US3530367A - Zener diode voltage regulator circuit - Google Patents

Description

SePt- 22, 1970 R. A. ARDENGHI 3,530,367

ZENIER DIODE VOLTAGE REGULATOR CIRCUIT Filed March 7, 1969 PRIOR ART FIG. I.

wn'NEssEs: v INVE NToR l RoberrA-G0rdenghi United States Patent O ZENER DIODE VOLTAGE REGULATOR CIRCUIT Robert A. Gardenghi, Baltimore, Md., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 7, 1969, Ser. No. 805,131 Int. Cl. Gf 1/60 U.S. Cl. 323-8 5 Claims ABSTRACT OF THE DISCLOSURE A Zener diode voltage regulator circuit wherein a plurality of Zener diodes are each connected to a respective impedance element with a like plurality of conventional diodes connecting a load impedance across each Zener diode. The conventional diodes allow current to the load impedance and block current between Zener diodes.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates generally to Zener diode voltage regulator circuits and more particularly relates to regulator circuits for ensuring power sharing between a plurality of Zener diodes.

Description of the prior art The maximum power capability of a Zener diode regulator is limited by the largest Zener diode available. Zener diodes cannot readily be connected in parallel to obtain higher power rating unless they are precisely identical and maintained at the some temperature. This is virtually impossible and the parallel connection of Zener diodes should be avoided.

An object of the present invention is to provide a Zener diode voltage regulator circuit allowing the attainment of virtually any high power level desired.

Another object of the present invention is to provide a high power voltage regulator circuit without the necessity of precise matching of the components.

Another object of the present invention is to provide a Zener diode voltage regulator circuit of increased power capability and greater reliability than heretofore available.

SUMMARY OF THE INVENTION The present invention accomplishes the above cited objects and advantages by providing a plurality of Zener diodes each connected through a respective impedance element to a voltage source. A like plurality of conventional diodes are connected in an OR gate function to allow current to the load impedance and yet block current between Zener diodes.

BRIEF DESCRIPTION OF THE INVENTION Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing, in which:

FIG. 1 is an electrical schematic diagram in accordance with the prior art; and

FIG. 2 is an electrical schematic diagram of an illustrative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the well known shunt Zener regulator circuit. The current through impedance element 2 is the sum of currents through a Zener diode 4 and a load impedance 6. As the magnitude of the voltage V1 at the input means varies or as a magnitude of the load impedance 6 varies, the resistance of the Zener diode 4 varies, thereby changing the current through the Zener 3,530,367 Patented Sept. 22, 1970 ICC Vi-Vz Rs where RS is the value of the impedance element 2. The Zener diode must be capable of dissipating the power associated with this maximum current.

When greater power capability is desired any attempt to parallel Zener diodes is usually doomed because of the ditliculty in obtaining precisely identical Zener diodes. The Zener diode which assumes all of the load fails when the remaining Zener diodes do not share the load.

The present allows the combining of any number of regulator circuits without precise matching of components. Each Zener diode 10, 12, 14 36 connect each connected with a respective current limiting resistor 20, 22, 24 26. Unilateral conducting means in the form of conventional diodes 30, 32, 34 36 connect each Zener diode to a load impedance 40. The diodes 30, 32, 34 36 allow the currents from all the regulators to flow into the load 40 and yet block the path between Zener diodes. The maximum current that can flow in any Zener diode for a given input voltage V1, therefore, is determined by the magnitude of its associated impedance element and the Zener voltage. The conventional diodes should be chosen to have similar voltage ratings and the impedance elements are to be of similar magnitude but precise matching is not necessary.

As the supply voltage V1 or the load impedance 40 is varied, the currents through all of the diodes will distribute according to the component tolerances. The maximum current in any one Zener diode, however, will never exceed the designed maximum, no current being fed to it by the other Zener diodes. Reliable operation is thereby insured.

More specifically, as the supply voltage V1 increases from a low value to a higher one the Zener diodes, will successively become conducting, starting with the Zener of lowest voltage break-over level. The load voltage will always remain between the value of the Zener which has become conducting and the break over voltage of the next higher voltage Zener. After the highest voltage Zener has become conducting no further increase in load voltage occurs. For example, assume a circuit with only 3 Zener diodes 10, 12 and 14 and that these were standard 10 volt 1-5% Zeners. The break-over voltage of any one could be anywhere between 9.5 volts and 10.5 volts since they are i5% diodes. For worst case, assume diodes 10, 12 and 14 have break-over voltages of 9.5, 10, and 10.5 volts respectively. The circuit would then regulate for any input, V1, over 9.5 volts. If V1 was greater than 9.5 but less than 10 volts, only Zener 10 would break over and regulate the output to 9.5 volts. If V1 were 10:3 volts, Zeners 10 and 12 would both conduct and the regulated output would be 10 volts. If V1 were greater than 10.5 volts all three Zeners 10, 12 and 14 would break-over and the regulated output would be 10.5 volts. This regulator provides a nominal l() volts since it actually varies over a 5% range. Or, stated another way, the maximum amount of regulation that can be obtained is a function of the tolerances between the diodes. This is not a handicap since this circuit does have the advantage of high power capability not obtainable otherwise.

Over the entire regulation range no individual Zener has a current through it greater than where Vm is the maximum expected value of the input voltage V1, VZ is the break-down voltage of any particular Zener, and Rs is the impedance value of a series resistor.

Changes with load resistance RL have a similar effect. Starting with RL=oo (and with V1 suiiiciently high) all Zeners are in conduction and VL-Vzm, where VZm is the breakdown voltage level of the highest voltage Zener.

As RL becomes smaller and the load current increases, one by one the Zeners go out of conduction and the load voltage is successively determined by that Zener of the next lowest voltage level. This continues until the lowest voltage Zener goes out of conduction at which point the load voltage is no longer regulated.

Thus the range of allowable load current variation has been extended by a factor of n, where n is the number of Zener diodes used.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications, substitutions, and alterations within the spirit and scope of the present invention are herein meant to be included.

I claim as my invention:

1. In a power regulator circuit the combination comprising; a plurality of parallel circuit combinations each including a series circuit combination of an impedance element and Zener diode; a load impedance; a like plurality of unilateral conducting means each connecting a respective common junction of said impedance element and said Zener diode to said load impedance.

2. The combination of claim 1 wherein said unilateral conducting means are poled to block current between Zener diodes.

3. The combination of claim 1 further comprising an input voltage source connected across each of said parallel circuit combinations.

4. The combination of claim 3 wherein said load impedance has a common connection to said input voltage source.

5. In a power regulator circuit the combination comprising; a load impedance; input voltage means; a plurality of parallel circuit combinations serially connected with said load impedance across said input means, each including a series circuit combination of an impedance element and a unilateral conducting means; and a like plurality of Zener. diode means each connecting a respective common junction between an impedance element and a unilatera1 conducting means to the common junction between said input means and said load impedance.

US. Cl. X.R.

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