In the datasheet - two issues are mentioned that can couse dropouts
8.3.2 OverCurrent Protection (OCP)
When the loudspeaker terminals are short-circuited or if one of the demodulated outputs
of the amplifier is short-circuited to one of the supply lines, this will be detected by the
OverCurrent Protection (OCP). If the output current exceeds the maximum output current
of 8 A, this current will be limited by the amplifier to 8 A while the amplifier outputs remain
switching (the amplifier is NOT shut-down completely).
The amplifier can distinguish between an impedance drop of the loudspeaker and a
low-ohmic short across the load. In the TDA8920B this impedance threshold (Zth)
depends on the supply voltage used.
When a short is made across the load causing the impedance to drop below the threshold
level (< Zth) then the amplifier is switched off completely and after a time of 100 ms it will
try to restart again. If the short circuit condition is still present after this time this cycle will
be repeated. The average dissipation will be low because of this low duty cycle.
8.3.4 Supply voltage protections
If the supply voltage drops below ±12.5 V, the UnderVoltage Protection (UVP) circuit is
activated and the system will shut-down correctly. If the internal clock is used, this
switch-off will be silent and without pop noise. When the supply voltage rises above the
threshold level, the system is restarted again after 100 ms. If the supply voltage exceeds
±33 V the OverVoltage Protection (OVP) circuit is activated and the power stages will
shut-down. It is re-enabled as soon as the supply voltage drops below the threshold level.
So in this case no timer of 100 ms is started.
8.3.2 OverCurrent Protection (OCP)
When the loudspeaker terminals are short-circuited or if one of the demodulated outputs
of the amplifier is short-circuited to one of the supply lines, this will be detected by the
OverCurrent Protection (OCP). If the output current exceeds the maximum output current
of 8 A, this current will be limited by the amplifier to 8 A while the amplifier outputs remain
switching (the amplifier is NOT shut-down completely).
The amplifier can distinguish between an impedance drop of the loudspeaker and a
low-ohmic short across the load. In the TDA8920B this impedance threshold (Zth)
depends on the supply voltage used.
When a short is made across the load causing the impedance to drop below the threshold
level (< Zth) then the amplifier is switched off completely and after a time of 100 ms it will
try to restart again. If the short circuit condition is still present after this time this cycle will
be repeated. The average dissipation will be low because of this low duty cycle.
8.3.4 Supply voltage protections
If the supply voltage drops below ±12.5 V, the UnderVoltage Protection (UVP) circuit is
activated and the system will shut-down correctly. If the internal clock is used, this
switch-off will be silent and without pop noise. When the supply voltage rises above the
threshold level, the system is restarted again after 100 ms. If the supply voltage exceeds
±33 V the OverVoltage Protection (OVP) circuit is activated and the power stages will
shut-down. It is re-enabled as soon as the supply voltage drops below the threshold level.
So in this case no timer of 100 ms is started.
I appreciate your help with this.
As you have probably already gathered, I am an electronics birdbrain.
I will measure the voltage at the caps after the psu.
I am also going to do some more frequency sweeps.
During some really low frequency tests last night, I did note that intermittant dropping out again. Could it be frequency related? At the low end?
As you have probably already gathered, I am an electronics birdbrain.
I will measure the voltage at the caps after the psu.
I am also going to do some more frequency sweeps.
During some really low frequency tests last night, I did note that intermittant dropping out again. Could it be frequency related? At the low end?
The possibility of it being fake did cross my mind until I discovered a fault in both the crossovers ( recently, the left and right crossovers were both adjusted "fiddled with" by a friend who has much more experience than I).
During frequency sweeps, at 1000 hertz the midrange sounded all crackly, which caused the 8920 to shut down.
Removing the crossover from the circuit fixed the fault.
I made sure by using another amp (Proton) with and without the crossover/s.
Same thing, with crossovers, frequency gets to 1000 hertz, then all of a sudden, crackly fizzling, then it shuts down.
Any ideas?
Should I move my query to another thread?
During frequency sweeps, at 1000 hertz the midrange sounded all crackly, which caused the 8920 to shut down.
Removing the crossover from the circuit fixed the fault.
I made sure by using another amp (Proton) with and without the crossover/s.
Same thing, with crossovers, frequency gets to 1000 hertz, then all of a sudden, crackly fizzling, then it shuts down.
Any ideas?
Should I move my query to another thread?
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