Based on scheme protect the amplifier Audio Analogue Aida - site his designer Federico Apartments Rovinj, http://www.pi.infn.it/~federico/unofficial.htm. I slightly developed and in mobile amplifier - also zaimstvovanno at Paoletti. Scheme applicable in any MIND, at the output which is a composite emitter repeater (2 cascades and more or one Darlington, of course - silicon, one or CMOS cascade).
In the source schema in traditional the protection circuit (the voltage drop across the emitter resistor opens the key, shunt BAE transition the output composite transistor) added two optocouplers (in the circuit of the shunt the base for the upper and lower shoulder). The current drawn by the shunt from the base, flows through the led of the optocoupler and opens galvanically unleashed key. Fine, but the the same node may not only autocratic turn the amplifier off, but to do this team from the outside. Need a couple of optocouplers, shunt BAE the transitions of the output transistors:
The threshold set divider R1-R2 based on the current limit on each transistor and resistance in the circuit, the emitter output. Total the resistance R1+R2 must be in the range 10..100 Ohms. Due to the circuit R3 is-C1-R4-D1, R8 is C2-R9-D2 (LPF) threshold triggering DC much higher than CC. In addition, the threshold decreases with increasing temperature T1, T2.
The first and fourth (vertical) optocouplers - protection sensors (closed=fault), the second and the third switches controlled by external signal (flowing current = off the MIND). In the circuit force off be sure to include current limiting resistor. Resistors R9-10 - I put instead of jumpers on the Board, whether they like they is probably not.
Despite incremental drop the voltage across the led circuit guaranteed off your MIND with repeater for single and double Darlington (0.33 Ohm under the emitter). Importantly, current, select T1, T2 from "triangle" - amplifier voltage was sufficient to guaranteed inclusion optocouplers (no less than 1 mA for TLP521). Optocouplers - any except Darlington (well, they can go to the devil, and not necessary here high gain). Required the current transfer ratio is determined by the currents and levels automation protection and shock, the shunt should select from "triangle". T1, T2 - any low-power low-voltage the saturation.
By the way, memorized by heart one and a half volts across the led is not quite true. On the led in TLP521 this scheme falls at room a temperature of not more than 0.9 In .
When designing the Board first "mind" actually placed The MIND and the protection circuit in the second a queue. The "earth" protection conducted separately and connect with other "lands" at the common point of the "stars". If car amplifier analog ground unleashed-current from the side of the earth, and the block automatics usually sits on side, the circuits R4D1 R9D2 to connect with power analog, and earth Tronov - side.
Publication: www.klausmobile.narod.ru, www.cxem.net