3V-5V level conversion circuit diagram

This article mainly talks about the 3V-5V level conversion circuit diagram. Let’s learn about it together:

As shown in the figure, the left end is connected to the 3.3VCMOS level, which can be the IO port of STM32, FPGA, etc., and the right end outputs the 5V level to achieve conversion from 3.3V to 5V level.

Now let’s analyze the role of each resistor (the core idea is that the Vbe of the triode is a constant value of about 0.7V when it is turned on):

Assuming there is no R87, when the high level of US_CH0 is directly applied to the BE of the transistor, where does the voltage >0.7V go?

Assuming there is no R91, when the US_CH0 level state is uncertain, by default, should Trig output a high level or a low level? Therefore, R91 plays the role of a fixed level. At the same time, if there is no R91, the transistor will be turned on as long as the input is >0.7V. The threshold voltage is too low, and R91 has the effect of increasing the threshold voltage (see the analysis of the buzzer in Section 2).

However, when adding R91, you have to pay attention: if R91 is too small, the base voltage will be approximately

Only when Vb>0.7V can US_CH0 be turned on when it is high level, Vb=1.36V in the above figure

Assuming there is no R83, when the input US_CH0 is high level (when the triode is turned on), D5V0 (5V high level) is directly added to the CE level of the triode, and the CE level of the triode, the triode is easily damaged.

Let’s further analyze its working mechanism:

When the input is high level, the transistor is turned on and the output is clamped at the Vce of the transistor. The circuit test result is only 0.1V.

When the input is low level, the transistor does not conduct, and the output is equivalent to using a 10K resistor to pull up the input of the next stage circuit. The actual test result is 5.0V (no load)

Please note:

For large current loads, the characteristics of the above circuit will not perform so well, so it has been emphasized here that this circuit is only suitable for level conversion of loads from 10 mA to tens of mA.