DE2250575B2 - CIRCUIT ARRANGEMENT FOR LOW LOSS OF CONSTANT RULES OF A DC VOLTAGE - Google Patents

Description

Load current permeable diode 21 arranged between the negative pole of the unregulated Betriebsgleichtpannung U 1 and the compound of the switching regulator 1 jTiit the inductor 12 11 is connected a locked by the voltage Ul diode having the function of a free-wheeling diode. The switching regulator 1 is switched by means of a Schmitt trigger 14, which is controlled by a control amplifier 15 with a differential input as a function of a setpoint comparison made for the direct current flowing in the throttle 12, which is carried out at the differential input of the control amplifier. The actual value of the Prosse's current is detected at the ohmic measuring resistor 13 and fed as a voltage to the comparison input of the differential input via a low-pass filter 16 and a setpoint value for the inductor current specified by a constant direct voltage is fed directly to the reference capture of the differential input 21 of the load 3 and also a storage capacitor 22 and a high-resistance voltage divider 23 are connected in parallel. The second switching regulator is also switched by means of a Schmitt trigger 24, which is controlled by a control amplifier 25 with a differential input as a function of a setpoint / actual value comparison carried out at this differential input for the constant control of the direct voltage t / 2. The actual value of the voltage i / 2 detected at the high-resistance voltage divider 23 and via a low-pass filter 26 to the comparison input of the differential input :; and a setpoint value LA «// for t / 2 given by a constant DC voltage is fed directly to the reference input of the differential input. The mode of operation of the circuit will now be explained below.

The two switching regulators 1 and 2 work like two-point switching regulators in the circuit described above. In the quasi-stationary operation of the circuit, the direct current in the throttle 12 is given an almost sawtooth curve due to the switching activity of the sound controller 1, which fluctuates around a mean value of the direct current which is specified by the setpoint value present at the differential input of the control amplifier 15. The fluctuation amplitudes of this current are determined by the switching hysteresis of the Schmitt trigger 14 and the switching times of the switching regulator 1 are dependent on this and also on the inductance of the choke 12 13 causes the actual value detected and keeps interference pulses, which can arise due to parasitic reactances, away from the input of the amplifier 15. The switching frequency and the switch-on ratio of the switching regulator 1 are set automatically in two-point switching operation and are otherwise determined by the influences listed above. The ripple of the direct current in the choke decreases at a given voltage t / l, the greater the inductance L of the choke 12, the higher the switching frequency, the smaller the ohmic resistance in the load circuit and the lower the hysteresis of the trigger 14. Furthermore, the switching frequency depends on whether the switching regulator 2 is open or closed, because in the latter case the throttle also carries the current that flows through the switching regulator 2.

Assuming a low ripple of the choke current / with a triangular current curve, the switch-on time ftf and the switch-off time M of the switching regulator 1 for the four possible switching states of the switching regulators 1 and 2 can be represented simply by the following relationships. It is taken into account that the inductor current can continue to flow via the diode il during the switch-off time. Let Δ I <I = ho ” and t / 2 = const, R = ohmic resistance of the choke 12, then the following applies when the switching regulator 2 is closed

and

L-M '' ~ Ul- IR

L- M

therefore

• i. Ί, + Ί

IR

t / i

= Switch-on ratio

and

/ R (IZl -IR)

^U '-' ^r '- ¹ '"" LIJ- Ll

with the switching regulator open 2

= Switching frequencies /:

and

therefore

L- I /
II - VI - IR

L- I /
t'2- IR

I ₁ +

VI- IR

U \ -2 IR

One-to-one ratio

and

I / C /.

(t / I - L'2-IR) {V2-IR) L I / (t / l - 2IR)

-Switching frequencies /.

From the formula for the switch-on time t'i. it can be seen that when the denominator r'c disappears, the inductor current / (^) becomes stationary. However, this can be avoided and the effective losses in the choke can be kept small if its ohmic resistance R is small and the voltage difference t / l- U 2 is correspondingly small.

With constant regulation of the direct current in the choke 12, the load current is correspondingly constant regulated, and the switching voltage pulses caused by the switching regulator 1 are controlled by the choke

5_s 12 recorded, so that the direct voltage switched through to the load has a ripple. With the aid of the switching regulator 2 and the capacitor 22, this ripple can be reduced with little loss and the load voltage I) 2 can be constantly regulated to a predetermined setpoint value Uson. At the times when the ripple DC voltage and the voltage of the capacitor 22 have decreased to a minimum value, the switching regulator 2 is controlled in the open state. An almost constant current then flows

6j via the switching controller 1, the choke 12 and the diode 21 into the capacitor 22, whereby the voltage across the capacitor increases. Has the voltage on the capacitor reaches a maximum value, the

Switching regulator 2 is again controlled in the closed state, and a discharge current then flows from the capacitor via the load 3. The switching regulator 2 is switched by a Schmitt trigger 24, which is triggered by a control amplifier 25 with a differential input depending on the set-actual value comparison for the Load voltage U 2 is controlled. This nominal / actual value comparison is carried out at the differential input of the amplifier 25 by means of a nominal voltage Usoii, the actual value of the load voltage being detected at the voltage divider 23 and being fed to the comparison input of the amplifier 25 via a low-pass filter 26.

If the voltage U = U 2 has a low ripple requirement, the charging time ii and the discharging time Ie of the capacitor 22 are given by the following relationships. Be there

Δ U <U = t / 2 = ΙΛ0 // and / = const., C = capacitance and / 1 = charging current of capacitor 22,
then applies when the switching regulator is closed 2

with the switching regulator open 2

'= TT ^w

With a vanishing denominator, ie when / i - »■ / goes, fi becomes very large. Here the circuit goes into current limitation, and it becomes U = U2 = / · /?, The current is then limited by the resistor R and other neglected resistances of the load circuit.

By the circuit described as a whole it is achieved once that the fluctuations in the direct current in the choke 12 - as already mentioned above - the smaller the greater the inductance of the choke and the smaller the hysteresis of the trigger 14, i. H. the higher the switching frequency of switching regulator 1 is. To the on the other hand, the lower the ripple in the voltage across the capacitor 22 and thus in the load voltage achieved, the greater the capacitance of the capacitor 22 and the lower the hysteresis of the trigger 24, d. H. the higher the switching frequency of the switching regulator 2, which is under the aforementioned conditions accordingly results.

In the event of an overvoltage occurring at the output of the circuit, the circuit reacts advantageously in the Way that the switching regulator 2 is instantly controlled in the closing state, the switching regulator 1 can remain unchanged. On the other hand, the circuit according to the invention has the advantage that it also - as already said - is short-circuit proof. In the event of a short circuit at the output of the circuit, the Switching regulator 1 is immediately controlled to a maximum possible duty cycle, with the switching frequency can adjust freely.

1 sheet of drawings

Claims (2)

Patent claims: 1. Circuit arrangement for low-loss constant control a DC voltage on a load, with a first two-point switching regulator, a choke with a freewheeling diode and an ohmic resistor in series with the load and with a trigger switching the switching regulator, which is triggered by a control amplifier as a function of a set-actual value comparison for the direct current in the choke with actual value acquisition on the ohmic Resistance is controllable, characterized in that that a second two-point switching regulator (2) via one for the Load current permeable diode (21) a capacitor (22) and a high-resistance voltage divider (23) and also the load (3) is connected in parallel that a trigger switching this switching regulator (2) (24) by a control amplifier (25) as a function of a setpoint / actual value comparison for the DC voltage at the load is controlled with actual value detection on the voltage divider (23) and that regardless of this, the first two-point switching regulator (1) in each case for constant regulation of the direct current in the choke (12) and for limiting the load current is used. 2. Circuit arrangement according to claim 1, characterized in that the control amplifier (15,25) for the two-point switching controllers (1, 2) each have a differential input for comparing the Soü actual value are and that the actual values of the load current and the load-side DC voltage, respectively fed to the differential input of the associated control amplifier via a low-pass filter (16 or 26) are. The invention relates to a circuit for low-loss constant control of a direct voltage a load, with a first two-point switching regulator, a choke with a freewheeling diode and an ohmic one Resistance connected in series with the load and with a trigger that switches the switching regulator, which by a control amplifier as a function of a set-actual value comparison for the direct current with actual value acquisition can be controlled at the ohmic resistor. It is such a circuit without a choke and free-wheeling diode with a single switching regulator in Series connection with a load known (RCA-Silicon Power Circuits Manual, Technical / Series SP-50, RCA 1967, p. 189), in which the switching regulator according to Fig. 207 for constant control of the direct voltage is used and in which a high-resistance voltage divider is used in parallel to the load, at which the voltage isl value for the controller is detected, is connected in parallel. Circuits with a switching transistor used as a switching regulator result in a relatively low power loss in the switching transistor, as the transistor either has a high or a has low forward resistance. A transistor switching regulator delivers a constantly regulated one, however Insufficiently smoothed DC voltage. The still existing ripple of the DC voltage is at a known arrangement for low-loss stabilization Sizing a DC voltage (cf. DT-AS 16 16 728) largely eliminated by connecting an actuator and a switching regulator in series with the load and by the fact that the actuator is dependent on a setpoint / actual value comparison of a voltage derived from the stabilized DC voltage mn of a separate setpoint voltage is controlled. This known arrangement is provided with a current limiter which consists in the switching regulator supplying constant current instead of constant voltage in the event of a load short circuit There are similar circuits with a switching regulator and a control regulator connected in series with the load in DT-OS 15 13 420 and 15 88 157 described, the have essentially the same properties as the known circuit explained above. The circuit described in DT-OS 15 88157 also contains a device for achieving a largely linear control characteristic. The invention is now based on the object of a circuit of the type described above for a To set up constant control of a highly loaded DC voltage, such that the constant control also takes place with little loss and the highly loaded DC voltage is largely smoothed and that also a z. B. effective current limitation is achieved in a load short circuit. In the above-described known circuits, the ripple of the DC voltage increases when the load is high and the load current is greater than with a low load. This is accompanied by an increase in Actuator losses. According to the invention, a direct voltage loaded with a high load current is used to regulate constant in accordance with the task set out above, a second two-point switching regulator via one for the Load current permeable diode a capacitor and a high-resistance voltage divider as well as the Load connected in parallel, furthermore a trigger that switches this switching regulator is through a control amplifier in Dependence on a set-actual value comparison for the direct voltage at the load with actual value acquisition at Voltage divider controlled, and it is independent of the first two-point switching regulator for each Constant regulation of the direct current in the choke and used to limit the load current. According to a further embodiment of the invention, the control amplifiers for the two-point switching regulator are included one differential input each for a set-actual value comparison executed, and there are the actual values of the load current and the load-side DC voltage each supplied via a low-pass filter to the differential input of the assigned control amplifier. An embodiment of the invention is shown in the drawing, which is described below. The drawing shows the basic circuit according to the invention. Two switching transistors are used as switching regulators 1 and 2, by means of which an unregulated DC operating voltage U \ can be constantly regulated to a predetermined setpoint value LW and is available as a DC voltage Ό2 with low ripple at a load 3 connected to the output of the circuit if this load is available draws a large load current. A first switching regulator 1 is connected in series with a choke 12 and with the load 3 and also with an ohmic measuring resistor 13, and there is one for the in this series connection between the choke t2 and the load 3.