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Triode voltage regulator circuit simulation problem.

Hardware design
12月 02, 2020 by Edison 1186

1. When I was simulating the voltage regulator circuit of a triode, I found that if the load resistance RL is not connected, the output is not 5V, but 11V. This situation is very different from using an LDO. The LDO should output 5V without load. It is a bit unclear. .

2. In addition, for example, 5V is connected with a single-chip microcomputer, can I simulate it with a resistive load? What is the power consumption of a general MCU? For example, the figure above


3. Later, I can also test to remove the resistor R2. This R2 should be a current limiting resistor. It reduces the voltage of VCE and increases the output current. P=Ic*Vce is the power of the transistor. Is it out of power consumption?

If R2 is removed: P=1.2W, VCE=24-5=19V, Imax=P/VCE=63mA, if the MCU requires 100mA, which exceeds the total power consumption of the transistor, will the transistor be damaged?

すべてのコメント

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Annette ポストする December 2, 2020

Generally, the power consumption of a single-chip microcomputer is about a few mA to tens of hundreds of mA. You can read the manual for the power consumption. If the LDO no-load output is definitely the nominal value. It should be possible to simulate with resistance.

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Stuart ポストする December 2, 2020

R2 can indeed reduce the voltage of VCE and reduce the power consumption of the transistor. But this resistance also needs to consider power issues. The transistor cannot exceed its maximum Imax, and at the same time, heat dissipation must be considered. P=1.2W should be done for heat dissipation, please refer to the manual for details.

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Reina ポストする December 2, 2020

1. LDO is possible, because LDO generally has FB feedback inside, so even if it is not loaded, it has 5V output, but the power consumption of LDO is (VIN-VO)*I, which is easy to exceed when the voltage drop is too large. Its power dissipation can cause damage, so generally LDO is suitable for small differential voltage. If there is no load, an effective circuit cannot be formed with a triode. Therefore, it is normal for the test voltage to be incorrect, and it will also be affected by your load in actual use, so the requirements are not very high. Improvise

2. The power consumption of the single-chip microcomputer mainly depends on the state of your IO port. If you use open drain to supply power through an external power supply, the power consumption may be a few mA, but if many I/0 ports use push-pull structure output, it will be relatively large. , Maybe tens to hundreds of mA. In actual power supply design, the efficiency and driving capability of the power supply are generally tested through electronic loads.

3. R2 is a current-limiting resistor. Your idea is correct, but it is said that your design is rarely used now, and the performance is relatively poor. It is recommended to use an off-the-shelf chip. You can choose the internal integrated MOS for the small current. The DC-DC chip of tube and inductor has advantages in size and high efficiency

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