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å ¥åé»å§\(V_{IN}=12{\mathrm{V}}\)ããåºåé»å§\(V_{OUT}=5{\mathrm{V}}\)ã«å€æãã仿§ãå€ãã£ãé ã¯å ¥åºåé»å§å·®ã7Vãªã®ã§ãããããã¢ãŠãé»å§\(V_{DO}\)ã倧ãããŠããããæšæºã®ã·ãªãŒãºã¬ã®ã¥ã¬ãŒã¿(\(V_{DO}=2{\mathrm{V}}\)çšåºŠ)ã䜿çšããŠãåé¡ãããŸããã§ããã
ãããã3.3V黿ºã®ICãåºãŠãããšãå ¥åé»å§\(V_{IN}=5{\mathrm{V}}\)ããåºåé»å§\(V_{OUT}=3.3{\mathrm{V}}\)ã«å€æããããšãå¿ èŠã«ãªãå ŽåããããŸãããæšæºã®ã·ãªãŒãºã¬ã®ã¥ã¬ãŒã¿ã¯ããããã¢ãŠãé»å§\(V_{DO}\)ã¯2VçšåºŠã§ããã5Vãã3.3Vãäœãããšãã§ããªããããããããã¢ãŠãé»å§\(V_{DO}\)ãå°ããLDOãäœãããŸããã
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LDOã¯å¶åŸ¡çŽ åã«ãPNPåãã€ããŒã©ãã©ã³ãžã¹ã¿ãã®å Žåã¯é£œåé åããPãã£ãã«åMOSFETãã®å Žåã¯ç·åœ¢é åã§çšããŠããã®ã§ãå¶åŸ¡çŽ åã«ãããé»å§ãäœãããããšãã§ããŸãããã®ãããããããã¢ãŠãé»å§\(V_{DO}\)ãäœãããããšãã§ããŸãã
LDOã®ãåŒããšãåäœåçã
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äžå³ã«ç€ºããŠããLDOã®ãåºåé»å§\(V_{OUT}\)ãšå ¥å黿µ\(I_{IN}\)ã®åŒããšãåäœåçãã«ã€ããŠãããã説æããŸãã
LDOã®ãåºåé»å§\(V_{OUT}\)ãšå ¥å黿µ\(I_{IN}\)ã®åŒã
äžå³ã«ç€ºããŠããLDOã®åºåé»å§\(V_{OUT}\)ãšå ¥å黿µ\(I_{IN}\)ã¯æ¬¡åŒã§è¡šãããŸãã
V_{OUT}&=&V_{REF}\left(1+\frac{R_1}{R_2}\right)+I_{BIAS}R_1\\
\\
I_{IN}&=&I_{OUT}
\end{eqnarray}
äžåŒã§éèŠãªã®ã¯ãåºåé»å§\(V_{OUT}\)ã®åŒã«å ¥åé»å§\(V_{IN}\)ãå ¥ã£ãŠããªãããšã§ããåºåé»å§\(V_{OUT}\)ã¯åºæºé»å§\(V_{REF}\)ãšæµæ\(R_1\),\(R_2\)ãšãªãã¢ã³ãã®éåè»¢å ¥å端å("+"ã®ç«¯å)ã«æµãã黿µ\(I_{BIAS}\)(âå ¥åãã€ã¢ã¹é»æµãšåŒã°ããŠããŸã)ã«ãã£ãŠæ±ºãŸããŸãããªããPNPãã©ã³ãžã¹ã¿ã«æµããããŒã¹é»æµ\(I_B\)ã¯éåžžã«å°ããã®ã§ç¡èŠããŠããŸãã
åºåé»å§\(V_{OUT}\)ã¯äžèšã®ããã«å°åºããŠããŸãã
\begin{eqnarray}
V_{OUT}&=&V_{REF}+R_1ã®é»å§éäž\\
\\
&=&V_{REF}+R_1\left(\frac{V_{REF}}{R_2}+I_{BIAS}\right)\\
\\
&=&V_{REF}\left(1+\frac{R_1}{R_2}\right)+I_{BIAS}R_1
\end{eqnarray}
ããã§ããªãã¢ã³ãã®åè»¢å ¥å端åã«æµãã黿µ\(I_{BIAS}\)ã¯éåžžã«å°ããã®ã§ã\(I_{BIAS}R_1\)ãçç¥ãããšãåºåé»å§\(V_{OUT}\)ã¯æ¬¡åŒãšãªããŸãã
\begin{eqnarray}
V_{OUT}&=&V_{REF}\left(1+\frac{R_1}{R_2}\right)
\end{eqnarray}
äžåŒã¯äžèšã®ããã«åå§ãçšããŠãæ±ããããšãã§ããŸãã
\begin{eqnarray}
&&V_{OUT}ïŒV_{REF}=R_1+R_2ïŒR_2\\
\\
{\Leftrightarrow}&&V_{OUT}=V_{REF}\left(1+\frac{R_1}{R_2}\right)
\end{eqnarray}
LDOã®ãåäœåçã
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- åºå黿µ\(I_{OUT}\)ãæ¥å¢ããæ
- åºå黿µ\(I_{OUT}\)ãæ¥æžããæ
è² è·å€åã«ãããåºå黿µ\(I_{OUT}\)ãæ¥å¢ãããšãåºåé»å§\(V_{OUT}\)ãäœäžããŸãããã®çµæãåºåé»å§ãæµæ\(R_1\)ããã³æµæ\(R_2\)ã§åå§ãã\(V_1\)ã®é»å§ãäœäžããŸããé»å§\(V_1\)ã¯ãªãã¢ã³ãã®éåè»¢å ¥å端å("+"ã®ç«¯å)ã«å ¥åãããé»å§ã§ãããé»å§\(V_1\)ãåºæºé»å§\(V_{REF}\)ãããå°ãããªããšããªãã¢ã³ãã®åºå端å(ãã©ã³ãžã¹ã¿\(Q_1\)ã®ããŒã¹é»å§\(V_B\)ãäœäžããŸããããŒã¹é»å§\(V_B\)ãäœäžãããšãããŒã¹é»æµ\(I_B\)ãäžæããããããšããã¿ã³ã¬ã¯ã¿éé»å§\(V_{EC}\)ãäœäžããŸããããã«ãã£ãŠãåºåé»å§\(V_{OUT}\)ãäžæããã®ã§å®å®ããŸãã
è² è·å€åã«ãããåºå黿µ\(I_{OUT}\)ãæ¥æžãããšãåºåé»å§\(V_{OUT}\)ãäžæããŸãããã®çµæãåºåé»å§ãæµæ\(R_1\)ããã³æµæ\(R_2\)ã§åå§ãã\(V_1\)ã®é»å§ãäžæããŸããé»å§\(V_1\)ã¯ãªãã¢ã³ãã®éåè»¢å ¥å端å("+"ã®ç«¯å)ã«å ¥åãããé»å§ã§ãããé»å§\(V_1\)ãåºæºé»å§\(V_{REF}\)ããã倧ãããªããšããªãã¢ã³ãã®åºå端å(ãã©ã³ãžã¹ã¿\(Q_1\)ã®ããŒã¹é»å§\(V_B\)ãäžæããŸããããŒã¹é»å§\(V_B\)ãäžæãããšãããŒã¹é»æµ\(I_B\)ãäœäžããããããšããã¿ã³ã¬ã¯ã¿éé»å§\(V_{EC}\)ãäžæããŸããããã«ãã£ãŠãåºåé»å§\(V_{OUT}\)ãäœäžããã®ã§å®å®ããŸãã
LDOã®ãå¹çã
äžå³ã«ç€ºããŠããã®ã¯PNPãã©ã³ãžã¹ã¿\(Q_1\)ããšã©ãŒã¢ã³ã(誀差æ€åºçšã®ãªãã¢ã³ã)ãåºæºé»å§æº\(V_{REF}\)ãæµæ\(R_1\),\(R_2\)ã§æ§æãããLDOã§ãã
ã\(I_{IN}=I_{OUT}\)ããšãããšãLDOã®å¹ç\({\eta}\)ã¯å ¥åé»å\(P_{IN}\)ãšåºåé»å\(P_{OUT}\)ã®å²åãªã®ã§ã次åŒã§è¡šãããŸãã
{\eta}&=&\frac{P_{OUT}}{P_{IN}}Ã100\\
\\
&=&\frac{V_{OUT}ÃI_{OUT}}{V_{IN}ÃI_{IN}}Ã100\\
\\
&=&\frac{V_{OUT}ÃI_{OUT}}{V_{IN}ÃI_{OUT}}Ã100\\
\\
&=&\frac{V_{OUT}}{V_{IN}}Ã100{\mathrm{[{\%}]}}\\
\end{eqnarray}
ããã§ãäžäŸãšããŠãåºåé»å§\(V_{OUT}\)ã3.3Vãåºå黿µ\(I_{OUT}\)ã1.0Aã®LDOã«ãããŠãå ¥åé»å§\(V_{IN}\)ã24V,12V,5V,5V,3.8Vã®æã§å¹ç\({\eta}\)ãã©ã®ããã«ãªããèšç®ããŠã¿ãŸãããã
- å ¥åé»å§\(V_{IN}\)ã24Vã®æ
- å ¥åé»å§\(V_{IN}\)ã12Vã®æ
- å ¥åé»å§\(V_{IN}\)ã5.3Vã®æ
- å ¥åé»å§\(V_{IN}\)ã5Vã®æ
- å ¥åé»å§\(V_{IN}\)ã3.8Vã®æ
\begin{eqnarray}
{\eta}&=&\frac{V_{OUT}}{V_{IN}}Ã100=\frac{3.3}{24}Ã100=13.75{\mathrm{[{\%}]}}
\end{eqnarray}
\begin{eqnarray}
{\eta}&=&\frac{V_{OUT}}{V_{IN}}Ã100=\frac{3.3}{12}Ã100=27.5{\mathrm{[{\%}]}}
\end{eqnarray}
\begin{eqnarray}
{\eta}&=&\frac{V_{OUT}}{V_{IN}}Ã100=\frac{3.3}{5.3}Ã100=62.26{\mathrm{[{\%}]}}
\end{eqnarray}
\begin{eqnarray}
{\eta}&=&\frac{V_{OUT}}{V_{IN}}Ã100=\frac{3.3}{5}Ã100=66{\mathrm{[{\%}]}}
\end{eqnarray}
\begin{eqnarray}
{\eta}&=&\frac{V_{OUT}}{V_{IN}}Ã100=\frac{3.3}{3.8}Ã100=86.84{\mathrm{[{\%}]}}
\end{eqnarray}
ãã®ããã«ãLDOã¯å ¥åé»å§\(V_{IN}\)ãåºåé»å§\(V_{OUT}\)ã«è¿ã¥ãã»ã©ãå¹ç\({\eta}\)ãäžããããšãåãããŸãã
å ¥åé»å§\(V_{IN}=3.8{\mathrm{V}}\)ããåºåé»å§\(V_{OUT}=3.3{\mathrm{V}}\)ã«å€æããå Žåã®å¹ç\({\eta}\)ã¯çŽ86%ãšãªããããLDOã䜿ã£ãŠããã¹ã€ããã³ã°ã¬ã®ã¥ã¬ãŒã¿äžŠã¿ã®å¹çãå®çŸå¯èœã«ãªããŸããäžæ¹ãæšæºã®ã·ãªãŒãºã¬ã®ã¥ã¬ãŒã¿ã䜿ãå Žåã«ã¯ãããããã¢ãŠãé»å§\(V_{DO}\)ã2VçšåºŠãªã®ã§ãåºåé»å§\(V_{OUT}=3.3{\mathrm{V}}\)ãå®çŸããã«ã¯ãå ¥åé»å§\(V_{IN}=5.3{\mathrm{V}}\)å¿ èŠã§ããããã®å Žåãå¹ç\({\eta}\)ã¯çŽ62%ã«ãªããŸãã
ãã®ããã«ãLDOã¯å ¥åºåé»å§å·®ãå°ããå Žåãå¹ç\({\eta}\)ãé«ãããããšãã§ãããããè²¢ç®åºŠã¯éåžžã«é«ããã®ã«ãªããŸãããªããå ¥åºåé»å§å·®ã倧ããå Žå(äŸãã°ãå ¥åé»å§\(V_{IN}\)ã12Vãåºåé»å§\(V_{OUT}\)ã3.3Vã®å Žåãªã©)ã§ã¯ãLDOãçšããŠãæšæºã®ã·ãªãŒãºã¬ã®ã¥ã¬ãŒã¿ãçšããŠãå¹çã¯å€ãããŸããã
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