US3577065A

US3577065A - Switching regulator having a diode connected to an intermediate tap of a choke

Info

Publication number: US3577065A
Application number: US777654A
Authority: US
Inventors: Franz Ludwig Putzrath; Charles Allan Michel
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1968-11-21
Filing date: 1968-11-21
Publication date: 1971-05-04
Anticipated expiration: 1988-05-04

Abstract

A switching regulator having a switching device, a choke and a load connected in series with a pair of input terminals. The regulator further includes a diode tapped back on the choke to prevent current spikes at the output. By tapping the diode back on the choke, a voltage is induced in the tapped portion at the time the switch becomes short circuited and this voltage limits the current flowing through the switch during the time necessary for the diode to become reversed biased.

Description

United States Patent [72] Inventors Franz Ludwig Putzrath;

- Charles Allan Michel, Haddonfield, NJ. [21 Appl. No. 777,654 [22] Filed Nov. 21, 1968 [45] Patented May 4, 1971 [73] Assignee RCA Corporation [54] SWITCHING REGULATOR HAVING A DIODE CONNECTED TO AN INTERMEDIATE TAP OF A CHOKE 9 Claims, 2 Drawing Figs.

[52] US. Cl 323/22, 323/38 [51 Int. Cl G05I 1/56 [50] EieldoISearch 323/16- 19,22 (T), 38, 100 (F l3),22(V), (Cursory); 32/2, 45 (C); 37/123 (RM) [56] References Cited UNITED STATES PATENTS 3,112,436 11/1963 Cornelissen 323/22(V) Primary Examiner-J. D. Miller Assistant Examiner-A. D. Pellinen Attorney-Edward J. Norton ABSTRACT: A switching regulator having a switching device,

a choke and a load connected in series with a pair of input terminals. The regulator further includes a diode tapped back on the choke to prevent current spikes at the output. By tapping the diode back on the choke, a voltage is induced in the tapped portion at the time the switch becomes short circuited and this voltage limits the current flowing through the switch during the time necessary for the diode to become reversed biased.

SWITCHING REGULATOR HAVING A DIODE CONNECTED TO AN INTERMEDIATE TAP OF A CHOKE This invention relates to switching regulators and more particularly an improved switching regulator in which the current spikes are substantially removed.

In prior art switching regulators one of the major problems has been the occurrence of a current spike at the output of the regulator each time the switching device became short circuited. The spike lasted for approximately the duration of the time required for the diode to become reverse biased. For good regulation, these spikes must be eliminated. Furthermore, by eliminating them, considerable power is saved. In the past the problem has been overcome by either using fast turnofi diodes or very large filter capacitors of which are expensive and the latter of which does not t-...t itself to a compact unit.

Accordingly, a switching regulator is provided herein in which the diode is tapped to an intermediate tap of the choke so that a voltage is induced in the tapped portion of the choke that limits the short circuit current flowing through the switch during the diode turnoff time.

It is therefore an object of this invention to provide an improved switching regulator.

The invention is described in more detail hereinafter with reference to the following FIGS. in which:

FIG. 1 is a schematic drawing partially in block fonn, of the improved switching regulator, and

FIG. 2 is a more detailed circuit diagram for FIG. 1.

Referring to FIG. 1, in which an embodiment of the improved switching regulator is shown, a source of unregulated voltage E; is applied to input terminals 12 and 14 and a regulated output voltage E, appears across a pair of

output terminals

16 and 18.

Terminals

16 and 18 are connected to opposite ends of resistor 20. A switching device 22, a choke 24 and resistor are connected between the input terminals 12 and 14. Capacitor 26 is coupled in parallel with resistor 20. A diode 28 is coupled from one end of resistor 20 to an intermediate tap 30 of reference 24.

The other end of resistor 20 is coupled to one input of comparator circuit 32, the other input of which is a reference voltage V, applied from terminal 36. The output of comparator circuit 32 is coupled through driver 34 to switch 22 and maintains the switch in either the open circuit state or the closed circuit state. Comparator 32 pulse width and frequency modulates switch 22 by comparing the output load voltage with the reference voltage V,. When the output voltage reaches a certain value, circuit 32 applies a signal through driver 34 and closes switch 22 thereby allowing current to flow into choke 24. On the other hand, when the output voltage reaches a second value, greater than the first value, circuit 32 applies a second signal through driver 34 to switch 22 and opens switch 22 so that no further current is applied from the input terminals l2 and 14 to the choke 24.

In operation the circuit in FIG. 1 regulates the input voltage in the following manner. When switch 22 is closed, current is applied to choke 24 and energy is stored therein. The current continues through choke 24 and through load 20 and back to the other input terminal 14. During the time switch 22 is closed diode 28 is reverse biased because the cathode is more positive than the anode. When the current at terminal 16 reaches a specific value, circuit 32 sends a signal through driver 24 which opens switch 22. At this time the energy which is stored in choke 24 begins to discharge through the loop consisting of resistor 20 and diode 28, which is no longer reverse biased when switch 22 is open. The current continues in this manner until the voltage at terminal 16 falls .to the second value and then circuit 32 sends a signal through driver 34 which again closes switch 22.

At this time current is applied to choke 24 from switch 22 and from diode 28 since it takes a finite amount of time to reverse bias diode 28 when switch 22 closes. However, since the cathode of the diode 28 is tapped back at point 30 on choke 24, a voltage is induced in the tapped portion of choke 24 due to the rapidly changing current when switch 22 is opened and this voltage limits the current through switch 22 so that the current flow is substantially constant through choke 24. When diode 28 becomes reverse biased, the current is not changing so rapidly so the induced voltage will no longer inhibit the current flow through switch 22.

Referring now to FIG. 2 a more complete circuit diagram for the partial block diagram of FIG. 1 is shown. Like components in FIGS. 1 and 2 are given like numeral designations for easy comparison of the two circuits. The unregulated input voltage E, is filtered by capacitors 38 and 40 and inductor 42 before being applied to switch 22. Switch 22 comprises a transistor 44 which has collector 46, emitter 48, and base 50. The filtered input current is applied to collector 46 of transistor 44 and emitter 48 is coupled to choke 24 as the output of switch 22. Base 50 is coupled through resistor 60 to emitter 48 of transistor 44. Transistor 44 is biased to operate in either the cutoff state or the essentially saturated state so that it acts as a switch. By essentially saturated it is meant that transistor 44 is held slightly out of saturation by the amount of the saturation voltage across driver circuit 34.

The driver circuit 34 comprises transistor 52 which has a collector 54, emitter 56, and base 58. The collector 54 of transistor 52 is coupled to base 50 of transistor 44, and emitter 56 is coupled to collector 46 and base 58 is coupled through a parallel resistor 62capacitor 64 combination to collector 46, of transistor 44.

Comparator circuit 32 includes a differential amplifier 66 which pulse width and frequency modulates the duty cycle and frequency of a unijunction-type relaxation oscillator 68. Oscillator 68 consists of unijunction transistor 70, capacitor 72 and transistor 74. It is modulated by the differential outputs 76 and 78 of differential amplifier 66. Differential amplifier 66 consists of transistors 80 and 82 arranged in a conventional manner. Oscillator 68 is modulated by comparing the output voltage taken from terminal 16 with reference voltage V, taken from terminal 36. Output terminal 16 is coupled to the base of transistor 82 through resistor 84. Resistor 86 couples the junction of resistor 84 and the base of transistor 82 to the other output terminal 18. Reference voltage V, is derived by voltage dividingthe voltage across Zener diodes 88 and 90.

When the voltage at terminal 16 reaches the highest allowable value, circuit 32 and driver 34 cause transistor 44 to be biased into the cutoff region. On the other hand, when the voltage at terminal 16 reaches the lowest allowable value, transistor 44 is caused to be biased in the essentially saturated region. Thus, transistor 44 acts as a switch.

A circuit similar to the one shown in FIG. 2 was constructed in which the current spikes through choke 24 were considerably reduced and a 4 to 6 watt power saving at 8.6 amps. load current was achieved. In this circuit, the following components were used:

Capacitor 26200p.f Capacitor 38-100 f Capacitor 4:0200y.f. Capacitor 64-3,900pf. Capacitor 72160pf.

Diode 28-1N391 0.

Inductor 4:225p.h.

Resistor 20L0ad value. Resistor 60820 ohm. Resistor 62-680 ohm.

Resistor 842.15K ohm, 1%. Resistor 86-2.15K ohm, 1%. Resistor 921.5K ohm. Resistor 941.96K ohm, 1%. Resistor 96-4313 K ohm, 1%. Resistor 981.5K ohm. Resistor 100-470 ohm. Resistor 102-910 ohm. Resistor 104--1.5K ohm. Transistor 44-2N3265. Transistor 52-2N2905A. Transistor 702N489. Transistor 742N 1711. Transistor 80-2N2905A.

5 Transistor 822N2905A.

Choke 24150p.h; 27 turns #16 wire-tapped at 5 turns.

3 We claim; 1. A switching voltage regulator comprising: a pair of input terminals,

a source of unregulated voltage which is applied to said pair of input terminals,

a switching device,

a choke,

a load,

said switching device, said load and said choke being coupled in a series circuit between said input terminals,

a comparator circuit coupled between said load and said switching device for opening said switching device when said voltage across said load reaches a first value and for closing said switching device when said voltage across said load reaches a second value, and

a diode connected across said load and a portion of said choke and poled to conduct when said switching device is in the open state, said remaining portion of said choke having a voltage induced therein which when said switching device goes from the open to the closed state limits the current through said closed switch during the reverse recovery time of said diode.

2. The invention according to claim 1, wherein a capacitance is in shunt with said load.

5. The invention according to claim 4, wherein said comparator circuit includes a unijunction relaxation oscillator, the duty cycle of which is modulated by a differential amplifier.

6. A switching regulator for applying a regulated DC output voltage to a air of output terminals in response to the application of an unregulated DC input voltage applied to a pair of input terminals thereof, said regulator comprising:

a switching device, responsive to a control signal,

a choke having a winding with a plurality of turns,

a load resistance coupled between said output terminals,

said switching device, said choke and said load resistance being serially connected between said input terminals,

a comparator circuit coupled across said output terminals for applying said control signal to said switching device which open-circuits said device when the voltage at one of said output terminals reaches a first value and which short circuits said device when the voltage at said one output terminal reaches a second value,

a diode coupled across said load resistance and a certain number of said turns which are on the load resistance side of said choke,

said diode being poled to be forward biased when said switching device is open circuited, and

the remaining number of said turns having a voltage induced therein when said device changes to the short circuit state, said voltage being sufficient to limit the current flowing through said device during the time necessary for said diode to become reverse biased.

7. The invention according to claim 6, wherein a capacitor is in shunt with said load resistance.

8. The invention according to claim 6, wherein said switching device is a transistor which operates in only the cutoff or essentially saturated regions in response to said control signal from said comparator circuit.

9. The invention according to claim 8, wherein said comparator circuit includes a differential amplifier and a unijunc tion-type relaxation oscillator, said amplifier comparing said output voltage with a reference voltage to pulse width and frequency modulating the output of said oscillator, said oscillator output being proportional to said control signal.

Claims

1. A switching voltage regulator comprising: a pair of input terminals, a source of unregulated voltage which is applied to said pair of input terminals, a switching device, a choke, a load, said switching device, said load and said choke being coupled in a series circuit between said input terminals, a comparator circuit coupled between said load and said switching device for opening said switching device when said voltage across said load reaches a first value and for closing said switching device when said voltage across said load reaches a second value, and a diode connected across said load and a portion of said choke and poled to conduct when said switching device is in the open state, said remaining portion of said choke having a voltage induced therein which when said switching device goes from the open to the closed state limits the current through said closed switch during the reverse recovery time of said diode.

3. The invention according to claim 1, wherein said switching device is a transistor.

4. The invention according to claim 3, wherein said comparator circuit drives said transistor into the cutoff region of operation when said voltage across said load is said first value, and which drives said transistor into the essentially saturated region of operation when said voltage across said load is said second value.

6. A switching regulator for applying a regulated DC output voltage to a air of output terminals in response to the application of an unregulated DC input voltage applied to a pair of input terminals thereof, said regulator comprising: a switching device, responsive to a control signal, a choke having a winding with a plurality of turns, a load resistance coupled between said output terminals, said switching device, said choke and said load resistance being serially connected between said input terminals, a comparator circuit coupled across said output terminals for applying said control signal to said switching device which open-circuits said device when the voltage at one of said output terminals reaches a first value and which short circuits said device when the voltage at said one output terminal reaches a second value, a diode coupled across said load resistance and a certain number of said turns which are on the load resistance side of said choke, said diode being poled to be forward biased when said switching device is open circuited, and the remaining number of said turns having a voltage induced therein when said device changes to the short circuit state, said voltage being sufficient to limit the current flowing through said device during the time necessary for said diode to become reverse biased.

9. The invention according to claim 8, wherein said comparator circuit includes a differential amplifier and a unijunction-type relaxation oscillator, said amplifier comparIng said output voltage with a reference voltage to pulse width and frequency modulating the output of said oscillator, said oscillator output being proportional to said control signal.