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Browse Prior Art Database

Switching Transistor Protection Circuit

IP.com Disclosure Number: IPCOM000084847D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Beesley, JP: AUTHOR

Abstract

The diode, resistor, battery portion of the circuit shown in Fig. 1 absorbs energy during the diode recovery as the transistor is turned from on to off, thus reducing the turnoff energy which the transistor releases in the form of heat and the peak power dissipation in the transistor.

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Switching Transistor Protection Circuit

The diode, resistor, battery portion of the circuit shown in Fig. 1 absorbs energy during the diode recovery as the transistor is turned from on to off, thus reducing the turnoff energy which the transistor releases in the form of heat and the peak power dissipation in the transistor.

Inverter circuits, such as a push-push inverter, allow a different implementation of this protective circuit, as shown on Fig. 2. In the push-push inverter, both switches are on simultaneously for a brief period of time with one coming on slightly before the other goes off. Thus, the turning on of transistor Q2 slightly before transistor Q1 is turned off causes current, limited by resistor R2, to flow in diode D2. This stores charge in D2.

When transistor Q1 is turned off, the stored charge in diode D2 will cause current to flow backward in D2 until D2 recovers, thus reducing the current in transistor Q1 and consequently reducing the peak power dissipation and the total energy released in transistor Q1.

The associated winding on transformer T2 performs the battery function by providing a pulse of voltage at the required time. The diode recovery current flowing backward through diode D2 provides output energy. Resistor R1, diode D1, and the associated winding on transformer T1, perform this protection function for transistor Q2.

In summary, the circuit of Fig. 2 makes use of windings on the output transformer T1 to supply diode current to produ...