Transistor protection circuit

Abstract

Abstract PURPOSE: To prevent the thermal breakdown of a transistor, by bypassing the input current of a starting resistor to lengthen the inverse bias time of the transistor when a short circuit takes place on the load side of a switching regulator type power supply circuit. CONSTITUTION: A resistor 18 is coupled between the transistor 6 and the starting resistor 4 of the ringing-choke switching regulator type power supply circuit. A resistor 19 and a diode 20 are connected in series with each other between an output capacitor 13 and the connection point A of the resistor 4 with the resistor 18. Normally, the potential on the connection point A is almost equal to an output voltage. When there is a short circuit on the load side of the power supply circuit, a current flows to the load side through the resistor 19 and the potential on the connection point A falls. At that time, the time of return of the base potential of the transistor 6 from a negative level to zero lengthens and the period of unstable operating state of the transistor shortens. As a result, the heating of the transistor is reduced and it is protected from thermal breakdown. COPYRIGHT: (C)1980,JPO&Japio

Inventors

• 👤 Kimito Kosaka
• 👤 Junichi Yamase
• 👤 Yoshihiro Arakawa

Bibliographic Details