## 6 Practical Realizations of Piezoelectric Power Conversion Circuits  
### Examples of Comercially Avaliable Monolithic Micro-Power Electronic AC-DC Converters  
In the last few years, based on the systematic approaches presented in the previous section and the structure of well-known circuit configurations, various commercially available monolithic integrated circuits, such as [96; 97; 98], which have a relatively low power consumption and small dimensions, such as the effective area of a semiconductor chip, have been developed. Moreover, these types of integrated circuits contain functional blocks of a rectifier or voltage multiplier and a DC-DC converter, as well as some additional blocks for the charge management of rechargeable batteries or supercapacitors connected in the output port. Some of these integrated circuits also have functional stages to include an additional non-rechargeable battery (or backup primary battery), in case the input signal is of insufficient amplitude to ensure the charging of the energy storage elements connected to the output of the integrated circuit. Also, some of them include functional blocks for connection via a standard interface with a microcontroller or other digital circuit. Exemplary energy harvesters that use a monolithic integrated circuit to convert an AC voltage received from a piezoelectric generator into a DC signal for charging a supercapacitor or battery are given in [3] and [11], respectively. The analysis of the literary sources also showed the presence of electronic converters in which, instead of commercially available circuits [82; 84; 86; 87; 88; 89; 91; 92; 93], specialized integrated circuits designed for specific applications are used. One of the popular commercially available integrated circuits that provides the conversion of mechanical vibrations from piezoelectric elements is the LTC3588-1 (from Analog Devices) [96]. The LTC3588-1 is a specialized integrated circuit designed for energy harvesting that has relatively low self-consumption and small physical dimensions. Furthermore, the internal structure of the LTC3588-1 includes some interesting microelectronic techniques that can produce a wide operating dynamic range and a relatively high value of electrical energy efficiency. As shown in Figure 31, the LTC3588-1 contains a built-in rectifier at the input after which a high-efficiency step-down converter is connected, which is optimized for operation with photovoltaics, piezoelectrics, and electromagnetic transducers. The input operating voltage is from 2.7 V to 20 V. The output voltage is digitally selectable from the fixed values of 1.8 V, 2.5 V, 3.3 V, and 3.6 V. The guaranteed output current is 100 mA. There is a digital output signal indicating at a logic high level that the output voltage is at 92% of the set value, which can be used to enable integrated circuits relying on this voltage for power. Figure 31: Block diagram of a low-power circuit configuration for energy harvesting using LTC3588-1 [96]. The voltage generated by the piezoelectric is rectified by the built-in diode rectifier, which has a small drop in the typical value of current from such a source (10 \(\mu\)A). This voltage is output to pin Vin, to which the external capacitor \(C_{storage}\) (or \(C_{STO}\)) is connected. The voltage on it is limited by the built-in Zener diode. This voltage is used to power the integrated circuit as well as the input voltage to the step-down converter that maintains the output voltage. It is set by the digital signals \(D_{0}\) and \(D_{1}\). The output SW is the point between the two switching transistors that are part of the converter. An inductance is externally connected to it. The output voltage is monitored through a \(V_{out}\) pin. The voltage from this pin passes through a controllable resistor voltage divider. Its output is used to enable the buck converter, via the SLEEP comparator, and also to set the PGOOD output logic level, which indicates that the output voltage has reached the reference.