Hi
Now i am moving towards the trend of using class D rather than my all time favorite and outdated LM1875 gainclones ... as far as i know class AB amplifiers can tolerate no load operation but for class D i've learnt from mistake through damaging the zobel resistor on my TDA8950 module ...
this time round, ive thought that what if i insert a 560ohm 10W or higher resistor at the output? when there is no load connected or bad enough for the speaker leads to be disconnected by accident with signal on during playing will the dummy load 560ohm tame the high voltage generated by the LC tank on the class D output? if make sense the dummy load resistor gets hot i might locate a heat sensor on top of the dummy resistor if it does get hot during the case of no load it might trigger a protection circuit to mute the input or to shut down the amplifier all together? That day having a friend of mine to install an amplifier speaker setup only realize he use only one channel instead of two lucky it was a conventional class AB amplifier.
i posted this question due to i might build a few class D amplifier to sell to close friend of mine which was not really electronic and amplifier well understood. i know this is common sense that really it needs a load for class D not to run into damage but some others might not know.
thanks
Now i am moving towards the trend of using class D rather than my all time favorite and outdated LM1875 gainclones ... as far as i know class AB amplifiers can tolerate no load operation but for class D i've learnt from mistake through damaging the zobel resistor on my TDA8950 module ...
this time round, ive thought that what if i insert a 560ohm 10W or higher resistor at the output? when there is no load connected or bad enough for the speaker leads to be disconnected by accident with signal on during playing will the dummy load 560ohm tame the high voltage generated by the LC tank on the class D output? if make sense the dummy load resistor gets hot i might locate a heat sensor on top of the dummy resistor if it does get hot during the case of no load it might trigger a protection circuit to mute the input or to shut down the amplifier all together? That day having a friend of mine to install an amplifier speaker setup only realize he use only one channel instead of two lucky it was a conventional class AB amplifier.
i posted this question due to i might build a few class D amplifier to sell to close friend of mine which was not really electronic and amplifier well understood. i know this is common sense that really it needs a load for class D not to run into damage but some others might not know.
thanks
Dear Danny,
If the controlled variable is the capacitor voltage (itself), the inverter would transfer power from the load (capacitor) back to the power supply as soon as the control loop sees a positive voltage error. Thus the no-load condition is no problem to a switching amplifier that uses post-filter feedback, as in a synchronous buck regulator.
All the best.
If the controlled variable is the capacitor voltage (itself), the inverter would transfer power from the load (capacitor) back to the power supply as soon as the control loop sees a positive voltage error. Thus the no-load condition is no problem to a switching amplifier that uses post-filter feedback, as in a synchronous buck regulator.
All the best.
i've been wondering if the TDA8950 uses the post filter feedback? last time one channel has load connected another ones doesnt see any load and it does damage to the zobel resistor to the channel that doesnt have any load ... so i wonder if something such as low value 56 Ohms or so might act as a dummy to represent a speaker load if so happen that the amp was playing and accidentally the speaker leads were disconnected will it cause such damage? thanks
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Well, it doesn't seem to be, at least from the datasheet. However, since it maybe possible to design a control loop external to the IC, it's better if you obtain the circuit diagram for the PCB (amplifier) in question.
I have never had to use any dummy resistor, but I must admit that I haven't used pre-filter feedback either, maybe someone else here has..