Hello,
We use the LM4766 in bridged mode as a driver for the coil of a linear motor. The coil has resistance of 33 Ohms and an inductance 62 mH. In some cases, we connect two motor coils in parallel. So we have a RL of 16.5 Ohms.
Our schematic is similar to the figure 5 of the datasheet, but our load has a resistance of 16.5 Ohms, because we have two 33 Ohms in parallel. For the power supply of the amplifier we connected -30 V to Pin 4 and +30 V to Pin 2 and 15.
My question is how much output power is possible?
For the case if we connect two motor coils in parallel we have 16.5 Ohms. We measured a maximum voltage of 48.5 V over the load. So I think the power is
The power is needed for a peak of 20 ms. After that the amplifier is silent for a minimum 2 minutes.
In figure 17 of the datasheet the output power is shown as a function of the load.
I interpret the figure that for a single output with a load of 16.5 Ohms the output power is around 22 W. For the bridge mode I assume that the output is at least the double which is 44 W.
If I calculate the power for the bridged mode, I will get the following.
At a specified time t we get
The power at the output is
Because of the symmetrical push-pull output amplifier, the outputs of the amplifier are inverted. The following pictures shows the outputs of both amplifiers.
The ouput power of the symmetrical push-pull amplifier is
So the output power of the circuit above is
That confirms the statement on page 16 of the datasheet, which says that the output power for bridged mode is theoretical four times the output of a single amplifier. That is the theoretical value. I think internal the amplifier is will no absorb the power dissipation which is needed for a four times power output.
Please tell me what is the actual value which can be achieved in practice for the power output of a bridged amplifier LM4766?
The second question is what happens to the LM4766 when no load is connected? Again, we use the bridge mode, but the load is not connected in some cases. So we do not have a connection between the two amplifier. The single amplifiers are just connected to their feedback loops. The amplifiers get an input signal, but the load is not connected. Might that be a problem for the amplifier?
Thanks
Bjoern
