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Chapter 11:
Passive Switch-Mode Voltage-to-Power Converters in Laser Systems
Some applications require a stabilized laser beam power. For this purpose, many low-power LDs have a photodiode attached to the rear facet. Light penetrates the rear facet mirror and is converted by the photodiode into a signal proportional to the laser beam power. This signal is used to stabilize the laser beam power, but in some LD systems it can be preferable to stabilize the electrical power of the LD assembly. Another application where a CPS is beneficial involves charging energystoring capacitors in pulsed laser systems. The advantage of a CPS-type capacitor charger compared to a CCS type is that it provides a constant load on the primary source of electrical energy during the charging cycle. Unlike the CPS, a CCS-type capacitor charger increases the power consumption from the primary source with an increased storage capacitor voltage. The electrical power in a CPS can be stabilized by an active feedback loop using the product of the LD current signal and the voltage signal according to the block diagram depicted in Fig. 5.4(a). However, there is a passive means (without feedback) of power stabilization. The working principal of this converter is based on charging a capacitor with a constant frequency up to a certain voltage and the subsequent discharge into the load.
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