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a) EXTERNAL npn SWITCH

b) EXTERNAL pnp SATURATED SWITCH (see Note A)

MC33063A, MC34063A

1.5-A PEAK BOOST/BUCK/INVERTING SWITCHING REGULATORS

SLLS636J – DECEMBER 2004 – REVISED OCTOBER 2005

A.

If the output switch is driven into hard saturation (non-Darlington configuration) at low switch currents (

≤300 mA) and

high driver currents (

≥30 mA), it may take up to 2 µs to come out of saturation. This condition will shorten the off time

at frequencies

≥30 kHz and is magnified at high temperatures. This condition does not occur with a Darlington

configuration because the output switch cannot saturate. If a non-Darlington configuration is used, the output drive

configuration in Figure 7b is recommended.

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