.

Figure 5 Power supply for radio receiver.

Figure 6 Power supply for refrigerator door alarm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. la shows the basic invention principle, whereby the load 2 is fed by the non-polar capacitor 1. As mentioned, the maximum current, after initial surge, is essentially equal to or less than the current that would flow in the capacitor connected alone to the voltage source, e.g., mains voltage.

Fig. 1 b shows an arrangement whereby the safe connection of the ballast/power supply can be ascertained. As was mentioned above, it may be desirable to have the power output at neutral voltage level. In order to ensure that the wall socket is properly wired (live (L) to the right of the socket and neutral (N) to the left), and that the neutral terminal is in fact connected, two indicators, such as the neon bulbs 30 shown in the Figure are connected from live to ground, and from live to neutral, of the device plug, respectively via dropping resistors 31.

Fig. 1c depicts a switching arrangement whereby the current through, and therefore the power of the load are changed as desired. Obviously, any switching device, whether mechanical or electronic would produce the same effect. Thus, without the use of phase controls a dimming effect can be produced. As mentioned, however, the color of the light produced in an incandescent bulb load is different since the voltage is lower, although full-cycle, as opposed to the partial-cycle pulses of the phase controls.

As one example of this phenomenon, the following Table gives data for various incandescent bulbs through which current flows from mains via a nominal 2.0 uf (non-polar) capacitor: the measured capacitance (measured by the current admittance to 50-cycle mains voltage) was 1.84 uf, approx.

Maximum volt- Power dis- Bulb Nominal bulb age measured sipated in filament wattage across bulb bulb, W color 40W 1 63V 15.0 yellow-white 60 91 8.34 orange-yellow 75 72 6.65 orange 100 31 2.83 red (faint) From this Table it can be seen that if the voltage drop on the bulb is too low (because of too small capacitance value) the light evolved is too weak to be useful. On the other hand, a limit is reached where there is almost no dimming; this could be useful, however, to prolong the lifetime of the bulb, as it is known that even a small reduction from the nominal bulb voltage rating increases lifetime immensely. Thus, a series capacitor of proper value could be used instead of the diode button, or other devices, used to lengthen bulb life. This benefit would be obtained automatically when the capacitor is used for dimming, as above.

Fig. 1d shows a simple means of ensuring that, if desired, the output voltage from the ballast capacitor 1 never rises above the desired load voltage (except for possible initial peak): by using a make-before-break jack 10. This means could also, of course, be used with the d.c. controls, to be described below. As mentioned, short-circuiting the capacitor current has no deleterious effect.

Fig. 2 illustrates the use of a 24-hour electric switch timer 14 to switch the ballast capacitor in and out of the home wiring. The timer lugs would be so set that all of the day and a portion of the night the timer switch 14a would be tripped ON, so that full a.c. power would flow to the electric loads in the home, e.g., lamps 2a and 2b. For a portion of the later night and/or early morning the switch would be disconnected so that the only flow of current would be via the capacitor 1, dimming the lamp 2a, connected to the power by wall switch 31. Resistor 15 may be used to reduce the discharge current when switch 14a closes in the morning.

It should be noted that this method will not work for fluorescent lighting: the lights blink on and off incessantly. Also, in general, care must be taken not to connect to a large inductance, to prevent resonance or near-resonance.

Fig. 3 shows how to control the leading current via a triac 16. The triac is fired in the 1 + and Ill- modes, as the gate current supplied via resistor 17 and tap resistor 18 is in phase with the mains voltage. As shown in Patent AN 8,114,861, the triac may be switched on and off by the non-shunting or shunting of the triac gate at terminals R and N, by any suitable shunting means. The gate feed here is "quasi-d.c.," i.e., it continues for a long time after the gate is turned on (when there is no shunt present).

Fig. 4 shows basic d.c. power supplies using the invention principle. In most cases the current supplied is constant, as the resistance of the load 2 is less than 20% of the capacitor 1 reactance. Thus, in case the load resistance conducts less than the supplied current, means must be available to take up the excess current, which said means will be shown. This is another difference from, for example, a transformer power supply, the quiescent current of which is low. However, changing the capacitance will change the current, as understood.

Fig. 4a shows the simplest type of d.c. supply, using diode 4 as half-wave rectifier. It is necessary to provide means for current return on the other half-cycle, and this is by means of diode 11. In most d.c. supplies, as opposed to the above a.c. supplies/ballasts, a protective resistance 3 is needed to protect the load 2 and any other sensitive components present from the initial current pulse at power-up. Also, in most cases, the current should be filtered and smoothed by filter capacitor 6.

Fig. 4b shows a full-wave power supply where the diode bridge 4 gives full-wave rectification.

The other components function as in Fig. 4a.

Fig. 4c shows the input to the supply of Fig. 4b, with the addition of resistance 8 to discharge feed capacitor 1, to prevent electric shock to anyone touching the device plug after disconnection from the wall socket.

Figs. 4d-f demonstrate means to limit the maximum voltage available to the load, when either the latter is initially non-connected, or the value of which changes.

In Fig. 4d the input to the bridge is paralleled by non-polar capacitor 7a, which, as its capacitance is higher than that of the feed capacitance, drops a lower voltage, the maximum of which is within desired limits. In this case, where there is no load connected to the bridge output, no real power is wasted (except in protective resistance 3).

Fig. 4e shows the use of a zener diode 5 across the bridge output. Thus, the output voltage can be almost constant for large variations in load dissipation. While the zener dissipates power, it is more economical, and smaller, than the capacitor 7a of Fig. 4d.

Fig. 4f shows an even simpler means of limiting maximum voltage: the use of an auxiliary resistance 7 with a value giving a voltage a few times or more greater than the maximum load voltage. The actual value used will depend on the trade-off between voltage rating of filter capacitor 6, and quiescent dissipation of said added resistance.

Fig. 5 shows a possible power supply for a radio receiver. It incorporates actually all the elements of Figs. 4b, c, e, and f; this is taking an extra precaution in case zener 5 were to fail, in which case, without auxiliary resistance 7 the load and filter capacitor 6 would be destroyed.

Capacitor 9 is a filter capacitor to prevent RFI to the receiver; of course, if it were large enough to serve as voltage limiter, as 7a of Fig. 4d, it would then serve a dual purpose, also acting as the filter. Also, the make-before-break jack of Fig. 1d could replace some of the components here, if desired, as it would limit the voltage (to zero) with no load connected.

The utility of such power supplies for radio receivers will depend on the noise rejection capabilities of the receiver.

Fig. 6 depicts an alarm unit for a refrigerator to warn of the opening of the door for longer than the prescribed period. The said alarm is claimed in copending Application No. YYYYY. As may be seen, the d.c. power supply for the alarm is empowered when the N.C, door switch 21 is opened, allowing current to flow from the indicator light 20 contacts via the supply capacitor 1. Components 1, 3, 4, 5, 6 and 7 have the same function as above, while the load is the buzzer 2 and the (Darlington) transistor 2a-b. The action is described in the said copending Application.

It would also be possible to use a low-voltage refrigerator indicator bulb powered by the capacitive feed of this invention. Then, a relatively-low voltage would appear across the said bulb, and this could be rectified. Were the alarm to go off, it could be powered by the said rectified voltage.

It should finally be noted that "non-polar" capacitor embraces also the equivalent combination of power capacitors and diodes connected so as to give a non-polar capacitor, when the rated voltages of said permit connection to the voltage source.

Claims (21)

1. The circuit comprising a non-polar or equivalent source capacitor connected between a source of essentially sinusoidal voltage and an essentially resistive load, whereby the voltage on said load is reduced, and the current is limited essentially at, or below, the value of the reactive current that would flow through the said capacitance if it were connected alone to the said voltage source, and which said circuit optionally includes a capacitor-pulse protective means, e.g., a series resistor, and/or optionally a source capacitor discharge means.

2. A circuit as in claim 1 where said lowered load voltage is an a.c. voltage.

3. A circuit as in claim 1 where said lowered load voltage is a d.c. voltage obtained using a full-wave or half-wave rectifying means, said half-wave rectifying circuit having current-return means for the half-cycle unused, and which said rectified voltage may be smoothed by a filter capacitor.

4. A circuit according to any of claims 1 through 3 where said voltage source is the mains voltage

5. A circuit according to claim 2 or 3 where said load voltage may vary between about 20% to about 0% of the said source voltage and whereby an essentially constant current is attained through the load.

6. A circuit as in claim 1 where said load has a relatively-small inductive component, and wher correction in said source capacitor value and voltage rating is made because of decrease in effective capacitive reactance due to its neutralization by said inductive-component reactance.

7. A separate power supply unit as in claim 1 comprising: means connecting to voltage source; said capacitor means; means connecting to said load; and, optionally, means for limiting voltage available to load to no more than the maximum allowable value.

8. A circuit as in claim 1 or 7 including a maximum-output voltage limiting means chosen from one or more of the group comprising: make-before-break connector, such as a jack; non-polar or equivalent capacitor connected across a.c. input to load; zener diode or two back-to-back zener diodes across load; and, auxiliary load resistance means across load.

9. The diminishing of the light output of an incandescent lamp which is the said load in claim 1, and which said diminishing of output lengthens the life of the said lamp.

10. The separate unit of claim 7 with additional incandescent-lamp connection means, such as a socket.

11. The diminishing of the light output of said incandescent lamp load of claim 9 by lowering said load voltage to the extent that its filament color is in the range between yellow and orangered.

12. The combination of the light-diminishing circuit of claim 9 with a diurnal timer which negates said light-diminishing action for that portion of the day when it is not desired.

13. The variation in the dimming of the light of an incandescent lamp as in claim 9 by varying the said source capacitance by any suitable switching means.

14. The switching of the output voltage as in claim 2 or 3 using a bidirectional or unidirectional semiconductor thyristor, respectively.

15. A circuit as in claim 4 where the said mains voltage live terminal is connected to the said source capacitor while its neutral terminal serves as an output connection, which may be handled if desired, with an optional indicating means to ensure that the said output voltage is at or near the neutral of the mains voltage and that said neutral terminal is effectively connected to the said load.

16. A radio-receiver power supply as in claim 8 with the addition of RFI filter means, such as a filter capacitor connected across input to said rectifier, and optionally with a plurality of outputvoltage limiting means.

17. The circuit of claim 1 wherein said load is a refrigerator open-door alarm where opening of refrigerator door for more than the allowable period enables said alarm.

18. The circuit of claim 1 wherein said load is one of the group comprising.

an a.c. load, such as: incandescent lamps; heating elements; and, vacuum-tube filament string; and, a d.c. load, such as: an electroplating device; a low-power amplifying device; and, a buzzer.

19. The use of a non-polar or equivalent capacitor to lower the voltage from an essentiallysinusoidal voltage source to an essentially-resistive load and limit the current supplied through said load with the optional addition of a capacitor-pulse protection means, such as a series resistance.

20. A ballast substantially described herein with reference to any of Figs. 1-6.

21. A power supply essentially described herein with reference to any of Figs. 1-6.