TL783_15 Datasheet, PDF (14/27 Pages) Texas Instruments – TL783 High-voltage Adjustable Regulator

TL783
SLVS036N – SEPTEMBER 1981 – REVISED JANUARY 2015
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Typical Application (continued)
9.2.2.2 Protection Circuitry
The TL783 regulator includes built-in protection circuits capable of guarding the device against most overload
conditions encountered in normal operation. These protective features are current limiting, safe-operating-area
protection, and thermal shutdown. These circuits protect the device under occasional fault conditions only.
Continuous operation in the current limit or thermal shutdown mode is not recommended.
The internal protection circuits of the TL783 protect the device up to maximum-rated V_I as long as certain
precautions are taken. If V_l is switched on instantaneously, transients exceeding maximum input ratings may
occur, which can destroy the regulator. Usually, these are caused by lead inductance and bypass capacitors
causing a ringing voltage on the input. In addition, when rise times in excess of 10 V/ns are applied to the input,
a parasitic npn transistor in parallel with the DMOS output can be turned on, causing the device to fail. If the
device is operated over 50 V and the input is switched on, rather than ramped on, a low-Q capacitor, such as
tantalum or aluminum electrolytic, should be used, rather than ceramic, paper, or plastic bypass capacitors. A Q
factor of 0.015, or greater, usually provides adequate damping to suppress ringing. Normally, no problems occur
if the input voltage is allowed to ramp upward through the action of an ac line rectifier and filter network.
Similarly, when an instantaneous short circuit is applied to the output, both ringing and excessive fall times can
result. A tantalum or aluminum electrolytic bypass capacitor is recommended to eliminate this problem. However,
if a large output capacitor is used, and the input is shorted, addition of a protection diode may be necessary to
prevent capacitor discharge through the regulator. The amount of discharge current delivered is dependent on
output voltage, size of capacitor, and fall time of V_l. A protective diode (see Figure 21) is required only for
capacitance values greater than:
C_o (μF) = 3 × 10⁴ / (V_O)²
Care always should be taken to prevent insertion of regulators into a socket with power on. Power should be
turned off before removing or inserting regulators.
TL783
V_I
IN
OUT
V_O
ADJ
R1
C_o
R2
Figure 21. Regulator With Protective Diode
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