SU1721750A1 - Dc converter - Google Patents

Abstract

This invention relates to electrical engineering and can be used in secondary power supply sources. The goal is to expand the field of application of the converter by reducing the switching time of the power transistor. The converter contains a power transistor 1, a power transformer 6, a current transformer 2 that turns on 1.1 and turns off 12 transistors and a bias source 15. When unlocked the turn-on transistor

Description

11, a short pulse causes the fast turning on of the power transistor 1, the open state of which is maintained by winding 3 of the positive feedback of the current transformer 2. When unlocked by a short pulse of the turning off transistor 12, a forced locking of the power transistor 1 occurs through the small internal resistance of the bias source 15. 1 ffl, 2 ill.

The invention relates to a technique of secondary power supply of electronic devices, namely, high-frequency voltage converters, and is intended for use in power supplies (IWE) of communication equipment.

A stabilized voltage converter is known, comprising a power transistor, a power transformer, a feedback device including a galvanic isolation node. A feature of this converter is the realization of the relay (two-position) principle of regulation, with the power transistor turned on by a control pulse and kept open by the winding of the power transformer.

The disadvantages of this device include a significant variation of the base current of the transistor from the supply voltage. Thus, there are significant losses in the control circuit of the power transistor, which leads to a decrease in the efficiency of the entire converter. In addition, the excess base current increases the resorption time of minority carriers in the base of the power transistor, which limits the functionality of the entire device, i.e. its field of application for high frequency conversion.

A voltage converter is known which comprises a power transistor, a power transformer, a current transformer, and two control transistors associated with a current transformer and a winding of the power transformer.

This converter has the following disadvantages. The current transformer operates in the linear mode of magnetization reversal; therefore, this circuit is operable only in the PWM mode. For converters with a PFM or with a relay control principle, it is necessary to count the current transformer at the lowest frequency, which leads to an increase in the size of the current transformer and an increase in power loss in it. At the time of formation of the front of the power transistor to its transition base-emitter

A low-power source of reverse voltage is applied, since the voltage on the locking winding of the power transformer is no longer present. This leads to an increase in the duration of the switching-off front, an increase in the dynamic losses when the power transistor is turned off, and, as a result, limits the frequency range of the converter.

Closest to the proposed technical entity is a voltage converter, which contains a power transistor, a power transformer, a current transformer that turns the transistors on and off. A short unlocking pulse comes from the control device directly to the base of the power transistor, after unlocking which the further power supply of the base circuit comes from the base winding of the current transformer. A diode is connected in series with the base winding of the current transformer; it prevents the opening pulse bypassing by a low base impedance

winding current transformer. At the same time, the base current charges the capacitor of the bias device. At the end of the open time of the power transistor, the control unit forms a locking

a pulse arriving at the input-transistor transistor, which is unlocked and connects the capacitor of the bias device to the base-emitter junction of the power transistor in reverse polarity. Locking of the power transistor occurs and until the next unlocking pulse arrives, a locking bias is maintained at the base-emitter junction of the power transistor, since the resistor

connected between the base and the emitter of the power transistor, is rather high impedance, and the capacitor of the bias device is not discharged to zero. After the next trigger pulse arrives

repeats.

This device has the following disadvantages. The energy stored in the capacitor of the bias device depends on the duty cycle of the power transistor,

what does not allow to effectively lock the power transistor when operating in the mode

large duty cycle, for example, in the mode of overcurrent and short circuit at the output, when it is necessary to have the open state of the power switch to have a minimum time and turn it off quickly at a large duty cycle of its operation. This significantly narrows the range of application of this converter, especially at higher frequencies in devices with PWM. In addition, when operating in the high-duty cycle mode, there are problems with maintaining the locking bias at the base of the power transistor during its closed state, since the discharge time of the capacitor of the bias device increases significantly and the stored energy decreases. It also reduces the possibility of using this converter in PFM systems and with the relay control principle.

Unlocking the power transistor with a pulse arriving at its base directly from the control device is also a disadvantage of this converter, since when operating in the continuous current mode of the power throttle if necessary, you need to have a minimum unlocking front, the power of the trigger pulse must be sufficiently large, which leads to and the complexity of the control device and is an obstacle to the use of this device in the specified modes. The disadvantage of this converter is that in series with the base winding of the current transformer it is necessary to install a diode to disconnect the switching pulse from the base winding, and the capacitor of the bias device needs to be charged to a sufficiently high voltage, which significantly reduces the efficiency of the current-key control of the power switch in terms of efficiency, increases the size and size of the current transformer and the entire device.

The purpose of the invention is to expand the field of application by reducing the switching time of the power transistor.

The goal is achieved by the inclusion of a power transistor produced by narrow pulses arriving at the base of the switching transistor, the collector of which includes the current transformer winding, and also during the charge dissipation phase of the base transistor of the power transistor is applied the locking voltage from the winding of the power transformer, and at the stage of forming the front, when the voltage on the windings of the power transformer drops, the emitter-base is applied to the junction are parallel circuit voltage of the capacitor. This provides a reduction in on and off times.

In a DC / DC converter containing a power transistor, the emitter of which is connected to the first input terminal, the collector is connected via

0 primary windings of the current transformer and power transformer with the second input terminal, and the base is connected to the first output of the bias source, the base winding of the current transformer, the first output

5 of which is connected to the first, the output of the first diode, which turns on and off the transistors, the bases of which are connected to the control outputs, and the emitter of the turning off transistor is connected to

0 to the first input terminal, the second and third diodes are inserted, including the winding of the current transformer and the additional winding of the power transformer, connected between the base of the power transistor and

5 by the first terminal of the second diode, the second terminal of which is connected to the switching-off transistor collector and to the second output of the first diode; the switching winding of the current transformer is connected through the third diode between the second input terminal and the collector of the switching-on transistor, the emitter of which is connected to the first input terminal, and the base winding of the current transformer is connected between

5 with the second terminal of the offset source and the first input terminal.

Introduction of the locking winding in the power transformer and its connection through the diode to the locking collector

The 0 of the transistor allows you to forcefully dissipate the charge of minority carriers in the base area of the power transistor during its turn-off. The introduction of a parallel connection of a capacitor and a diode 5 of a resistor circuit connected in series to the base current of the power transistor simultaneously with the diode connected to the collector of the switching transistor allows the reverse voltage to be applied to the base-emitter junction of the power transistor, such this reduces both the resorption time and the duration of the front during

5 shutdown. This makes it possible to reliably and quickly turn off the power transistor regardless of the duty cycle of its operation, which expands the range of application of the converter, since it allows it to be used both in devices in PWM with a wide range of variation in the duty cycle, and in a BAT device, as well as in devices with the relay principle of regulation at higher conversion frequencies.

The introduction of a turn-on winding into a current transformer connected through a diode to a switching-on transistor makes it possible to make the unlocking pulse powerful enough and to reduce the duration of the unlocking front of the power transistor, which makes it possible to use this converter with both forward and reverse switching of the rectifying diode in continuous throttle mode without additional complication of the control device.

Figure 1 shows a voltage converter circuit; FIG. 2 shows diagrams explaining his work.

The converter consists of a power transistor 1, a current transformer 2, its primary winding 3, including winding 4 and base winding 5, a power transformer 6 consisting of a primary winding 7 and an additional secondary winding 8, two input terminals 9 and 10, a turning on transistor 11 switching off the transistor 12, the first diode 13 connected between the collector of the turning on transistor 11 and the first terminal of the winding 4 of the current transformer, the second diode 14 connected between the collector of the transistor 12 and one of the terminals of the winding, 8 power transf of the armature, parallel to the CRD circuit 15, consisting of a capacitor 16, a resistor 17 and a diode 18, and this circuit is connected between the base of the power transistor 1 and one of the terminals of the base winding 5 of the current transformer, to the same terminal of the winding 5 is connected via a diode 19 collector of the switching transistor. The other end of the winding 8 of the power transformer is connected to the base of the power transistor 1, the emitters of all transistors and the other end of the winding 5 are connected to the input terminal 10, and the input terminal 9 is connected simultaneously to the second output of the turn-on winding 4 of the current transformer and to one of the primary windings 7 power transformer. The other end of the winding 7 through the primary winding 3 of the current transformer is connected to the collector of the power transistor 1, respectively the switching pulses on and off are fed to the inputs of the turning on and off transistors.

The device works as follows.

When a control pulse appears on the base of a starting transistor 11, it opens and a current flows through

Circuit: + DBX (terminal 9), including the winding 4 of the current transformer 2, the first diode 13, turning on the transistor 11, -Kvh (terminal 10). The potential from the base winding 5 of the current transformer arrives at the base of the power transistor 1 through a CRD circuit (16, 17, 18). Power transistor 1 begins to open. Due to the presence of positive feedback carried out by the current transformer 2, the power transistor opens and goes avalanche to saturation mode, and transformer 2 goes into current transformation mode. The magnitude of the currents flowing through the current and base windings of the current transformer 2 is proportional to the load current. The voltage on the switching winding 4 of the current transformer induced from the base winding in some modes may exceed the input voltage, and then the diode 13 protects the transistor 11 from the reverse voltage. If the voltage on the winding 4 is less than the input voltage, then the difference of these voltages is applied to the closed transistor 11 (since the control pulse is narrow). When a pulse appears at the input of the switching transistor 12, it opens and goes into saturation mode. In this case, the base winding 5 of the current transformer is short-circuited through the diode 19 and the current for the base of the power transistor is sharply reduced. At the same time, the voltage from the additional winding of the power transformer is applied to the emitter-base junction and shuts it down, while there is an intense resorption of excess carriers accumulated in the base of the power transistor. After the resorption process is completed, the power transistor 1 begins to lock, therefore the voltage across the additional winding of the power transistor decreases. transformer. At this point in time, the reverse voltage from the capacitor 16 of the CRD circuit is applied to the emitter-base junction of the transistor 1, which significantly reduces the switching-off front of the power transistor. After the switching off of the switching transistor, which was previously opened during the time of the short switching pulse and its own resorption time, a negative voltage is formed on the base winding 5 of the current transformer. As a result, demagnetization of the current transformer core occurs. The demagnetization time is determined by the off-state interval of the power transistor of the converter. When the converter operates in the relay control mode, the lower operating frequency is unlimited, since the control of the on and off transistors is pulsed, and the volt-second limitation, which is necessarily introduced in this case for the power transformer, automatically limits the volt-second interval for the current transformer.

In the next cycle of operation of the voltage converter, another short pulse arrives at the switching-on transistor 11, it opens, and then all the processes proceed as described.

Claims (2)

Claim 1. A DC / DC converter containing a power transistor, the emitter of which is connected to the first input terminal, the collector is connected through the primary windings of the current transformer and the power transformer to the second input terminal, and the base is connected to the first output of the bias source, the base winding current transformer, the first terminal of which is connected to the first terminal of the first diode, which turns on and off the transistors, whose bases are connected to the control outputs, and the emitter The switching-off transistor is connected to the first input terminal, characterized in that, in order to expand the application area by reducing the switching time of the power transistor, the second and third diodes are inserted, including the current transformer winding and the additional power transformer winding connected between the base of the power transistor and the first output of the second the diode, the second output of which is connected to the collector of the switching-off transistor and to the second output of the first diode, with the turn-on winding of the current transformer VC yuchena via a third diode between the second input terminal and a collector comprising a transistor whose emitter is connected to the first input terminal, and the base current of the transformer is connected between the second source terminal and the first bias input terminal. 2. The converter according to claim 1, of l and h a rout, and so that the source of bias is made in the form of a capacitor shunted by a series circuit of a resistor and a diode. "G P u in 1 4 6 8 П g P t, MKC ЈL 2 j eleven U tA d fl 2 5 (-L7 / 2 1st pr it about g Z f 0.9A I 8 ft ft, MKC . 68 Yu Sh, shs FIG. 2 g P t, MKC ЈL  rT d iwc  / 2 / 2   S 12 t, f “c 8 ft ft, MKC