Application principle of uPC1237H

The internal circuit principle of 1237H is shown in Figure 2-122. It has four independent detectors inside, which can complete
their respective detection tasks. When an abnormality occurs in the circuit, it can immediately drive the relay and disconnect the output circuit to protect the speaker
and related circuits from damage. The relay driving current output by rvPC1237H can reach 80rnA. There are two reset methods for the overload protection circuit and
the midpoint voltage offset protection circuit. One is the automatic reset method, that is, the 3rd pin passes a
0-02t.eF capacitor. Grounded, the relay is closed when a fault occurs in the circuit, and the relay is automatically released after the fault is eliminated. The
other is a shutdown reset method, that is, pin 3 is directly connected to the ground. At this time, there is a self-locking function in the circuit. Once the relay is closed, it
will not be released even after the fault disappears. The circuit must be shut down before the circuit can be reset. Both methods have their own merits. When using it,
you should flexibly choose according to your own situation. oLePC1237H adopts single power supply mode, has a wide operating voltage range, and
can work reliably between 25V - 60V.
    The power-on protection circuit is composed of Rzo, R2l, and Cll (R12.Ril and island in Figure 2-122). Pin 7 is the power-on protection input
terminal. After the power is turned on, vc charges cll through ‰ and R2l. Due to the delay function of C5, the relay
remains closed during the delay time after power-on . After the power amplifier pre-stage and push stage enter a stable state, the delay ends and the relay is released to turn on
the speaker, thus avoiding the power-on shock. The delay time can be determined by the formula Cii-Rzl-ln[(V8 - V7)/V8]. According to
the value in the figure, the delay time is 1.7 seconds.
    The midpoint offset protection circuit is composed of Rj4, island (min, Q in Figure 2-122), and pin 2 is
the input terminal of the midpoint voltage offset protection. Its positive level detection threshold voltage is 0 - 62V, and its negative level detection threshold voltage is -0.17V. Such a high
index will cause frequent relay action in practical applications, affecting the listening effect. Therefore, the protection circuits in practical applications
are equipped with expansion circuits.
    The overload protection circuit consists of Vr5, VT4, Rio, Rll and R It is composed of other components (VTs, VT7, Ri, R2
and Ro in Figure 2-122), and pin 1 is the overload protection input terminal. When the output is overloaded, the voltage drop on R6 increases, which triggers VT4
to turn on and VTs to turn on, which in turn triggers pin 1 to make the relay close. The protection sensitivity can be changed by adjusting the ratio of Rio and Rl1
. The
    shutdown protection circuit is composed of VI wind, RL9 and C12 (VI wind, R10, C4 in Figure 2-122), and pin 4 is the shutdown protection
input terminal. When the circuit is working, the power supply rectified by VD7 is stepped down by R19 and filtered by C4 to establish a stable DC
level at pin 4. As soon as pin 4 loses power, the relay will close immediately. Since the capacity of C12 is much smaller than the capacity of the power supply filter capacitor,
as soon as the power is turned off, pin 4 loses power immediately, effectively preventing the shutdown impact.