RU168275U1 - POWER KEY SHUTTER DRIVER - Google Patents

Abstract

The utility model relates to power converting technology, in particular to switching power supplies. The device can be used to control a power switch in cases where galvanic isolation of the power switch from the control circuit is required or if there is a potential difference between them, in particular to control the “upper” keys in bridge and similar circuits. The technical result of the proposed solution is to increase reliability the operation of the key by eliminating the dependence of the opening voltage on the gate of the key on the duty cycle of the pulses. The device contains a control transformer T1, auxiliary Tel'nykh MOSFET Q1, a diode D2, a resistor R1, a two-way zener diode D1. Contact X1 is connected to the output of the control circuit providing sufficient currents and flows to control the power switch, contact X2 to the common wire of the control circuit, contact X3 to the gate of the power switch through resistor R1, contact X4 to the source of the power switch. Contact X5 is connected to the "plus" power supply of the control circuit. 1 ill.

Description

The utility model relates to power converting technology, in particular to switching power supplies. The device can be used to control a power switch in cases where galvanic isolation of the power switch from the control circuit is required or if there is a potential difference between them, in particular for controlling the “upper” keys in bridge and similar circuits.

The prototype of this utility model is the well-known scheme cited in many foreign manuals (in particular, in the article [1], its Russian translation in the book [2] - see Appendix 1).

The circuit includes a transformer T1, the primary winding of 1-2 of which is connected to the control circuit, and the secondary winding of 3-4 is connected respectively to the gate and source of the power switch. In this case, the contact X1 at the input of the primary winding is connected to the output of the control circuit, providing incoming and outgoing currents sufficient to control the power switch. Contact X2 of the primary winding is connected to the common wire of the control circuit, contact X3 of the secondary winding 3-4 to the gate of the power switch, contact X4 of the secondary winding 3-4 to the source of the power switch. The capacitor C1 at the input of the primary winding eliminates the flow of the DC component of the current through the winding, and thereby prevents saturation of the transformer core. The resistor R1 at the output of the secondary winding determines the overcharge current of the input capacitance of the power switch, the Zener diode D1 protects the gate of the power switch from the surge, due to the presence of stray inductance of the transformer.

The disadvantages of this scheme are well known and described, in particular, in the article [3], its Russian translation [4]. The first drawback is that the opening voltage at the gate of the key depends on the duty cycle of the pulses. So, if the turns in the transformer windings are equal and the fill factor is 10%, the gate voltage will be 90% of the output voltage of the control circuit, and if the fill factor is 50%, it will be only 50%, which may not be enough to open the transistor. This problem is solved by increasing the transformation ratio, but then additional difficulties arise. Firstly, such a transformer is less technologically advanced, secondly, the output of the control circuit should provide more current, and thirdly, it will be necessary to provide a fairly narrow range of the supply voltage of the control circuit. The latter is necessary so that for any combination of supply voltage and duty cycle, on the one hand, ensure reliable opening of the transistor, and at the same time limit the maximum voltage at the gate to a safe level.

The second disadvantage is that the isolation capacitor and the magnetizing inductance of the winding form an oscillatory circuit, because of which low-frequency oscillations can be superimposed on the gate control pulses, especially at the moments of a sharp change in the duty cycle. This, in turn, can lead to a decrease in the gate opening voltage below the transistor opening threshold. To eliminate this effect, it is necessary to choose the right capacity and carefully test the circuit in transient conditions.

Thus, overcoming these shortcomings causes certain costs in the form of a rise in price of the circuit and an increase in the time for debugging it.

The technical result of the proposed solution is to increase the reliability of the switch by eliminating the dependence of the opening voltage on the switch of the switch on the duty cycle of the pulses.

To achieve the stated result, the power switch shutter driver containing a transformer, the primary winding of which is connected to the control circuit, and the secondary winding through a series-connected resistor is connected to the gate and the source of the power switch, as well as a two-sided zener diode connected between the gate and the source of the power switch connection diagram of the primary winding of the transformer to the control circuit. To do this, a MOS transistor is introduced into the circuit, connected by a gate and drain to the primary winding of the transformer, and a source to the common wire of the control circuit, and a diode connected by the anode to the drain of the MOS transistor, and by the cathode to the power plus of the control circuit.

This solution contributes to the formation of amplitude-constant control pulses on the key gate at any value of the pulse duty ratio in the range 0-50%, and regardless of the speed and direction of change of the pulse duty factor, which eliminates the dependence of the amplitude of the control pulse on the gate of the power switch on the pulse duty factor in the range from 0% to 50%, and also eliminates the possibility of spurious oscillations due to the presence of an isolation capacitor, which increases reliability work key.

The proposed device is shown in FIG. 1. The device contains a control transformer T1, an auxiliary MOS transistor Q1, a diode D2, a resistor R1, a two-sided zener diode D1. Contact X1 is connected to the output of the control circuit providing sufficient currents and flows to control the power switch, contact X2 to the common wire of the control circuit, contact X3 to the gate of the power switch through resistor R1, contact X4 to the source of the power switch. Contact X5 is connected to the "plus" power supply of the control circuit.

The device operates as follows. A positive voltage pulse generated at the output of the control circuit opens Q1, as a result of which terminal 2 of the transformer T1 is switched to the common wire of the control circuit and a voltage close to the output voltage of the control circuit is applied to the primary winding 1-2 of the transformer T1. This voltage is transformed into the secondary winding 3-4 and is applied to the gate of the power switch, ensuring its opening. Resistor R1 determines the overcharge current of the input capacitance of the power switch, and D1 protects the gate of the power switch from voltage surges that occur during switching due to the stray leakage inductance of transformer T1. At the end of the control pulse, the voltage at the output of the control circuit becomes close to zero, and Q1 closes. Accordingly, the voltage at terminal 1 T1 is close to zero, and the voltage at terminal 2 T1 can take a value from zero to the supply voltage of the control circuit, thanks to two clamping diodes: the "upper" diode D2 and the "lower" diode, which uses an internal parasitic diode Db of transistor Q1. At the stage of turning off the power switch, the discharge current of its input capacitance passes through a resistor R1 and a winding 3-4 from terminal 3 to terminal 4 T1, is transformed into a winding 1-2 from terminal 2 to terminal 1, and is closed via a stray diode Db to a common wire, while the voltage across the windings T1 is close to zero. At this stage, the magnitude of the overcharge current of the input capacitance of the key is determined only by the resistance R1, assuming the ideality of the circuit elements. At the end of the stage of recharging the input capacitance of the power switch, the magnetization current of the transformer is closed through the diode D2 to the “plus” of the power supply to the control circuit, and a reverse voltage appears on winding 1-2, close to the supply voltage of the control circuit, which is a recovery voltage for the transformer. Upon completion of the restoration of the transformer, the currents and voltages on its windings are reduced to zero. When the fill factor is from 0% to 50%, the equality of the volt-second areas on the T1 windings in the forward and reverse directions is automatically ensured, which eliminates the saturation of the transformer core.

Thus, the claimed technical result is achieved. In addition, due to the achieved technical result, the proposed utility model has the following advantages with respect to the prototype:

1) a transformer with an equal number of turns in the windings is used, which minimizes the leakage inductance of the transformer and reduces the cost of winding;

2) the supply voltage of the control circuit can have a wider operating range, which simplifies the development of the circuit;

3) no additional margin is required for the load capacity of the output of the control circuit, which in some cases reduces the cost of the circuit;

4) there are no possible problems when working in transient conditions, which simplifies the development and increases the reliability of the circuit.

Literature:

[1] "UC3842 / 3/4/5 Provides Low-Cost Current-Mode Control" 1999, Texas Instruments Incorporated, p. 8;

[2] "Microcircuits for switching power supplies and their application" Moscow, Dodeka-XXI Publishing House, 2001, p. 110;

[3] "Gate Drive Design Tips" 2006, Dr. Ray Ridley, Ridley Engineering;

[4] "Power Transistor Gate Control Tips" COMPONENTS AND TECHNOLOGIES • No. 8 2008.

Claims (1)

A power switch gate driver comprising a transformer, the primary winding of which is connected to a contact that provides sufficient inward and outward currents to control the power switch, the secondary winding is connected through a series-connected resistor with a gate and a power switch source, between which a two-sided zener diode is also included, characterized in that it is supplemented by a MOS transistor, the gate and drain of which is connected to the primary winding of the transformer, and the source is connected to a common driver wire, and a diode, a cat ing anode connected to the drain of the MOS transistor, and katodom- to positive power driver.

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