SU754604A1 - Converter - Google Patents

Description

The invention relates to a converter technique and is intended for use in electronic equipment, in particular, for power supply.

Known converters with pulse control, used in power supplies £ D). The frequency of the converter is set by means of a switching choke. Control is performed by closing one transistor and automatically delaying the unlocking of the other until the polarity of the voltage on the transformer windings changes. A converter of this type 15 has good energy performance and reliability.

The disadvantage of such a converter is the propensity for one-sided magnetization of a transformer due to the 20 spread of characteristics of the elements used. This leads to lower efficiency and reliability of the converter.

The known converter is £ 2], which operates on the same principle as the -described £ ί], and is its improvement. The frequency of operation is also set by means of a switching choke, and the choke and the transformer are provided with additional windings,

ten

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thirty

which are connected opposite each other through a diode-resistor circuit. The balancing of the converter occurs by changing the voltage on the windings of the choke and, accordingly, the time of its switching in each half-period.

Also known is a converter, in which control is carried out using external synchronization £ s], containing a power inverter with self-excitation, with output transformer, rectifier and filter, synchronizing self-excited auto-oscillator, the output windings of which are connected to the inverter's transistor emitters through diodes. In this case, the transistors of the converter alternately switch to the open state under the action of external clock pulses. During each half cycle, the transistors are in the open or closed state under the action of the voltage on the windings of the positive feedback of the transformer. The control power is small, and switching occurs with minor losses.

If in converters in which the required mode of operation is set

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throttle saturation, the voltage of the additional windings of the transformer, under the action of which the magnetization reversal of the choke and after its saturation the locking of the transistor, is selected based on the need for symmetrical operation within 6-12 V (this reduces the effect of voltage drops on the diodes and transitions of the base transistor), in converters with external synchronization, the voltage for switching can be chosen much lower in magnitude, which ensures a further increase in efficiency (especially in high-power converters).

In power supplies, it is sometimes necessary to have, for example, to control

. signaling an additional power source that operates independently of the power inverter (for example, when the power inverter is turned off due to protection operation). In this case, additional equipment costs do not occur and converters with external synchronization have an advantage over converters without external synchronization.

However, such a converter is also prone to unilateral magnetization of the transformer. The difference in time has a particularly strong effect ^; resorption of minority carriers in the bases of power transistors, leading to a decrease in the duration of one half-period and, accordingly, to an increase in the duration of the other, i.e. to unilateral magnetization of the transformer. This reduces efficiency and reliability.

The aim of the invention is to increase efficiency and reliability.

This is achieved. In the converter, which contains a power inverter with self-excitation, a rectifier and a filter that synchronizes the self-excited auto-oscillator, the output windings of which are connected in parallel with the inverter-emitter base-to-emitter junctions more than the difference between the base-emitter voltage of the inverter's enabled transistor and the voltage drop across the diode, through which the winding is connected, but changed There is a cumulative voltage drop across this diode and a diode that shunts the baua-emitter junction of the inverter transistor.

In addition, the capacitors of the autogenerator can be bridged by a re-A life chain, the common point of which is connected to the common connection point of these capacitors.

The converter circuit is shown in the drawing.

The converter contains a synchronizing half-bridge oscillator with self-excitation, performed on transistors 1 and 2, capacitors 3 and 4 and a transformer with windings 5-9. Winding 8 and 9 are used to control the power inverter. The power inverter is made according to the scheme with self-excitation on transistors 10 and 11, capacitors 12 and 13 and a transformer with windings 14-16. When reverse synchronizing inverter voltage polarity changes on all windings 5-9. The winding 8 locks the transistor 10, and the winding 9 due to the diode 17 does not affect the transistor 11. After the switching process of the transistor 10 is completed, the voltage polarity changes across all windings 14-16. In the new half-period, transistors 1 and 10 are locked, and transistors 2 and 11 are open. The current through the winding 8 passes only when switching, i.e. in the time interval between the reverse of the synchronizing oscillator and the power inverter.

If, for example, the resorption time of minority carriers in the base of transistor 10 is longer than that of transistor 11, then this leads to an increase in the half-cycle duration when the transistor 10 is open. But since the time during which the current flows through the winding 8, also increases, then the capacitor 4 of the synchronizing autogenerator sits down more than in the next half-period of capacitor 3. The synchronizing autogenerator will operate at a higher voltage on the capacitor 3 and at a lower voltage on the capacitor 4. Accordingly and menitsya duration of half-periods, the half-life, will be opened when the transistor 1 will have a shorter duration compared with a half life when open tran ican 2. Thus there is automatic compensation for influence resorption time of minority carriers.

To increase the reliability of the converter in mass production conditions, when the number of asymmetric factors is difficult to take into account in advance, a resistor circuit made in the form of a variable resistor 18 can be used for additional correction. With this chain you can change the voltages on capacitors 3 and 4 and thus affect the duration half periods.

For normal operation of the circuit, the magnitude of the voltage is selected from the following considerations. Consider a half-period when the transistor 10 is open and the transistor tor 11 is closed. In order to avoid shunting the input circuit of the transistor, the following relationship should be:

/ ^and s! / ^and β / ^g (1)

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At the same time, the following relationship should be ensured:

. / and ₉ / = / and ₈ / </ and _{1 ()} / 4 / and ₂₂ /, ( ₂ )

where ₅ is the base voltage,

the emitter of the included transistor;

and _{9 , and ₂₀ , and ₈ , and _d - voltage drop across the diodes 19, 20 and windings 8 ,. 9.

After the reverse voltage generator on its windings change its polarity and the process of locking the emitter junction of transistor 10 begins (no changes in the current occur in the control circuits of transistor 11). Since the potential of the base of the transistor 10 remains approximately constant from the moment of polarity change on the windings of the oscillator until the emitter junction is closed, the current of the resistor 21 does not change, and a current through the winding 8 equal to the sum of the current through the resistor 21 and the resorption current of the transistor 10 base carriers. this for intensive resorption is enough to meet the following conditions:

""five

M + 1 ^ 1> 1 ^ 1 (3)

By considering together equations (1) and (3), one gets

/ and ₈ /> / and _e / - Yu (M

This voltage has a magnitude of a few tenths of a volt.

Taking into account equation (2) receive

/ and + 9 / ♦ 1 ^and 1> / ^and / / / ^and e-M '(5) where and _§ is the base-emitter voltage of the open transistor.

In real conditions, it is necessary to take into account the additional voltage drop in the active resistance of synchronization circuits, but with proper design it is insignificant.

It should be noted that a significant factor is the scatter of the values of p transistors 1, 2. Due to different coefficients [5, the synchronizing oscillator is "warped", which leads to the asymmetry of the power inverter. Since the transformer of the synchronizing autogenerator operates according to the limit cycle, i.e. twice during the period its core comes to saturation, other parameters of transistors (for example, resorption time) do not affect the operation of the generator.

The initial setting is provided by a variable resistor 18. With temperature fluctuations, given that the nature of the change from temperature for transistors of the same type is almost the same (this property is used in various low-power differential balance cascades), the effect of temperature dependence is negligible. Such well-known measures

how unloading transistors in power, as well as the installation of transistors 1 and 2 on one plate, is enough.

In self-excited inverters with pulsed external synchronization, synchronization failures may occur. This phenomenon occurs when the induction amplitude in the core is less, equal to or slightly higher than the value of residual induction B. In this case, at the end of the half-period, the core does not slip from _Bt to _Bp and does not reverse the circuit. Therefore, usually choose the value of B> Br on. sufficient value. Split cores can also be used. Since, when switching converters with light commutation, power losses depend on the magnitude of the magnetizing current (this current flows through the collector of the transistor when the circuit reverses), and also to reduce losses in the core of the transformer, it is advisable to reduce the induction amplitude in the core. In order to eliminate possible malfunctions in the operation of the inverter, it is proposed to connect parallel to diodes 17 and 19 passive chains 22, 23 (for example, resistors or chains of a series-connected resistor and capacitor).

In this case, the voltage on the windings 8 and 9 should be greater than the threshold voltage и§. _These transistors 10 and 11. Through the input chains flow currents, ki, which at the beginning of each half-cycle include the corresponding transistor 10 or 11. The magnitude of these currents is chosen less than the magnitude of the currents flowing through the circuits of the excitation windings 14 and 15, therefore, the impact on the processes switching circuits do not have input, and power losses are insignificant, the power inverter can be connected to the output terminals through a rectifier with a filter 24.

The effectiveness of the proposal is that in the converter with external synchronization the one-sided magnetization of the transformer is eliminated, i.e. the converter has greater efficiency and reliability compared to the prototype.

The elimination of synchronization failures also contributes to increased efficiency and reliability, as it gives an opportunity to work with small values of induction in a transformer.

Claims (3)

Claim 1. A converter containing a power self-excited inverter with an output transformer, a rectifier and a filter, a synchronizing self-excited auto generator, the output windings of which are connected in parallel to the base-emitter junction of the inverter transistors through diodes, 7 754604 eight characterized in that, in order to increase efficiency and reliability, the auto-oscillator is made according to the half-bridge inverter scheme, with the auto-generator output windings greater than the difference between the base-emitter voltage of the inverter and the voltage drop across the diode, through which the winding is connected, but less than the total drop the voltage across this diode and the diode shunting the base-emitter junction of the inverter transistor. 2. Converter pop. 1, characterized in that the capacitors of the oscillator are shunted by a resistor chain, the common point of which is connected to the common connection point of these capacitors. 3. Converter pop. 1, characterized in that parallel diodes connected in series with the output windings of the synchro ⁵ sighting inverter include passive elements.