ꢀ ꢁꢁꢂ ꢃ ꢄ ꢅ ꢆ ꢀ ꢁ ꢁꢂ ꢃ ꢄ ꢇ ꢆ ꢀꢁ ꢁꢂ ꢃ ꢄ ꢄ
ꢀ ꢁꢁꢈ ꢃ ꢄ ꢅ ꢆ ꢀ ꢁ ꢁꢈ ꢃ ꢄ ꢇ ꢆ ꢀꢁ ꢁꢈ ꢃ ꢄ ꢄ
SLUS499A – NOVEMBER 2001 – REVISED JANUARY 2002
APPLICATION INFORMATION
half-bridge operation and inductor selection (continued)
Waveforms for the UCC3976 half-bridge circuit operated with a 12-Vdc input are shown in Figure 14. P- and
N-Channel MOSFETs are driven out of phase with 50% duty cycle producing a square wave at the drains (see
Figure15: trace 1). Inductor LRES and the PZT primary capacitance form a low-pass filter. The resulting in a
near sinusoid across the PZT primary (trace 2). Due to the high Q of the PZT, lamp voltage (trace 4) is sinusoidal.
Lamp current is sensed by the half-wave rectification circuit at RCS (trace 3). Lamp current is in phase with lamp
current since the load is primarily resistive with some capacitance due to the reflector’s proximity to the lamp.
The lamp reflector should be grounded for safety reasons and in order to keep the secondary capacitance
constant allowing the PZT load to be constant.
V
V
= 12 Vdc
IN
LAMP
= 600 V
Figure 14. UCC3976 Half-Bridge Waveforms
18
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