| 摘要 |
<p>19 Amplifier arrangement comprising a protection circuit. A protection circuit for a power amplifier in which feedback is applied from the output (8) to the inverting input (2) of the amplifier by a negative feedback network comprising a first resistor (R2), a second resistor (R1) and a capacitor (C2), comprises a voltage-current converter (12) whose input is connected to the output of the amplifier which is loaded by a load (RL) and whose output is connected to the junction point of the second resistor (R1) and the capacitor (C2). When the protection circuit is activated if the output transistors of the amplifier are loaded excessively for example due to short-circuiting of the load, the input voltage of the voltage-current converter (12), for low frequencies, is converted into a current which is re-converted into a voltage in the capacitor (C2), which voltage is added to the normal negative-feed-back voltage provided by the voltage divider comprising the first resistor (R2) and the second resistor (R1). This provides a strong negative feedback and hence a satisfactory protection. For higher frequencies the capacitor (C2) constitutes a short circuit, so that the negative feedback changes to the normal feedback, thus ensuring that the amplifier remains stable under all conditions. The amplifier is then protected by the thermal cut-out which is normally present. - Figure 4.</p> |
