DE3445340A1 - MOSFET two-way switch with current limiting - Google Patents

Abstract

The application deals with a MOSFET two-way switch with current limiting, which is overvoltage- and short-circuit-resistant. Using parts of the circuit, a one-way switch with current limiting, overvoltage protection and short-circuit protection can also be built, or a two-way or one-way switch with the characteristics of current limiting, overvoltage protection or short-circuit protection or a combination of these characteristics.

Description

Description:

If UG 1,2 = 0 or less than UGS th, then both FETs are blocked. (Image 1). Depending on the polarity at D1 and D2, FET 1 is blocked and the integrated one FET 2 diode conducting or vice versa.

If you put the control voltage between UGs and S1 (also possible if S2) is on, both FETs are conductive.

If the voltage drop across R1 is $ 0.6V, the transistors are Tr.l and Tr.2 blocked. If the voltage drop at R1 increases to> 0.6 V, depending according to the polarity of one of the transistors Tr.l and Tr, 2 being conductive and thereby reduces the control voltage UGs of the two FETs, so that there is a state of equilibrium sets in which the current through R1 causes a voltage drop, that of the UBE Corresponds to the voltage of T1 or T2.

The circuit according to Figure 3 works on the same principle, however as a facility switch.

A further development of Figure 1 is the circuit shown in Figure 2 The overvoltage protection is achieved by the diodes Da, Db, D3 and Zl. if UDS at the transistors FET1 and FET2 increases to greater than Uz, the voltage changed at G1,2 towards more positive values, the two fets open and thereby build the overvoltage energy.

Short-circuit resistance is achieved with the transistors FET 3 and FET 4.

When the load is short-circuited, the current increases in the on-state to the limited value. When this is achieved, the current alternating voltage appears to D1, D2 and via the diodes Da and Db to the drain of FET 3. The gate voltage on FET 3 is positive when the circuit is activated. The voltage level at source of FET 3 is equal to that of the gate of FET 4 and is also positive, so FET 4 conducts. This causes the voltage G1 2 to drop to values <UGS th of FET 1 and FET 2 and the bidirectional switch switches off.

Criticism of the state of the art: short-circuit-proof output stages with overvoltage protection are still quite complex today, especially when it comes to bidirectional switches acts for higher voltages.

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Claims (2)

Designation: MOSFET two-directional switch with current limitation Claims: 1. CMOS compatible MOSFET bidirectional switch with current limiting, d u r c h e k e n n n z e i c h n e t that two MOS transistors with a common gate (Fig. 1) are connected so that the two source electrodes (S1 and via a low-resistance Resistor (R1) are connected. The collectors are on the common gate connection of the transistors T1 and T2 switched. The UBE route from T1 and T2 is above the resistors R2 baw. R3 parallel to R1, with the emitter from T2 to S2 and the Emitter from transistor T1 to the switch output points are the drains of FET 1 and FET 2. The control voltage is between S1 (or and the common Gate connection applied. 2. CMOS-compatible MOSFET bidirectional switch with current limiting, Overvoltage protection and short-circuit protection according to claim 1 d a d u r c h g e k It is noted that in addition (Fig. 2) the diode lines D and Db, with common Cathode, connected to D1 and a D1 D2; the cathode is connected to the Zener diode Zl, the is in series with the diode D3, the cathode of which is connected to the common gate (G1,2); further in addition a FET (FET4) whose: nraiS - via resistor R5 to G1,2 - and its source is at S1 (or S2); another FET (FET3) with drain on the common cathode from Da and Db, source to gate of FET4 and across resistor from a R6 to point S1 with the gate switched to the plus point of the input1 and also the common Collector of T1 and T2 via resistor R4 on the common gate of FET1 and FET2 lies. A current limiting MOSFET switch according to claim 1, d a d u r c h it is not noted that 'FET2, T2 and R3 are omitted and the load at the points D1 and S2 are (Fig. 3 '- one-way switch) MOSFET switch with current limiting, Overvoltage and short-circuit protection according to claim 1, but only for one direction, d a d u r c h g e k e n n n z e i c h n e t that the components FET2, Tr.2, R3, R4, D and Db are omitted, and a the load is on D1 and S2. MOSFET switch according to Claim 1, 2, 3 and 4 d a d u r c h g e k e n n z e i n e t that all components are monolithically integrated.