Protection circuit for switch and switch-type electric source

Application Number: 00106971
Application Date: 2000.04.27
Publication Number: 1273451
Publication Date: 2000.11.15
Priority Information: 1999/5/6 DE 19920625.2
International: H02M3/335;H04N5/63
Applicant(s) Name: Deutsche Thomson-Brandt GmbH
Inventor(s) Name: Leijinhard Keger;Jukin Kitzman;Jea-Paull Lauver
Patent Agency Code: 11105
Patent Agent: lu xiaozhang
Abstract The protection circuit for a switch (T1) has an energy-storage means (C1), which is connected to a control input (G) of the switch (T1) and which is charged with a delay via resistance means (R1) when a control voltage (Ug) is present and is discharged via switching means (D2) when the control voltage (Ug) is low or absent, and has a switching stage (T2, T3) which is connected to a supply voltage (VCC), is switched on when a specific threshold voltage is present across the energy-storage means (C1) and in this way reduces the supply voltage (VCC). In one exemplary embodiment, when the switching stage (T2, T3) is switched on, the charge which is dissipated from the supply voltage (VCC) is at least partially routed to the energy-storage means (C1) via a diode (D2) which is connected in parallel with the said energy-storage means (C1), so that the phase during which the switching stage (T2, T3) is switched on is lengthened and the energy-storage means (C1), in this case a capacitor, is completely discharged. The protection circuit is particularly suitable for switched-mode power supplies which are used in consumer electronics equipment.