AN2300 STMICROELECTRONICS | Alldatasheet

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Technical content

Datasheet sections

  • 1 Capacitive converter
  • 2 Modified Buck converter
  • 2.1 Experimental results
  • 2.2 EMI measurements
  • 2.3 Higher output power
  • 2.4 Efficiency comparison
  • 2.5 Different output voltages
  • 3 Conclusions
  • 4 Revision history

and EMI, under the same output power conditions (about 0.6W). output power level to higher values, up to 1.1W. The main specifications of the converters are listed in Table 1. Table 1. Power supplies main specifications

1 Capacitive converter

converter is given in Table 2. Figure 1. Capacitive converter schematic Table 2. Capacitive converter part list

2 Modified Buck converter

provides two outputs with reversed polarity, V out1 = 12V and Vout2 = -5V. Figure 2. Buck converter modified schematic for power conversion. The voltage is then filtered by the LC filter made up by L and C1. the second output cannot supply more current than the first one.

  1. Considering discontinuous conduction mode (DCM), during the conduction of the switch

S the input DC bus is connected to the output and supplies the load, as shown in Figure 3.). shown in Figure 4.), until it zeroes and the output capacitor C1 feeds the load.

Figure 9. PCB layout based on schematic B Table 3. Buck converter part list (schematic A) Table 4. Buck converter part list (schematic B)

2.1 Experimental results

= 230VAC and full load (i.e. I out1 = 30mA and Iout2 = 40mA). Figure 10. Buck waveforms (schematic A) Figure 11. Buck waveforms (schematic B)

Figure 15. Efficiency vs V in

2.2 EMI measurements

standard, using a 50Ω LISN and a spectrum analyzer. results are shown under full load conditions at nominal 230V ac input voltage. Figure 16. Capacitive converter: conducted Figure 17. Capacitive converter: conducted

2.3 Higher output power

on the 12V output and 100mA on the -5V output, as listed in Table 5. VR1/R1≈7/R1=120mA, therefore R1 = 56 Ω for schematic B (see Figure 8. ). dissipation across the bleeder. In Table 6. the part list of the modified components is given. Figure 18. Buck converter: conducted Figure 19. Buck converter: conducted Table 5. Higher output power requirements

2.4 Efficiency comparison

where Iout1 and Iout2 are expressed in mA. The efficiency comparison between the two converters, based on (6), is shown in Figure 27. power case it features a slightly lower efficiency (3÷4%). Figure 27. Efficiency comparison between schematics A and B for I Dz2 = 30mA

2.5 Different output voltages

1 VR1B

Modified Buck converter AN2300 18/21 Rev1 This means that, if Vout2 is fixed at 5V, the allowed range of Vout1 in the schematic A will be about 4V ÷ 11V; if not, these limits will be moved together upwards or downwards depending on the value of V Dz2 (≅ Vout2). Thus, for the schematic B the minimum allowable value of V out1 is 9V, quite apart from the value of Vout2. The resistor R2 is optional and can be experimentally fixed between 0 and 1k Ω if a tune of the output voltage is needed. Schematic B 9V V out1 16V<< (8)(Figure 29.)

3 Conclusions

Two versions of a very low cost Buck converter based on VIPer12A have been proposed and compared with a Capacitive converter in terms of output voltage regulation, input power consumption, EMI and efficiency, in the same output power conditions. As a result of the analysis, it can be pointed out that: – the efficiency of both the Buck converters is higher than the efficiency of the Capacitive network; – the output capacitors needed in the Capacitive power supply are much bigger and expensive than those required in the Buck converters (1mF and 4.7mF vs 33 µF); – due to the switching operation of the Buck converter, an EMI input filter has to be inserted, as shown in figures 5 and 6; – the Buck solution is less expensive than the Capacitive one, with a cost saving of about 10 ÷ 15%.

4 Revision history

Table 7. Document revision history

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publicatio n are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectro nics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2006 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Ital y - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America