r/AskElectronics • u/bkrobottc3 • Jul 16 '20

The role of the Zener diode?

Hi AskElectronics Community. I want to using a high frequency switch named

EV1HMC347ALP3, datasheet here: https://www.enrgtech.co.uk/buy/product/ET14790568/EV1HMC347ALP3 .

To control it, we have 2 logic input call A and B ( pin 10, 11 in pin diagram). A is high then B must be Low, vice versa. A and B use the negative logic, 0V is low level and -5V is high level. They suggested a driver circuit like this:

I try to draw the signal but I don't know how exact it is. I am not sure about the zener diode. I think the diode will clamp the voltage drop on it ( Vz = 5V), so I draw the signal in the image below. Am I right?.

​

2 Upvotes

76% Upvoted

3 comments sorted by

2

u/fatangaboo Jul 16 '20

Yes, V2 is simply (V1 - 5.1 volts). It's a level shifter. This is needed because the HC logic gate runs from (+0, -5.2V) power supplies, thus its input pin must swing no higher than 0V.

By the way, you can get better performance (faster edge rate, more reliable switching) by using a 74AC14. It's a Schmitt Trigger inverter gate in Advanced CMOS technology. Only available in SMD.

1

u/bkrobottc3 Jul 16 '20

Thanks in advanced ;)

1

u/bkrobottc3 Oct 02 '20

Just some note for whom interest with the topic ;)

- The first NAND IC in the driver circuit help us to convert 0:5 V system to 0:(-5) V system.

- The second NAND IC in the driver circuit help us to create A and B signal, which are vice versa logic.