RU230329U1 - Pump current source - Google Patents

Abstract

The utility model relates to current pulse generation technology, in particular to power supply devices for laser diode matrices for pumping solid-state lasers. A pump current source made in the form of a closed circuit consisting of a series-connected storage capacitor, a choke, a pump radiation source, a transistor switch with a control circuit and a current sensor, as well as a damper diode connected in parallel to the choke and the pump radiation source, the choke and the pump radiation source with a damper diode are connected between the terminal of the transistor switch and the high-voltage electrode of the storage capacitor, the other output of the transistor switch is connected to the contact of the current sensor, the second contact of which is connected to the second electrode of the storage capacitor and the zero bus, and the control circuit includes a threshold device connected to the current sensor, and a control pulse former connected to the control input of the transistor switch, a filter capacitor with a capacity of is introduced between the low-voltage terminal of the pump radiation source and the zero potential bus where t _on is the diode turn-on time; I is the current in the inductive circuit; U _Cf is the permissible voltage on the filter capacitor at the end of the time t _on . The damper diode can be implemented on the basis of a transistor in diode connection. The technical result of the utility model consists in reducing voltage surges and reducing the weight and size parameters of the current pulse generator. 2 clauses, 4 fig.

Description

The utility model relates to the technology of generating current pulses, in particular to power supply devices for pumping sources of solid-state lasers.

A device for pumping a solid-state laser using a pulsed pump lamp is known [1], through which a discharge of a storage capacitor is produced by breaking down the discharge gap of the lamp and passing a discharge current pulse of a given duration T through the lamp, determined by the capacity of the storage capacitor and the inductance of the choke in the discharge circuit. Such circuits have large energy losses in the circuit, since the current through the lamp during the discharge process varies within wide limits and differs for a significant part of the time from the optimal value, at which the useful light output of the lamp is maximum. This is especially noticeable when forming current pulses of 1 ms or more duration, required, for example, for pumping erbium glass lasers operating in a safe wavelength range. In addition, such circuits have significant dimensions due to the large inductance of the choke.

These shortcomings are partly eliminated in a pulse current generator, made in the form of a closed circuit consisting of a series-connected storage capacitor, a transistor switch with a control circuit, a choke and a pump radiation source (a gas-filled lamp), as well as a damper diode forming a second circuit, connected in parallel to the choke and the pump radiation source [2].

In the specified generator, the control input of the key with the control circuit is under high voltage of the storage capacitor. This leads to the need to use high-voltage elements, and, consequently, to an increase in the cost of the device and an increase in its dimensions. In addition, the speed of the circuit and current consumption deteriorate, since additional energy and time are spent on recharging the circuit capacities to switch high-voltage voltages.

The closest in technical essence to the proposed utility model is a current pulse generator, implemented in the form of a closed circuit consisting of a series-connected storage capacitor, a choke, a pump radiation source, a transistor switch with a control circuit and a current sensor, as well as a damper diode connected in parallel to the choke and the pump radiation source, wherein the choke and the pump radiation source with the damper diode are connected between the terminal of the transistor switch and the high-voltage electrode of the storage capacitor, the second output of the transistor switch is connected to the current sensor, the other output of which is connected to the zero potential bus connected to the second output of the storage capacitor, and the control circuit is implemented in the form of a former of a control pulse of fixed duration and contains a threshold device connected via its signal input to the current sensor, and via its output to the pulse former connected to the input of the transistor switch [3].

The disadvantage of this technical solution is overvoltage when the transistor switch is opened due to the self-induction EMF of the choke E [4].

E=L ΔI/Δt, (1)

where L is the inductance of the choke;

ΔI/Δt - rate of current increase in the choke circuit.

After the damper diode opens, the circuit enters the normal mode, but during the transient process, excess voltage E acts on the damper diode and the key. This forces the use of higher-voltage diodes, which leads to an increase in the cost of the device and an increase in its weight and dimensions.

Example 1

The nominal current in the inductive circuit ΔI=40 A increases in Δt=2 μs. With the choke inductance L=100 μH, the self-induction EMF E=L ΔI/Δt=2000 V.

The objective of the utility model is to reduce voltage surges and reduce the weight and size parameters of the current pulse generator.

This problem is solved due to the fact that in the known pump current source, implemented in the form of a closed circuit consisting of a series-connected storage capacitor, a choke, a pump radiation source, a transistor switch with a control circuit and a current sensor, as well as a damper diode connected in parallel to the choke and the pump radiation source, the choke and the pump radiation source with the damper diode are connected between the terminal of the transistor switch and the high-voltage electrode of the storage capacitor, the other output of the transistor switch is connected to the contact of the current sensor, the second contact of which is connected to the second electrode of the storage capacitor and the zero bus, and the control circuit includes a threshold device connected to the current sensor, and a control pulse generator connected to the control input of the transistor switch, a filter capacitor with a capacity of is introduced between the low-voltage terminal of the pump radiation source and the zero bus where t _on is the diode turn-on time; I is the current in the inductive circuit; U _Cf is the permissible voltage on the filter capacitor at the end of the time t _on .

The damper diode can be made on the basis of a transistor in diode connection.

Fig. 1 shows the circuit diagram of the pulse current generator. Fig. 2a) and Fig. 2b) represent the basic versions of the damper diode design based on a bipolar (Fig. 2a) and a field-effect (Fig. 2b) transistor. Fig. 3a) shows the voltage diagram U _b at point b and the current I in the discharge circuit, and Fig. 3b) shows the graph of the change in the voltage pulse peak U _ab on the damper diode 7 after the transistor switch is closed at the moment T _0. Curves A, B and C correspond to the absence of the shunt capacitor (curve A), its nominal capacity (curve B) and the aperiodic mode (curve C). The moments of time _TA , _TB and _TB correspond to the time of switching on the damper diode in these modes.

The device in Fig. 1 consists of a series-connected storage capacitor 1, choke 2, pump source 3, transistor switch 4 with control circuit 5 and current sensor - resistance 6, forming a capacitive circuit for supplying the pump source. The choke - pump source circuit is shunted by a damper diode 7, closing the inductive circuit for supplying the pump source when the switch is open. The capacitive discharge circuit is closed by connecting the lower terminals of the storage capacitor and current sensor to the zero bus. The control circuit consists of a threshold device and a pulse former. The output of the pulse shaper is connected to the control input of the transistor switch 4. The storage capacitor is charged from an external source 9. The radiation of the pump source is fed to the external active element of the solid-state laser 10. The filter capacitor 8 is connected between the low-voltage terminal of the pump source 3 and the zero bus. The damper diode 7 can be made on a bipolar (Fig. 2a) or field-effect (Fig. 2b) transistor.

The pulse current generator operates as follows.

In the initial state, the storage capacitor 1 is charged to the nominal voltage. The transistor switch 4 is closed. After it is opened by a pulse from the control circuit 5, the capacitor 1 begins to discharge in the discharge circuit, through the choke 2, the pump source 3, the switch 4 and the current sensor 6. The discharge current increases at a rate determined by the capacitance of the storage capacitor 1 and the inductance of the choke 2. The voltage drop on the current sensor 6 is proportional to the current I flowing through it (Fig. 3a). As soon as the current reaches the upper limit I _max of the specified nominal interval, the voltage drop on the sensor 6 causes the control circuit 5 to operate, forming a control pulse supplied to the input of the transistor switch 4 and the locking switch. When the switch 4 is closed, the current through the pump source is maintained along the inductive circuit choke 2 - pump source 3 - damper diode 7 due to the energy accumulated in the choke. This current decreases exponentially with a time constant τ _L = L / R _L , where R _L is the total resistance of the pump source and the damping diode. At the moment τ _L (Fig. 3a) when switch 4 opens, the current in the capacitive circuit is interrupted, and until damping diode 7 opens, a self-induction pulse of the choke arises. In the absence of the proposed differences, this pulse can reach an unacceptable value (dashed line in Fig. 3a). In the presence of capacitor 8, when switch 4 opens, the self-induction current is closed through the pump source to the zero bus during the damping diode turn-on time T _on , determined by the recharge of the discharge circuit capacitances and the carrier absorption time [5]. This time determines the required capacitance C _f of capacitor 8 [6]: C _f ≥ _{T on} / πL. Thus, when maintaining the operating current through the pump source, the surge in the choke self-induction voltage is eliminated, and dangerous overvoltages do not occur in the circuit on the low-voltage elements of the circuit.

During the control pulse, the current through the pump source, maintained by the energy accumulated in the choke, decreases to the lower limit I _min of the specified nominal interval (Fig. 3a). At the end of the control pulse, the control circuit opens switch 4 again. After this, the pump source is powered by the energy contained in the storage capacitor, and the current through the pump source increases until it reaches the upper limit. The described process is repeated until the charge of the storage capacitor is exhausted. After this, the current pulse through the pump source stops.

With this design of the current generator, the current of optimal intensity is constantly maintained in the circuit, and the inductance value of the choke does not have to meet the requirements for the formation of the pump current pulse duration and the times of its rise and fall, as in other analogs [1]. In the proposed circuit, the choke serves only to maintain the rates of rise and fall of the current in the pump source when the switch is closed and opened. This allows for a significant reduction in inductance and, accordingly, the mass and dimensions of the choke and the entire current generator as a whole.

Example 2

The energy of the current pulse through the pump source required to pump the active element is E=1 J. With the capacity of the storage capacitor C=100 μF, the required voltage U on it is determined by the well-known formula E=CU ² /2 and is U=141 V.

Example 3

If, according to the excitation mode of the laser active element, the duration of the pump current pulse should be 2 ms, which corresponds to one half-period T ₀ /2 of the current in the LC circuit then the value of the inductance with the known design of the current generator [1] should be L = T ₀ ² /4π ² C = 1 mH.

According to the proposed solution, the switching frequency of the transistor key should be as high as possible - while the required inductance of the choke decreases. The maximum switching frequency is limited by the speed of the existing elements. It has been experimentally determined that the frequency optimal in terms of the circuit efficiency should be about 100 kHz. It is assumed that the periods of increase and decrease of the current through the pump source are approximately 5 μs. I _max ~ 50 A. I _min = 0.9I _max = 45 A. Thus, the rate of increase-decrease of the current through the pump source is (50 - 45) / 5 = 1 A / μs.

The experimentally substantiated value of the inductance L is L=100-150 μH. This value is significantly less than that of the analogue [1], and at the same time ensures the specified stability of maintaining the current in the pump source with the open and closed switch 4.

Binding the control circuits of the transistor switch and the control circuit to the zero potential of the case allows, firstly, to simplify the circuit design of the switch and the control circuit. Secondly, this makes it possible to use low-voltage, relatively inexpensive elements in them, which increases reliability and reduces the cost of the device. Thirdly, control of the switch using a low-voltage circuit eliminates the need to recharge the circuit and parasitic capacitances during the switching process, which in the known device [2] requires additional energy.

The use of a semiconductor laser matrix as a pump source offers a number of other advantages. This source has a significantly higher efficiency factor compared to a gas-discharge lamp, and the choice of the radiation wavelength in a narrow spectral band allows the pump radiation to be best matched to the absorption band of the active element, which further enhances efficiency. The relatively low voltage drop on the pump source simplifies the circuit design of the current source and increases its reliability.

The use of a transistor in a diode connection as a damper diode reduces losses in this element of the circuit and helps to reduce the weight and dimensions of the device as a whole.

It is known that the voltage drop on an open diode at currents of 20-100 A reaches 1.5-2.0 V. This is comparable with the voltage drop on the laser diode matrix and leads to a significant decrease in the pump efficiency.

It is also known that MOSFETs with an isolated gate have a low channel resistance [5, 7], reaching 3-4 mOhm. At a current of 40 A, the voltage drop on such a transistor does not exceed 0.2 V, which practically eliminates losses during the inductive pumping cycle, especially when transistors are connected in parallel. In addition, transistor keys have a short turn-on delay T _on [7] - this is important in terms of reducing losses during circuit switching and preventing gross errors in the case of simultaneous opening of keys 4 and 7, leading to a short circuit and putting the circuit out of order.

When the transistor switch 4 is switched off and there is no capacitor 8 on the damper diode 7, a surge of U _dd EMF of self-induction of the choke 2 is released (Fig. 4, curve A). Shunting the diode 7 with the capacitor 8 eliminates this surge. The aperiodic transient process of voltage U _ab (t) on the damper diode (Fig. 3b) is ensured under the condition [6].

where L is the inductance of choke 2;

С _ф - capacitance of filter capacitor 8;

R - resistance of pump source 3.

From (2) follows the condition of an aperiodic process (Fig. 3 curve B).

Example 4

L=100 μH; R=2 Ohm.

With _fap = 100 MKf.

This solution seems to be redundant in essence and undesirable in design, since the capacitor in the 100 V and 50 A circuit with such a capacity has large dimensions.

Condition (2) does not take into account the occurrence of high conductivity of the damper diode 7 when it is forward biased by voltage U _ab (Fig. 3, 4), after which the current of the choke 2 closes through the diode 7, and the capacitor 8 does not participate in the further process. Therefore, it is sufficient to suppress the surge of self-induction of the choke during the time T _on the damper diode.

For short times t≤t _on, the formula [4] is valid for the voltage U _b (Fig. 3a) on a capacitor with a capacitance C _f with a current I flowing through it.

where

(5)

Example 5

I=50 A; t _on =10 ^-7 s; U _C =50B.

With _f = 0.1 μF.

Fig. 4 shows the nature of the transient process with such a value of the capacitor 12 (curve B), as well as in the absence of a capacitor (curve A) and with a capacitor capacitance that ensures an aperiodic transient process according to example 4 (curve B).

Fig. 3b) shows a graph of voltage U _ab between points a) and b) of the circuit in Fig. 1.

In accordance with the proposed utility model, a prototype of a current pulse generator was developed and tested as part of a laser rangefinder.

The transistor switch 4 is based on the APT 8024 transistor, and the control circuit is based on the MAX 4420 microcircuit [3]. Compared with the analog [2] (the IRG4SPC71UD transistor and the IR2125 microcircuit), the specified elements and their circuit binding provide a more compact design of the current generator, they have an order of magnitude higher reliability and a significantly lower cost. The damper diode 7 is based on the IRFB4110PbF transistor with an insulated gate and an n-type channel induced by the channel, having a channel resistance of 4 mOhm at a current of 75 A. In the closed state of the transistor, the voltage on it does not exceed 100 V, taking into account the surge when the inductive circuit is turned on. The capacitance of the filter capacitor C _f = 0.1 μF.

Thus, the proposed device provides a solution to the set problem, namely, a reduction in voltage surges and a reduction in the weight and size parameters of the current pulse generator.

Sources of information

1. Laser reconnaissance device LPR-1. Technical description and operating instructions.

2. V.V. Togatov, P.A. Gnatyuk. High-frequency discharge module for power supply of pump lamps of solid-state lasers. "Instruments and experimental equipment". No. 5, 2003. - pp. 89-95.

3. Current pulse generator. Russian Federation patent for invention No. 2494532 based on application No. 2012147412 of 08.11.2012 - prototype.

4. L.A. Bessonov. Theoretical foundations of electrical engineering. Moscow, Higher School, 1996, 344 p.

5. V.G. Gusev. Electronics and microprocessor technology: textbook. M., KNORUS, 2016. - 798 p.

6. Transient processes in RLC circuits. Practical formulas. https://gorchilin.com/articles/math/transition_process_RLC.

7. Field-effect transistors with insulated gate and induced channel n-type IRFB4110PbF. Technical characteristics.

Claims (2)

1. A pump current source made in the form of a closed circuit consisting of a series-connected storage capacitor, a choke, a pump radiation source, a transistor switch with a control circuit and a current sensor, as well as a damper diode connected in parallel to the choke and the pump radiation source, the choke and the pump radiation source with the damper diode are connected between the terminal of the transistor switch and the high-voltage electrode of the storage capacitor, the other output of the transistor switch is connected to the contact of the current sensor, the second contact of which is connected to the second electrode of the storage capacitor and the zero bus, and the control circuit includes a threshold device connected to the current sensor, and a control pulse generator connected to the control input of the transistor switch, characterized in that a filter capacitor with a capacity of is introduced between the low-voltage terminal of the pump radiation source and the zero bus where t _on is the diode turn-on time; I is the current in the inductive circuit; U _Cf is the permissible voltage on the filter capacitor at the end of the time t _on . 2. A current source according to paragraph 1, characterized in that the damper diode is made on the basis of a transistor in a diode connection.

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