A linear three-terminal regulator expansion flow circuit,
the circuit is very common to a linear three-terminal regulator expansion flow circuit.
1. The power of the shortcomings of
1.1 This power is a linear regulator circuit, all Its unique internal power loss, all of the pressure drop is converted to heat loss and low efficiency. So pay special attention to heat dissipation.
1.2 components as the core of the work of 7805 is not too high speed, so the input voltage or load current slow response to rapid change.
1.3 This circuit does not add power protection circuit itself has over 7805 current and temperature protection transistor TIP32C expansion flow, but did not increase protection, so there is a big drawback, if the protection of the state after 7805, the circuit output will be Vin-Vce,Circuit output than expected value, this special attention.
2. The power advantage.
2.1 circuit is simple and stable. Debug convenient (almost without debugging).
2.2 cheap, suitable for cost-demanding products.
2.3 almost no high frequency circuit or the low-frequency signal components of radiation, low frequency, EMI and so easy to control.
3. the circuit works.
Io=Ioxx Ic.
Ioxx=IREG - IQ (IQ is the quiescent 7805 current, typically 4-8mA)
IREG=IR Ib=IR Ic / ß (ß is TIP32C current magnification)
IR=VBE/R1 (VBE the base for the TIP32 turn-on voltage)
So Ioxx=IREG - IQ=IR Ib - IQ
\u003d VBE/R1 IC/ß- IQ
IQ is very small as can be omitted, then: Ioxx=VBE/R1 IC / ß
Search TIP32C manual, VBE=1.2V, the ß desirable 10
Ioxx=1.2 / R Ic / ß=1.2/22 Ic/10=0.0545 Ic/10 (here take the main map in the 22 OHM)
Ic=10 * (Ioxx - 0.0545)
assumption Ioxx=100mA, Ic=10 * (100- 0.0545 * 1000)=455 (mA)
is Io=Ioxx Ic=100 455=555 mA.
Suppose Ioxx=200A, Ic=10 * (200 - 0.0545 * 1000)=1955mA
Io=Ioxx Ic=200 1955=2155mA
can be seen from the above two examples, the output current is greatly improved.
keep abreast of all the above calculation tells a lot, some can be carefully deduced.
3.2 The size of resistors R
R by the size of the adjustment 7805 of the current of a great relationship, different values \u200b\u200binto the above equation can be seen.
R is larger, the output current of the same situation the current flowing through 7805 to be smaller, and vice versa.
Usually this the circuit, the expansion flow transistor TIP32 additional heat sink, and no need for 7805, but the R value can not be too large, the condition is: R lt VBE / (IREG - IB).
3.37805 circuit input capacitance value is a mistake, in front of friends has been analyzed, mainly cause surge in the moment of power output than 5V, the subsequent damage to the circuit. The actual use of the time, in order to 7805's self-oscillation suppression, the capacitor is usually taken 0.33uF (most common spec. are recommended for this parameter)
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